| Internet-Draft | IKEv2 PQTH Auth | November 2024 |
| Jun & Morioka | Expires 7 May 2025 | [Page] |
One IPsec area that would be impacted by Cryptographically Relevant Quantum Computer (CRQC) is IKEv2 authentication based on traditional asymmetric cryptograph algorithms: e.g RSA, ECDSA; which are widely deployed authentication options of IKEv2. There are new Post-Quantum Cryptograph (PQC) algorithms for digital signature like NIST [ML-DSA], however it takes time for new cryptograph algorithms to mature, so there is security risk to use only the new algorithm before it is field proven. This document describes a IKEv2 hybrid authentication scheme that could contain both traditional and PQC algorithms, so that authentication is secure as long as one algorithm in the hybrid scheme is secure.¶
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A Cryptographically Relevant Quantum Computer (CRQC) could break traditional asymmetric cryptograph algorithms: e.g RSA, ECDSA; which are widely deployed authentication options of IKEv2. New Post-Quantum Cryptograph (PQC) algorithms for digital signature were recently published like NIST [ML-DSA], however consider potential flaws in the new algorithm's specifications and implementations, it will take time for these new PQC algorithms to be field proven. So it is risky to only use PQC algorithms before they are mature. There is more detailed discussion on motivation of a hybrid approach for authentication in Section 1.3 of [I-D.ietf-pquip-hybrid-signature-spectrums].¶
This document describes an IKEv2 hybrid authentication scheme that contains both traditional and PQC algorithms, so that authentication is secure as long as one algorithm in the hybrid scheme is secure.¶
Each IPsec peer announce the support of hybrid authentication via SUPPORTED_AUTH_METHODS notification as defined in [RFC9593], generates and verifies AUTH payload using composite signature like the procedures defined in [I-D.ietf-lamps-pq-composite-sigs].¶
Following two types of setup are covered:¶
Type-1: A single certificate that has composite key as defined in [I-D.ietf-lamps-pq-composite-sigs]¶
Type-2: Two certificates, one with traditional algorithm key and one with PQC algorithm key¶
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.¶
Cryptographically Relevant Quantum Computer (CRQC): A quantum computer that is capable of breaking real world cryptographic systems.¶
Post-Quantum Cryptograph (PQC) algorithms: Asymmetric cryptograph algorithms are thought to be secure against CRQC.¶
Traditional Cryptograph algorithms: Existing asymmetric cryptograph algorithms could be broken by CRQC, like RSA, ECDSA ..etc.¶
There is no changes introduced in this document to the IKEv2 key exchange process, although it MUST be also resilient to CRQC when using along with the PQ/T hybrid authentication, for example key exchange using the PPK as defined in [RFC8784], or hybrid key exchanges that include PQC algorithm via multiple key exchange process as defined in [RFC9370].¶
The hybrid authentication exchanges is illustrated in an example depicted in Figure 1, the key exchange uses PPK, however it could be other key exchanges that involves PQC algorithm since how key exchange is done is transparent to authentication.¶
Initiator Responder
-------------------------------------------------------------------
HDR, SAi1, KEi, Ni,
N(USE_PPK) -->
<-- HDR, SAr1, KEr, Nr, [CERTREQ,] N(USE_PPK),
N(SUPPORTED_AUTH_METHODS)
HDR, SK {IDi, CERT+, [CERTREQ,]
[IDr,] AUTH, SAi2,
TSi, TSr, N(PPK_IDENTITY, PPK_ID),
N(SUPPORTED_AUTH_METHODS)} -->
<-- HDR, SK {IDr, CERT+, [CERTREQ,]
AUTH, [N(PPK_IDENTITY)]}
Announcement of support hybrid authentication is through SUPPORTED_AUTH_METHODS notification as defined in [RFC9593], which includes a list of acceptable authentication methods announcements, this document defines a hybrid authentication announcements with following format:¶
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length (>=2) | Auth Method | Cert Link 1 | Alg 1 flag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Alg 1 Len | |
+-+-+-+-+-+-+-+-+ |
~ AlgorithmIdentifier 1 ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cert Link 2 | Alg 2 flag | Alg 2 Len | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
~ AlgorithmIdentifier 2 ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cert Link 3 | Alg 3 flag | Alg 3 Len | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
~ AlgorithmIdentifier N ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The announcement include a list of N algorithms could be used for hybrid signature¶
Auth Method: A new value to be allocated by IANA¶
