Composite Signatures For Use In Internet PKI
draft-ounsworth-pq-composite-sigs-09
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| Authors | Mike Ounsworth , John Gray , Massimiliano Pala | ||
| Last updated | 2023-05-29 (Latest revision 2023-03-13) | ||
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draft-ounsworth-pq-composite-sigs-09
LAMPS M. Ounsworth
Internet-Draft J. Gray
Intended status: Standards Track Entrust
Expires: 30 November 2023 M. Pala
CableLabs
29 May 2023
Composite Signatures For Use In Internet PKI
draft-ounsworth-pq-composite-sigs-09
Abstract
The migration to post-quantum cryptography is unique in the history
of modern digital cryptography in that neither the old outgoing nor
the new incoming algorithms are fully trusted to protect data for the
required data lifetimes. The outgoing algorithms, such as RSA and
elliptic curve, may fall to quantum cryptanalysis, while the incoming
post-quantum algorithms face uncertainty about both the underlying
mathematics as well as hardware and software implementations that
have not had sufficient maturing time to rule out classical
cryptanalytic attacks and implementation bugs.
Cautious implementers may wish to layer cryptographic algorithms such
that an attacker would need to break all of them in order to
compromise the data being protected using either a Post-Quantum /
Traditional Hybrid, Post-Quantum / Post-Quantum Hybrid, or
combinations thereof. This document, and its companions, defines a
specific instantiation of hybrid paradigm called "composite" where
multiple cryptographic algorithms are combined to form a single key,
signature, or key encapsulation mechanism (KEM) such that they can be
treated as a single atomic object at the protocol level.
This document defines the structures CompositeSignatureValue, and
CompositeSignatureParams, which are sequences of the respective
structure for each component algorithm. The explicit variant is
defined which allows for a set of signature algorithm identifier OIDs
to be registered together as an explicit composite signature
algorithm and assigned an OID.
This document is intended to be coupled with corresponding documents
that define the structure and semantics of composite public and
private keys and encryption [I-D.ounsworth-pq-composite-keys],
however may also be used with non-composite keys, such as when a
protocol combines multiple certificates into a single cryptographic
operation.
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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 30 November 2023.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Changes in version -09 . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Algorithm Selection Criteria . . . . . . . . . . . . . . 4
2.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
3. Composite Signature Structures . . . . . . . . . . . . . . . 6
3.1. Composite Keys . . . . . . . . . . . . . . . . . . . . . 6
3.1.1. Key Usage Bits . . . . . . . . . . . . . . . . . . . 6
3.2. sa-CompositeSignature . . . . . . . . . . . . . . . . . . 7
3.3. CompositeSignatureValue . . . . . . . . . . . . . . . . . 8
3.4. CompositeSignatureParameters . . . . . . . . . . . . . . 8
3.5. Encoding Rules . . . . . . . . . . . . . . . . . . . . . 9
4. Algorithm Identifiers . . . . . . . . . . . . . . . . . . . . 9
4.1. Notes on id-Dilithium3-RSA-PSS . . . . . . . . . . . . . 12
5. Composite Signature Processes . . . . . . . . . . . . . . . . 12
5.1. Composite Signature Generation Process . . . . . . . . . 13
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5.2. Composite Signature Verification Process . . . . . . . . 14
6. ASN.1 Module . . . . . . . . . . . . . . . . . . . . . . . . 16
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
8. Security Considerations . . . . . . . . . . . . . . . . . . . 16
8.1. Policy for Deprecated and Acceptable Algorithms . . . . . 17
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. Normative References . . . . . . . . . . . . . . . . . . 17
9.2. Informative References . . . . . . . . . . . . . . . . . 19
Appendix A. Work in Progress . . . . . . . . . . . . . . . . . . 20
A.1. Combiner modes (KofN) . . . . . . . . . . . . . . . . . . 20
Appendix B. Samples . . . . . . . . . . . . . . . . . . . . . . 21
B.1. Explicit Composite Signature Examples . . . . . . . . . . 21
Appendix C. Implementation Considerations . . . . . . . . . . . 21
C.1. Backwards Compatibility . . . . . . . . . . . . . . . . . 21
C.1.1. Parallel PKIs . . . . . . . . . . . . . . . . . . . . 21
C.1.2. Hybrid Extensions (Keys and Signatures) . . . . . . . 22
Appendix D. Intellectual Property Considerations . . . . . . . . 22
Appendix E. Contributors and Acknowledgements . . . . . . . . . 23
E.1. Making contributions . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Changes in version -09
* Removed SPHINCS+ hybrids.
