RFC 5126 - CMS Advanced Electronic Signatures (CAdES)
(Formats: TXT)
Network Working Group D. Pinkas
Request for Comments: 5126 Bull SAS
Obsoletes: 3126 N. Pope
Category: Informational Thales eSecurity
J. Ross
Security and Standards
February 2008
|
CMS Advanced Electronic Signatures (CAdES)
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Abstract
This document defines the format of an electronic signature that can
remain valid over long periods. This includes evidence as to its
validity even if the signer or verifying party later attempts to deny
(i.e., repudiates) the validity of the signature.
The format can be considered as an extension to RFC 3852 and RFC
2634, where, when appropriate, additional signed and unsigned
attributes have been defined.
The contents of this Informational RFC amount to a transposition of
the ETSI Technical Specification (TS) 101 733 V.1.7.4 (CMS Advanced
Electronic Signatures -- CAdES) and is technically equivalent to it.
The technical contents of this specification are maintained by ETSI.
The ETSI TS and further updates are available free of charge at:
http://www.etsi.org/WebSite/Standards/StandardsDownload.aspx
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Table of Contents
1. Introduction ....................................................6
2. Scope ...........................................................6
3. Definitions and Abbreviations ...................................8
3.1. Definitions ................................................8
3.2. Abbreviations .............................................11
4. Overview .......................................................12
4.1. Major Parties .............................................13
4.2. Signature Policies ........................................14
4.3. Electronic Signature Formats ..............................15
4.3.1. CAdES Basic Electronic Signature (CAdES-BES) .......15
4.3.2. CAdES Explicit Policy-based Electronic
Signatures (CAdES-EPES) ............................18
4.4. Electronic Signature Formats with Validation Data .........19
4.4.1. Electronic Signature with Time (CAdES-T) ...........20
4.4.2. ES with Complete Validation Data References
(CAdES-C) ..........................................21
4.4.3. Extended Electronic Signature Formats ..............23
4.4.3.1. EXtended Long Electronic Signature
(CAdES-X Long) ............................24
4.4.3.2. EXtended Electronic Signature with
Time Type 1 ...............................25
4.4.3.3. EXtended Electronic Signature with
Time Type 2 ...............................26
4.4.3.4. EXtended Long Electronic Signature
with Time (CAdES-X Long ...................27
4.4.4. Archival Electronic Signature (CAdES-A) ............27
4.5. Arbitration ...............................................28
4.6. Validation Process ........................................29
5. Electronic Signature Attributes ................................30
5.1. General Syntax ............................................30
5.2. Data Content Type .........................................30
5.3. Signed-data Content Type ..................................30
5.4. SignedData Type ...........................................31
5.5. EncapsulatedContentInfo Type ..............................31
5.6. SignerInfo Type ...........................................31
5.6.1. Message Digest Calculation Process .................32
5.6.2. Message Signature Generation Process ...............32
5.6.3. Message Signature Verification Process .............32
5.7. Basic ES Mandatory Present Attributes .....................32
5.7.1. content-type .......................................32
5.7.2. Message Digest .....................................33
5.7.3. Signing Certificate Reference Attributes ...........33
5.7.3.1. ESS signing-certificate Attribute
Definition ................................34
5.7.3.2. ESS signing-certificate-v2
Attribute Definition ......................34
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5.7.3.3. Other signing-certificate
Attribute Definition ......................35
5.8. Additional Mandatory Attributes for Explicit
Policy-based Electronic Signatures ........................36
5.8.1. signature-policy-identifier ........................36
5.9. CMS Imported Optional Attributes ..........................38
5.9.1. signing-time .......................................38
5.9.2. countersignature ...................................39
5.10. ESS-Imported Optional Attributes .........................39
5.10.1. content-reference Attribute .......................39
5.10.2. content-identifier Attribute ......................39
5.10.3. content-hints Attribute ...........................40
5.11. Additional Optional Attributes Defined in the
Present Document .........................................40
5.11.1. commitment-type-indication Attribute ..............41
5.11.2. signer-location Attribute .........................43
5.11.3. signer-attributes Attribute .......................43
5.11.4. content-time-stamp Attribute ......................44
5.12. Support for Multiple Signatures ..........................44
5.12.1. Independent Signatures ............................44
5.12.2. Embedded Signatures ...............................45
6. Additional Electronic Signature Validation Attributes ..........45
6.1. signature time-stamp Attribute (CAdES-T) ..................47
6.1.1. signature-time-stamp Attribute Definition ..........47
6.2. Complete Validation Data References (CAdES-C) .............48
6.2.1. complete-certificate-references Attribute
Definition .........................................48
6.2.2. complete-revocation-references Attribute
Definition .........................................49
6.2.3. attribute-certificate-references Attribute
Definition .........................................51
6.2.4. attribute-revocation-references Attribute
Definition .........................................52
6.3. Extended Validation Data (CAdES-X) ........................52
6.3.1. Time-Stamped Validation Data (CAdES-X Type
1 or Type 2) .......................................53
6.3.2. Long Validation Data (CAdES-X Long, CAdES-X
Long Type 1 or 2) ..................................53
6.3.3. certificate-values Attribute Definition ............54
6.3.4. revocation-values Attribute Definition .............54
6.3.5. CAdES-C-time-stamp Attribute Definition ............56
6.3.6. time-stamped-certs-crls-references
Attribute Definition ...............................57
6.4. Archive Validation Data ...................................58
6.4.1. archive-time-stamp Attribute Definition ............58
7. Other Standard Data Structures .................................60
7.1. Public Key Certificate Format .............................60
7.2. Certificate Revocation List Format ........................60
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7.3. OCSP Response Format ......................................60
7.4. Time-Stamp Token Format ...................................60
7.5. Name and Attribute Formats ................................60
7.6. AttributeCertificate ......................................61
8. Conformance Requirements .......................................61
8.1. CAdES-Basic Electronic Signature (CAdES-BES) ..............62
8.2. CAdES-Explicit Policy-based Electronic Signature ..........63
8.3. Verification Using Time-Stamping ..........................63
8.4. Verification Using Secure Records .........................63
9. References .....................................................64
9.1. Normative References ......................................64
9.2. Informative References ....................................65
Annex A (normative): ASN.1 Definitions ............................69
A.1. Signature Format Definitions Using
X.208 ASN.1 Syntax ...................................69
A.2. Signature Format Definitions Using
X.680 ASN.1 Syntax ...................................77
Annex B (informative): Extended Forms of Electronic Signatures ....86
B.1. Extended Forms of Validation Data ....................86
B.1.1. CAdES-X Long ..................................87
B.1.2. CAdES-X Type 1 ................................88
B.1.3. CAdES-X Type 2 ................................90
B.1.4. CAdES-X Long Type 1 and CAdES-X Long Type 2 ...91
B.2. Time-Stamp Extensions ................................93
B.3. Archive Validation Data (CAdES-A) ....................94
B.4. Example Validation Sequence ..........................97
B.5. Additional Optional Features ........................102
Annex C (informative): General Description .......................103
C.1. The Signature Policy ................................103
C.2. Signed Information ..................................104
C.3. Components of an Electronic Signature ...............104
C.3.1. Reference to the Signature Policy ............104
C.3.2. Commitment Type Indication ...................105
C.3.3. Certificate Identifier from the Signer .......106
C.3.4. Role Attributes ..............................106
C.3.4.1. Claimed Role .......................107
C.3.4.2. Certified Role .....................107
C.3.5. Signer Location ..............................108
C.3.6. Signing Time .................................108
C.3.7. Content Format ...............................108
C.3.8. content-hints ................................109
C.3.9. Content Cross-Referencing ....................109
C.4. Components of Validation Data .......................109
C.4.1. Revocation Status Information ................109
C.4.1.1. CRL Information .....................110
C.4.1.2. OCSP Information ....................110
C.4.2. Certification Path ...........................111
C.4.3. Time-stamping for Long Life of Signatures ....111
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C.4.4. Time-stamping for Long Life of Signature
before CA key Compromises ....................113
C.4.4.1. Time-stamping the ES with
Complete Validation Data ...........113
C.4.4.2. Time-Stamping Certificates and
Revocation Information References ..114
C.4.5. Time-stamping for Archive of Signature .......115
C.4.6. Reference to Additional Data .................116
C.4.7. Time-Stamping for Mutual Recognition .........116
C.4.8. TSA Key Compromise ...........................117
C.5. Multiple Signatures .................................118
Annex D (informative): Data Protocols to Interoperate with TSPs ..118
D.1. Operational Protocols ...............................118
D.1.1. Certificate Retrieval ........................118
D.1.2. CRL Retrieval ................................118
D.1.3. Online Certificate Status ....................119
D.1.4. Time-Stamping ................................119
D.2. Management Protocols ................................119
D.2.1. Request for Certificate Revocation ...........119
Annex E (informative): Security Considerations ...................119
E.1. Protection of Private Key ...........................119
E.2. Choice of Algorithms ................................119
Annex F (informative): Example Structured Contents and MIME ......120
F.1. General Description .................................120
F.1.1. Header Information ...........................120
F.1.2. Content Encoding .............................121
F.1.3. Multi-Part Content ...........................121
F.2. S/MIME ..............................................122
F.2.1. Using application/pkcs7-mime .................123
F.2.2. Using application/pkcs7-signature ............124
Annex G (informative): Relationship to the European Directive
and EESSI .................................125
G.1. Introduction ........................................125
G.2. Electronic Signatures and the Directive .............126
G.3. ETSI Electronic Signature Formats and the Directive .127
G.4. EESSI Standards and Classes of Electronic Signature .127
G.4.1. Structure of EESSI Standardization ...........127
G.4.2. Classes of Electronic Signatures .............128
G.4.3. Electronic Signature Classes and the ETSI
Electronic Signature Format ..................128
Annex H (informative): APIs for the Generation and Verification
of Electronic Signatures Tokens ...........129
H.1. Data Framing ........................................129
H.2. IDUP-GSS-APIs Defined by the IETF ...................131
H.3. CORBA Security Interfaces Defined by the OMG ........132
Annex I (informative): Cryptographic Algorithms ..................133
I.1. Digest Algorithms ...................................133
I.1.1. SHA-1 ........................................133
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I.1.2. General ......................................133
I.2. Digital Signature Algorithms ........................134
I.2.1. DSA ..........................................134
I.2.2. RSA ..........................................135
I.2.3. General ......................................135
Annex J (informative): Guidance on Naming ........................137
J.1. Allocation of Names .................................137
J.2. Providing Access to Registration Information ........138
J.3. Naming Schemes ......................................138
J.3.1. Naming Schemes for Individual Citizens .......138
J.3.2. Naming Schemes for Employees of an
Organization .................................139
1. Introduction
This document is intended to cover electronic signatures for various
types of transactions, including business transactions (e.g.,
purchase requisition, contract, and invoice applications) where
long-term validity of such signatures is important. This includes
evidence as to its validity even if the signer or verifying party
later attempts to deny (i.e., repudiates; see ISO/IEC 10181-5
[ISO10181-5]) the validity of the signature.
