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
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].
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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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.
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.
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 }
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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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.
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 }
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 <see section 1.1) is required by the signer the
object identifier for this attribute must be included.
The mandatedCertificateRef identifies whether just the signer's
certificate, or all the full certificate path must be provided by the
signer.
CertRefReq ::= ENUMERATED {
signerOnly (1),
-- Only reference to signer cert mandated
fullpath (2)
-- References for full cert path up to a trust point required
}
The mandatedCertificateInfo field identifies whether a signer's
certificate, or all certificates in the certification path to the
trust point must be provided by the signer in the certificates field
of SignedData.
CertInfoReq ::= ENUMERATED {
none (0) ,
-- No mandatory requirements
signerOnly (1) ,
-- Only reference to signer cert mandated
fullpath (2)
-- References for full cert path up to a
-- trust point mandated
}
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The verifier rules identify:
* The CMS unsigned attributes that must be present under this
policy and must be added by the verifier if not added by the
signer.
VerifierRules ::= SEQUENCE {
mandatedUnsignedAttr MandatedUnsignedAttr,
signPolExtensions SignPolExtensions OPTIONAL
}
MandatedUnsignedAttr ::= CMSAttrs
-- Mandated CMS unsigned attributed
The SigningCertTrustCondition, TimestampTrustCondition and
AttributeTrustCondition (defined in subsequent sub-sections) make use
of two ASN1 structures which are defined below: CertificateTrustTrees
and CertRevReq.
The certificateTrustTrees identifies a set of self signed
certificates for the trust points used to start (or end) certificate
path processing and the initial conditions for certificate path
validation as defined RFC 2459 [7] section 4. This ASN1 structure is
used to define policy for validating the signing certificate, the
TSA's certificate and attribute certificates.
CertificateTrustTrees ::= SEQUENCE OF CertificateTrustPoint
CertificateTrustPoint ::= SEQUENCE {
trustpoint Certificate,
-- self-signed certificate
pathLenConstraint [0] PathLenConstraint OPTIONAL,
acceptablePolicySet [1] AcceptablePolicySet OPTIONAL,
-- If not present "any policy"
nameConstraints [2] NameConstraints OPTIONAL,
policyConstraints [3] PolicyConstraints OPTIONAL }
The trustPoint field gives the self signed certificate for the CA
that is used as the trust point for the start of certificate path
processing.
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The pathLenConstraint field gives the maximum number of CA
certificates that may be in a certification path following the
trustpoint. A value of zero indicates that only the given trustpoint
certificate and an end-entity certificate may be used. If present,
the pathLenConstraint field must be greater than or equal to zero.
Where pathLenConstraint is not present, there is no limit to the
allowed length of the certification path.
PathLenConstraint ::= INTEGER (0..MAX)
The acceptablePolicySet field identifies the initial set of
certificate policies, any of which are acceptable under the signature
policy. AcceptablePolicySet ::= SEQUENCE OF CertPolicyId
CertPolicyId ::= OBJECT IDENTIFIER
The nameConstraints field indicates a name space within which all
subject names in subsequent certificates in a certification path must
be located. Restrictions may apply to the subject distinguished name
or subject alternative names. Restrictions apply only when the
specified name form is present. If no name of the type is in the
certificate, the certificate is acceptable.
Restrictions are defined in terms of permitted or excluded name
subtrees. Any name matching a restriction in the excludedSubtrees
field is invalid regardless of information appearing in the
permittedSubtrees.
NameConstraints ::= SEQUENCE {
permittedSubtrees [0] GeneralSubtrees OPTIONAL,
excludedSubtrees [1] GeneralSubtrees OPTIONAL }
GeneralSubtrees ::= SEQUENCE SIZE (1..MAX) OF GeneralSubtree
GeneralSubtree ::= SEQUENCE {
base GeneralName,
minimum [0] BaseDistance DEFAULT 0,
maximum [1] BaseDistance OPTIONAL }
BaseDistance ::= INTEGER (0..MAX)
The policyConstraints extension constrains path processing in two
ways. It can be used to prohibit policy mapping or require that each
certificate in a path contain an acceptable policy identifier.