* Removed all references to generic composite.
* Added selection criteria note about requesting new explicit
combinations.
2. 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 and time to discover and fix implementation bugs.
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
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* _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.
* _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 concerns by building on [I-D.ounsworth-pq-composite-keys]
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 using composite in conjunction with a non-composite
hybrid mode such as that described in
[I-D.becker-guthrie-noncomposite-hybrid-auth].
This document is intended for general applicability anywhere that
digital signatures are used within PKIX and CMS structures.
2.1. Algorithm Selection Criteria
The composite algorithm combinations defined in this document were
chosen according to the following guidelines:
1. A single RSA combination is provided (but RSA modulus size not
mandated), matched with NIST PQC Level 3 algorithms.
2. Elliptic curve algorithms are provided with combinations on each
of the NIST [RFC6090], Brainpool [RFC5639], and Edwards [RFC7748]
curves. NIST PQC Levels 1 - 3 algorithms are matched with
256-bit curves, while NIST levels 4 - 5 are matched with 384-bit
elliptic curves. This provides a balance between matching
classical security levels of post-quantum and traditional
algorithms, and also selecting elliptic curves which already have
wide adoption.
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3. NIST level 1 candidates (Falcon512 and Kyber512) are provided,
matched with 256-bit elliptic curves, intended for constrained
use cases. The authors wish to note that although all the
composite structures defined in this and the companion documents
[I-D.ounsworth-pq-composite-keys] and
[I-D.ounsworth-pq-composite-kem] specifications are defined in
such a way as to easily allow 3 or more component algorithms, it
was decided to only specify explicit pairs. This also does not
preclude future specification of explicit combinations with three
or more components.
To maximize interoperability, use of the specific algorithm
combinations specified in this document is encouraged. If other
combinations are needed, a separate specification should be submitted
to the IETF LAMPS working group. To ease implementation, these
specifications are encouraged to follow the construction pattern of
the algorithms specified in this document.
2.2. 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:
ALGORITHM: A standardized cryptographic primitive, as well as any
ASN.1 structures needed for encoding data and metadata needed to use
the algorithm. This document is primarily concerned with algorithms
for producing digital signatures.
BER: Basic Encoding Rules (BER) as defined in [X.690].
CLIENT: Any software that is making use of a cryptographic key. This
includes a signer, verifier, encrypter, decrypter.
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 3.
DER: Distinguished Encoding Rules as defined in [X.690].
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LEGACY: For the purposes of this document, a legacy algorithm is any
cryptographic algorithm currently is use which is not believe to be
resistant to quantum cryptanalysis.
PKI: Public Key Infrastructure, as defined in [RFC5280].
POST-QUANTUM ALGORITHM: Any cryptographic algorithm which is believed
to be resistant to classical and quantum cryptanalysis, such as the
algorithms being considered for standardization by NIST.
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.
STRIPPING ATTACK: An attack in which the attacker is able to
downgrade the cryptographic object to an attacker-chosen subset of
original set of component algorithms in such a way that it is not
detectable by the receiver. For example, substituting a composite
public key or signature for a version with fewer components.
3. Composite Signature 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].
3.1. Composite Keys
A composite signature MAY be associated with a composite public key
as defined in [I-D.ounsworth-pq-composite-keys], but MAY also be
associated with multiple public keys from different sources, for
example multiple X.509 certificates, or multiple cryptographic
modules. In the latter case, composite signatures MAY be used as the
mechanism for carrying multiple signatures in a non-composite hybrid
authentication mechanism such as those described in
[I-D.becker-guthrie-noncomposite-hybrid-auth].
3.1.1. 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.
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If the keyUsage extension is present in a Certification Authority
(CA) certificate that indicates a composite key, then any combination
of the following values MAY be present:
digitalSignature;
nonRepudiation;
keyCertSign; and
cRLSign.