Thus, the present document can be used for any transaction between an
individual and a company, between two companies, between an
individual and a governmental body, etc. The present document is
independent of any environment; it can be applied to any environment,
e.g., smart cards, Global System for Mobile Communication Subscriber
Identity Module (GSM SIM) cards, special programs for electronic
signatures, etc.
The European Directive on a community framework for Electronic
Signatures defines an electronic signature as: "Data in electronic
form which is attached to or logically associated with other
electronic data and which serves as a method of authentication".
An electronic signature, as used in the present document, is a form
of advanced electronic signature, as defined in the Directive.
2. Scope
The scope of the present document covers electronic signature formats
only. The aspects of Electronic Signature Policies are defined in
RFC 3125 [RFC3125] and ETSI TR 102 272 [TR102272].
The present document defines a number of electronic signature
formats, including electronic signatures that can remain valid over
long periods. This includes evidence as to its validity even if the
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signer or verifying party later attempts to deny (repudiates) the
validity of the electronic signature.
The present document specifies use of Trusted Service Providers
(e.g., Time-Stamping Authorities) and the data that needs to be
archived (e.g., cross-certificates and revocation lists) to meet the
requirements of long-term electronic signatures.
An electronic signature, as defined by the present document, can be
used for arbitration in case of a dispute between the signer and
verifier, which may occur at some later time, even years later.
The present document includes the concept of signature policies that
can be used to establish technical consistency when validating
electronic signatures, but it does not mandate their use.
The present document is based on the use of public key cryptography
to produce digital signatures, supported by public key certificates.
The present document also specifies the use of time-stamping and
time-marking services to prove the validity of a signature long after
the normal lifetime of critical elements of an electronic signature.
This document also, as an option, defines ways to provide very
long-term protection against key compromise or weakened algorithms.
The present document builds on existing standards that are widely
adopted. These include:
- RFC 3852 [4]: "Cryptographic Message Syntax (CMS)";
- ISO/IEC 9594-8/ITU-T Recommendation X.509 [1]: "Information
technology - Open Systems Interconnection - The Directory:
Authentication framework";
- RFC 3280 [2]: "Internet X.509 Public Key Infrastructure (PKIX)
Certificate and Certificate Revocation List (CRL) Profile";
- RFC 3161 [7]: "Internet X.509 Public Key Infrastructure
Time-Stamp Protocol (TSP)".
NOTE: See Section 11 for a full set of references.
The present document describes formats for advanced electronic
signatures using ASN.1 (Abstract Syntax Notation 1) [14]. ASN.1 is
encoded using X.690 [16].
These formats are based on CMS (Cryptographic Message Syntax) defined
in RFC 3852 [4]. These electronic signatures are thus called CAdES,
for "CMS Advanced Electronic Signatures".
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Another document, TS 101 903 [TS101903], describes formats for XML
advanced electronic signatures (XAdES) built on XMLDSIG as specified
in [XMLDSIG].
In addition, the present document identifies other documents that
define formats for Public Key Certificates, Attribute Certificates,
and Certificate Revocation Lists and supporting protocols, including
protocols for use by trusted third parties to support the operation
of electronic signature creation and validation.
Informative annexes include:
- illustrations of extended forms of Electronic Signature formats
that protect against various vulnerabilities and examples of
validation processes (Annex B);
- descriptions and explanations of some of the concepts used in
the present document, giving a rationale for normative parts of
the present document (Annex C);
- information on protocols to interoperate with Trusted Service
Providers (Annex D);
- guidance on naming (Annex E);
- an example structured content and MIME (Annex F);
- the relationship between the present document and the directive
on electronic signature and associated standardization
initiatives (Annex G);
- APIs to support the generation and verification of electronic
signatures (Annex H);
- cryptographic algorithms that may be used (Annex I); and
- naming schemes (see Annex J).
3. Definitions and Abbreviations
3.1. Definitions
For the purposes of the present document, the following terms and
definitions apply:
Arbitrator: an arbitrator entity may be used to arbitrate a dispute
between a signer and verifier when there is a disagreement on the
validity of a digital signature.
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Attribute Authority (AA): an authority that assigns privileges by
issuing attribute certificates.
Authority Certificate: a certificate issued to an authority (e.g.,
either to a certification authority or an attribute authority).
Attribute Authority Revocation List (AARL): a revocation list
containing a list of references to certificates issued to AAs that
are no longer considered valid by the issuing authority.
Attribute Certificate Revocation List (ACRL): a revocation list
containing a list of references to attribute certificates that are no
longer considered valid by the issuing authority.
Certification Authority Revocation List (CARL): a revocation list
containing a list of public key certificates issued to certification
authorities that are no longer considered valid by the certificate
issuer.
Certification Authority (CA): an authority trusted by one or more
users to create and assign public key certificates; optionally, the
certification authority may create the users' keys.
NOTE: See ITU-T Recommendation X.509 [1].
Certificate Revocation List (CRL): a signed list indicating a set of
public key certificates that are no longer considered valid by the
certificate issuer.
Digital Signature: data appended to, or a cryptographic
transformation of, a data unit that allows a recipient of the data
unit to prove the source and integrity of the data unit and protect
against forgery, e.g., by the recipient.
NOTE: See ISO 7498-2 [ISO7498-2].
Electronic Signature: data in electronic form that is attached to or
logically associated with other electronic data and that serves as a
method of authentication.
NOTE: See Directive 1999/93/EC of the European Parliament and of
the Council of 13 December 1999 on a Community framework for
electronic signatures [EUDirective].
Extended Electronic Signatures: electronic signatures enhanced by
complementing the baseline requirements with additional data, such as
time-stamp tokens and certificate revocation data, to address
commonly recognized threats.
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Explicit Policy-based Electronic Signature (EPES): an electronic
signature where the signature policy that shall be used to validate
it is explicitly specified.
Grace Period: a time period that permits the certificate revocation
information to propagate through the revocation process to relying
parties.
Initial Verification: a process performed by a verifier done after an
electronic signature is generated in order to capture additional
information that could make it valid for long-term verification.
Public Key Certificate (PKC): public keys of a user, together with
some other information, rendered unforgeable by encipherment with the
private key of the certification authority that issued it.
NOTE: See ITU-T Recommendation X.509 [1].
Rivest-Shamir-Adleman (RSA): an asymmetric cryptography algorithm
based on the difficulty to factor very large numbers using a key
pair: a private key and a public key.
Signature Policy: a set of rules for the creation and validation of
an electronic signature that defines the technical and procedural
requirements for electronic signature creation and validation, in
order to meet a particular business need, and under which the
signature can be determined to be valid.
Signature Policy Issuer: an entity that defines and issues a
signature policy.
Signature Validation Policy: part of the signature policy that
specifies the technical requirements on the signer in creating a
signature and verifier when validating a signature.
Signer: an entity that creates an electronic signature.
Subsequent Verification: a process performed by a verifier to assess
the signature validity.
NOTE: Subsequent verification may be done even years after the
electronic signature was produced by the signer and completed by
the initial verification, and it might not need to capture more
data than those captured at the time of initial verification.
Time-Stamp Token: a data object that binds a representation of a
datum to a particular time, thus establishing evidence that the datum
existed before that time.
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Time-Mark: information in an audit trail from a Trusted Service
Provider that binds a representation of a datum to a particular time,
thus establishing evidence that the datum existed before that time.
Time-Marking Authority: a trusted third party that creates records in
an audit trail in order to indicate that a datum existed before a
particular point in time.
Time-Stamping Authority (TSA): a trusted third party that creates
time-stamp tokens in order to indicate that a datum existed at a
particular point in time.
Time-Stamping Unit (TSU): a set of hardware and software that is
managed as a unit and has a single time-stamp token signing key
active at a time.
Trusted Service Provider (TSP): an entity that helps to build trust
relationships by making available or providing some information upon
request.
Validation Data: additional data that may be used by a verifier of
electronic signatures to determine that the signature is valid.
Valid Electronic Signature: an electronic signature that passes
validation.
Verifier: an entity that verifies evidence.
NOTE 1: See ISO/IEC 13888-1 [ISO13888-1].
NOTE 2: Within the context of the present document, this is an
entity that validates an electronic signature.