The policyConstraints field, if present specifies requirement for
explicit indication of the certificate policy and/or the constraints
on policy mapping.
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PolicyConstraints ::= SEQUENCE {
requireExplicitPolicy [0] SkipCerts OPTIONAL,
inhibitPolicyMapping [1] SkipCerts OPTIONAL }
SkipCerts ::= INTEGER (0..MAX)
If the inhibitPolicyMapping field is present, the value indicates the
number of additional certificates that may appear in the path
(including the trustpoint's self certificate) before policy mapping
is no longer permitted. For example, a value of one indicates that
policy mapping may be processed in certificates issued by the subject
of this certificate, but not in additional certificates in the path.
If the requireExplicitPolicy field is present, subsequent
certificates must include an acceptable policy identifier. The value
of requireExplicitPolicy indicates the number of additional
certificates that may appear in the path (including the trustpoint's
self certificate) before an explicit policy is required. An
acceptable policy identifier is the identifier of a policy required
by the user of the certification path or the identifier of a policy
which has been declared equivalent through policy mapping.
The RevocRequirements field specifies minimum requirements for
revocation information, obtained through CRLs and/or OCSP responses,
to be used in checking the revocation status of certificates. This
ASN1 structure is used to define policy for validating the signing
certificate, the TSA's certificate and attribute certificates.
CertRevReq ::= SEQUENCE {
endCertRevReq RevReq,
caCerts [0] RevReq
}
Certificate revocation requirements are specified in terms of checks
required on:
* endCertRevReq: end certificates (i.e., the signers certificate,
the attribute certificate or the time-stamping authority
certificate).
* caCerts: CA certificates.
RevReq ::= SEQUENCE {
enuRevReq EnuRevReq,
exRevReq SignPolExtensions OPTIONAL}
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An authority certificate is certificate issued to an authority (e.g.,
either to a certification authority or to an attribute authority
(AA)).
A Time-Stamping Authority (TSA) is a trusted third party that creates
time-stamp tokens in order to indicate that a datum existed at a
particular point in time. See [TSP].
EnuRevReq ::= ENUMERATED {
clrCheck (0),
--Checks must be made against current CRLs
-- (or authority revocation lists (ARL))
ocspCheck (1), -- The revocation status must be checked
-- using the Online Certificate Status Protocol
-- (OCSP),RFC 2450.
bothCheck (2),
-- Both CRL and OCSP checks must be carried out
eitherCheck (3),
-- At least one of CRL or OCSP checks must be
-- carried out
noCheck (4),
-- no check is mandated
other (5)
-- Other mechanism as defined by signature policy
-- extension
}
Revocation requirements are specified in terms of:
* clrCheck: Checks must be made against current CRLs (or
authority revocation lists);
* ocspCheck: The revocation status must be checked using the
Online Certificate Status Protocol (RFC 2450);
* bothCheck: Both OCSP and CRL checks must be carried out;
* eitherCheck: Either OCSP or CRL checks must be carried out;
* noCheck: No check is mandated.
The SigningCertTrustCondition field identifies trust conditions for
certificate path processing used to validate the signing certificate.
SigningCertTrustCondition ::= SEQUENCE {
signerTrustTrees CertificateTrustTrees,
signerRevReq CertRevReq
}
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The TimeStampTrustCondition field identifies trust conditions for
certificate path processing used to authenticate the timstamping
authority and constraints on the name of the time-stamping authority.
This applies to the time-stamp that must be present in every ES-T.
