Network Working Group J. Ross
Request for Comments: 3125 Security & Standards
Category: Experimental D. Pinkas
Integris
N. Pope
Security & Standards
September 2001
Electronic Signature Policies
Status of this Memo
This memo defines an Experimental Protocol for the Internet
community. It does not specify an Internet standard of any kind.
Discussion and suggestions for improvement are requested.
Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
This document defines signature policies for electronic signatures. A
signature policy is a set of rules for the creation and validation of
an electronic signature, under which the validity of signature can be
determined. A given legal/contractual context may recognize a
particular signature policy as meeting its requirements.
A signature policy has a globally unique reference, which is bound to
an electronic signature by the signer as part of the signature
calculation.
The signature policy needs to be available in human readable form so
that it can be assessed to meet the requirements of the legal and
contractual context in which it is being applied.
To allow for the automatic processing of an electronic signature
another part of the signature policy specifies the electronic rules
for the creation and validation of the electronic signature in a
computer processable form. In the current document the format of the
signature policy is defined using ASN.1.
The contents of this document is based on the signature policy
defined in ETSI TS 101 733 V.1.2.2 (2000-12) Copyright (C).
Individual copies of this ETSI deliverable can be downloaded from
http://www.etsi.org.
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Table of Contents
1. Introduction 3
2. Major Parties 3
3. Signature Policy Specification 5
3.1 Overall ASN.1 Structure 5
3.2 Signature Validation Policy 6
3.3 Common Rules 7
3.4 Commitment Rules 8
3.5 Signer and Verifier Rules 9
3.5.1 Signer Rules 9
3.5.2 Verifier Rules 11
3.6 Certificate and Revocation Requirements 11
3.6.1 Certificate Requirements 11
3.6.2 Revocation Requirements 13
3.7 Signing Certificate Trust Conditions 14
3.8 Time-Stamp Trust Conditions 15
3.9 Attribute Trust Conditions 16
3.10 Algorithm Constraints 17
3.11 Signature Policy Extensions 18
4. Security Considerations 18
4.1 Protection of Private Key 18
4.2 Choice of Algorithms 18
5. Conformance Requirements 19
6. References 19
7. Authors' Addresses 20
Annex A (normative): 21
A.1 Definitions Using X.208 (1988) ASN.1 Syntax 21
A.2 Definitions Using X.680 (1997) ASN.1 Syntax 27
Annex B (informative): 34
B.1 Signature Policy and Signature Validation Policy 34
B.2 Identification of Signature Policy 36
B.3 General Signature Policy Information 36
B.4 Recognized Commitment Types 37
B.5 Rules for Use of Certification Authorities 37
B.5.1 Trust Points 38
B.5.2 Certification Path 38
B.6 Revocation Rules 39
B.7 Rules for the Use of Roles 39
B.7.1 Attribute Values 39
B.7.2 Trust Points for Certified Attributes 40
B.7.3 Certification Path for Certified Attributes 40
B.8 Rules for the Use of Time-Stamping and Timing 40
B.8.1 Trust Points and Certificate Paths 41
B.8.2 Time-Stamping Authority Names 41
B.8.3 Timing Constraints - Caution Period 41
B.8.4 Timing Constraints - Time-Stamp Delay 41
B.9 Rules for Verification Data to be followed 41
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B.10 Rules for Algorithm Constraints and Key Lengths 42
B.11 Other Signature Policy Rules 42
B.12 Signature Policy Protection 42
Full Copyright Statement 44
1. Introduction
This document is intended to cover signature policies which can be
used with electronic signatures for various types of transactions,
including business transactions (e.g., purchase requisition,
contract, and invoice applications). Electronic signatures can be
used for any transaction between an individual and a company, between
two companies, between an individual and a governmental body, etc.
This document is independent of any environment. It can be applied
to any environment e.g., smart cards, GSM SIM cards, special programs
for electronic signatures etc.
The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" in this document (in uppercase,
as shown) are to be interpreted as described in [RFC2119].
2. Major Parties
The document uses the following terms:
* the Signature Policy Issuer;
* the Signer;
* the Verifier;
* the Arbitrator;
* Trusted Service Providers (TSP);
The Signature Policy Issuer (which is a Trusted Service Provider
(TSP)) issues signatures policies that define the technical and
procedural requirements for electronic signature creation, and
validation/ verification, in order to meet a particular business
need.
The Signer is the entity that creates the electronic signature. When
the signer digitally signs over an signature policy identifier, it
represents a commitment on behalf of the signing entity that the data
being signed is signed under the rules defined by the signature
policy.
The Verifier is the entity that validates the electronic signature,
it may be a single entity or multiple entities. The verifier MUST
validate the electronic signature under the rules defined by the
electronic signature policy for the signature to be valid.
