LAMPS M. Ounsworth
Internet-Draft Entrust
Intended status: Standards Track M. Pala
Expires: January 13, 2022 CableLabs
July 12, 2021
Composite Signatures For Use In Internet PKI
draft-ounsworth-pq-composite-sigs-05
Abstract
With the widespread adoption of post-quantum cryptography will come
the need for an entity to possess multiple public keys on different
cryptographic algorithms. Since the trustworthiness of individual
post-quantum algorithms is at question, a multi-key cryptographic
operation will need to be performed in such a way that breaking it
requires breaking each of the component algorithms individually.
This requires defining new structures for holding composite signature
data.
This document defines the structures CompositeSignatureValue, and
CompositeParams, which are sequences of the respective structure for
each component algorithm. This document also defines processes for
generating and verifying composite signatures. This document makes
no assumptions about what the component algorithms are, provided that
their algorithm identifiers and signature generation and verification
processes are defined.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 13, 2022.
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Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Composite Identifiers and Structures . . . . . . . . . . . . 4
2.1. Algorithm Identifier . . . . . . . . . . . . . . . . . . 5
2.2. Composite Keys . . . . . . . . . . . . . . . . . . . . . 5
2.2.1. Key Usage Bits . . . . . . . . . . . . . . . . . . . 5
2.3. Composite Signature . . . . . . . . . . . . . . . . . . . 6
2.4. Encoding Rules . . . . . . . . . . . . . . . . . . . . . 6
3. Composite Signature Processes . . . . . . . . . . . . . . . . 7
3.1. Composite Signature Generation Process . . . . . . . . . 7
3.2. Composite-OR Signature Generation Process . . . . . . . . 8
3.3. Composite Signature Verification Process . . . . . . . . 9
3.4. Composite-OR Signature Verification . . . . . . . . . . . 10
3.4.1. Composite-OR Legacy Mode . . . . . . . . . . . . . . 11
4. In Practice . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1. Cryptographic protocols . . . . . . . . . . . . . . . . . 13
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
6. Security Considerations . . . . . . . . . . . . . . . . . . . 14
6.1. Policy for Deprecated and Acceptable Algorithms . . . . . 14
7. Appendices . . . . . . . . . . . . . . . . . . . . . . . . . 14
7.1. ASN.1 Module . . . . . . . . . . . . . . . . . . . . . . 14
7.2. Intellectual Property Considerations . . . . . . . . . . 16
8. Contributors and Acknowledgements . . . . . . . . . . . . . . 16
8.1. Making contributions . . . . . . . . . . . . . . . . . . 16
9. Normative References . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
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1. Introduction
During the transition to post-quantum cryptography, there will be
uncertainty as to the strength of cryptographic algorithms; we will
no longer fully trust traditional cryptography such as RSA, Diffie-
Hellman, DSA and their elliptic curve variants, but we will also not
fully trust their post-quantum replacements until they have had
sufficient scrutiny. Unlike previous cryptographic algorithm
migrations, the choice of when to migrate and which algorithms to
migrate to, is not so clear. Even after the migration period, it may
be advantageous for an entity's cryptographic identity to be composed
of multiple public-key algorithms.
The deployment of composite signatures using post-quantum algorithms
will face two challenges
o Algorithm strength uncertainty: During the transition period, some
post-quantum signature and encryption algorithms will not be fully
trusted, while also the trust in legacy public key algorithms will
start to erode. A relying party may learn some time after
deployment that a public key algorithm has become untrustworthy,
but in the interim, they may not know which algorithm an adversary
has compromised.
o Backwards compatibility: During the transition period, post-
quantum algorithms will not be supported by all clients.
This document provides a mechanism to address algorithm strength
uncertainty by building on ~~ reference draft-ounsworth-pq-composite-
pubkeys ~~ by providing formats for encoding multiple signature
values into existing public signature fields, as well as the process
for validating a composite signature. Backwards compatibility is
addressed via the Composite-OR mechanism described herein.
This document is intended for general applicability anywhere that
digital signatures are used within PKIX and CMS structures.
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
The following terms are used in this document:
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ALGORITHM: An information object class for identifying the type of
cryptographic operation to be performed. This document is primarily
concerned with algorithms for producing digital signatures.