TimestampTrustCondition ::= SEQUENCE {
ttsCertificateTrustTrees [0] CertificateTrustTrees
OPTIONAL,
ttsRevReq [1] CertRevReq
OPTIONAL,
ttsNameConstraints [2] NameConstraints
OPTIONAL,
cautionPeriod [3] DeltaTime
OPTIONAL,
signatureTimestampDelay [4] DeltaTime
OPTIONAL }
DeltaTime ::= SEQUENCE {
deltaSeconds INTEGER,
deltaMinutes INTEGER,
deltaHours INTEGER,
deltaDays INTEGER }
If ttsCertificateTrustTrees is not present then the same rule as
defined in certificateTrustCondition applies to certification of the
time-stamping authorities public key.
The tstrRevReq specifies minimum requirements for revocation
information, obtained through CRLs and/or OCSP responses, to be used
in checking the revocation status of the time-stamp that must be
present in the ES-T.
If ttsNameConstraints is not present then there are no additional
naming constraints on the trusted time-stamping authority other than
those implied by the ttsCertificateTrustTrees.
The cautionPeriod field specifies a caution period after the signing
time that it is mandated the verifier must wait to get high assurance
of the validity of the signer's key and that any relevant revocation
has been notified. The revocation status information forming the ES
with Complete validation data must not be collected and used to
validate the electronic signature until after this caution period.
The signatureTimestampDelay field specifies a maximum acceptable time
between the signing time and the time at which the signature time-
stamp, as used to form the ES Time-Stamped, is created for the
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verifier. If the signature time-stamp is later that the time in the
signing-time attribute by more than the value given in
signatureTimestampDelay, the signature must be considered invalid.
If the attributeTrustCondition field is not present then any
certified attributes may not considered to be valid under this
validation policy. The AttributeTrustCondition field is defined as
follows:
AttributeTrustCondition ::= SEQUENCE {
attributeMandated BOOLEAN,
-- Attribute must be present
howCertAttribute HowCertAttribute,
attrCertificateTrustTrees [0] CertificateTrustTrees OPTIONAL,
attrRevReq [1] CertRevReq OPTIONAL,
attributeConstraints [2] AttributeConstraints OPTIONAL }
If attributeMandated is true then an attribute, certified within the
following constraints, must be present. If false, then the signature
is still valid if no attribute is specified.
The howCertAttribute field specifies whether attributes uncertified
attributes "claimed" by the signer, or certified attributes (i.e.,
Attribute Certificates) or either using the signer attributes
attribute defined in [ES-FORMATS] section 3.12.3.
HowCertAttribute ::= ENUMERATED {
claimedAttribute (0),
certifiedAttribtes (1),
either (2) }
The attrCertificateTrustTrees specifies certificate path conditions
for any attribute certificate. If not present the same rules apply
as in certificateTrustCondition.
The attrRevReq specifies minimum requirements for revocation
information, obtained through CRLs and/or OCSP responses, to be used
in checking the revocation status of Attribute Certificates, if any
are present.
If the attributeConstraints field is not present then there are no
constraints on the attributes that may be validated under this
policy. The attributeConstraints field is defined as follows:
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AttributeConstraints ::= SEQUENCE {
attributeTypeConstarints [0] AttributeTypeConstraints
OPTIONAL,
attributeValueConstarints [1] AttributeValueConstraints
OPTIONAL }
If present, the attributeTypeConstarints field specifies the
attribute types which are considered valid under the signature
policy. Any value for that attribute is considered valid.
AttributeTypeConstraints ::= SEQUENCE OF AttributeType
If present, the attributeTypeConstraints field specifies the specific
attribute values which are considered valid under the signature
policy.
AttributeValueConstraints ::= SEQUENCE OF AttributeTypeAndValue
The algorithmConstrains fields, if present, identifies the signing
algorithms (hash, public key cryptography, combined hash and public
key cryptography) that may be used for specific purposes and any
minimum length. If this field is not present then the policy applies
no constraints.
