Andrew Cagney <[email protected]> wrote:
> How can it do that when it hasn't got an encrypted SA?
> To get encrypted, you have to do the KEM too.
According to RFC 7296 and RFC 9242 (Section 3), the symmetric crypto keys
(SK_e/SK_a) are derived immediately after the IKE_SA_INIT exchange.
This is why any subsequent messages—whether they are IKE_INTERMEDIATE or
IKE_AUTH—are already strictly encapsulated within an Encrypted (SK) payload
(structured as HDR, SK {...}) on the wire. The additional KEMs running inside
IKE_INTERMEDIATE are for augmenting quantum resistance, not for enabling
initial encryption.
Therefore, at the identity junction of IKE_AUTH, the responder absolutely
possesses the valid SK_e/SK_a keys to reply with a symmetrically encrypted
COLLISION_ABORT notification, successfully protecting the packet from spoofing
while bypassing the asymmetric PQC signing.
Best regards,
Wang Xi
-----Original Message-----
From: Michael Richardson <[email protected]>
Sent: Thursday, September 3, 2026 9:41 AM
To: Wang Xi <[email protected]>; Andrew Cagney <[email protected]>;
Valery Smyslov <[email protected]>; Wang Xi
<[email protected]>; IPsec WG <[email protected]>
Subject: Re: [IPsec] Re: fail Child SA with TEMPORARY_FAILURE response during
IKE_AUTH
Wang Xi <[email protected]> wrote:
> Thanks for the insights. Glad to hear we are aligned on keeping this
> purely within the application layer
> If we strictly wait for the response to arrive as per RFC 7296, the
> responder (the loser) is still forced to execute the heavy PQC signing
> just to generate that doomed response. This completely defeats the
> purpose of mitigating PQC overhead.
Yes, this is a problem for a responder that sees that the SA in question will
not be the winning SA. If the initiator doesn't implement the sensible
heuristic I am proposing, the responders only real choice here is to discard
the packet, and risk retransmission.
(If the SA *would* be the winning SA, then the responder should stop/delay the
SA it is initiating, and it should do the signature...)
> To solve this without breaking the state machine or risking a spoofing
> DoS, I am NOT suggesting a standard DELETE payload. Instead, once the
> responder verifies the collision via local identity checks, it should
> reply with an encrypted, lightweight COLLISION_ABORT Notify Payload
> using the IKE_SA_INIT keys, and instantly tear down the state.
How can it do that when it hasn't got an encrypted SA?
To get encrypted, you have to do the KEM too.
> To be precise, this mechanism does not eliminate 100% of the PQC
> overhead, as the initiator has already computed and sent its initial
> IKE_AUTH request. However, it completely saves the responder from
> running the heavy asymmetric PQC signing for the response. Since the
> reply comes from the responder, it perfectly honors the standard
> Request-Response flow, while successfully shielding the responder's
> CPU.
I think, responsder can just unilaterally protect its CPU by dropping traffic.
Maybe it's time for the puzzles to return.
A long time ago, that's how FreeS/WAN protected itself against IKEv1 aggressive
mode.
--
Michael Richardson <[email protected]> . o O ( IPv6 IøT consulting )
Sandelman Software Works Inc, Ottawa and Worldwide
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