3.2. Abbreviations
For the purposes of the present document, the following abbreviations
apply:
AA Attribute Authority
AARL Attribute Authority Revocation List
ACRL Attribute Certificate Revocation List
API Application Program Interface
ASCII American Standard Code for Information Interchange
ASN.1 Abstract Syntax Notation 1
CA Certification Authority
CAD Card Accepting Device
CAdES CMS Advanced Electronic Signature
CAdES-A CAdES with Archive validation data
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CAdES-BES CAdES Basic Electronic Signature
CAdES-C CAdES with Complete validation data
CAdES-EPES CAdES Explicit Policy Electronic Signature
CAdES-T CAdES with Time
CAdES-X CAdES with eXtended validation data
CAdES-X Long CAdES with EXtended Long validation data
CARL Certification Authority Revocation List
CMS Cryptographic Message Syntax
CRL Certificate Revocation List
CWA CEN (European Committee for Standardization) Workshop
Agreement
DER Distinguished Encoding Rules (for ASN.1)
DSA Digital Signature Algorithm
EDIFACT Electronic Data Interchange For Administration,
Commerce and Transport
EESSI European Electronic Signature Standardization
Initiative
EPES Explicit Policy-based Electronic Signature
ES Electronic Signature
ESS Enhanced Security Services (enhances CMS)
IDL Interface Definition Language
MIME Multipurpose Internet Mail Extensions
OCSP Online Certificate Status Provider
OID Object IDentifier
PKC Public Key Certificate
PKIX Public Key Infrastructure using X.509
(IETF Working Group)
RSA Rivest-Shamir-Adleman
SHA-1 Secure Hash Algorithm 1
TSA Time-Stamping Authority
TSP Trusted Service Provider
TST Time-Stamp Token
TSU Time-Stamping Unit
URI Uniform Resource Identifier
URL Uniform Resource Locator
XML Extensible Markup Language
XMLDSIG XML Digital Signature
4. Overview
The present document defines a number of Electronic Signature (ES)
formats that build on CMS (RFC 3852 [4]) by adding signed and
unsigned attributes.
This section:
- provides an introduction to the major parties involved
(Section 4.1),
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- introduces the concept of signature policies (Section 4.2),
- provides an overview of the various ES formats (Section 4.3),
- introduces the concept of validation data, and provides an
overview of formats that incorporate validation data
(Section 4.4), and
- presents relevant considerations on arbitration
(Section 4.5) and for the validation process (Section 4.6).
The formal specifications of the attributes are specified in Sections
5 and 6; Annexes C and D provide rationale for the definitions of the
different ES forms.
4.1. Major Parties
The major parties involved in a business transaction supported by
electronic signatures, as defined in the present document, are:
- the signer;
- the verifier;
- Trusted Service Providers (TSP); and
- the arbitrator.
The signer is the entity that creates the electronic signature. When
the signer digitally signs over data using the prescribed format,
this represents a commitment on behalf of the signing entity to the
data being signed.
The verifier is the entity that validates the electronic signature;
it may be a single entity or multiple entities.
The Trusted Service Providers (TSPs) are one or more entities that
help to build trust relationships between the signer and verifier.
They support the signer and verifier by means of supporting services
including: user certificates, cross-certificates, time-stamp tokens,
CRLs, ARLs, and OCSP responses. The following TSPs are used to
support the functions defined in the present document:
- Certification Authorities;
- Registration Authorities;
- CRL Issuers;
- OCSP Responders;
- Repository Authorities (e.g., a Directory);
- Time-Stamping Authorities;
- Time-Marking Authorities; and
- Signature Policy Issuers.
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Certification Authorities provide users with public key certificates
and a revocation service.
Registration Authorities allow the identification and registration of
entities before a CA generates certificates.
Repository Authorities publish CRLs issued by CAs, signature policies
issued by Signature Policy Issuers, and optionally public key
certificates.
Time-Stamping Authorities attest that some data was formed before a
given trusted time.
Time-Marking Authorities record that some data was formed before a
given trusted time.
Signature Policy Issuers define the signature policies to be used by
signers and verifiers.
In some cases, the following additional TSPs are needed:
- Attribute Authorities.
Attributes Authorities provide users with attributes linked to public
key certificates.
An Arbitrator is an entity that arbitrates in disputes between a
signer and a verifier.
4.2. Signature Policies
The present document includes the concept of signature policies that
can be used to establish technical consistency when validating
electronic signatures.
When a comprehensive signature policy used by the verifier is either
explicitly indicated by the signer or implied by the data being
signed, then a consistent result can be obtained when validating an
electronic signature.
When the signature policy being used by the verifier is neither
indicated by the signer nor can be derived from other data, or the
signature policy is incomplete, then verifiers, including
arbitrators, may obtain different results when validating an
electronic signature. Therefore, comprehensive signature policies
that ensure consistency of signature validation are recommended from
both the signer's and verifier's point of view.
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Further information on signature policies is provided in:
- TR 102 038 [TR102038];
- Sections 5.8.1, C.1, and C.3.1 of the present document;
- RFC 3125 [RFC3125]; and
- TR 102 272 [TR102272].
4.3. Electronic Signature Formats
The current section provides an overview for two forms of CMS
advanced electronic signature specified in the present document,
namely, the CAdES Basic Electronic Signature (CAdES-BES) and the
CAdES Explicit Policy-based Electronic Signature (CAdES-EPES).
Conformance to the present document mandates that the signer create
one of these formats.
4.3.1. CAdES Basic Electronic Signature (CAdES-BES)
A CAdES Basic Electronic Signature (CAdES-BES), in accordance with
the present document, contains:
- The signed user data (e.g., the signer's document), as defined
in CMS (RFC 3852 [4]);
- A collection of mandatory signed attributes, as defined in CMS
(RFC 3852 [4]) and in ESS (RFC 2634 [5]);
- Additional mandatory signed attributes, defined in the present
document; and
- The digital signature value computed on the user data and, when
present, on the signed attributes, as defined in CMS (RFC 3852
[4]).
A CAdES Basic Electronic Signature (CAdES-BES), in accordance with
the present document, may contain:
- a collection of additional signed attributes; and
- a collection of optional unsigned attributes.
The mandatory signed attributes are:
- Content-type. It is defined in RFC 3852 [4] and specifies the
type of the EncapsulatedContentInfo value being signed. Details
are provided in Section 5.7.1 of the present document.
Rationale for its inclusion is provided in Annex C.3.7;
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- Message-digest. It is defined in RFC 3852 [4] and specifies the
message digest of the eContent OCTET STRING within
encapContentInfo being signed. Details are provided in Section
5.7.2;
- ESS signing-certificate OR ESS signing-certificate-v2. The ESS
signing-certificate attribute is defined in Enhanced Security
Services (ESS), RFC 2634 [5], and only allows for the use of
SHA-1 as a digest algorithm. The ESS signing-certificate-v2
attribute is defined in "ESS Update: Adding CertID Algorithm
Agility", RFC 5035 [15], and allows for the use of any digest
algorithm. A CAdES-BES claiming compliance with the present
document must include one of them. Section 5.7.3 provides the
details of these attributes. Rationale for its inclusion is
provided in Annex C.3.3.
Optional signed attributes may be added to the CAdES-BES, including
optional signed attributes defined in CMS (RFC 3852 [4]), ESS (RFC
2634 [5]), and the present document. Listed below are optional
attributes that are defined in Section 5 and have a rationale
provided in Annex C:
- Signing-time: as defined in CMS (RFC 3852 [4]), indicates the
time of the signature, as claimed by the signer. Details and
short rationale are provided in Section 5.9.1. Annex C.3.6
provides the rationale.
- content-hints: as defined in ESS (RFC 2634 [5]), provides
information that describes the innermost signed content of a
multi-layer message where one content is encapsulated in
another. Section 5.10.1 provides the specification details.
Annex C.3.8 provides the rationale.
- content-reference: as defined in ESS (RFC 2634 [5]), can be
incorporated as a way to link request and reply messages in an
exchange between two parties. Section 5.10.1 provides the
specification details. Annex C.3.9 provides the rationale.
- content-identifier: as defined in ESS (RFC 2634 [5]), contains
an identifier that may be used later on in the previous
content-reference attribute. Section 5.10.2 provides the
specification details.
- commitment-type-indication: this attribute is defined by the
present document as a way to indicate the commitment endorsed by
the signer when producing the signature. Section 5.11.1
provides the specification details. Annex C.3.2 provides the
rationale.
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- signer-location: this attribute is defined by the present
document. It allows the signer to indicate the place where the
signer purportedly produced the signature. Section 5.11.2
provides the specification details. Annex C.3.5 provides the
rationale.
- signer-attributes: this attribute is defined by the present
document. It allows a claimed or certified role to be
incorporated into the signed information. Section 5.11.3
provides the specification details. Annex C.3.4 provides the
rationale.
- content-time-stamp: this attribute is defined by the present
document. It allows a time-stamp token of the data to be signed
to be incorporated into the signed information. It provides
proof of the existence of the data before the signature was
created. Section 5.11.4 provides the specification details.
Annex C.3.6 provides the rationale.
A CAdES-BES form can also incorporate instances of unsigned
attributes, as defined in CMS (RFC 3852 [4]) and ESS (RFC 2634 [5]).
- CounterSignature, as defined in CMS (RFC 3852 [4]); it can be
incorporated wherever embedded signatures (i.e., a signature on
a previous signature) are needed. Section 5.9.2 provides the
specification details. Annex C.5 in Annex C provides the
rationale.
The structure of the CAdES-BES is illustrated in Figure 1.
+------Elect.Signature (CAdES-BES)------+
|+----------------------------------- + |
||+---------+ +----------+ | |
|||Signer's | | Signed | Digital | |
|||Document | |Attributes| Signature | |
||| | | | | |
||+---------+ +----------+ | |
|+------------------------------------+ |
+---------------------------------------+
Figure 1: Illustration of a CAdES-BES
The signer's conformance requirements of a CAdES-BES are defined in
Section 8.1.
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NOTE: The CAdES-BES is the minimum format for an electronic
signature to be generated by the signer. On its own, it does not
provide enough information for it to be verified in the longer
term. For example, revocation information issued by the relevant
certificate status information issuer needs to be available for
long-term validation (see Section 4.4.2).
