The EAP-PQPAKE Authentication Method

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Table of Contents

1. Introduction

The Extensible Authentication Protocol (EAP) [RFC3748] supports multiple authentication methods between an EAP peer and an EAP server. Several EAP methods use passwords directly, including EAP-pwd [RFC5931] and EAP-EKE [RFC6124]. These methods address the operational need for authentication from a human-memorable password while limiting the value of passive observation and offline dictionary attacks.¶

Existing password-based EAP methods are built from classical public-key assumptions. A quantum-capable attacker that records authentication exchanges today may later be able to recover keying material when those classical assumptions fail. This is undesirable for deployments where the confidentiality or integrity of subsequent traffic remains valuable after the authentication exchange has completed.¶

This document specifies EAP-PQPAKE, an EAP method that encapsulates CPaceOQUAKE+ from Section 8.3 of [I-D.vos-cfrg-pqpake], revision draft-vos-cfrg-pqpake-03. CPaceOQUAKE+ is a hybrid asymmetric PAKE that combines a classical PAKE component with a post-quantum KEM-based component. EAP-PQPAKE defines the EAP message flow, packet formats, method transcript, exported MSK and EMSK derivation, fragmentation behavior, and IANA registries needed to use CPaceOQUAKE+ as an EAP method.¶

CPaceOQUAKE+ is derived from CPaceOQUAKE, a hybrid symmetric PAKE that sequentially composes CPace and OQUAKE. CPace contributes a classical PAKE whose transcript is unconditionally password hiding, while OQUAKE contributes a post-quantum KEM-based PAKE component.¶

EAP-PQPAKE assumes that the server has been provisioned with the CPaceOQUAKE+ password verifiers for the peer. The registration procedure used to create those verifiers is specified by CPaceOQUAKE+ and is outside the EAP authentication exchange defined in this document. The registered verifier consists of (v, pk, kem_blind); the server also stores the salt, configuration, and registration identities. Registration MUST authenticate the server and protect the confidentiality and integrity of the verifier material.¶

Either endpoint may derive the verifier: a server configured with the password derives it and erases the password, or the peer derives it and uploads it using the protected registration procedure described above. The peer stores no persistent verifier state.¶

Note: This document version is experimental and relies on a work in progress PAKE algorithm.¶

2. Conventions and Definitions

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 throughout this document:¶

EAP peer:

The endpoint being authenticated by the EAP server.¶

EAP server:

The endpoint that selects the EAP method, stores the peer's CPaceOQUAKE+ verifier state, and authenticates the peer.¶

PRS:

The password-related string input to CPaceOQUAKE+. This is commonly the password after local password processing.¶

U:

The peer identity used when registering the CPaceOQUAKE+ verifier.¶

S:

The server identity used when registering the CPaceOQUAKE+ verifier.¶

kem_blind:

A secret, random 32-octet part of the registered verifier. It blinds password-derived KEM key generation and is sent to the peer only in encrypted form during password confirmation.¶

public_context:

Public session information encoded with EncodePublicContext as specified in Appendix C.1 of [I-D.vos-cfrg-pqpake].¶

secret_context:

Confidential context shared by the PAKE endpoints. EAP-PQPAKE passes the empty octet string as this input to CPaceOQUAKE+.¶

Config:

A registered set of CPaceOQUAKE+ algorithms and parameters.¶

Method key:

The 32-octet client_key or server_key output by the CPaceOQUAKE+ password confirmation stage. EAP-PQPAKE expands this value to the MSK and EMSK.¶

uint8, uint16, uint32:

Unsigned integers encoded in network byte order.¶

opaque16:

A variable-length octet string encoded as a uint16 length followed by that many octets.¶

3. Protocol Overview

EAP is a lock-step request/response protocol in which the EAP server sends each Request and the EAP peer sends the corresponding Response. CPaceOQUAKE+ is initiated by the client. EAP-PQPAKE therefore uses a server request carrying the salt and a fresh nonce to solicit the first CPaceOQUAKE+ message from the peer after identity and configuration negotiation have completed.¶