BER: Basic Encoding Rules (BER) as defined in [X.690].
COMPONENT ALGORITHM: A single basic algorithm which is contained
within a composite algorithm.
COMPOSITE ALGORITHM: An algorithm which is a sequence of two or more
component algorithms, as defined in Section 2.
DER: Distinguished Encoding Rules as defined in [X.690].
LEGACY: For the purposes of this document, a legacy key or signature
is a non-composite key or signature.
PUBLIC / PRIVATE KEY: The public and private portion of an asymmetric
cryptographic key, making no assumptions about which algorithm.
SIGNATURE: A digital cryptographic signature, making no assumptions
about which algorithm.
2. Composite Identifiers and Structures
In order for signatures to be composed of multiple algorithms, we
define encodings consisting of a sequence of signature primitives
(aka "component algorithms") such that these structures can be used
as a drop-in replacement for existing signature fields such as those
found in PKCS#10 [RFC2986], CMP [RFC4210], X.509 [RFC5280], CMS
[RFC5652].
This section defines the following structures:
o The id-alg-composite is an AlgorithmIdentifier identifying a
composite signature object.
The sa-CompositeSignature AlgorithmIdentifier and the
corresponding CompositeParams identify the algorithm(s) used in a
composite signature.
o The CompositeSignatureValue, carries a sequence of signatures that
are generated by a CompositePrivateKey, and can be verified with
the corresponding CompositePublicKey.
EDNOTE 2: the choice to define composite algorithm parameters as a
sequence inside the existing fields avoids the exponential
proliferation of OIDs that are needed for each combination of
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signature algorithms in other schemes for achieving multi-key
certificates. This scheme also naturally extends from 2-keypair to
n-keypair keys and certificates.
EDNOTE 2a: We have heard community feedback that the ASN.1 structures
presented here are too flexible in that allow arbitrary combinations
of an arbitrary number of signature algorithms. The feedback is that
this is too much of a "footgun" for implementors and sysadmins. We
are working on an alternative formulation using ASN.1 information
object classes that allow for compiling explicit pairs of
algorithmIDs. We would love community feedback on which approach is
preferred. See slide 30 of this presentation:
https://datatracker.ietf.org/meeting/interim-2021-lamps-01/materials/
slides-interim-2021-lamps-01-sessa-position-presentation-by-mike-
ounsworth-00.pdf
2.1. Algorithm Identifier
The following object identifier is used for identifying a composite
signature. Additional encoding information is provided below for
each of these objects.
id-alg-composite OBJECT IDENTIFIER ::= {
iso(1) identified-organization(3) dod(6) internet(1) private(4)
enterprise(1) OpenCA(18227) Algorithms(2) id-alg-composite(1) }
EDNOTE 3: this is a temporary OID for the purposes of prototyping.
We are requesting IANA to assign a permanent OID, see Section 5.
2.2. Composite Keys
A Composite signature MUST be associated with a Composite public key
as defined in ~~ reference draft-ounsworth-pq-composite-pubkey ~~.
2.2.1. Key Usage Bits
For protocols such as X.509 [RFC5280] that specify key usage along
with the public key, then the composite public key associated with a
composite signature MUST have a signing-type key usage.
If the keyUsage extension is present in a Certification Authority
(CA) certificate that indicates id-composite-key, then any
combination of the following values MAY be present:
digitalSignature;
nonRepudiation;
keyCertSign; and
cRLSign.
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If the keyUsage extension is present in an End Entity (EE)
certificate that indicates id-composite-key, then any combination of
the following values MAY be present:
digitalSignature; and
nonRepudiation;
2.3. Composite Signature
The ASN.1 algorithm object for a composite signature is:
sa-CompositeSignature SIGNATURE-ALGORITHM ::= {
IDENTIFIER id-alg-composite
VALUE CompositeSignatureValue
PARAMS TYPE CompositeParams ARE required
PUBLIC-KEYS { pk-Composite }
SMIME-CAPS { IDENTIFIED BY id-alg-composite } }
}
The following algorithm parameters MUST be included:
CompositeParams ::= SEQUENCE SIZE (2..MAX) OF AlgorithmIdentifier
The signature's CompositeParams sequence MUST contain the same
component algorithms listed in the same order as in the associated
CompositePrivateKey and CompositePublicKey.