The CAdES-BES satisfies the legal requirements for electronic
signatures, as defined in the European Directive on Electronic
Signatures, (see Annex C for further discussion on the relationship
of the present document to the Directive). It provides basic
authentication and integrity protection.
The semantics of the signed data of a CAdES-BES or its context may
implicitly indicate a signature policy to the verifier.
Specification of the contents of signature policies is outside the
scope of the present document. However, further information on
signature policies is provided in TR 102 038 [TR102038], RFC 3125
[RFC3125], and Sections 5.8.1, C.1, and C.3.1 of the present
document.
4.3.2. CAdES Explicit Policy-based Electronic Signatures (CAdES-EPES)
A CAdES Explicit Policy-based Electronic Signature (CAdES-EPES), in
accordance with the present document, extends the definition of an
electronic signature to conform to the identified signature policy.
A CAdES Explicit Policy-based Electronic Signature (CAdES-EPES)
incorporates a signed attribute (sigPolicyID attribute) indicating
the signature policy that shall be used to validate the electronic
signature. This signed attribute is protected by the signature. The
signature may also have other signed attributes required to conform
to the mandated signature policy.
Section 5.7.3 provides the details on the specification of
signature-policy-identifier attribute. Annex C.1 provides a short
rationale. Specification of the contents of signature policies is
outside the scope of the present document.
Further information on signature policies is provided in TR 102 038
[TR102038] and Sections 5.8.1, C.1, and C.3.1 of the present
document.
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The structure of the CAdES-EPES is illustrated in Figure 2.
+------------- Elect.Signature (CAdES-EPES) ---------------+
| |
|+-------------------------------------------------------+ |
|| +-----------+ | |
|| | | +---------------------------+ | |
|| | | | +----------+ | | |
|| | Signer's | | |Signature | Signed | Digital | |
|| | Document | | |Policy ID | Attributes |Signature| |
|| | | | +----------+ | | |
|| | | +---------------------------+ | |
|| +-----------+ | |
|+-------------------------------------------------------+ |
| |
+----------------------------------------------------------+
Figure 2: Illustration of a CAdES-EPES
The signer's conformance requirements of CAdES-EPES are defined in
Section 8.2.
4.4. Electronic Signature Formats with Validation Data
Validation of an electronic signature, in accordance with the present
document, requires additional data needed to validate the electronic
signature. This additional data is called validation data, and
includes:
- Public Key Certificates (PKCs);
- revocation status information for each PKC;
- trusted time-stamps applied to the digital signature, otherwise
a time-mark shall be available in an audit log.
- when appropriate, the details of a signature policy to be used
to verify the electronic signature.
The validation data may be collected by the signer and/or the
verifier. When the signature-policy-identifier signed attribute is
present, it shall meet the requirements of the signature policy.
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Validation data includes CA certificates as well as revocation status
information in the form of Certificate Revocation Lists (CRLs) or
certificate status information (OCSP) provided by an online service.
Validation data also includes evidence that the signature was created
before a particular point in time; this may be either a time-stamp
token or time-mark.
The present document defines unsigned attributes able to contain
validation data that can be added to CAdES-BES and CAdES-EPES,
leading to electronic signature formats that include validation data.
The sections below summarize these formats and their most relevant
characteristics.
4.4.1. Electronic Signature with Time (CAdES-T)
An electronic signature with time (CAdES-T), in accordance with the
present document, is when there exits trusted time associated with
the ES.
The trusted time may be provided by:
- a time-stamp attribute as an unsigned attribute added to the ES;
and
- a time-mark of the ES provided by a Trusted Service Provider.
The time-stamp attribute contains a time-stamp token of the
electronic signature value. Section 6.1.1 provides the specification
details. Annex C.4.3 provides the rationale.
A time-mark provided by a Trusted Service would have a similar effect
to the signature-time-stamp attribute, but in this case, no attribute
is added to the ES, as it is the responsibility of the TSP to provide
evidence of a time-mark when required to do so. The management of
time marks is outside the scope of the present document.
Trusted time provides the initial steps towards providing long-term
validity. Electronic signatures with the time-stamp attribute or a
time-marked BES/EPES, forming the CAdES-T are illustrated in Figure
3.
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+-------------------------------------------------CAdES-T ---------+
|+------ CAdES-BES or CAdES-EPES -------+ |
||+-----------------------------------+ | +----------------------+ |
|||+---------+ +----------+ | | | | |
||||Signer's | | Signed | Digital | | | Signature-time-stamp | |
||||Document | |Attributes| Signature | | | attribute required | |
|||| | | | | | | when using time | |
|||+---------+ +----------+ | | | stamps. | |
||+-----------------------------------+ | | | |
|+--------------------------------------+ | or the BES/EPES | |
| | shall be time-marked | |
| | | |
| | Management and | |
| | provision of time | |
| | mark is the | |
| | responsibility of | |
| | the TSP. | |
| +----------------------+ |
+------------------------------------------------------------------+
Figure 3: Illustration of CAdES-T formats
NOTE 1: A time-stamp token is added to the CAdES-BES or CAdES-EPES
as an unsigned attribute.
NOTE 2: Time-stamp tokens that may themselves include unsigned
attributes required to validate the time-stamp token, such as the
complete-certificate-references and complete-revocation-references
attributes, as defined by the present document.
4.4.2. ES with Complete Validation Data References (CAdES-C)
Electronic Signature with Complete validation data references
(CAdES-C), in accordance with the present document, adds to the
CAdES-T the complete-certificate-references and
complete-revocation-references attributes, as defined by the present
document. The complete-certificate-references attribute contains
references to all the certificates present in the certification path
used for verifying the signature. The complete-revocation-references
attribute contains references to the CRLs and/or OCSPs responses used
for verifying the signature. Section 6.2 provides the specification
details. Storing the references allows the values of the
certification path and the CRLs or OCSPs responses to be stored
elsewhere, reducing the size of a stored electronic signature format.
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Sections C.4.1 to C.4.2 provide rationale on the usage of validation
data and when it is suitable to generate the CAdES-C form.
Electronic signatures, with the additional validation data forming
the CAdES-C, are illustrated in Figure 4.
+------------------------- CAdES-C --------------------------------+
|+----------------------------- CAdES-T ---------+ |
|| +----------+ | +-------------+ |
|| |Timestamp | | | | |
|| |attribute | | | | |
||+- CAdES-BES or CAdES-EPES ------+|over | | | | |
||| ||digital | | | Complete | |
|||+---------++----------+ ||signature | | | certificate | |
||||Signer's || Signed | Digital ||is | | | and | |
||||Document ||Attributes|Signature||mandatory | | | revocation | |
|||| || | ||if is not | | | references | |
|||+---------++----------+ ||timemarked| | | | |
||+--------------------------------++----------+ | | | |
|+-----------------------------------------------+ +-------------+ |
+------------------------------------------------------------------+
Figure 4: Illustration of CAdES-C format
NOTE 1: The complete certificate and revocation references are
added to the CAdES-T as an unsigned attribute.
NOTE 2: As a minimum, the signer will provide the CAdES-BES or,
when indicating that the signature conforms to an explicit signing
policy, the CAdES-EPES.
NOTE 3: To reduce the risk of repudiating signature creation, the
trusted time indication needs to be as close as possible to the
time the signature was created. The signer or a TSP could provide
the CAdES-T; if not, the verifier should create the CAdES-T on
first receipt of an electronic signature because the CAdES-T
provides independent evidence of the existence of the signature
prior to the trusted time indication.
NOTE 4: A CAdES-T trusted time indication must be created before a
certificate has been revoked or expired.
NOTE 5: The signer and TSP could provide the CAdES-C to minimize
this risk, and when the signer does not provide the CAdES-C, the
verifier should create the CAdES-C when the required component of
revocation and validation data become available; this may require
a grace period.
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NOTE 6: A grace period permits certificate revocation information
to propagate through the revocation processes. This period could
extend from the time an authorized entity requests certificate
revocation to when the information is available for the relying
party to use. In order to make sure that the certificate was not
revoked at the time the signature was time-marked or time-stamped,
verifiers should wait until the end of the grace period. A
signature policy may define specific values for grace periods.
An illustration of a grace period is provided in Figure 5.
+<--------------Grace Period --------->+
----+-------+-------+--------+---------------------+----------+
^ ^ ^ ^ ^ ^
| | | | | |
| | | | | |
Signature | First | Second |
creation | revocation | revocation |
time | status | status |
| checking | checking |
| | |
Time-stamp Certification Build
or path CAdES-C
time-mark construction
over & verification
signature
Figure 5: Illustration of a grace period
NOTE 7: CWA 14171 [CWA14171] specifies a signature validation
process using CAdES-T, CAdES-C, and a grace period. Annex B
provides example validation processes. Annex C.4 provides
additional information about applying grace periods during the
validation process.
The verifier's conformance requirements are defined in Section 8.3
for time-stamped CAdES-C, and Section 8.4 for time-marked CAdES-C.
The present document only defines conformance requirements for the
verifier up to an ES with Complete validation data (CAdES-C). This
means that none of the extended and archive forms of electronic
signatures, as defined in Sections 4.4.3 to 4.4.4, need to be
implemented to achieve conformance to the present document.
4.4.3. Extended Electronic Signature Formats
CAdES-C can be extended by adding unsigned attributes to the
electronic signature. The present document defines various unsigned
attributes that are applicable for very long-term verification, and
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for preventing some disaster situations that are discussed in Annex
C. Annex B provides the details of the various extended formats, all
the required unsigned attributes for each type, and how they can be
used within the electronic signature validation process. The
sections below give an overview of the various forms of extended
signature formats in the present document.