AlgorithmConstraintSet ::= SEQUENCE { -- Algorithm constrains on:
signerAlgorithmConstraints [0] AlgorithmConstraints OPTIONAL,
-- signer
eeCertAlgorithmConstraints [1] AlgorithmConstraints OPTIONAL,
-- issuer of end entity certs.
caCertAlgorithmConstraints [2] AlgorithmConstraints OPTIONAL,
-- issuer of CA certificates
aaCertAlgorithmConstraints [3] AlgorithmConstraints OPTIONAL,
-- Attribute Authority
tsaCertAlgorithmConstraints [4] AlgorithmConstraints OPTIONAL
-- Time-Stamping Authority
}
AlgorithmConstraints ::= SEQUENCE OF AlgAndLength
AlgAndLength ::= SEQUENCE {
algID OBJECT IDENTIFIER,
minKeyLength INTEGER OPTIONAL,
-- Minimum key length in bits
other SignPolExtensions OPTIONAL
}
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An Attribute Authority (AA)is authority which assigns privileges by
issuing attribute certificates
Additional signature policy rules may be added to:
* the overall signature policy structure, as defined in section
3.1;
* the signature validation policy structure, as defined in
section 3.2;
* the common rules, as defined in section 3.3;
* the commitment rules, as defined in section 3.4;
* the signer rules, as defined in section 3.5.1;
* the verifier rules, as defined in section 3.5.2;
* the revocation requirements in section 3.6.2;
* the algorithm constraints in section 3.10.
These extensions to the signature policy rules must be defined using
an ASN.1 syntax with an associated object identifier carried in the
SignPolExtn as defined below:
SignPolExtensions ::= SEQUENCE OF SignPolExtn
SignPolExtn ::= SEQUENCE {
extnID OBJECT IDENTIFIER,
extnValue OCTET STRING }
The extnID field must contain the object identifier for the
extension. The extnValue field must contain the DER (see ITU-T
Recommendation X.690 [4]) encoded value of the extension. The
definition of an extension, as identified by extnID must include a
definition of the syntax and semantics of the extension.
The security of the electronic signature mechanism defined in this
document depends on the privacy of the signer's private key.
Implementations must take steps to ensure that private keys cannot be
compromised.
Implementers should be aware that cryptographic algorithms become
weaker with time. As new cryptoanalysis techniques are developed and
computing performance improves, the work factor to break a particular
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cryptographic algorithm will reduce. Therefore, cryptographic
algorithm implementations should be modular allowing new algorithms
to be readily inserted. That is, implementers should be prepared for
the set of mandatory to implement algorithms to change over time.
Signer and verifier systems shall be able to process an electronic
signature in accordance with the specification of the signature
policy signature policy referenced identifiable by an Object
Identifier, see section 3.
[TS101733] ETSI Standard TS 101 733 V.1.2.2 (2000-12) Electronic
Signature Formats. Note: copies of ETSI TS 101 733 can
be freely download from the ETSI web site www.etsi.org.
[ES-FORMATS] Pinkas, D., Ross, J. and N. Pope, "Electronic Signature
Formats for Long Term Electronic Signatures", RFC 3126,
June 2001.
[TSP] Adams, C, Pinkas, D., Zuccherato, R. and P. Cain,
"Internet X.509 Public Key Infrastructure Time-Stamp
Protocol (TSP)", RFC 3161, August 2001.
[OCSP] Myers, M., Ankney, R., Malpani, R., Galperin, S. and C.
Adams, "On-line Status Certificate Protocol", RFC 2560,
June 1999.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[ESS] Hoffman, P., "Enhanced Security Services for S/MIME",
RFC 2634, June 1999.
[CMS] Housley, R., "Cryptographic Message Syntax", RFC 2630,
June 1999.
[RFC2459] Housley, R., Ford, W., Polk, W. and D. Solo, "Internet
X.509 Public Key Infrastructure, Certificate and CRL
Profile," RFC 2459, January 1999.