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An arbitrator, is an entity which arbitrates disputes between a
signer and a verifier. It acts as verifier when it verifies the
electronic signature after it has been previously validated.
The Trusted Service Providers (TSPs) are one or more entities that
help to build trust relationships between the signer and verifier.
Use of TSP specific services MAY be mandated by signature policy.
TSP supporting services include: user certificates, cross-
certificates, time-stamping tokens,CRLs, ARLs, OCSP responses.
A Trusted Service Providers (TSPs) MAY be a Signature Policy Issuer,
as Such, the TSP MUST define the technical and procedural
requirements for electronic signature creation and validation, in
order to meet a particular business need.
The following other TSPs are used to support the functions defined in
this document:
* Certification Authorities;
* Registration Authorities;
* Repository Authorities (e.g., a Directory);
* Time-Stamping Authorities;
* One-line Certificate Status Protocol responders;
* Attribute Authorities.
Certification Authorities provide users with public key certificates.
Registration Authorities allows the registration of entities before a
CA generates certificates.
Repository Authorities publish CRLs issued by CAs, , cross-
certificates (i.e., CA certificates) issued by CAs, signature
policies issued by Signature Policy Issuers and optionally public key
certificates (i.e., leaf certificates) issued by CAs.
Time-Stamping Authorities attest that some data was formed before a
given trusted time.
One-line Certificate Status Protocol responders (OSCP responders)
provide information about the status (i.e., revoked, not revoked,
unknown) of a particular certificate.
Attributes Authorities provide users with attributes linked to public
key certificates
An Arbitrator is an entity that arbitrates disputes between a signer
and a verifier.
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3. Signature Policy Specification
A signature policy specification includes general information about
the policy, the validation policy rules and other signature policy
information.
This document mandates that:
* an electronic signature must be processed by the signer and
verifier in accordance with the signature policy referenced by
the signer;
* the signature policy referenced by the signer must be
identifiable by an Object Identifier;
* there must exist a specification of the signature policy;
* for a given signature policy there must be one definitive form
of the specification which has a unique binary encoding;
* a hash of the definitive specification, using an agreed
algorithm, must be provided by the signer and checked by the
verifier.
This document defines but does not mandate the form of the signature
policy specification. The signature policy may be specified either:
* in a free form document for human interpretation; or
* in a structured form using an agreed syntax and encoding.
This document defines an ASN.1 based syntax that may be used to
define a structured signature policy. Future versions of this
document may include structured a signature policy specification
using XML.
3.1 Overall ASN.1 Structure
The overall structure of a signature policy defined using ASN.1 is
given in this section. Use of this ASN.1 structure is optional.
This ASN.1 syntax is encoded using the Distinguished Encoding Rules
(DER).
In this structure the policy information is preceded by an identifier
for the hashing algorithm used to protect the signature policy and
followed by the hash value which must be re-calculated and checked
whenever the signature policy is passed between the issuer and
signer/verifier.
The hash is calculated without the outer type and length fields.
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SignaturePolicy ::= SEQUENCE {
signPolicyHashAlg AlgorithmIdentifier,
signPolicyInfo SignPolicyInfo,
signPolicyHash SignPolicyHash OPTIONAL }
SignPolicyHash ::= OCTET STRING
SignPolicyInfo ::= SEQUENCE {
signPolicyIdentifier SignPolicyId,
dateOfIssue GeneralizedTime,
policyIssuerName PolicyIssuerName,
fieldOfApplication FieldOfApplication,
signatureValidationPolicy SignatureValidationPolicy,
signPolExtensions SignPolExtensions
OPTIONAL
}
SignPolicyId ::= OBJECT IDENTIFIER
PolicyIssuerName ::= GeneralNames
FieldOfApplication ::= DirectoryString
The policyIssuerName field identifies the policy issuer in one or
more of the general name forms.
The fieldofApplication is a description of the expected application
of this policy.
The signature validation policy rules are fully processable to allow
the validation of electronic signatures issued under that form of
signature policy. They are described in the rest of this section.
The signPolExtensions is a generic way to extend the definition of
any sub-component of a signature policy.
3.2 Signature Validation Policy
The signature validation policy defines for the signer which data
elements must be present in the electronic signature he provides and
for the verifier which data elements must be present under that
signature policy for an electronic signature to be potentially valid.
The signature validation policy is described as follows:
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SignatureValidationPolicy ::= SEQUENCE {
signingPeriod SigningPeriod,
commonRules CommonRules,
commitmentRules CommitmentRules,
signPolExtensions SignPolExtensions OPTIONAL
}
The signingPeriod identifies the date and time before which the
signature policy SHOULD NOT be used for creating signatures, and an
optional date after which it should not be used for creating
signatures.