4.4.3.1. EXtended Long Electronic Signature (CAdES-X Long)
Extended Long format (CAdES-X Long), in accordance with the present
document, adds the certificate-values and revocation-values
attributes to the CAdES-C format. The first one contains the whole
certificate path required for verifying the signature; the second one
contains the CRLs and/OCSP responses required for the validation of
the signature. This provides a known repository of certificate and
revocation information required to validate a CAdES-C and prevents
such information from getting lost. Sections 6.3.3 and 6.3.4 give
specification details. Annex B.1.1 gives details on the production
of the format. Annexes C4.1 to C.4.2 provide the rationale.
The structure of the CAdES-X Long format is illustrated in Figure 6.
+----------------------- CAdES-X-Long -----------------------------+
|+------------------------------------ CadES-C --+ |
|| +----------+ | +-------------+ |
||+------ CAdES -------------------+|Timestamp | | | | |
||| || over | | | Complete | |
|||+---------++----------+ ||digital | | | certificate | |
||||Signer's || Signed | Digital ||signature | | | and | |
||||Document ||Attributes|Signature|| | | | revocation | |
|||| || | ||Optional | | | data | |
|||+---------++----------+ ||when | | | | |
||+--------------------------------+|timemarked| | | | |
|| +----------+ | | | |
|| +-------------+ | +-------------+ |
|| | Complete | | |
|| | certificate | | |
|| | and | | |
|| | revocation | | |
|| | references | | |
|| +-------------+ | |
|+-----------------------------------------------+ |
| |
+------------------------------------------------------------------+
Figure 6: Illustration of CAdES-X-Long
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4.4.3.2. EXtended Electronic Signature with Time Type 1
(CAdES-X Type 1)
Extended format with time type 1 (CAdES-X Type 1), in accordance with
the present document, adds the CAdES-C-time-stamp attribute, whose
content is a time-stamp token on the CAdES-C itself, to the CAdES-C
format.
This provides an integrity and trusted time protection over all the
elements and references. It may protect the certificates, CRLs, and
OCSP responses in case of a later compromise of a CA key, CRL key, or
OCSP issuer key. Section 6.3.5 provides the specification details.
Annex B.1.2 gives details on the production of the time-stamping
process. Annex C.4.4.1 provides the rationale.
The structure of the CAdES-X Type 1 format is illustrated in Figure
7.
+----------------------- CAdES-X-Type 1 ------------------------------+
|+-------------------------------------- CAdES-C -----+ |
|| +-------------+ | +-----------+ |
||+--------- CAdES ------------------+| Timestamp | | | | |
||| || over | | | | |
|||+---------++----------+ || digital | | | | |
||||Signer's || Signed | Digital || signature | | | Timestamp | |
||||Document ||Attributes| Signature || | | | over | |
|||| || | || Optional | | | CAdES-C | |
|||+---------++----------+ || when | | | | |
||+----------------------------------+| time-marked | | | | |
|| +-------------+ | | | |
|| +-------------+ | +-----------+ |
|| | Complete | | |
|| | certificate | | |
|| | and | | |
|| | revocation | | |
|| | references | | |
|| +-------------+ | |
|+----------------------------------------------------+ |
+---------------------------------------------------------------------+
Figure 7: Illustration of CAdES-X Type 1
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4.4.3.3. EXtended Electronic Signature with Time Type 2
(CAdES-X Type 2)
Extended format with time type 2 (CAdES-X Type 2), in accordance with
the present document, adds to the CAdES-C format the
CAdES-C-time-stamped-certs-crls-references attribute, whose content
is a time-stamp token on the certification path and revocation
information references. This provides an integrity and trusted time
protection over all the references.
It may protect the certificates, CRLs and OCSP responses in case of a
later compromise of a CA key, CRL key or OCSP issuer key.
Both CAdES-X Type 1 and CAdES-X Type 2 counter the same threats, and
the usage of one or the other depends on the environment. Section
6.3.5 provides the specification details. Annex B.1.3 gives details
on the production of the time-stamping process. Annex C.4.4.2
provides the rationale.
The structure of the CAdES-X Type 2 format is illustrated in Figure
8.
+------------------------- CAdES-X-Type 2 ----------------------------+
|+----------------------------------------CAdES-C ---+ |
|| +------------+| |
||+----- CAdES -----------------------+| Timestamp || |
||| || over || |
|||+---------+ +----------+ || digital || +-------------+|
||||Signer's | | Signed | Digital || signature || | Time-stamp ||
||||Document | |Attributes| signature || || | only over ||
|||| | | | || optional || | complete ||
|||+---------+ +----------+ || when || | certificate ||
||+-----------------------------------+| timemarked || | and ||
|| +------------+| | revocation ||
|| +-------------+ | | references ||
|| | Complete | | +-------------+|
|| | certificate | | |
|| | and | | |
|| | revocation | | |
|| | references | | |
|| +-------------+ | |
|+---------------------------------------------------+ |
+---------------------------------------------------------------------+
Figure 8: Illustration of CAdES-X Type 2
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4.4.3.4. EXtended Long Electronic Signature with Time (CAdES-X Long
Type 1 or 2)
Extended Long with Time (CAdES-X Long Type 1 or 2), in accordance
with the present document, is a combination of CAdES-X Long and one
of the two former types (CAdES-X Type 1 and CAdES-X Type 2). Annex
B.1.4 gives details on the production of the time-stamping process.
Annex C.4.8 in Annex C provides the rationale.
The structure of the CAdES-X Long Type 1 and CAdES-X Long Type 2
format is illustrated in Figure 9.
+------------------ CAdES-X Long Type 1 or 2 -----------------------+
| +--------------+|
|+-------------------------------------- CAdES-C --+|+------------+||
|| ||| Timestamp |||
||+------- CAdES --------------------++----------+ ||| over |||
||| ||Timestamp | ||| CAdES-C |||
||| ||over | ||+------------+||
|||+---------++----------+ ||digital | || OR ||
||||Signer's || Signed | Digital ||signature | ||+------------+||
||||Document ||Attributes| signature || | ||| Timestamp |||
|||| || | ||Optional | ||| only over |||
|||+---------++----------+ ||when | ||| complete |||
||+----------------------------------+|timemarked| ||| certificate|||
|| +----------+ ||| and |||
|| ||| Revocation |||
|| +-------------+ ||| References |||
|| | Complete | ||+------------+||
|| | certificate | |+--------------+|
|| | and | | +------------+ |
|| | revocation | | | Complete | |
|| | references | | |certificate | |
|| +-------------+ | | and | |
|+-------------------------------------------------+ |revocation | |
| | value | |
| +------------+ |
+-------------------------------------------------------------------+
Figure 9: Illustration of CAdES-X Long Type 1 and CAdES Long Type 2
4.4.4. Archival Electronic Signature (CAdES-A)
Archival Form (CAdES-A), in accordance with the present document,
builds on a CAdES-X Long or a CAdES-X Long Type 1 or 2 by adding one
or more archive-time-stamp attributes. This form is used for
archival of long-term signatures. Successive time-stamps protect the
whole material against vulnerable hashing algorithms or the breaking
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of the cryptographic material or algorithms. Section 6.4 contains
the specification details. Sections C.4.5 and C.4.8 provide the
rationale.
The structure of the CAdES-A form is illustrated in Figure 10.
+---------------------------CAdES-A ---------------------------------+
|+----------------------------------------------------+ |
|| +--------------+| +----------+ |
||+----------------------CAdES-C ----+|+------------+|| | | |
||| +----------+ ||| Timestamp ||| | | |
|||+---- CAdES-BES ----+|Timestamp | ||| over ||| | | |
|||| or CAdeS-EPES || over | ||| CAdES-C ||| | Archive | |
|||| ||digital | ||+------------+|| | | |
|||| ||signature | || or || |Timestamp | |
|||| || | ||+------------+|| | | |
|||| ||Optional | ||| Timestamp ||| | | |
|||| ||when | ||| only over ||| | | |
|||| ||Timemarked| ||| complete ||| | | |
|||+-------------------+| | ||| certificate||| +----------+ |
||| +----------+ ||| and ||| |
||| +-------------+ ||| revocation ||| |
||| | Complete | ||| references ||| |
||| | certificate | ||+------------+|| |
||| | and | |+--------------+| |
||| | revocation | | +------------+ | |
||| | references | | | Complete | | |
||| +-------------+ | |certificate | | |
||| | | and | | |
||+----------------------------------+ |revocation | | |
|| | values | | |
|| +------------+ | |
|+----------------------------------------------------+ |
+--------------------------------------------------------------------+
Figure 10: Illustration of CAdES-A
4.5. Arbitration
The CAdES-C may be used for arbitration should there be a dispute
between the signer and verifier, provided that:
- the arbitrator knows where to retrieve the signer's certificate
(if not already present), all the cross-certificates and the
required CRLs, ACRLs, or OCSP responses referenced in the
CAdES-C;
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- when time-stamping in the CAdES-T is being used, the certificate
from the TSU that has issued the time-stamp token in the CAdES-T
format is still within its validity period;
- when time-stamping in the CAdES-T is being used, the certificate
from the TSU that has issued the time-stamp token in the CAdES-T
format is not revoked at the time of arbitration;
- when time-marking in the CAdES-T is being used, a reliable audit
trail from the Time-Marking Authority is available for
examination regarding the time;
- none of the private keys corresponding to the certificates used
to verify the signature chain have ever been compromised;
- the cryptography used at the time the CAdES-C was built has not
been broken at the time the arbitration is performed; and
- if the signature policy can be explicitly or implicitly
identified, then an arbitrator is able to determine the rules
required to validate the electronic signature.
4.6. Validation Process
The validation process validates an electronic signature; the output
status of the validation process can be:
- invalid;
- incomplete validation; or
- valid.
An invalid response indicates that either the signature format is
incorrect or that the digital signature value fails verification
(e.g., the integrity check on the digital signature value fails, or
any of the certificates on which the digital signature verification
depends is known to be invalid or revoked).
An incomplete validation response indicates that the signature
validation status is currently unknown. In the case of incomplete
validation, additional information may be made available to the
application or user, thus allowing them to decide what to do with the
electronic signature. In the case of incomplete validation, the
electronic signature may be checked again at some later time when
additional information becomes available.