[PKCS9] RSA Laboratories, "The Public-Key Cryptography Standards
(PKCS)", RSA Data Security Inc., Redwood City,
California, November 1993 Release.
Ross, et al. Experimental [Page 19]
RFC 3125 Electronic Signature Policies September 2001
[ISONR] ISO/IEC 10181-5: Security Frameworks in Open Systems.
Non-Repudiation Framework. April 1997.
This Experimental RFC has been produced in ETSI TC-SEC.
ETSI
F-06921 Sophia Antipolis, Cedex - FRANCE
650 Route des Lucioles - Sophia Antipolis
Valbonne - FranceTel: +33 4 92 94 42 00 Fax: +33 4 93 65 47 16
secretariat@etsi.fr
http://www.etsi.org
Contact Point
Harri Rasilainen
ETSI
650 Route des Lucioles
F-06921 Sophia Antipolis Cedex
FRANCE
EMail: harri.rasilainen@etsi.fr
John Ross
Security & Standards
192 Moulsham Street
Chelmsford, Essex
CM2 0LG
United Kingdom
EMail: ross@secstan.com
Denis Pinkas
Integris, Bull.
68, Route de Versailles
78434 Louveciennes CEDEX
FRANCE
EMail: Denis.Pinkas@bull.net
Nick Pope
Security & Standards
192 Moulsham Street
Chelmsford, Essex
CM2 0LG
United Kingdom
EMail: pope@secstan.com
Ross, et al. Experimental [Page 20]
RFC 3125 Electronic Signature Policies September 2001
Annex A (normative):
ASN.1 Definitions This annex provides the reference definition of the
ASN.1 syntax signature policies definitions for new syntax defined in
this document.
The definition of electronic signature mentions: "a commitment has
been explicitly endorsed under a "Signature Policy", at a given time,
by a signer under an identifier, e.g., a name or a pseudonym, and
optionally a role."
Electronic signatures are commonly applied within the context of a
legal or contractual framework. This establishes the requirements on
the electronic signatures and any special semantics (e.g., agreement,
intent). These requirements may be defined in very general abstract
terms or in terms of detailed rules. The specific semantics
associated with an electronic signature implied by a legal or
contractual framework are outside the scope of this document.
If the signature policy is recognized, within the legal/contractual
context, as providing commitment, then the signer explicitly agrees
with terms and conditions which are implicitly or explicitly part of
the signed data.
When two independent parties want to evaluate an electronic
signature, it is fundamental that they get the same result. It is
therefore important that the conditions agreed by the signer at the
time of signing are indicated to the verifier and any arbitrator. An
aspect that enables this to be known by all parties is the signature
policy. The technical implications of the signature policy on the
electronic signature with all the validation data are called the
"Signature Validation Policy". The signature validation policy
specifies the rules used to validate the signature.
This document does not mandate the form and encoding of the
specification of the signature policy. However, for a given
signature policy there must be one definitive form that has a unique
binary encoded value.
This document includes, as an option, a formal structure for
signature validation policy based on the use of Abstract Syntax
Notation 1 (ASN.1).
Given the specification of the signature policy and its hash value an
implementation of a verification process must obey the rules defined
in the specification.
This document places no restriction on how it should be implemented.
Provide the implementation conforms to the conformance requirements
as define in section 5 implementation options include:
Ross, et al. Experimental [Page 34]
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A validation process that supports a specific signature policy as
identified by the signature policy OID. Such an implementation
should conform to a human readable description provided all the
processing rules of the signature policy are clearly defined.
However, if additional policies need to be supported, then such an
implementation would need to be customized for each additional
policy. This type of implementation may be simpler to implement
initially, but can be difficult to enhance to support numerous
additional signature policies.
A validation process that is dynamically programmable and able to
adapt its validation rules in accordance with a description of the
signature policy provided in a computer-processable language. This
present document defines such a policy using an ASN.1 structure (see
6.1). This type of implementation could support multiple signature
policies without being modified every time, provided all the
validation rules specified as part of the signature policy are known
by the implementation. (i.e., only requires modification if there
are additional rules specified).