The output of the composite signature algorithm is the DER encoding
of the following structure:
CompositeSignatureValue ::= SEQUENCE SIZE (2..MAX) OF BIT STRING
Where each BIT STRING within the SEQUENCE is a signature value
produced by one of the component keys. It MUST contain one signature
value produced by each component algorithm, and in the same order as
in the associated CompositeParams object.
The choice of "SEQUENCE OF BIT STRING", rather than for example a
single BIT STRING containing the concatenated signature values, is to
gracefully handle variable-length signature values by taking
advantage of ASN.1's built-in length fields.
2.4. Encoding Rules
Many protocol specifications will require that composite signature
data structures be represented by an octet string or bit string.
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When an octet string is required, the DER encoding of the composite
data structure SHALL be used directly.
When a bit string is required, the octets of the DER encoded
composite data structure SHALL be used as the bits of the bit string,
with the most significant bit of the first octet becoming the first
bit, and so on, ending with the least significant bit of the last
octet becoming the last bit of the bit string.
In the interests of simplicity and avoiding compatibility issues,
implementations that parse these structures MAY accept both BER and
DER.
3. Composite Signature Processes
This section specifies the processes for generating and verifying
composite signatures.
This process addresses algorithm strength uncertainty by providing
the verifier with parallel signatures from all the component
signature algorithms; thus breaking the composite signature would
require breaking all of the component signatures.
3.1. Composite Signature Generation Process
Generation of a composite signature involves applying each component
algorithm's signature process to the input message according to its
specification, and then placing each component signature value into
the CompositeSignatureValue structure defined in Section 2.3.
The following process is used to generate composite signature values.
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Input:
K1, K2, .., Kn Private keys for the n component signature
algorithms, a CompositePrivateKey
M Message to be signed, an octet string
Output:
S The signatures, a CompositeSignatureValue
Signature Generation Process:
1. Generate the n component signatures independently,
according to their algorithm specifications.
for i := 1 to n
Si := Sign( Ki, M )
2. Encode each component signature S1, S2, .., Sn into a BIT STRING
according to its algorithm specification.
S ::= Sequence { S1, S2, .., Sn }
3. Output S
Since recursive composite public keys are disallowed in ~~ Reference
draft-ounsworth-pq-composite-pubkeys sec-composite-pub-keys ~~, no
component signature may itself be a composite; ie the signature
generation process MUST fail if one of the private keys K1, K2, ..,
Kn is a composite with the OID id-alg-composite.
A composite signature MUST produce and include in the output a
signature value for every component key in the corresponding
CompositePrivateKey. For this mode, please see Composite-OR in
section Section 3.2.
3.2. Composite-OR Signature Generation Process
EDNOTE: This section was written with the intention of keeping the
primary Composite OID reserved for the simple and strict mode; if you
want to do either a simple OR, or a custom policy then we have given
a different OID. We are still debating whether this is useful to
specify at issuing time, or whether this is adding needless
complexity to the draft.
If the algorithm ID of the public key associated with this signature
is id-composite-or-key then the signer MAY use only a subset of the
component keys and therefore produce fewer signatures than the number
of component keys.
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Composite-OR signature generation uses the same structures and
algorithms as Composite, with the difference that the signature
generation process may emit a null instead of a signature value in
step 1 for one or more component algorithms. A Composite-OR
signature MUST NOT be entirely null; it must contain at least one
valid signature.
The design intent of this mode is to support migration scenarios
where an end entity has been issued keys on algorithms that either
itself or the peer with which it is communicating do not (yet)
support. This design allows for both the mode where the signer omits
signatures that it knows its peer cannot process in order to save
bandwidth and performance, and the mode where it includes all
component signatures and allows the verifier to choose how many to
verify. The latter is RECOMMENDED for signatures that need both
sort-term backwards compatibility as well as long-term security.
EDNOTE: Do we want to allow a Composite-OR with only a single
signature to produce non-composite signatureAlgorithm and
signatureValua as per [RFC5280]? Advantages: bandwidth savings of an
extra OID and some sequences with one element. Disadvantages:
ambiguous whether a signature is traditional or composite until you
look at the corresponding public key.