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NOTE: For example, an incomplete validation may be because all the
required certificates are not available or the grace period is not
completed.
A valid response indicates that the signature has passed
verification, and it complies with the signature validation policy.
Example validation sequences are illustrated in Annex B.
5. Electronic Signature Attributes
This section builds upon the existing Cryptographic Message Syntax
(CMS), as defined in RFC 3852 [4], and Enhanced Security Services
(ESS), as defined in RFC 2634 [5]. The overall structure of an
Electronic Signature is as defined in CMS. The Electronic Signature
(ES) uses attributes defined in CMS, ESS, and the present document.
The present document defines ES attributes that it uses and that are
not defined elsewhere.
The mandated set of attributes and the digital signature value is
defined as the minimum Electronic Signature (ES) required by the
present document. A signature policy may mandate that other signed
attributes be present.
5.1. General Syntax
The general syntax of the ES is as defined in CMS (RFC 3852 [4]).
NOTE: CMS defines content types for id-data, id-signedData,
id-envelopedData, id-digestedData, id-encryptedData, and
id-authenticatedData. Although CMS permits other documents to
define other content types, the ASN.1 type defined should not be a
CHOICE type. The present document does not define other content
types.
5.2. Data Content Type
The data content type of the ES is as defined in CMS (RFC 3852 [4]).
NOTE: If the content type is id-data, it is recommended that the
content be encoded using MIME, and that the MIME type is used to
identify the presentation format of the data. See Annex F.1 for
an example of using MIME to identify the encoding type.
5.3. Signed-data Content Type
The Signed-data content type of the ES is as defined in CMS (RFC 3852
[4]).
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5.4. SignedData Type
The syntax of the SignedData of the ES is as defined in CMS (RFC 3852
[4]).
The fields of type SignedData are as defined in CMS (RFC 3852 [4]).
The identification of a signer's certificate used to create the
signature is always signed (see Section 5.7.3). The validation
policy may specify requirements for the presence of certain
certificates. The degenerate case, where there are no signers, is
not valid in the present document.
5.5. EncapsulatedContentInfo Type
The syntax of the EncapsulatedContentInfo type ES is as defined in
CMS (RFC 3852 [4]).
For the purpose of long-term validation, as defined by the present
document, it is advisable that either the eContent is present, or the
data that is signed is archived in such as way as to preserve any
data encoding. It is important that the OCTET STRING used to
generate the signature remains the same every time either the
verifier or an arbitrator validates the signature.
NOTE: The eContent is optional in CMS :
- When it is present, this allows the signed data to be
encapsulated in the SignedData structure, which then
contains both the signed data and the signature. However,
the signed data may only be accessed by a verifier able to
decode the ASN.1 encoded SignedData structure.
- When it is missing, this allows the signed data to be sent
or stored separately from the signature, and the SignedData
structure only contains the signature. It is, in the case
of the signature, only the data that is signed that needs to
be stored and distributed in such as way as to preserve any
data encoding.
The degenerate case where there are no signers is not valid in the
present document.
5.6. SignerInfo Type
The syntax of the SignerInfo type ES is as defined in CMS (RFC 3852
[4]).
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Per-signer information is represented in the type SignerInfo. In the
case of multiple independent signatures (see Annex B.5), there is an
instance of this field for each signer.
The fields of type SignerInfo have the meanings defined in CMS (RFC
3852 [4]), but the signedAttrs field shall contain the following
attributes:
- content-type, as defined in Section 5.7.1; and
- message-digest, as defined in Section 5.7.2;
- signing-certificate, as defined in Section 5.7.3.
5.6.1. Message Digest Calculation Process
The message digest calculation process is as defined in CMS (RFC 3852
[4]).
5.6.2. Message Signature Generation Process
The input to the message signature generation process is as defined
in CMS (RFC 3852 [4]).
5.6.3. Message Signature Verification Process
The procedures for message signature verification are defined in CMS
(RFC 3852 [4]) and enhanced in the present document: the input to the
signature verification process must be the signer's public key, which
shall be verified as correct using the signing certificate reference
attribute containing a reference to the signing certificate, i.e.,
when SigningCertificateV2 from RFC 5035 [16] or SigningCertificate
from ESS [5] is used, the public key from the first certificate
identified in the sequence of certificate identifiers from
SigningCertificate must be the key used to verify the digital
signature.
5.7. Basic ES Mandatory Present Attributes
The following attributes shall be present with the signed-data
defined by the present document. The attributes are defined in CMS
(RFC 3852 [4]).
5.7.1. content-type
The content-type attribute indicates the type of the signed content.
The syntax of the content-type attribute type is as defined in CMS
(RFC 3852 [4]) Section 11.1.
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NOTE 1: As stated in RFC 3852 [4] , the content-type attribute
must have its value (i.e., ContentType) equal to the eContentType
of the EncapsulatedContentInfo value being signed.
NOTE 2: For implementations supporting signature generation, if
the content-type attribute is id-data, then it is recommended that
the eContent be encoded using MIME. For implementations
supporting signature verification, if the signed data (i.e.,
eContent) is MIME-encoded, then the OID of the content-type
attribute must be id-data. In both cases, the MIME
content-type(s) must be used to identify the presentation format
of the data. See Annex F for further details about the use of
MIME.
5.7.2. Message Digest
The syntax of the message-digest attribute type of the ES is as
defined in CMS (RFC 3852 [4]).
5.7.3. Signing Certificate Reference Attributes
The Signing certificate reference attributes are supported by using
either the ESS signing-certificate attribute or the
ESS-signing-certificate-v2 attribute.
These attributes shall contain a reference to the signer's
certificate; they are designed to prevent simple substitution and
reissue attacks and to allow for a restricted set of certificates to
be used in verifying a signature. They have a compact form (much
shorter than the full certificate) that allows for a certificate to
be unambiguously identified.
One, and only one, of the following alternative attributes shall be
present with the signedData, defined by the present document:
- The ESS signing-certificate attribute, defined in ESS [5], must
be used if the SHA-1 hashing algorithm is used.
- The ESS signing-certificate-v2 attribute, defined in "ESS
Update: Adding CertID Algorithm Agility", RFC 5035 [15], which
shall be used when other hashing algorithms are to be used.
The certificate to be used to verify the signature shall be
identified in the sequence (i.e., the certificate from the signer),
and the sequence shall not be empty. The signature validation policy
may mandate other certificates be present that may include all the
certificates up to the trust anchor.
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5.7.3.1. ESS signing-certificate Attribute Definition
The syntax of the signing-certificate attribute type of the ES is as
defined in Enhanced Security Services (ESS), RFC 2634 [5], and
further qualified in the present document.
The sequence of the policy information field is not used in the
present document.
The ESS signing-certificate attribute shall be a signed attribute.
The encoding of the ESSCertID for this certificate shall include the
issuerSerial field.
If present, the issuerAndSerialNumber in SignerIdentifier field of
the SignerInfo shall match the issuerSerial field present in
ESSCertID. In addition, the certHash from ESSCertID shall match the
SHA-1 hash of the certificate. The certificate identified shall be
used during the signature verification process. If the hash of the
certificate does not match the certificate used to verify the
signature, the signature shall be considered invalid.
NOTE: Where an attribute certificate is used by the signer to
associate a role, or other attributes of the signer, with the
electronic signature; this is placed in the signer-attributes
attribute as defined in Section 5.8.3.
5.7.3.2. ESS signing-certificate-v2 Attribute Definition
The ESS signing-certificate-v2 attribute is similar to the ESS
signing-certificate defined above, except that this attribute can be
used with hashing algorithms other than SHA-1.
The syntax of the signing-certificate-v2 attribute type of the ES is
as defined in "ESS Update: Adding CertID Algorithm Agility", RFC 5035
[15], and further qualified in the present document.
The sequence of the policy information field is not used in the
present document.
This attribute shall be used in the same manner as defined above for
the ESS signing-certificate attribute.
The object identifier for this attribute is:
id-aa-signingCertificateV2 OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 47 }
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If present, the issuerAndSerialNumber in SignerIdentifier field of
the SignerInfo shall match the issuerSerial field present in
ESSCertIDv2. In addition, the certHash from ESSCertIDv2 shall match
the hash of the certificate computed using the hash function
specified in the hashAlgorithm field. The certificate identified
shall be used during the signature verification process. If the hash
of the certificate does not match the certificate used to verify the
signature, the signature shall be considered invalid.
NOTE 1: Where an attribute certificate is used by the signer to
associate a role, or other attributes of the signer, with the
electronic signature; this is placed in the signer-attributes
attribute as defined in Section 5.8.3.
NOTE 2: RFC 3126 was using the other signing-certificate attribute
(see Section 5.7.3.3) for the same purpose. Its use is now
deprecated, since this structure is simpler.
5.7.3.3. Other signing-certificate Attribute Definition
RFC 3126 was using the other signing-certificate attribute as an
alternative to the ESS signing-certificate when hashing algorithms
other than SHA-1 were being used. Its use is now deprecated, since
the structure of the signing-certificate-v2 attribute is simpler.
Its description is however still present in this version for
backwards compatibility.
id-aa-ets-otherSigCert OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 19 }
The other-signing-certificate attribute value has the ASN.1 syntax
OtherSigningCertificate:
OtherSigningCertificate ::= SEQUENCE {
certs SEQUENCE OF OtherCertID,
policies SEQUENCE OF PolicyInformation OPTIONAL
-- NOT USED IN THE PRESENT DOCUMENT }
OtherCertID ::= SEQUENCE {
otherCertHash OtherHash,
issuerSerial IssuerSerial OPTIONAL }
OtherHash ::= CHOICE {
sha1Hash OtherHashValue, -- This contains a SHA-1 hash
otherHash OtherHashAlgAndValue}
OtherHashValue ::= OCTET STRING
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OtherHashAlgAndValue ::= SEQUENCE {
hashAlgorithm AlgorithmIdentifier,
hashValue OtherHashValue }
5.8. Additional Mandatory Attributes for Explicit Policy-based
Electronic Signatures
5.8.1. signature-policy-identifier
The present document mandates that for CAdES-EPES, a reference to the
signature policy is included in the signedData. This reference is
explicitly identified. A signature policy defines the rules for
creation and validation of an electronic signature, and is included
as a signed attribute with every Explicit Policy-based Electronic
Signature. The signature-policy-identifier shall be a signed
attribute.