The precise content of a signature policy is not mandated by the
current document. However, a signature policy must be sufficiently
definitive to avoid any ambiguity as to its implementation
requirements. It must be absolutely clear under which conditions an
electronic signature should be accepted. For this reason, it should
contain the following information:
* General information about the signature policy which includes:
- a unique identifier of the policy;
- the name of the issuer of the policy;
- the date the policy was issued;
- the field of application of the policy.
* The signature verification policy which includes:
- the signing period,
- a list of recognized commitment types;
- rules for Use of Certification Authorities;
- rules for Use of Revocation Status Information;
- rules for Use of Roles;
- rules for use of Time-Stamping and Timing;
- signature verification data to be provided by the
signer/collected by verifier;
- any constraints on signature algorithms and key lengths.
* Other signature policy rules required to meet the objectives of
the signature.
Variations of the validation policy rules may apply to different
commitment types.
Ross, et al. Experimental [Page 35]
RFC 3125 Electronic Signature Policies September 2001
When data is signed the signer indicates the signature policy
applicable to that electronic signature by including an object
identifier for the signature policy with the signature. The signer
and verifier must apply the rules specified by the identified policy.
In addition to the identifier of the signature policy the signer must
include the hash of the signature policy, so it can be verified that
the policy selected by the signer is the identical to the one being
used the verifier.
A signature policy may be qualified by additional information. This
can includes:
* A URL where a copy of the Signature Policy may be obtained;
* A user notice that should be displayed when the signature is
verified;
If no signature policy is identified then the signature may be
assumed to have been generated/verified without any policy
constraints, and hence may be given no specific legal or contractual
significance through the context of a signature policy.
A "Signature Policy" will be identifiable by an OID (Object
Identifier) and verifiable using a hash of the signature policy.
General information should be recorded about the signature policy
along with the definition of the rules which form the signature
policy as described in subsequent subsections. This should include:
* Policy Object Identifier: The "Signature Policy" will be
identifiable by an OID (Object Identifier) whose last component
(i.e., right most) is an integer that is specific to a
particular version issued on the given date.
* Date of issue: When the "Signature Policy" was issued.
* Signature Policy Issuer name: An identifier for the body
responsible for issuing the Signature Policy. This may be used
by the signer or verifying in deciding if a policy is to be
trusted, in which case the signer/verifier must authenticate
the origin of the signature policy as coming from the
identified issuer.
* Signing period: The start time and date, optionally with an end
time and date, for the period over which the signature policy
may be used to generate electronic signatures.
Ross, et al. Experimental [Page 36]
RFC 3125 Electronic Signature Policies September 2001
* Field of application: This defines in general terms the general
legal/contract/application contexts in which the signature
policy is to be used and the specific purposes for which the
electronic signature is to be applied.
The signature validation policy may recognize one or more types of
commitment as being supported by electronic signatures produced under
the security policy. If an electronic signature does not contain a
recognized commitment type then the semantics of the electronic
signature is dependent on the data being signed and the context in
which it is being used.
Only recognized commitment types are allowed in an electronic
signature.
The definition of a commitment type includes:
* the object identifier for the commitment;
* the contractual/legal/application context in which the
signature may be used (e.g., submission of messages);
* a description of the support provided within the terms of the
context (e.g., proof that the identified source submitted the
message if the signature is created when message submission is
initiated).
The definition of a commitment type can be registered:
* as part of the validation policy;
* as part of the application/contract/legal environment;
* as part of generic register of definitions.
The legal/contractual context will determine the rules applied to the
signature, as defined by the signature policy and its recognized
commitment types, make it fit for purpose intended.
The certificate validation process of the verifier, and hence the
certificates that may be used by the signer for a valid electronic
signature, may be constrained by the combination of the trust point
and certificate path constraints in the signature validation policy.