If the keyUsage extension is present in an End Entity (EE)
certificate that indicates a composite key, then any combination of
the following values MAY be present:
digitalSignature; and
nonRepudiation;
3.2. sa-CompositeSignature
The ASN.1 algorithm object for a composite signature is:
sa-CompositeSignature SIGNATURE-ALGORITHM ::= {
IDENTIFIER TYPE OBJECT IDENTIFIER
VALUE CompositeSignatureValue
PARAMS ANY DEFINED BY ALGORITHM
PUBLIC-KEYS { pk-Composite }
SMIME-CAPS ANY DEFINED BY ALGORITHM }
The following is an explanation how SIGNATURE-ALGORITHM elements are
used to create Composite Signatures:
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+=====================+=============================================+
| SIGNATURE-ALGORITHM | Definition |
| element | |
+=====================+=============================================+
| IDENTIFIER | The Object ID used to identify |
| | the composite Signature Algorithm |
+---------------------+---------------------------------------------+
| VALUE | The Sequence of BIT STRINGS for |
| | each component signature value |
+---------------------+---------------------------------------------+
| PARAMS | Signature parameters either |
| | declared ABSENT, or defined with |
| | a type and encoding |
+---------------------+---------------------------------------------+
| PUBLIC-KEYS | The composite key required to |
| | produce the composite signature |
+---------------------+---------------------------------------------+
| SMIME_CAPS | Not needed for composite |
+---------------------+---------------------------------------------+
Table 1
3.3. CompositeSignatureValue
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 CompositeSignatureParams object.
A CompositeSignatureValue MUST contain the same number of component
signatures as the corresponding public and private keys, and the
order of component signature values MUST correspond to the component
public keys.
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.
3.4. CompositeSignatureParameters
Composite signature parameters are defined as follows and MAY be used
when a composite signature is used with an AlgorithmIdentifier:
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CompositeSignatureParams ::= SEQUENCE SIZE (2..MAX) OF
AlgorithmIdentifier{SIGNATURE-ALGORITHM, {SignatureAlgSet}}
The signature's CompositeSignatureParams sequence MUST contain the
same component algorithms listed in the same order as in the
associated CompositePublicKey.
For explicit algorithms, it is not strictly necessary to carry a
CompositeSignatureParams with the list of component algorithms in the
signature algorithm parameters because clients can infer the expected
component algorithms from the algorithm identifier. The PARAMS is
left optional because some types of component algorithms will require
parameters to be carried, such as RSASSA-PSS-params as defined in
[RFC8017]. Section 3.2 defines PARAMS ANY DEFINED BY ALGORITHM so
that explicit algorithms may define params as ABSENT, or use
CompositeSignatureParams as defined in ASN.1 module.
3.5. Encoding Rules
Many protocol specifications will require that composite signature
data structures be represented by an octet string or bit string.
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.
4. Algorithm Identifiers
This section defines the algorithm identifiers for explicit
combinations. For simplicity and prototyping purposes, the signature
algorithm object identifiers specified in this document are the same
as the composite key object Identifiers specified in {draft-
ounsworth-pq-composite-keys}. A proper implementation should not
presume that the object ID of a composite key will be the same as its
composite signature algorithm.
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This section is not intended to be exhaustive and other authors may
define others composite signature algorithms so long as they are
compatible with the structures and processes defined in this and
companion public and private key documents.
Some use-cases desire the flexibility for clients to use any
combination of supported algorithms, while others desire the rigidity
of explicitly-specified combinations of algorithms.