The following object identifier identifies the
signature-policy-identifier attribute:
id-aa-ets-sigPolicyId OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 15 }
signature-policy-identifier attribute values have ASN.1 type
SignaturePolicyIdentifier:
SignaturePolicyIdentifier ::= CHOICE {
signaturePolicyId SignaturePolicyId,
signaturePolicyImplied SignaturePolicyImplied
-- not used in this version
}
SignaturePolicyId ::= SEQUENCE {
sigPolicyId SigPolicyId,
sigPolicyHash SigPolicyHash,
sigPolicyQualifiers SEQUENCE SIZE (1..MAX) OF
SigPolicyQualifierInfo OPTIONAL}
SignaturePolicyImplied ::= NULL
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The sigPolicyId field contains an object-identifier that uniquely
identifies a specific version of the signature policy. The syntax of
this field is as follows:
SigPolicyId ::= OBJECT IDENTIFIER
The sigPolicyHash field optionally contains the identifier of the
hash algorithm and the hash of the value of the signature policy.
The hashValue within the sigPolicyHash may be set to zero to indicate
that the policy hash value is not known.
NOTE: The use of a zero sigPolicyHash value is to ensure backwards
compatibility with earlier versions of the current document. If
sigPolicyHash is zero, then the hash value should not be checked
against the calculated hash value of the signature policy.
If the signature policy is defined using ASN.1, then the hash is
calculated on the value without the outer type and length fields, and
the hashing algorithm shall be as specified in the field
sigPolicyHash.
If the signature policy is defined using another structure, the type
of structure and the hashing algorithm shall be either specified as
part of the signature policy, or indicated using a signature policy
qualifier.
SigPolicyHash ::= OtherHashAlgAndValue
OtherHashAlgAndValue ::= SEQUENCE {
hashAlgorithm AlgorithmIdentifier,
hashValue OtherHashValue }
OtherHashValue ::= OCTET STRING
A Signature Policy Identifier may be qualified with other information
about the qualifier. The semantics and syntax of the qualifier is as
associated with the object-identifier in the sigPolicyQualifierId
field. The general syntax of this qualifier is as follows:
SigPolicyQualifierInfo ::= SEQUENCE {
sigPolicyQualifierId SigPolicyQualifierId,
sigQualifier ANY DEFINED BY sigPolicyQualifierId }
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The present document specifies the following qualifiers:
- spuri: this contains the web URI or URL reference to the
signature policy, and
- sp-user-notice: this contains a user notice that should be
displayed whenever the signature is validated.
sigpolicyQualifierIds defined in the present document:
SigPolicyQualifierId ::= OBJECT IDENTIFIER
id-spq-ets-uri OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 1 }
SPuri ::= IA5String
id-spq-ets-unotice OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 2 }
SPUserNotice ::= SEQUENCE {
noticeRef NoticeReference OPTIONAL,
explicitText DisplayText OPTIONAL}
NoticeReference ::= SEQUENCE {
organization DisplayText,
noticeNumbers SEQUENCE OF INTEGER }
DisplayText ::= CHOICE {
visibleString VisibleString (SIZE (1..200)),
bmpString BMPString (SIZE (1..200)),
utf8String UTF8String (SIZE (1..200)) }
5.9. CMS Imported Optional Attributes
The following attributes may be present with the signed-data; the
attributes are defined in CMS (RFC 3852 [4]) and are imported into
the present document. Where appropriate, the attributes are
qualified and profiled by the present document.
5.9.1. signing-time
The signing-time attribute specifies the time at which the signer
claims to have performed the signing process.
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Signing-time attribute values for ES have the ASN.1 type SigningTime
as defined in CMS (RFC 3852 [4]).
NOTE: RFC 3852 [4] states that dates between January 1, 1950 and
December 31, 2049 (inclusive) must be encoded as UTCTime. Any
dates with year values before 1950 or after 2049 must be encoded
as GeneralizedTime.
5.9.2. countersignature
The countersignature attribute values for ES have ASN.1 type
CounterSignature, as defined in CMS (RFC 3852 [4]). A
countersignature attribute shall be an unsigned attribute.
5.10. ESS-Imported Optional Attributes
The following attributes may be present with the signed-data defined
by the present document. The attributes are defined in ESS and are
imported into the present document and are appropriately qualified
and profiled by the present document.
5.10.1. content-reference Attribute
The content-reference attribute is a link from one SignedData to
another. It may be used to link a reply to the original message to
which it refers, or to incorporate by reference one SignedData into
another. The content-reference attribute shall be a signed
attribute.
content-reference attribute values for ES have ASN.1 type
ContentReference, as defined in ESS (RFC 2634 [5]).
The content-reference attribute shall be used as defined in ESS (RFC
2634 [5]).
5.10.2. content-identifier Attribute
The content-identifier attribute provides an identifier for the
signed content, for use when a reference may be later required to
that content; for example, in the content-reference attribute in
other signed data sent later. The content-identifier shall be a
signed attribute.
content-identifier attribute type values for the ES have an ASN.1
type ContentIdentifier, as defined in ESS (RFC 2634 [5]).
The minimal content-identifier attribute should contain a
concatenation of user-specific identification information (such as a
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user name or public keying material identification information), a
GeneralizedTime string, and a random number.
5.10.3. content-hints Attribute
The content-hints attribute provides information on the innermost
signed content of a multi-layer message where one content is
encapsulated in another.
The syntax of the content-hints attribute type of the ES is as
defined in ESS (RFC 2634 [5]).
When used to indicate the precise format of the data to be presented
to the user, the following rules apply:
- the contentType indicates the type of the associated content.
It is an object identifier (i.e., a unique string of integers)
assigned by an authority that defines the content type; and
- when the contentType is id-data, the contentDescription shall
define the presentation format; the format may be defined by
MIME types.
When the format of the content is defined by MIME types, the
following rules apply:
- the contentType shall be id-data, as defined in CMS (RFC 3852
[4]);
- the contentDescription shall be used to indicate the encoding of
the data, in accordance with the rules defined RFC 2045 [6]; see
Annex F for an example of structured contents and MIME.
NOTE 1: id-data OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
rsadsi(113549) pkcs(1) pkcs7(7) 1 }
NOTE 2: contentDescription is optional in ESS (RFC 2634 [5]). It may
be used to complement contentTypes defined elsewhere; such
definitions are outside the scope of the present document.
5.11. Additional Optional Attributes Defined in the Present Document
This section defines a number of attributes that may be used to
indicate additional information to a verifier:
a) the type of commitment from the signer, and/or
b) the claimed location where the signature is performed, and/or
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c) claimed attributes or certified attributes of the signer,
and/or
d) a content time-stamp applied before the content was signed.
5.11.1. commitment-type-indication Attribute
There may be situations where a signer wants to explicitly indicate
to a verifier that by signing the data, it illustrates a type of
commitment on behalf of the signer. The commitment-type-indication
attribute conveys such information.
The commitment-type-indication attribute shall be a signed attribute.
The commitment type may be:
- defined as part of the signature policy, in which case, the
commitment type has precise semantics that are defined as part
of the signature policy; and
- be a registered type, in which case, the commitment type has
precise semantics defined by registration, under the rules of
the registration authority. Such a registration authority may
be a trading association or a legislative authority.
The signature policy specifies a set of attributes that it
"recognizes". This "recognized" set includes all those commitment
types defined as part of the signature policy, as well as any
externally defined commitment types that the policy may choose to
recognize. Only recognized commitment types are allowed in this
field.
The following object identifier identifies the
commitment-type-indication attribute:
id-aa-ets-commitmentType OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 16}
commitment-type-indication attribute values have ASN.1 type
CommitmentTypeIndication.
CommitmentTypeIndication ::= SEQUENCE {
commitmentTypeId CommitmentTypeIdentifier,
commitmentTypeQualifier SEQUENCE SIZE (1..MAX) OF
CommitmentTypeQualifier OPTIONAL}
CommitmentTypeIdentifier ::= OBJECT IDENTIFIER
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CommitmentTypeQualifier ::= SEQUENCE {
commitmentTypeIdentifier CommitmentTypeIdentifier,
qualifier ANY DEFINED BY commitmentTypeIdentifier }
The use of any qualifiers to the commitment type is outside the scope
of the present document.
The following generic commitment types are defined in the present
document:
id-cti-ets-proofOfOrigin OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 1}
id-cti-ets-proofOfReceipt OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 2}
id-cti-ets-proofOfDelivery OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 3}
id-cti-ets-proofOfSender OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 4}
id-cti-ets-proofOfApproval OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 5}
id-cti-ets-proofOfCreation OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16)
cti(6) 6}
These generic commitment types have the following meanings:
Proof of origin indicates that the signer recognizes to have created,
approved, and sent the message.
Proof of receipt indicates that signer recognizes to have received
the content of the message.
Proof of delivery indicates that the TSP providing that indication
has delivered a message in a local store accessible to the recipient
of the message.
Proof of sender indicates that the entity providing that indication
has sent the message (but not necessarily created it).
Proof of approval indicates that the signer has approved the content
of the message.
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Proof of creation indicates that the signer has created the message
(but not necessarily approved, nor sent it).