3.3. Composite Signature Verification Process
Verification of a composite signature involves applying each
component algorithm's verification process according to its
specification.
In the absence of an application profile specifying otherwise,
compliant applications MUST output "Valid signature" (true) if and
only if all component signatures were successfully validated, and
"Invalid signature" (false) otherwise.
The following process is used to perform this verification.
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Input:
P Signer's composite public key
M Message whose signature is to be verified, an octet string
S Composite Signature to be verified
A Composite Algorithm identifier
Output:
Validity "Valid signature" (true) if the composite signature
is valid, "Invalid signature" (false) otherwise.
Signature Verification Procedure::
1. Parse P, S, A into the component public keys, signatures,
and algorithm identifiers
P1, P2, .., Pn := Desequence( P )
S1, S2, .., Sn := Desequence( S )
A1, A2, .., An := Desequence( A )
If Error during Desequencing, or the three sequences have
different numbers of elements, or any of the public keys P1, P2, .., Pn or
algorithm identifiers A1, A2, .., An are composite with the OID
id-alg-composite then output "Invalid signature" and stop.
2. Check each component signature individually, according to its
algorithm specification.
If any fail, then the entire signature validation fails.
for i := 1 to n
if not verify( Pi, M, Si ), then
output "Invalid signature"
if all succeeded, then
output "Valid signature"
Since recursive composite public keys are disallowed in ~~ Reference
draft-ounsworth-pq-composite-keys sec-composite-pub-keys ~~, no
component signature may be composite; ie the signature verification
procedure MUST fail if any of the public keys P1, P2, .., Pn or
algorithm identifiers A1, A2, .., An are composite with the OID id-
alg-composite.
3.4. Composite-OR Signature Verification
EDNOTE: This section was written with the intention of keeping the
primary Composite OID reserved for the simple and strict mode; if you
want to do either a simple OR, or a custom policy then we have given
a different OID. We are still debating whether this is useful to
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specify at issuing time, or whether this is adding needless
complexity to the draft.
When the public key associated with the signature being verified has
algorithm id-composite-or-key, then an alternate verification
processes MAY be used, at the discretion of the implementor. In this
section we provide some examples of alternate verification processes.
If the signature is a traditional (non-composite) algorithm and value
or a composite signature with a single component, then it MAY be
considered valid if it verifies under one of the component keys.
If the signature is composite, then the implementor MAY implement
policy for which combinations are acceptable.
EDNOTE: Does this mean Composite-OR end entity certificates need to
be issued by a PKI that is marked as Composite-OR all the way to the
top so that verifiers that do not support all the algorithms don't
fail? Need to think more about the security implications of allowing
a Composite-or in an end entity cert implicitely turning all
Composite algIDs into Composite-or algIDs in its cert chain.
EDNOTE: Do we need to specify the semantics of verifying an "n of m"
subset signature? I suspect that specifying this in general will be
a rat's nest of edge cases, so I propose to "leave this to the
implementor".
3.4.1. Composite-OR Legacy Mode
The Composite-OR Legacy Mode is provided to facilitate migration by
allowing existing PKI entities (including root CAs, intermediate CAs,
and end entities) to have their existing keys re-certified inside a
Composite-OR structure along with Post-Quantum keys, and for
signatures made by that key prior to the migration to remain valid.
Note that Composite-OR Legacy Mode is only provided for signature
verification, and not for signature generation; legacy signatures
SHOULD NOT be produced from a Composite key.
EDNOTE: to further solidify this, we could add a clause that Legacy
Mode signatures are to fail if the signature was produced after
notBefore date of the Composite-OR certificate?
In Composite-OR Legacy Mode, a legacy signature algorithm and legacy
signature value MAY be validated against a Composite-OR public key.
The legacy signature algorithm is to be interpreted by the verifier
as a sa-CompositeSignature with CompositeParams in the following way:
CompositeParams {legacyAlgorithmIdentifier, null, .., null}
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with the correct number of nulls to match the Composite-OR public key
that the signature is being verified against. For the purposes of a
signature validation under Composite-OR Legacy Mode, a null
AlgorithmIdentifier is considered to be a match for the corresponding
algorithm in the Composite-OR public key.