SigningPeriod ::= SEQUENCE {
notBefore GeneralizedTime,
notAfter GeneralizedTime OPTIONAL }
3.3 Common Rules
The CommonRules define rules that are common to all commitment types.
These rules are defined in terms of trust conditions for
certificates, time-stamps and attributes, along with any constraints
on attributes that may be included in the electronic signature.
CommonRules ::= SEQUENCE {
signerAndVeriferRules [0] SignerAndVerifierRules
OPTIONAL,
signingCertTrustCondition [1] SigningCertTrustCondition
OPTIONAL,
timeStampTrustCondition [2] TimestampTrustCondition
OPTIONAL,
attributeTrustCondition [3] AttributeTrustCondition
OPTIONAL,
algorithmConstraintSet [4] AlgorithmConstraintSet
OPTIONAL,
signPolExtensions [5] SignPolExtensions
OPTIONAL
}
If a field is present in CommonRules then the equivalent field must
not be present in any of the CommitmentRules (see below). If any of
the following fields are not present in CommonRules then it must be
present in each CommitmentRule:
* signerAndVeriferRules;
* signingCertTrustCondition;
* timeStampTrustCondition.
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3.4 Commitment Rules
The CommitmentRules consists of the validation rules which apply to
given commitment types:
CommitmentRules ::= SEQUENCE OF CommitmentRule
The CommitmentRule for given commitment types are defined in terms of
trust conditions for certificates, time-stamps and attributes, along
with any constraints on attributes that may be included in the
electronic signature.
CommitmentRule ::= SEQUENCE {
selCommitmentTypes SelectedCommitmentTypes,
signerAndVeriferRules [0] SignerAndVerifierRules
OPTIONAL,
signingCertTrustCondition [1] SigningCertTrustCondition
OPTIONAL,
timeStampTrustCondition [2] TimestampTrustCondition
OPTIONAL,
attributeTrustCondition [3] AttributeTrustCondition
OPTIONAL,
algorithmConstraintSet [4] AlgorithmConstraintSet
OPTIONAL,
signPolExtensions [5] SignPolExtensions
OPTIONAL
}
SelectedCommitmentTypes ::= SEQUENCE OF CHOICE {
empty NULL,
recognizedCommitmentType CommitmentType }
If the SelectedCommitmentTypes indicates "empty" then this rule
applied when a commitment type is not present (i.e., the type of
commitment is indicated in the semantics of the message). Otherwise,
the electronic signature must contain a commitment type indication
that must fit one of the commitments types that are mentioned in
CommitmentType.
A specific commitment type identifier must not appear in more than
one commitment rule.
CommitmentType ::= SEQUENCE {
identifier CommitmentTypeIdentifier,
fieldOfApplication [0] FieldOfApplication OPTIONAL,
semantics [1] DirectoryString OPTIONAL }
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The fieldOfApplication and semantics fields define the specific use
and meaning of the commitment within the overall field of application
defined for the policy.
3.5 Signer and Verifier Rules
The following rules apply to the format of electronic signatures
defined using [ES-FORMATS].
The SignerAndVerifierRules consists of signer rule and verification
rules as defined below:
SignerAndVerifierRules ::= SEQUENCE {
signerRules SignerRules,
verifierRules VerifierRules }
3.5.1 Signer Rules
The signer rules identify:
* if the eContent is empty and the signature is calculated using
a hash of signed data external to CMS structure.
* the CMS signed attributes that must be provided by the signer
under this policy;
* the CMS unsigned attribute that must be provided by the signer
under this policy;
* whether the certificate identifiers from the full certification
path up to the trust point must be provided by the signer in
the SigningCertificate attribute;
* whether a signer's certificate, or all certificates in the
certification path to the trust point must be by the signer in
the * certificates field of SignedData.
SignerRules ::= SEQUENCE {
externalSignedData BOOLEAN OPTIONAL,
-- True if signed data is external to CMS structure
-- False if signed data part of CMS structure
-- Not present if either allowed
mandatedSignedAttr CMSAttrs,
-- Mandated CMS signed attributes
mandatedUnsignedAttr CMSAttrs,
-- Mandated CMS unsigned attributed
mandatedCertificateRef [0] CertRefReq DEFAULT signerOnly,
-- Mandated Certificate Reference
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mandatedCertificateInfo [1] CertInfoReq DEFAULT none,
-- Mandated Certificate Info
signPolExtensions [2] SignPolExtensions OPTIONAL
}
CMSattrs ::= SEQUENCE OF OBJECT IDENTIFIER
The mandated SignedAttr field must include the object identifier for
all those signed attributes required by this document as well as
additional attributes required by this policy.
The mandatedUnsignedAttr field must include the object identifier for
all those unsigned attributes required by this document as well as
additional attributes required by this policy. For example, if a
signature time-stamp
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