The following table summarizes the details for each explicit
composite signature algorithms:
The OID referenced are TBD for prototyping only, and the following
prefix is used for each:
replace <CompSig> with the String "2.16.840.1.114027.80.5.1"
Therefore <CompSig>.1 is equal to 2.16.840.1.114027.80.5.1.1
Signature public key types:
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+======================+============+==========+=======================+
|Composite Signature |OID |First |Second Algorithm |
|AlgorithmID | |Algorithm | |
+======================+============+==========+=======================+
|id-Dilithium3-RSA-PSS |<CompSig>.14|Dilithium3|SHA256WithRSAPSS |
+----------------------+------------+----------+-----------------------+
|id-Dilithium3-RSA- |<CompSig>.1 |Dilithium3|SHA256WithRSAEncryption|
|PKCS15-SHA256 | | | |
+----------------------+------------+----------+-----------------------+
|id-Dilithium3-ECDSA- |<CompSig>.2 |Dilithium3|SHA256withECDSA |
|P256-SHA256 | | | |
+----------------------+------------+----------+-----------------------+
|id-Dilithium3-ECDSA- |<CompSig>.3 |Dilithium3|SHA256withECDSA |
|brainpoolP256r1-SHA256| | | |
+----------------------+------------+----------+-----------------------+
|id-Dilithium3-Ed25519 |<CompSig>.4 |Dilithium3|Ed25519 |
+----------------------+------------+----------+-----------------------+
|id-Dilithium5-ECDSA- |<CompSig>.5 |Dilithium5|SHA384withECDSA |
|P384-SHA384 | | | |
+----------------------+------------+----------+-----------------------+
|id-Dilithium5-ECDSA- |<CompSig>.6 |Dilithium5|SHA384withECDSA |
|brainpoolP384r1-SHA384| | | |
+----------------------+------------+----------+-----------------------+
|id-Dilithium5-Ed448 |<CompSig>.7 |Dilithium5|Ed448 |
+----------------------+------------+----------+-----------------------+
|id-Falcon512-ECDSA- |<CompSig>.8 |Falcon512 |SHA256withECDSA |
|P256-SHA256 | | | |
+----------------------+------------+----------+-----------------------+
|id-Falcon512-ECDSA- |<CompSig>.9 |Falcon512 |SHA256withECDSA |
|brainpoolP256r1-SHA256| | | |
+----------------------+------------+----------+-----------------------+
|id-Falcon512-Ed25519 |<CompSig>.10|Falcon512 |Ed25519 |
+----------------------+------------+----------+-----------------------+
Table 2: Explicit Composite Signature Algorithms
The table above contains everything needed to implement the listed
explicit composite algorithms. See the ASN.1 module in section
Section 6 for the explicit definitions of the above Composite
signature algorithms.
Full specifications for the referenced algorithms can be found as
follows:
* _Dilithium_: [I-D.ietf-lamps-dilithium-certificates]
* _ECDSA_: [RFC5480]
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* _Ed25519 / Ed448_: [RFC8410]
* _Falcon_: TBD
* _RSAES-PKCS-v1_5_: [RFC8017]
* _RSASSA-PSS_: [RFC8017]
4.1. Notes on id-Dilithium3-RSA-PSS
Use of RSA-PSS [RFC8017] deserves a special explanation.
When the id-Dilithium3-RSA-PSS object identifier is used with an
AlgorithmIdentifier, the AlgorithmIdentifier.parameters MUST be of
type `CompositeSignatureParams as follows:
SEQUENCE {
AlgorithmIdentifier {
id-Dilithium3TBD
},
AlgorithmIdentifier {
id-RSASSA-PSS,
RSASSA-PSS-params
}
}
EDNOTE: We probably should pick concrete crypto for the RSASSA-PSS-
params. Once the crypto is fixed, we could omit the parameters
entirely and expect implementations to re-constitute the params
structures as necessary in order to call into lower-level crypto
libraries.
TODO: there must be a way to put all this the ASN.1 Module rather
than just specifying it as text?
5. 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 forging the composite signature would
require forging all of the component signatures.
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5.1. 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 3.2.
The following process is used to generate composite signature values.
Input:
K1, K2, .., Kn Signing private keys. See note below on
composite inputs.
A1, A2, ... An Component signature algorithms. See note below on
composite inputs.
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, Ai, 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
Note on composite inputs: the method of providing the list of
component keys and algorithms is flexible and beyond the scope of
this pseudo-code, for example they may be carried in
CompositePrivateKey and CompositeSignatureParams structures. It is
also possible to generate a composite signature that combines
signatures from distinct keys stored in separate software or hardware
keystores. Variations in the process to accommodate particular
private key storage mechanisms are considered to be conformant to
this document so long as it produces the same output as the process
sketched above.
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Since recursive composite public keys are disallowed in
[I-D.ounsworth-pq-composite-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 or an explicit composite OID.