Cert Link N: Links corresponding signature algorithm N with a particular CA. as defined in Section 3.2.2 of [RFC9593]¶
Alg N Flag:¶
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|C|S| RESERVED |
+-+-+-+-+-+-+-+-+
AlgorithmIdentifier N: The variable-length ASN.1 object that is encoded using Distinguished Encoding Rules (DER) [X.690] and identifies the algorithm of a composite signature as defined in Section 7 of [I-D.ietf-lamps-pq-composite-sigs].¶
As defined in [RFC9593], responder include SUPPORTED_AUTH_METHODS in IKE_SA_INIT response (and potentially also in IKE_INTERMEDIATE response), while initiator include the notification in IKE_AUTH request.¶
Sender include a hybrid authentication announcement in SUPPORTED_AUTH_METHODS, which contains 0 or N composite signature AlgorithmIdentifiers sender accepts, each AlgorithmIdentifier identifies a combination of algorithms:¶
a traditional PKI algorithm with corresponding hash algorithm (e.g. id-RSASA-PSS with id-sha256)¶
a PQC algorithm (e.g. id-ML-DSA-44)¶
in case of Hash ML-DSA, there is also a pre-hash algorithm (e.g. id-sha256)¶
In case of type-2 setup, even though the certificate is not composite key certificate, system still uses a composite signature algorithm that corresponds to the combination of two certificates PKI algorithms and hash algorithm(s).¶
C and S bits in flag field are set according to whether sender accept the algorithm combination in type-1/type-2 setup.¶
Announcement without any AlgorithmIdentifiers signals that there is no particular restrictions on algorithm.¶
If hybrid authentication announcement is received, and receiver choose to authenticate itself using hybrid authentication, then based on its local policy and certificates, one AlgorithmIdentifier (which identify a combination of algorithms) in the hybrid authentication announcement and a PKI setup (type-1 or type-2) are chosen to create its AUTH and CERT payload(s).¶
The IKEv2 AUTH payload has following format as defined in Section 3.8 of [RFC7296]:¶
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Payload |C| RESERVED | Payload Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Auth Method | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Authentication Data ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
For hybrid authentication, the AUTH Method has value defined in Section 5.1¶
The Authentication Data field follows format defined in Section 3 of [RFC7427]:¶
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ASN.1 Length | AlgorithmIdentifier ASN.1 object |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ AlgorithmIdentifier ASN.1 object continuing ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Signature Value ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Based on selected AlgorithmIdentifier and setup type, the Signature Value is created via procedure defined in Section 5.2.1, Section 5.2.2.¶
Assume selected AlgorithmIdentifier is A.¶
There is no change on data to be signed, e.g. InitiatorSignedOctets/ResponderSignedOctets as defined in Section 2.15 of [RFC7296]¶
Follow Sign operation identified by A, e.g. Section 4.2.1 of [I-D.ietf-lamps-pq-composite-sigs] or Section 4.3.1 of [I-D.ietf-lamps-pq-composite-sigs]; the ctx input is the string of "IKEv2-PQT-Hybrid-Auth".¶
Following is an initiator example:¶
A is id-HashMLDSA44-RSA2048-PSS-SHA256, which uses Hash ML-DSA-44¶
Follow Section 4.3.1 of [I-D.ietf-lamps-pq-composite-sigs] with following input:¶
The signing composite certificate MUST be the first CERT payload.¶
The procedure is same as Type-1, use private key of traditional and PQC certificate accordingly; e.g. in Sign procedure define in Section 4.2.1 of [I-D.ietf-lamps-pq-composite-sigs], the mldsaSK is the private key of ML-DSA certificate, while tradSK is the private key of traditional certificate.¶
With the example in Section 5.2.1:¶
mldsaSK is the private key of ML-DSA certificate, tradSK is the private key of the RSA certificate¶
M is InitiatorSignedOctets¶
ctx is "IKEv2-PQT-Hybrid-Auth"¶
PH is SHA256¶
The signing PQC certificate MUST be the first CERT payload in the IKEv2 message, while traditional certificate MUST be the second CERT payload.¶
The security of general PQ/T hybrid authentication is discussed in [I-D.ietf-pquip-hybrid-signature-spectrums].¶
This document uses mechanisms defined in [I-D.ietf-lamps-pq-composite-sigs], [RFC7427] and [RFC9593], the security discussion in the corresponding RFCs also apply.¶
This document requests a value in "IKEv2 Authentication Method" subregistry under IANA "Internet Key Exchange Version 2 (IKEv2) Parameters" registry¶
TODO acknowledge.¶