A successful EAP-PQPAKE exchange has the following shape:¶

 EAP peer                                      EAP server
 --------                                      ----------

                          EAP-PQPAKE-Start/Request
                  <---------------------------------
 EAP-PQPAKE-Start/Response
 --------------------------------->

                          EAP-PQPAKE-PAKE1/Request
                  <---------------------------------
 EAP-PQPAKE-PAKE1/Response  (msg1: Ya)
 --------------------------------->

                          EAP-PQPAKE-PAKE2/Request
                          (msg2: Yb, s, T, rho)
                  <---------------------------------
 EAP-PQPAKE-PAKE2/Response  (msg3: ct, h)
 --------------------------------->

                          EAP-PQPAKE-Confirm/Request
                          (msg4: enc_c, client_confirm)
                  <---------------------------------
 EAP-PQPAKE-Confirm/Response  (msg5: server_confirm)
 --------------------------------->

                          EAP-Success
                  <---------------------------------

The Start exchange negotiates one CPaceOQUAKE+ configuration and identifies the peer and server. After receiving the peer identity, the server locates the stored (v, pk, kem_blind) and salt for that peer and selected configuration. The PAKE1 and PAKE2 exchanges carry the first three CPaceOQUAKE+ messages. The Confirm exchange carries the password confirmation challenge msg4 and response msg5. The field rho in the diagram denotes the public matrix seed of ML-BUA-sKEM.¶

On success, both endpoints derive the EAP MSK and EMSK from the CPaceOQUAKE+ method key. On failure, either endpoint can send an EAP-PQPAKE-Failure message. The server terminates failed exchanges with EAP-Failure.¶

4. CPaceOQUAKE+ Use

EAP-PQPAKE uses the six CPaceOQUAKE+ functions in Section 8.3 of [I-D.vos-cfrg-pqpake]. The peer calls Init, InitiatorContinue, and InitiatorFinish; the server calls Respond, ResponderContinue, and ResponderFinish.¶

The CPaceOQUAKE+ messages carried by this method are opaque to EAP-PQPAKE. Implementations that implement CPaceOQUAKE+ directly, rather than using a CPaceOQUAKE+ library interface, MUST follow the selected CPaceOQUAKE+ configuration exactly. In particular, OQUAKE ciphertext lengths and parsing are determined by the BUA-sKEM parameters of that configuration and MUST NOT be inferred from public-key lengths. Kemeleon uniform encoding is applied only where CPaceOQUAKE+ specifies it, such as to the ML-BUA-sKEM public-key material, and MUST NOT be applied to ciphertexts unless the selected CPaceOQUAKE+ configuration explicitly requires it.¶

The peer computes the CPaceOQUAKE+ verifier material (v, seed) from PRS, salt, U, and S using GenVerifierMaterial. At registration, GenVerifier creates (v, pk, kem_blind): it samples a fresh kem_blind and derives the KEM key pair from DeriveKEMSeed(seed, kem_blind). The server MUST store v, pk, kem_blind, the 32-octet salt, the configuration, and the registration identities. It MUST NOT store seed or the corresponding KEM secret key. The server MUST NOT disclose kem_blind in the Start or PAKE1 exchange; CPaceOQUAKE+ carries it only inside the encrypted password confirmation challenge.¶

The EAP-PQPAKE session identifier sid and CPaceOQUAKE+ contexts are:¶

sid = H("EAP-PQPAKE sid" ||
        lv_encode(start_request_payload) ||
        lv_encode(start_response_payload) ||
        lv_encode(pake1_request_payload))
public_context = EncodePublicContext(sid, U, S)
secret_context = b""

Here H is the EAP hash selected by the configuration and lv_encode is the two-octet length-prefix encoding defined in [I-D.vos-cfrg-pqpake]. Each _payload value is the complete exchange-specific payload after reassembly, including its field length prefixes. It excludes the EAP header, Flags, PQPAKE-Exch, Total-Length, and fragmentation acknowledgements. Quoted labels are ASCII octets without a terminating zero.¶