A composite signature MUST produce, and include in the output, a
signature value for every component key in and include in the output,
a signature value for every component key in the corresponding
CompositePublicKey, and they MUST be in the same order; ie in the
output, S1 MUST correspond to K1, S2 to K2, etc.
5.2. 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:
P1, P2, .., Pn Public verification keys. See note below on
composite inputs.
M Message whose signature is to be verified,
an octet string
S1, S2, .., Sn Component signature values to be verified.
See note below on composite inputs.
A1, A2, ... An Component signature algorithms. See note
below on composite inputs.
Output:
Validity (bool) "Valid signature" (true) if the composite
signature is valid, "Invalid signature"
(false) otherwise.
Signature Verification Procedure::
1. Check keys, signatures, and algorithms lists for consistency.
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 or an explicit composite
OID 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, Ai ), then
output "Invalid signature"
if all succeeded, then
output "Valid signature"
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Note on composite inputs: the method of providing the list of
component keys, algorithms and signatures is flexible and beyond the
scope of this pseudo-code, for example they may be carried in
CompositePublicKey, CompositeSignatureParams, and
compositesignaturevalue structures. It is also possible to verify a
composite signature where the component public verification keys
belong, for example, to separate X.509 certificates or cryptographic
modules. Variations in the process to accommodate particular public
verification key storage mechanisms are considered to be conformant
to this document so long as it produces the same output as the
process sketched above.
Since recursive composite public keys are disallowed in
[I-D.ounsworth-pq-composite-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 OID id-alg-composite or an explicit
composite OID.
Some verification clients may include a policy mechanism for
specifying acceptable subsets of algorithms. In these cases,
implementer MAY, in the interest of performance of compatibility,
modify the above process to skip one or more signature validations as
per their local client policy. See
[I-D.pala-klaussner-composite-kofn] for a discussion of
implementation and associated risks.
6. ASN.1 Module
<CODE STARTS>
!! Composite-Signatures-2023.asn
<CODE ENDS>
7. IANA Considerations
This document registers the following in the SMI "Security for PKIX
Algorithms (1.3.6.1.5.5.7.6)" registry:
id-alg-composite OBJECT IDENTIFIER ::= {
iso(1) identified-organization(3) dod(6) internet(1) security(5)
mechanisms(5) pkix(7) algorithms(6) composite(??) }
Plus the ASN.1 Module OID for Composite-Signatures-2023.
8. Security Considerations
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8.1. 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), then clients performing
signatures or verifications should be updated to adhere to
appropriate policies.
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"
9. References
9.1. Normative References
[I-D.ietf-lamps-dilithium-certificates]
Massimo, J., Kampanakis, P., Turner, S., and B.
Westerbaan, "Internet X.509 Public Key Infrastructure:
Algorithm Identifiers for Dilithium", Work in Progress,
Internet-Draft, draft-ietf-lamps-dilithium-certificates-
01, 6 February 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-lamps-
dilithium-certificates-01>.
[I-D.massimo-lamps-pq-sig-certificates]
Massimo, J., Kampanakis, P., Turner, S., and B.
Westerbaan, "Algorithms and Identifiers for Post-Quantum
Algorithms", Work in Progress, Internet-Draft, draft-
massimo-lamps-pq-sig-certificates-00, 8 July 2022,
<https://datatracker.ietf.org/doc/html/draft-massimo-
lamps-pq-sig-certificates-00>.
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[I-D.ounsworth-pq-composite-keys]
Ounsworth, M., Gray, J., Pala, M., and J. Klaußner,
"Composite Public and Private Keys For Use In Internet
PKI", Work in Progress, Internet-Draft, draft-ounsworth-
pq-composite-keys-04, 13 March 2023,
<https://datatracker.ietf.org/doc/html/draft-ounsworth-pq-
composite-keys-04>.
[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>.
[RFC5480] Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk,
"Elliptic Curve Cryptography Subject Public Key
Information", RFC 5480, DOI 10.17487/RFC5480, March 2009,
<https://www.rfc-editor.org/info/rfc5480>.
[RFC5639] Lochter, M. and J. Merkle, "Elliptic Curve Cryptography
(ECC) Brainpool Standard Curves and Curve Generation",
RFC 5639, DOI 10.17487/RFC5639, March 2010,
<https://www.rfc-editor.org/info/rfc5639>.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009,
<https://www.rfc-editor.org/info/rfc5652>.
