From d85326a119c34789055c388fcd18bb0161fbfd21 Mon Sep 17 00:00:00 2001 From: Dimitri Staessens Date: Sat, 14 Feb 2026 14:33:50 +0100 Subject: irmd: Add strength-based crypto negotiation Each side's configured cipher, KDF, and KEX algorithm now represents a minimum security floor ("at least this strong"). Cipher and KDF use strongest-wins: the server compares ranks and selects the stronger of client vs server config. The negotiated values are sent in the response header. The client verifies the server's response meets its own minimum, which prevents downgrade attacks on the wire. KEX uses a minimum-floor check: the server extracts the client's algorithm from its public key and rejects if it ranks below the server's configured algorithm. A server configured with ML-KEM will reject all classical algorithms. Special case: for client-encap KEM, the client has already derived its key using its KDF, so the server must use the same KDF and can only reject if it is too weak. The supported_nids arrays are ordered weakest to strongest and serve as the single source of truth for ranking. Cipher ranking (weakest to strongest): aes-128-ctr, aes-192-ctr, aes-256-ctr, aes-128-gcm, aes-192-gcm, aes-256-gcm, chacha20-poly1305 KDF ranking (weakest to strongest): blake2s256, sha256, sha3-256, sha384, sha3-384, blake2b512, sha512, sha3-512 KEX ranking (weakest to strongest): ffdhe2048, prime256v1, X25519, ffdhe3072, secp384r1, ffdhe4096, X448, secp521r1, ML-KEM-512, ML-KEM-768, ML-KEM-1024, X25519MLKEM768, X448MLKEM1024 Negotiation outcomes: strong srv cipher + weak cli cipher -> use strongest weak srv cipher + strong cli cipher -> use strongest srv encryption + cli none -> server rejects srv none + cli encryption -> use client's strong srv KEX + weak cli KEX -> server rejects weak srv KEX + strong cli KEX -> succeeds wire tamper to weaker cipher -> client rejects Signed-off-by: Dimitri Staessens Signed-off-by: Sander Vrijders --- enc.conf.in | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'enc.conf.in') diff --git a/enc.conf.in b/enc.conf.in index 64502fbb..8f91d717 100644 --- a/enc.conf.in +++ b/enc.conf.in @@ -73,8 +73,8 @@ # sha3-256 SHA3-256 # sha3-384 SHA3-384 # sha3-512 SHA3-512 -# blake2b512 BLAKE2b-512 (requires OpenSSL 1.1.0+) -# blake2s256 BLAKE2s-256 (requires OpenSSL 1.1.0+) +# blake2b512 BLAKE2b-512 +# blake2s256 BLAKE2s-256 # # KEM Mode (kem_mode=): # --------------------- -- cgit v1.2.3