U is the Peer-ID value from Start/Response, excluding its type and length; S is the Server-ID value from Start/Request, excluding its type and length. These MUST be the exact octet strings used for verifier registration. A peer MUST check S against its configured registration before starting the PAKE. Implementations MUST NOT normalize these octet strings during the exchange. Changing either registration identity requires reprovisioning. The identity types and their wire encodings are also bound through sid.¶

EncodePublicContext MUST use the four-octet, big-endian length prefixes from Appendix C.1 of [I-D.vos-cfrg-pqpake]. Both endpoints pass the resulting public_context and the empty secret_context to their initial CPaceOQUAKE+ call. CPaceOQUAKE internally supplies the first stage's key and transcript hash as the contexts for OQUAKE.¶

The CPaceOQUAKE+ functions compute their own transcript hash th. Password confirmation uses the SK and th output by the symmetric CPaceOQUAKE stage: PC.Challenge(SK, th, pk, kem_blind) and PC.Respond(SK, th, seed, challenge). Implementations MUST preserve these inputs exactly; they MUST NOT substitute an EAP-specific transcript hash for th. The initial public context binds the EAP configuration negotiation, identities, salt, and server nonce, while the internal transcript hashes bind the subsequent PAKE messages. The final th is returned with client_key or server_key after successful password confirmation.¶

The intermediate SK MUST NOT be used for EAP key export. The server MUST NOT release or use the candidate key held in the state returned by ResponderContinue until ResponderFinish succeeds. The peer obtains its method key only after InitiatorFinish verifies the server's password confirmation value.¶

An implementation MUST abort the exchange if a CPaceOQUAKE+ operation raises AuthenticationError, CPaceError, or another surfaced cryptographic failure, if a received message has incorrect length or framing for the selected configuration, or if the selected configuration does not match one offered by the server.¶

OQUAKE's implicit rejection and random-key behavior MUST be preserved. An implementation MUST NOT expose a distinguishable error for an OQUAKE confirmation mismatch that the underlying protocol handles by returning an unrelated key. Such a mismatch is detected during the subsequent password confirmation exchange.¶

5. Configurations

An EAP-PQPAKE configuration identifies all cryptographic parameters needed by CPaceOQUAKE+ and the EAP exporter. This document defines one mandatory-to-implement configuration:¶

cpaceoquakeplus-x25519-mlbuaskem1024-xwing:

The preferred configuration in Section 9.5.1 of [I-D.vos-cfrg-pqpake], with the common parameters from Section 9.1.¶

The scrypt function is specified in [RFC7914]. For ML-BUA-sKEM-1024, Kemeleon.t is 132, Npk is 1596, Nt is 1564, the public matrix seed is 32 octets, and Nct is 1568. For the X-Wing password-confirmation KEM, Nseed is 32, Npk is 1216, and Nct is 1120. This configuration requires both ML-KEM-1024 for OQUAKE and ML-KEM-768 as used by X-Wing.¶

The domain separation tag is the following 32-octet value, shown in hexadecimal:¶

7de162c387ba1bad9c790e7e56bd245d6753d045185cbc3972eba34ddac1a9db

This CPaceOQUAKE+ DST MUST be used throughout CPace, OQUAKE, transcript hashing, verifier generation, and password confirmation. It MUST NOT be combined with the DST values of standalone CPaceOQUAKE or OQUAKE configurations.¶

Implementations conforming to this document MUST implement this configuration. Other configurations MAY be registered as described in Section 10. New configurations MUST specify the complete CPaceOQUAKE+ parameter set, satisfy Section 9.6 of [I-D.vos-cfrg-pqpake], and use a hybrid KEM for password confirmation. They MUST also specify the EAP hash and the HKDF hash used by Section 8.¶

This configuration and the -03 message formats are incompatible with the Ristretto255/Argon2id configuration and encodings in earlier versions of this EAP draft. Deployments using those versions MUST reprovision verifiers with GenVerifier from the referenced revision, including a fresh kem_blind. The old verifier material MUST NOT be reinterpreted as a registration for this configuration.¶