[RFC6090] McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic
Curve Cryptography Algorithms", RFC 6090,
DOI 10.17487/RFC6090, February 2011,
<https://www.rfc-editor.org/info/rfc6090>.
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[RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
for Security", RFC 7748, DOI 10.17487/RFC7748, January
2016, <https://www.rfc-editor.org/info/rfc7748>.
[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>.
[RFC8410] Josefsson, S. and J. Schaad, "Algorithm Identifiers for
Ed25519, Ed448, X25519, and X448 for Use in the Internet
X.509 Public Key Infrastructure", RFC 8410,
DOI 10.17487/RFC8410, August 2018,
<https://www.rfc-editor.org/info/rfc8410>.
[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.
9.2. Informative References
[Bindel2017]
Bindel, N., Herath, U., McKague, M., and D. Stebila,
"Transitioning to a quantum-resistant public key
infrastructure", 2017, <https://link.springer.com/
chapter/10.1007/978-3-319-59879-6_22>.
[I-D.becker-guthrie-noncomposite-hybrid-auth]
Becker, A., Guthrie, R., and M. J. Jenkins, "Non-Composite
Hybrid Authentication in PKIX and Applications to Internet
Protocols", Work in Progress, Internet-Draft, draft-
becker-guthrie-noncomposite-hybrid-auth-00, 22 March 2022,
<https://datatracker.ietf.org/doc/html/draft-becker-
guthrie-noncomposite-hybrid-auth-00>.
[I-D.guthrie-ipsecme-ikev2-hybrid-auth]
Guthrie, R., "Hybrid Non-Composite Authentication in
IKEv2", Work in Progress, Internet-Draft, draft-guthrie-
ipsecme-ikev2-hybrid-auth-00, 25 March 2022,
<https://datatracker.ietf.org/doc/html/draft-guthrie-
ipsecme-ikev2-hybrid-auth-00>.
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[I-D.ounsworth-pq-composite-kem]
Ounsworth, M. and J. Gray, "Composite KEM For Use In
Internet PKI", Work in Progress, Internet-Draft, draft-
ounsworth-pq-composite-kem-00, 11 July 2022,
<https://datatracker.ietf.org/doc/html/draft-ounsworth-pq-
composite-kem-00>.
[I-D.pala-klaussner-composite-kofn]
Pala, M. and J. Klaußner, "K-threshold Composite
Signatures for the Internet PKI", Work in Progress,
Internet-Draft, draft-pala-klaussner-composite-kofn-00, 15
November 2022, <https://datatracker.ietf.org/doc/html/
draft-pala-klaussner-composite-kofn-00>.
[RFC3279] Bassham, L., Polk, W., and R. Housley, "Algorithms and
Identifiers for the Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 3279, DOI 10.17487/RFC3279, April
2002, <https://www.rfc-editor.org/info/rfc3279>.
[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <https://www.rfc-editor.org/info/rfc7296>.
[RFC8017] Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch,
"PKCS #1: RSA Cryptography Specifications Version 2.2",
RFC 8017, DOI 10.17487/RFC8017, November 2016,
<https://www.rfc-editor.org/info/rfc8017>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[RFC8551] Schaad, J., Ramsdell, B., and S. Turner, "Secure/
Multipurpose Internet Mail Extensions (S/MIME) Version 4.0
Message Specification", RFC 8551, DOI 10.17487/RFC8551,
April 2019, <https://www.rfc-editor.org/info/rfc8551>.
Appendix A. Work in Progress
A.1. Combiner modes (KofN)
For content commitment use-cases, such as legally-binding non-
repudiation, the signer (whether it be a CA or an end entity) needs
to be able to specify how its signature is to be interpreted and
verified.
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For now we have removed combiner modes (AND, OR, KofN) from this
draft, but we are still discussing how to incorporate this for the
cases where it is needed (maybe a X.509 v3 extension, or a signature
algorithm param).
Appendix B. Samples
B.1. Explicit Composite Signature Examples
TODO
Appendix C. Implementation Considerations
This section addresses practical issues of how this draft affects
other protocols and standards.