The legacy signature value is to be interpreted by the verifier as a
sa-CompositeSignature with CompositeParams in the following way:
CompositeSignatureValue {legacySignatureValue, null, .., null}
with the correct number of nulls to match the Composite-OR public key
that the signature is being verified against. The verification
algorithm in section Section 3.4 applies.
Security consideration: when implementing Composite-OR Legacy Mode,
it is important to catch the edge case of {null, null, .., null} for
both AlgorithmIdentifier and SignatureValue and return Invalid
Signature.
It is RECOMMENDED that Composite-OR Legacy Mode be implemented as an
optional mode in the verifier that can be enabled or disabled by
runtime configuration or policy.
EDNOTE: the signing public key is often identified in the signed
document by issuer+serialNumber or by an SKI containing a hash of the
public key value. Might need X.509 extensions identifying the SKI of
the legacy cert it's replacing?
4. In Practice
This section addresses practical issues of how this draft affects
other protocols and standards.
~~~ BEGIN EDNOTE 10~~~
EDNOTE 10: Possible topics to address:
o The size of these certs and cert chains.
o In particular, implications for (large) composite keys /
signatures / certs on the handshake stages of TLS and IKEv2.
o If a cert in the chain is a composite cert then does the whole
chain need to be of composite Certs?
o We could also explain that the root CA cert does not have to be of
the same algorithms. The root cert SHOULD NOT be transferred in
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the authentication exchange to save transport overhead and thus it
can be different than the intermediate and leaf certs.
o We could talk about overhead (size and processing).
o We could also discuss backwards compatibility.
o We could include a subsection about implementation considerations.
~~~ END EDNOTE 10~~~
4.1. Cryptographic protocols
This section talks about how protocols like (D)TLS and IKEv2 are
affected by this specifications. It will not attempt to solve all
these problems, but it will explain the rationale, how things will
work and what open problems need to be solved. Obvious issues that
need to be discussed.
o How does the protocol declare support for composite signatures?
TLS has hooks for declaring support for specific signature
algorithms, however it would need to be extended, because the
client would need to declare support for both the composite
infrastructure, as well as for the various component signature
algorithms.
o How does the protocol use the multiple keys. The obvious way
would be to have the server sign using its composite public key;
is this sufficient.
o Overhead; including certificate size, signature processing time,
and size of the signature.
o How to deal with crypto protocols that use public key encryption
algorithms; this document only lists how to work with signature
algorithms. Encoding composite public keys is straightforward;
encoding composite ciphertexts is less so - we decided to put that
off to another draft.
5. IANA Considerations
The ASN.1 module OID is TBD. The id-alg-composite OID is to be
assigned by IANA. The authors suggest that IANA assign an OID on the
id-pkix arc:
id-alg-composite OBJECT IDENTIFIER ::= {
iso(1) identified-organization(3) dod(6) internet(1) security(5)
mechanisms(5) pkix(7) algorithms(6) composite(??) }
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6. Security Considerations
6.1. Policy for Deprecated and Acceptable Algorithms
Traditionally, a public key, certificate, or signature contains a
single cryptographic algorithm. If and when an algorithm becomes
deprecated (for example, RSA-512, or SHA1), it is obvious that
structures using that algorithm are implicitly revoked.
In the composite model this is less obvious since a single public
key, certificate, or signature may contain a mixture of deprecated
and non-deprecated algorithms. Moreover, implementers may decide
that certain cryptographic algorithms have complementary security
properties and are acceptable in combination even though neither
algorithm is acceptable by itself.
Specifying a modified verification algorithm to handle these
situations is beyond the scope of this draft, but could be desirable
as the subject of an application profile document, or to be up to the
discretion of implementers.
2. Check policy to see whether A1, A2, ..., An constitutes a valid
combination of algorithms.
if not checkPolicy(A1, A2, ..., An), then
output "Invalid signature"
While intentionally not specified in this document, implementors
should put careful thought into implementing a meaningfull policy
mechinism within the context of their signature verification engines,
for example only algorithms that provide similar security levels
should be combined together.