6. Packet Format

EAP-PQPAKE packets consist of the standard EAP header followed by an EAP-PQPAKE method header and the exchange-specific payload. Multi-octet integers are encoded in network byte order.¶

 0                   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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Code      |  Identifier   |             Length            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Type      |     Flags     |  PQPAKE-Exch  |   Data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Code, Identifier, Length, and Type are the EAP fields defined in [RFC3748]. The Type value for EAP-PQPAKE is TBD1.¶

The Flags field is defined as follows:¶

 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|L|M| Reserved  |
+-+-+-+-+-+-+-+-+

L:

Length included. When set, a uint16 Total-Length field appears at the start of Data.¶

M:

More fragments. When set, more fragments of the same EAP-PQPAKE message follow.¶

Reserved:

MUST be sent as zero and MUST be ignored by the receiver.¶

PQPAKE-Exch identifies the exchange payload:¶

If the L bit is set, Data begins with:¶

 0                   1
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|         Total-Length          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Total-Length is the length in octets of the unfragmented EAP-PQPAKE message, including the EAP header, EAP-PQPAKE method header, and payload.¶

 0                   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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Config-Count  |   Reserved    |        Config-ID[0]          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Config-ID[1] ...                                      ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Server-IDType |              Server-ID                       ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 0                   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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Selected-Config        | Peer-IDType   | Peer-ID      ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

peer_state, msg1 = CPaceOQUAKE+.Init(
    PRS, salt, U, S, public_context, secret_context)
server_state, msg2 = CPaceOQUAKE+.Respond(
    v, public_context, secret_context, msg1)
peer_state, msg3 = CPaceOQUAKE+.InitiatorContinue(
    peer_state, msg2)
server_state, msg4 = CPaceOQUAKE+.ResponderContinue(
    server_state, msg3, pk, kem_blind)
client_key, msg5, th = CPaceOQUAKE+.InitiatorFinish(
    peer_state, msg4)
server_key, th = CPaceOQUAKE+.ResponderFinish(server_state, msg5)

 0                   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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Server-Nonce                         ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                             Salt                              ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       CPaceOQUAKE-msg1                       ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       CPaceOQUAKE-msg2                       ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       CPaceOQUAKE-msg3                       ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         PC-Challenge                         ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                          PC-Response                         ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

7. Fragmentation

Post-quantum KEM public keys and ciphertexts can make EAP-PQPAKE messages larger than a lower layer's EAP payload limit. EAP-PQPAKE therefore supports fragmentation using the L and M flags in the method header.¶

Implementations MUST support receiving fragmented EAP-PQPAKE messages. An implementation MUST establish a fragmentation threshold. If the lower layer MTU is known, the threshold SHOULD be derived from that MTU. If no lower-layer limit is known, the threshold MUST be 1020 octets.¶

The first fragment of a fragmented message MUST set L and M and MUST include Total-Length. Intermediate fragments MUST set M and MUST NOT set L. The final fragment MUST NOT set M and MUST NOT set L. A non-fragmented message MUST NOT set L or M.¶

When the peer receives an EAP-PQPAKE Request fragment with M set, it MUST respond with an EAP-PQPAKE Response fragment acknowledgement. The acknowledgement uses the same PQPAKE-Exch value, has no payload, and has L and M cleared. When the server receives an EAP-PQPAKE Response fragment with M set, it MUST respond with an EAP-PQPAKE Request fragment acknowledgement with the same properties. The next fragment is sent only after the acknowledgement is received.¶

Receivers MUST reassemble all fragments before parsing the exchange-specific payload. A receiver MUST abort if Total-Length is inconsistent with the received fragments, if fragments from different exchanges are interleaved, or if the reassembled message exceeds a local policy limit.¶

8. Key Derivation

The peer obtains client_key and the final transcript hash th from CPaceOQUAKE+.InitiatorFinish after verifying Confirm/Request. The server obtains the matching server_key and th from CPaceOQUAKE+.ResponderFinish after verifying Confirm/Response. These keys are the method key used below. No intermediate PAKE key or unverified candidate key may be exported. EAP-PQPAKE exports MSK and EMSK as required by [RFC3748] and [RFC5247].¶