Ross, et al. Experimental [Page 37]
RFC 3125 Electronic Signature Policies September 2001
The signature validation policy defines the certification authority
trust points that are to be used for signature verification. Several
trust points may be specified under one signature policy. Specific
trust points may be specified for a particular type of commitment
defined under the signature policy. For a signature to be valid a
certification path must exists between the Certification Authority
that has granted the certificate selected by the signer (i.e., the
used user-certificate) and one of the trust point of the "Signature
Validation Policy".
There may be constraints on the use of certificates issued by one or
more CA(s) in the certificate chain and trust points. The two prime
constraints are certificate policy constraints and naming
constraints:
* Certificate policy constraints limit the certification chain
between the user certificate and the certificate of the trusted
point to a given set of certificate policies, or equivalents
identified through certificate policy mapping.
* The naming constraints limit the forms of names that the CA is
allowed to certify.
Name constraints are particularly important when a "Signature policy"
identifies more than one trust point. In this case, a certificate of
a particular trusted point may only be used to verify signatures from
users with names permitted under the name constraint.
Certificate Authorities may be organized in a tree structure, this
tree structure may represent the trust relationship between various
CA(s) and the users CA. Alternatively, a mesh relationship may exist
where a combination of tree and peer cross-certificates may be used.
The requirement of the certificate path in this document is that it
provides the trust relationship between all the CAs and the signers
user certificate. The starting point from a verification point of
view, is the "trust point". A trust point is usually a CA that
publishes self-certified certificates, is the starting point from
which the verifier verifies the certificate chain. Naming
constraints may apply from the trust point, in which case they apply
throughout the set of certificates that make up the certificate path
down to the signer's user certificate.
Policy constraints can be easier to process but to be effective
require the presence of a certificate policy identifier in the
certificates used in a certification path.
Ross, et al. Experimental [Page 38]
RFC 3125 Electronic Signature Policies September 2001
Certificate path processing, thus generally starts with one of the
trust point from the signature policy and ends with the user
certificate. The certificate path processing procedures defined in
RFC 2459 section 6 identifies the following initial parameters that
are selected by the verifier in certificate path processing:
* acceptable certificate policies;
* naming constraints in terms of constrained and excluded naming
subtree;
* requirements for explicit certificate policy indication and
whether certificate policy mapping are allowed;
* restrictions on the certificate path length.
The signature validation policy identifies constraints on these
parameters.
The signature policy should defines rules specifying requirements for
the use of certificate revocation lists (CRLs) and/or on-line
certificate status check service to check the validity of a
certificate. These rules specify the mandated minimum checks that
must be carried out.
It is expected that in many cases either check may be selected with
CRLs checks being carried out for certificate status that are
unavailable from OCSP servers. The verifier may take into account
information in the certificate in deciding how best to check the
revocation status (e.g., a certificate extension field about
authority information access or a CRL distribution point) provided
that it does not conflict with the signature policy revocation rules.
When signature under a role is mandated by the signature policy, then
either Attribute Certificates may be used or the signer may provide a
claimed role attribute. The acceptable attribute types or values may
be dependent on the type of commitment. For example, a user may have
several roles that allow the user to sign data that imply commitments
based on one or more of his roles.
Ross, et al. Experimental [Page 39]
RFC 3125 Electronic Signature Policies September 2001
When a signature under a certified role is mandated by the signature
policy, Attribute Authorities are used and need to be validated as
part of the overall validation of the electronic signature. The
trust points for Attribute Authorities do not need to be the same as
the trust points to evaluate a certificate from the CA of the signer.
Thus the trust point for verifying roles need not be the same as
trust point used to validate the certificate path of the user's key.
Naming and certification policy constraints may apply to the AA in
similar circumstance to when they apply to CA. Constraints on the AA
and CA need not be exactly the same.
AA(s) may be used when a signer is creating a signature on behalf of
an organization, they can be particularly useful when the signature
represents an organizational role. AA(s) may or may not be the same
authority as CA(s).