7. Appendices
7.1. ASN.1 Module
<CODE STARTS>
Composite-Signatures-2019
{ TBD }
DEFINITIONS IMPLICIT TAGS ::= BEGIN
EXPORTS ALL;
IMPORTS
PUBLIC-KEY, SIGNATURE-ALGORITHM
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FROM AlgorithmInformation-2009 -- RFC 5912 [X509ASN1]
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-algorithmInformation-02(58) }
SubjectPublicKeyInfo
FROM PKIX1Explicit-2009
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkix1-explicit-02(51) }
OneAsymmetricKey
FROM AsymmetricKeyPackageModuleV1
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
pkcs-9(9) smime(16) modules(0)
id-mod-asymmetricKeyPkgV1(50) } ;
--
-- Object Identifiers
--
id-alg-composite OBJECT IDENTIFIER ::= { TBD }
--
-- Public Key
--
pk-Composite PUBLIC-KEY ::= {
IDENTIFIER id-alg-composite
KEY CompositePublicKey
PARAMS ARE absent
PRIVATE-KEY CompositePrivateKey
}
CompositePublicKey ::= SEQUENCE SIZE (2..MAX) OF SubjectPublicKeyInfo
CompositePrivateKey ::= SEQUENCE SIZE (2..MAX) OF OneAsymmetricKey
--
-- Signature Algorithm
--
sa-CompositeSignature SIGNATURE-ALGORITHM ::= {
IDENTIFIER id-alg-composite
VALUE CompositeSignatureValue
PARAMS TYPE CompositeParams ARE required
PUBLIC-KEYS { pk-Composite }
SMIME-CAPS { IDENTIFIED BY id-alg-composite } }
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CompositeParams ::= SEQUENCE SIZE (2..MAX) OF AlgorithmIdentifier
CompositeSignatureValue ::= SEQUENCE SIZE (2..MAX) OF BIT STRING
END
<CODE ENDS>
7.2. Intellectual Property Considerations
The following IPR Disclosure relates to this draft:
https://datatracker.ietf.org/ipr/3588/
8. Contributors and Acknowledgements
This document incorporates contributions and comments from a large
group of experts. The Editors would especially like to acknowledge
the expertise and tireless dedication of the following people, who
attended many long meetings and generated millions of bytes of
electronic mail and VOIP traffic over the past year in pursuit of
this document:
John Gray (Entrust), Serge Mister (Entrust), Scott Fluhrer (Cisco
Systems), Panos Kampanakis (Cisco Systems), Daniel Van Geest (ISARA),
Tim Hollebeek (Digicert), and Francois Rousseau.
We are grateful to all, including any contributors who may have been
inadvertently omitted from this list.
This document borrows text from similar documents, including those
referenced below. Thanks go to the authors of those documents.
"Copying always makes things easier and less error prone" -
[RFC8411].
8.1. Making contributions
Additional contributions to this draft are weclome. Please see the
working copy of this draft at, as well as open issues at:
https://github.com/EntrustCorporation/draft-ounsworth-composite-sigs
9. Normative References
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2986] Nystrom, M. and B. Kaliski, "PKCS #10: Certification
Request Syntax Specification Version 1.7", RFC 2986,
DOI 10.17487/RFC2986, November 2000,
<https://www.rfc-editor.org/info/rfc2986>.
[RFC4210] Adams, C., Farrell, S., Kause, T., and T. Mononen,
"Internet X.509 Public Key Infrastructure Certificate
Management Protocol (CMP)", RFC 4210,
DOI 10.17487/RFC4210, September 2005,
<https://www.rfc-editor.org/info/rfc4210>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009,
<https://www.rfc-editor.org/info/rfc5652>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8411] Schaad, J. and R. Andrews, "IANA Registration for the
Cryptographic Algorithm Object Identifier Range",
RFC 8411, DOI 10.17487/RFC8411, August 2018,
<https://www.rfc-editor.org/info/rfc8411>.
[X.690] ITU-T, "Information technology - ASN.1 encoding Rules:
Specification of Basic Encoding Rules (BER), Canonical
Encoding Rules (CER) and Distinguished Encoding Rules
(DER)", ISO/IEC 8825-1:2015, November 2015.
Authors' Addresses
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Mike Ounsworth
Entrust Limited
2500 Solandt Road -- Suite 100
Ottawa, Ontario K2K 3G5
Canada
Email: mike.ounsworth@entrust.com
Massimiliano Pala
CableLabs
Email: director@openca.org
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