The Method-ID is:¶

Method-ID = H("EAP-PQPAKE Method-ID" ||
              uint16(Selected-Config) || lv_encode(th))

th is the final CPaceOQUAKE+ transcript hash, which binds the initial EAP public context and all five protocol messages, including both password confirmation values. It MUST NOT be replaced by the transcript hash of an intermediate PAKE stage. Selected-Config is encoded as the two-octet value selected in Start/Response.¶

The Session-ID is:¶

Session-ID = EAP-Type-Code || Method-ID

where EAP-Type-Code is the single-octet EAP method type assigned by IANA for EAP-PQPAKE.¶

Following the key naming guidance in [RFC4962], exported key names are:¶

MSK-name  = Session-ID || "MSK"
EMSK-name = Session-ID || "EMSK"

The MSK and EMSK are derived using HKDF [RFC5869] with the EAP HKDF hash selected by the configuration (SHA-256 for the mandatory configuration). Hash.length is that hash's output length in octets:¶

exporter_secret = HKDF-Extract(zeros(Hash.length), method_key)
key_material = HKDF-Expand(exporter_secret,
                           "EAP-PQPAKE Exported Keys" ||
                           Session-ID ||
                           Method-ID,
                           128)
MSK  = key_material[0:64]
EMSK = key_material[64:128]

The slice end indexes are exclusive; MSK and EMSK are each 64 octets.¶

After deriving the MSK and EMSK, both endpoints MUST erase the CPaceOQUAKE+ method key, intermediate PAKE secrets, KEM decapsulation secrets, password-confirmation state, and ephemeral copies of the password-derived seed and kem_blind. This does not erase the server's stored registration. Ephemeral secrets and any unexported candidate keys MUST also be erased when the method fails or times out.¶

9. Security Considerations

EAP-PQPAKE inherits the cryptographic security properties and limitations of CPaceOQUAKE+ [I-D.vos-cfrg-pqpake]. The EAP encapsulation defined here binds EAP identities, configuration negotiation, salt, server nonce, and all carried CPaceOQUAKE+ messages through its public context and internal transcript hashes. The following claims are stated in the style expected for EAP methods used in wireless LANs [RFC4017].¶

The hybrid security of CPaceOQUAKE+ depends on the CPaceOQUAKE+ composition specified in [I-D.vos-cfrg-pqpake]. The sequential composition relies on CPace being unconditionally password hiding: the CPace transcript does not reveal information about the password-related string even if the classical Diffie-Hellman assumption later fails. OQUAKE is not assumed to have that unconditional password-hiding property; it provides the post-quantum KEM-based component of the hybrid design. EAP-PQPAKE therefore does not define a parallel composition and does not permit substituting a different PAKE component unless that component is specified by a registered CPaceOQUAKE+ configuration with an applicable security analysis.¶

Section 11.2 of [I-D.vos-cfrg-pqpake] qualifies the post-quantum security analysis: the UC proofs use the classical random oracle model. OQUAKE-style protocols do not realize the standard UC PAKE functionality with quantum random-oracle access under the cited analysis, although this does not yield an attack recovering passwords or keys and a closely related protocol has a stand-alone game-based proof in that model. EAP-PQPAKE does not claim a stronger quantum UC result. Its security against quantum attackers relies on OQUAKE; CPace alone does not provide post-quantum PAKE security.¶

Passive attacks:

A passive attacker observing EAP-PQPAKE messages is not expected to learn the password, the CPaceOQUAKE+ method key, the MSK, or the EMSK. The method is intended to protect recorded exchanges against attackers with future quantum capabilities, subject to the hybrid security assumptions of CPaceOQUAKE+.¶

Active attacks:

An active attacker can drop, delay, replay, or modify EAP messages. Such modification causes transcript or confirmation failure unless the attacker knows the password or breaks the underlying CPaceOQUAKE+ assumptions. Implementations MUST reject unexpected exchange ordering, malformed encodings, and configuration mismatches, while preserving OQUAKE's implicit rejection behavior described in Section 4.¶

Dictionary attacks:

Password authentication methods cannot prevent online guessing. EAP servers MUST implement rate limits or equivalent controls for failed authentications. Implementations SHOULD avoid distinguishable error behavior between unknown identities and incorrect passwords.¶

Forward secrecy:

Compromise of the password after an exchange completes does not reveal earlier MSK or EMSK values unless the attacker also breaks the underlying assumptions for the recorded exchange. Compromise of the full registered verifier (v, pk, kem_blind) permits offline password guessing and server impersonation to the peer. It does not by itself permit client impersonation without recovering the password, the password-derived seed, or the corresponding decapsulation key, as discussed in Section 11.5 of [I-D.vos-cfrg-pqpake]. Affected credentials require reprovisioning.¶

Downgrade protection:

The selected configuration and the server's offered configuration list are included in the EAP-PQPAKE transcript. A downgrade attempt that changes negotiation messages is detected during password confirmation. Implementations MUST NOT offer configurations that are prohibited by local policy.¶

Identity protection:

EAP-PQPAKE does not encrypt the Start exchange. A passive observer can see the server and peer identities unless this method is used inside a protected tunnel. An anonymous outer EAP identity alone does not hide the identities in the Start exchange. This mapping uses the same identities for registration and the session public context; the underlying PAKE permits these to differ, but this document does not define such an identity mapping. Changing a registration identity requires recomputing and reprovisioning the verifier.¶

Verifier handling:

The server stores the salt and the CPaceOQUAKE+ verifier (v, pk, kem_blind). The password-derived seed used to derive the password-confirmation KEM key pair MUST NOT be stored by the server. Registration and reprovisioning are outside this method and need channel authentication, confidentiality, and integrity. A fresh secret kem_blind is required for each registration and MUST be protected with the rest of the verifier. The memory-hard password stretching used by CPaceOQUAKE+ hardens password-derived verifier material against offline guessing after verifier compromise; it does not replace online rate limiting for EAP authentication attempts.¶

Side channels:

CPaceOQUAKE+ discusses timing considerations for OQUAKE and ML-KEM processing. In addition to the Tempo construction used by OQUAKE, the augmented transformation blinds KEM key generation with kem_blind. Removing this blinding or disclosing kem_blind before password confirmation invalidates that protection. Implementations MUST preserve the blinding and its encryption, use constant-time comparison for confirmation values, and keep Kemeleon.EncodeEk randomness secret. They SHOULD use implementations of the selected primitives that address known timing attacks.¶

Denial of service:

The recommended configuration uses scrypt password stretching on the peer and post-quantum cryptography on both endpoints. Servers SHOULD apply admission control before expensive operations, for example by limiting concurrent sessions per peer, realm, or lower-layer attachment.¶

Fragmentation:

Fragmentation increases buffering requirements. Implementations MUST enforce local maximum reassembled lengths and discard incomplete fragmented messages on timeout.¶

10. IANA Considerations

IANA is requested to allocate one EAP Method Type from the "Method Types" registry:¶

IANA is requested to create the "EAP-PQPAKE Exchange Types" registry. The registration policy is Specification Required [RFC8126] for values 0x06 through 0x7f. Values 0x80 through 0xff are for Private Use. The initial values are listed in Section 6.¶

IANA is requested to create the "EAP-PQPAKE Configurations" registry. The registry contains 16-bit values. The registration policy is Specification Required for values 0x0002 through 0x7fff. Values 0x8000 through 0xffff are for Private Use. The initial contents are:¶

IANA is requested to create the "EAP-PQPAKE Identity Types" registry. The registry contains 8-bit values. The registration policy is Specification Required for values 0x04 through 0x7f. Values 0x80 through 0xff are for Private Use. The initial values are listed in Section 6.1.¶

IANA is requested to create the "EAP-PQPAKE Failure Codes" registry. The registry contains 32-bit values. The registration policy is Specification Required for values 0x00000007 through 0xfeffffff. Values 0xff000000 through 0xffffffff are for Private Use. The initial values are listed in Section 6.7.¶

11. References

Acknowledgments

TODO acknowledge contributors and reviewers.¶

Authors' Addresses