Thus, the Signature Policy identifies trust points that can be used
for Attribute Authorities, either by reference to the same trust
points as used for Certification Authorities, or by an independent
list.
Attribute Authorities may be organized in a tree structure in similar
way to CA where the AAs are the leafs of such a tree. Naming and
other constraints may be required on attribute certificate paths in a
similar manner to other electronic signature certificate paths.
Thus, the Signature Policy identify constraints on the following
parameters used as input to the certificate path processing:
* acceptable certificate policies, including requirements for
explicit certificate policy indication and whether certificate
policy mapping is allowed;
* naming constraints in terms of constrained and excluded naming
subtrees;
* restrictions on the certificate path length.
The following rules should be used when specifying, constraints on
the certificate paths for time-stamping authorities, constraints on
the time-stamping authority names and general timing constraints.
Ross, et al. Experimental [Page 40]
RFC 3125 Electronic Signature Policies September 2001
Signature keys from time-stamping authorities will need to be
supported by a certification path. The certification path used for
time-stamping authorities requires a trustpoint and possibly path
constraints in the same way that the certificate path for the
signer's key.
Before an electronic signature may really be valid, the verifier has
to be sure that the holder of the private key was really the only one
in possession of key at the time of signing. However, there is an
inevitable delay between a compromise or loss of key being noted, and
a report of revocation being distributed. To allow greater
confidence in the validity of a signature, a "cautionary period" may
be identified before a signature may be said to be valid with high
confidence. A verifier may revalidate a signature after this
cautionary signature, or wait for this period before validating a
signature.
The validation policy may specify such a cautionary period.
There will be some delay between the time that a signature is created
and the time the signer's digital signature is time-stamped.
However, the longer this elapsed period the greater the risk of the
signature being invalidated due to compromise or deliberate
revocation of its private signing key by the signer. Thus the
signature policy should specify a maximum acceptable delay between
the signing time as claimed by the signer and the time included
within the time-stamp.
By specifying the requirements on the signer and verifier the
responsibilities of the two parties can be clearly defined to
establish all the necessary information.
Ross, et al. Experimental [Page 41]
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These verification data rules should include:
* requirements on the signer to provide given signed attributes;
* requirements on the verifier to obtain additional certificates,
CRLs, results of on line certificate status checks and to use
time-stamps (if no already provided by the signer).
The signature validation policy may identify a set of signing
algorithms (hashing, public key, combinations) and minimum key
lengths that may be used:
* by the signer in creating the signature;
* in end entity public key Certificates;
* CA Certificates;
* attribute Certificates;
* by the time-stamping authority.
The signature policy may specify additional policy rules, for example
rules that relate to the environment used by the signer. These
additional rules may be defined in computer processable and/or human
readable form.
When signer or verifier obtains a copy of the Signature Policy from
an issuer, the source should be authenticated (for example by using
electronic signatures). When the signer references a signature
policy the Object Identifier (OID) of the policy, the hash value and
the hash algorithm OID of that policy must be included in the
Electronic Signature.
It is a mandatory requirement of this present document that the
signature policy value computes to one, and only one hash value using
the specified hash algorithm. This means that there must be a single
binary value of the encoded form of the signature policy for the
unique hash value to be calculated. For example, there may exist a
particular file type, length and format on which the hash value is
calculated which is fixed and definitive for a particular signature
policy.
Ross, et al. Experimental [Page 42]
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The hash value may be obtained by:
the signer performing his own computation of the hash over the
signature policy using his preferred hash algorithm permitted by
the signature policy, and the definitive binary encoded form.
the signer, having verified the source of the policy, may use both
the hash algorithm and the hash value included in the computer
processable form of the policy (see section 6.1).
Ross, et al. Experimental [Page 43]
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Full Copyright Statement
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Acknowledgement
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Ross, et al. Experimental [Page 44]