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0 pointstptacek3y ago0 comments

What does Bernstein's process complaint about NIST's process complaint about him have to do with which ciphersuites OpenSSH will support?

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3 comments · 1 top-level

chasil3y ago· 2 in thread

OpenSSH appears to have disregarded NIST, and made their own determination on a pq-kex.

Should NIST be disregarded?

NTRU-prime is not a finalist, but OpenSSH has decided that the NIST designation is irrelevant.

https://www.openssh.com/releasenotes.html

ssh(1), sshd(8): use the hybrid Streamlined NTRU Prime + x25519 key exchange method by default ("sntrup761x25519-sha512@openssh.com"). The NTRU algorithm is believed to resist attacks enabled by future quantum computers and is paired with the X25519 ECDH key exchange (the previous default) as a backstop against any weaknesses in NTRU Prime that may be discovered in the future. The combination ensures that the hybrid exchange offers at least as good security as the status quo.

We are making this change now (i.e. ahead of cryptographically- relevant quantum computers) to prevent "capture now, decrypt later" attacks where an adversary who can record and store SSH session ciphertext would be able to decrypt it once a sufficiently advanced quantum computer is available.

tptacekOP3y ago

I personally think NIST should be disregarded, but you can disregard NIST and still end up with CRYSTALS-KYBER as your default PQC KEM, on its own merits, which can include the fact that NIST's standardization spurs so much implementation of CRYSTALS-KYBER that it becomes a de facto standard in addition to a de jure standard. (Same for signatures, and so on).

People with qualms about NIST might also reasonably have qualms about AES. And there is a common cipher that people use outside of AES --- Chapoly. But it would be downright weird to use, like, Serpent or Twofish; it would be the cryptography equivalent of a "code smell". Chapoly and AES are the de facto standards, and OpenSSH supports both.

Again though: my question is just, what does this (frankly weird) Bernstein complaint have to do with any of it? Bernstein himself is a NISTPQC participant; he's on one of the (large) winning signature teams.

(I think all the technical details here are super interesting, but not especially motivating; I'm not a cryptographer and you should disregard me as well, but my basic take on QC crypto attacks is "Rodents of unusual size? I don't think they exist.")

chasil3y ago

I agree with your sentiment. I wish NIST had conducted the proceedings more professionally, and this collapse in confidence is their own fault.

The OpenSSH decision to promote NTRU-prime from an experimental feature to the preferred key exchange was breathtakingly rapid, and final. It is a tacit assertion that NIST is no longer relevant.

DJB was on several teams, and I think that OpenSSH would lend greater credence to him than any other council, deservedly so.

We might end up with SPHINCS+, but I will be surprised if KYBER is adopted.

This moved very fast.

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