C.1. Backwards Compatibility
The term "backwards compatibility" is used here to mean something
more specific; that existing systems as they are deployed today can
interoperate with the upgraded systems of the future. This draft
explicitly does not provide backwards compatibilitym, only upgraded
systems will understand the OIDs defined in this document.
If backwards compatibility is required, then additional mechanisms
will be needed. Migration and interoperability concerns need to be
thought about in the context of various types of protocols that make
use of X.509 and PKIX with relation to digital signature objects,
from online negotiated protocols such as TLS 1.3 [RFC8446] and IKEv2
[RFC7296], to non-negotiated asynchronous protocols such as S/MIME
signed email [RFC8551], document signing such as in the context of
the European eIDAS regulations [eIDAS2014], and publicly trusted code
signing [codeSigningBRsv2.8], as well as myriad other standardized
and proprietary protocols and applications that leverage CMS
[RFC5652] signed structures. Composite simplifies the protocol
design work because it can be implemented as a signature algorithm
that fits into existing systems.
C.1.1. Parallel PKIs
We present the term "Parallel PKI" to refer to the setup where a PKI
end entity possesses two or more distinct public keys or certificates
for the same identity (name), but containing keys for different
cryptographic algorithms. One could imagine a set of parallel PKIs
where an existing PKI using legacy algorithms (RSA, ECC) is left
operational during the post-quantum migration but is shadowed by one
or more parallel PKIs using pure post quantum algorithms or composite
algorithms (legacy and post-quantum).
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Equipped with a set of parallel public keys in this way, a client
would have the flexibility to choose which public key(s) or
certificate(s) to use in a given signature operation.
For negotiated protocols, the client could choose which public key(s)
or certificate(s) to use based on the negotiated algorithms, or could
combine two of the public keys for example in a non-composite hybrid
method such as [I-D.becker-guthrie-noncomposite-hybrid-auth] or
[I-D.guthrie-ipsecme-ikev2-hybrid-auth]. Note that it is possible to
use the signature algorithms defined in Section 4 as a way to carry
the multiple signature values generated by one of the non-composite
public mechanism in protocols where it is easier to support the
composite signature algorithms than to implement such a mechanism in
the protocol itself. There is also nothing precluding a composite
public key from being one of the components used within a non-
composite authentication operation; this may lead to greater
convenience in setting up parallel PKI hierarchies that need to
service a range of clients implementing different styles of post-
quantum migration strategies.
For non-negotiated protocols, the details for obtaining backwards
compatibility will vary by protocol, but for example in CMS
[RFC5652], the inclusion of multiple SignerInfo objects is often
already treated as an OR relationship, so including one for each of
the signer's parallel PKI public keys would, in many cases, have the
desired effect of allowing the receiver to choose one they are
compatible with and ignore the others, thus achieving full backwards
compatibility.
C.1.2. Hybrid Extensions (Keys and Signatures)
The use of Composite Crypto provides the possibility to process
multiple algorithms without changing the logic of applications, but
updating the cryptographic libraries: one-time change across the
whole system. However, when it is not possible to upgrade the crypto
engines/libraries, it is possible to leverage X.509 extensions to
encode the additional keys and signatures. When the custom
extensions are not marked critical, although this approach provides
the most backward-compatible approach where clients can simply ignore
the post-quantum (or extra) keys and signatures, it also requires all
applications to be updated for correctly processing multiple
algorithms together.
Appendix D. Intellectual Property Considerations
The following IPR Disclosure relates to this draft:
https://datatracker.ietf.org/ipr/3588/
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Appendix E. 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:
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].
E.1. Making contributions
Additional contributions to this draft are welcome. Please see the
working copy of this draft at, as well as open issues at:
https://github.com/EntrustCorporation/draft-ounsworth-composite-sigs
Authors' Addresses
Mike Ounsworth
Entrust Limited
2500 Solandt Road -- Suite 100
Ottawa, Ontario K2K 3G5
Canada
Email: mike.ounsworth@entrust.com
John Gray
Entrust Limited
2500 Solandt Road -- Suite 100
Ottawa, Ontario K2K 3G5
Canada
Email: john.gray@entrust.com
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Massimiliano Pala
CableLabs
858 Coal Creek Circle
Louisville, Colorado, 80027
United States of America
Email: director@openca.org
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