5.11.2. signer-location Attribute
The signer-location attribute specifies a mnemonic for an address
associated with the signer at a particular geographical (e.g., city)
location. The mnemonic is registered in the country in which the
signer is located and is used in the provision of the Public Telegram
Service (according to ITU-T Recommendation F.1 [11]).
The signer-location attribute shall be a signed attribute. The
following object identifier identifies the signer-location attribute:
id-aa-ets-signerLocation OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 17}
Signer-location attribute values have ASN.1 type SignerLocation:
SignerLocation ::= SEQUENCE {
-- at least one of the following shall be present:
countryName [0] DirectoryString OPTIONAL,
-- As used to name a Country in X.500
localityName [1] DirectoryString OPTIONAL,
-- As used to name a locality in X.500
postalAdddress [2] PostalAddress OPTIONAL }
PostalAddress ::= SEQUENCE SIZE(1..6) OF DirectoryString
5.11.3. signer-attributes Attribute
The signer-attributes attribute specifies additional attributes of
the signer (e.g., role). It may be either:
- claimed attributes of the signer; or
- certified attributes of the signer.
The signer-attributes attribute shall be a signed attribute. The
following object identifier identifies the signer-attribute
attribute:
id-aa-ets-signerAttr OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 18}
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signer-attributes values have ASN.1 type SignerAttribute:
SignerAttribute ::= SEQUENCE OF CHOICE {
claimedAttributes [0] ClaimedAttributes,
certifiedAttributes [1] CertifiedAttributes }
ClaimedAttributes ::= SEQUENCE OF Attribute
CertifiedAttributes ::= AttributeCertificate
-- as defined in RFC 3281: see Section 4.1.
NOTE 1: Only a single signer-attributes can be used.
NOTE 2: Attribute and AttributeCertificate are as defined
respectively in ITU-T Recommendations X.501 [9] and X.509 [1].
5.11.4. content-time-stamp Attribute
The content-time-stamp attribute is an attribute that is the
time-stamp token of the signed data content before it is signed. The
content-time-stamp attribute shall be a signed attribute.
The following object identifier identifies the content-time-stamp
attribute:
id-aa-ets-contentTimestamp OBJECT IDENTIFIER ::=
{ iso(1) member- body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 20}
content-time-stamp attribute values have ASN.1 type ContentTimestamp:
ContentTimestamp ::= TimeStampToken
The value of messageImprint of TimeStampToken (as described in RFC
3161 [7]) shall be a hash of the value of the eContent field within
encapContentInfo in the signedData.
For further information and definition of TimeStampToken, see Section
7.4.
NOTE: content-time-stamp indicates that the signed information was
formed before the date included in the content-time-stamp.
5.12. Support for Multiple Signatures
5.12.1. Independent Signatures
Multiple independent signatures (see Annex B.5) are supported by
independent SignerInfo from each signer.
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Each SignerInfo shall include all the attributes required under the
present document and shall be processed independently by the
verifier.
NOTE: Independent signatures may be used to provide independent
signatures from different parties with different signed
attributes, or to provide multiple signatures from the same party
using alternative signature algorithms, in which case the other
attributes, excluding time values and signature policy
information, will generally be the same.
5.12.2. Embedded Signatures
Multiple embedded signatures (see Annex C.5) are supported using the
countersignature unsigned attribute (see Section 5.9.2). Each
counter signature is carried in countersignature held as an unsigned
attribute to the SignerInfo to which the counter-signature is
applied.
NOTE: Counter signatures may be used to provide signatures from
different parties with different signed attributes, or to provide
multiple signatures from the same party using alternative
signature algorithms, in which case the other attributes,
excluding time values and signature policy information, will
generally be the same.
6. Additional Electronic Signature Validation Attributes
This section specifies attributes that contain different types of
validation data. These attributes build on the electronic signature
specified in Section 5. This includes:
- Signature-time-stamp applied to the electronic signature value
or a Time-Mark in an audit trail. This is defined as the
Electronic Signature with Time (CAdES-T); and
- Complete validation data references that comprise the time-stamp
of the signature value, plus references to all the certificates
(complete-certificate-references) and revocation (complete-
revocation-references) information used for full validation of
the electronic signature. This is defined as the Electronic
Signature with Complete data references (CAdES-C).
NOTE 1: Formats for CAdES-T are illustrated in Section 4.4, and
the attributes are defined in Section 6.1.1.
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NOTE 2: Formats for CAdES-C are illustrated in Section 4.4. The
required attributes for the CAdES-C signature format are defined
in Sections 6.2.1 to 6.2.2; optional attributes are defined in
Sections 6.2.3 and 6.2.4.
In addition, the following optional extended forms of validation data
are also defined; see Annex B for an overview of the extended forms
of validation data:
- CAdES-X with time-stamp: there are two types of time-stamps used
in extended validation data defined by the present document;
- Type 1(CAdES-X Type 1): comprises a time-stamp over the ES
with Complete validation data (CAdES-C); and
- Type 2 (CAdES-X Type2): comprises a time-stamp over the
certification path references and the revocation information
references used to support the CAdES-C.
NOTE 3: Formats for CAdES-X Type 1 and CAdES-X Type 2 are
illustrated in Sections B.1.2 and B.1.3, respectively.
- CAdES-X Long: comprises the Complete validation data
references (CAdES-C), plus the actual values of all the
certificates and revocation information used in the CAdES-C.
NOTE 4: Formats for CAdES-X Long are illustrated in Annex B.1.1.
- CAdES-X Long Type 1 or CAdES-X Long Type 2: comprises an
X-Time-Stamp (Type 1 or Type 2), plus the actual values of
all the certificates and revocation information used in the
CAdES-C as per CAdES-X Long.
This section also specifies the data structures used in Archive
validation data format (CAdES-A)of extended forms:
- Archive form of electronic signature (CAdES-A) comprises:
- the Complete validation data references (CAdES-C),
- the certificate and revocation values (as in a CAdES-X Long ),
- any existing extended electronic signature time-stamps
(CAdES-X Type 1 or CAdES-X Type 2), if present, and
- the signed user data and an additional archive time-stamp
applied over all that data.
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An archive time-stamp may be repeatedly applied after long
periods to maintain validity when electronic signature and
time-stamping algorithms weaken.
The additional data required to create the forms of electronic
signature identified above is carried as unsigned attributes
associated with an individual signature by being placed in the
unsignedAttrs field of SignerInfo. Thus, all the attributes defined
in Section 6 are unsigned attributes.
NOTE 5: Where multiple signatures are to be supported, as
described in Section 5.12, each signature has a separate
SignerInfo. Thus, each signature requires its own unsigned
attribute values to create CAdES-T, CAdES-C, etc.
NOTE 6: The optional attributes of the extended validation data
are defined in Sections 6.3 and 6.4.
6.1. signature time-stamp Attribute (CAdES-T)
An electronic signature with time-stamp is an electronic signature
for which part, but not all, of the additional data required for
validation is available (i.e., some certificates and revocation
information are available, but not all).
The minimum structure time-stamp validation data is:
- the signature time-stamp attribute, as defined in Section 6.1.1,
over the ES signature value.
6.1.1. signature-time-stamp Attribute Definition
The signature-time-stamp attribute is a TimeStampToken computed on
the signature value for a specific signer; it is an unsigned
attribute. Several instances of this attribute may occur with an
electronic signature, from different TSAs.
The following object identifier identifies the signature-time-stamp
attribute:
id-aa-signatureTimeStampToken OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 14}
The signature-time-stamp attribute value has ASN.1 type
SignatureTimeStampToken:
SignatureTimeStampToken ::= TimeStampToken
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The value of the messageImprint field within TimeStampToken shall be
a hash of the value of the signature field within SignerInfo for the
signedData being time-stamped.
For further information and definition of TimeStampToken, see Section
7.4.
NOTE 1: In the case of multiple signatures, it is possible to have
a:
- TimeStampToken computed for each and all signers; or
- TimeStampToken computed on one signer's signature; and no
- TimeStampToken on another signer's signature.
NOTE 2: In the case of multiple signatures, several TSTs, issued
by different TSAs, may be present within the same signerInfo (see
RFC 3852 [4]).
6.2. Complete Validation Data References (CAdES-C)
An electronic signature with Complete validation data references
(CAdES-C) is an electronic signature for which all the additional
data required for validation (i.e., all certificates and revocation
information) is available. This form is built on the CAdES-T form
defined above.
As a minimum, the Complete validation data shall include the
following:
- a time, which shall either be a signature-timestamp attribute,
as defined in Section 6.1.1, or a time-mark operated by a
Time-Marking Authority;
- complete-certificate-references, as defined in Section 6.2.1;
- complete-revocation-references, as defined in Section 6.2.2.
6.2.1. complete-certificate-references Attribute Definition
The complete-certificate-references attribute is an unsigned
attribute. It references the full set of CA certificates that have
been used to validate an ES with Complete validation data up to (but
not including) the signer's certificate. Only a single instance of
this attribute shall occur with an electronic signature.
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NOTE 1: The signer's certificate is referenced in the signing
certificate attribute (see Section 5.7.3).
id-aa-ets-certificateRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 21}
The complete-certificate-references attribute value has the ASN.1
syntax CompleteCertificateRefs.
CompleteCertificateRefs ::= SEQUENCE OF OtherCertID
OtherCertID is defined in Section 5.7.3.3.
The IssuerSerial that shall be present in OtherCertID. The certHash
shall match the hash of the certificate referenced.
NOTE 2: Copies of the certificate values may be held using the
certificate-values attribute, defined in Section 6.3.3.
This attribute may include references to the certification chain
for any TSUs that provides time-stamp tokens. In this case, the
unsigned attribute shall be added to the signedData of the
relevant time-stamp token as an unsignedAttrs in the signerInfos
field.
6.2.2. complete-revocation-references Attribute Definition
The complete-revocation-references attribute is an unsigned
attribute. Only a single instance of this attribute shall occur with
an electronic signature. It references the full set of the CRL, |
