feat(crypto): deterministic DLEQ nonce derivation (NUT-12)#1010
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robwoodgate wants to merge 2 commits into
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feat(crypto): deterministic DLEQ nonce derivation (NUT-12)#1010robwoodgate wants to merge 2 commits into
robwoodgate wants to merge 2 commits into
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Derive the DLEQ nonce `r` deterministically from the private key and proof context instead of from the RNG: r = HMAC-SHA256(key=a, "Cashu_DLEQ_R_v1" || A || B' || C' || ctr) mod n This removes the dependency on RNG quality. Reusing `r` across two proofs with different challenges would leak the private key. `step2_bob` now emits deterministic nonces for every signature; DLEQ verification is unaffected since (e, s) remain valid proofs. The `p_bytes` override is retained for the existing test vectors. Adds the NUT-12 deterministic-nonce test vector (cashubtc/nuts#368) plus reproducibility and context-sensitivity tests.
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## main #1010 +/- ##
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- Coverage 74.99% 74.96% -0.03%
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Lines 12065 12076 +11
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Implements the deterministic nonce derivation from cashubtc/nuts#368.
Summary
Derives the DLEQ nonce
rdeterministically from the mint's private key and the proof context, instead of sourcing it from the RNG:ais the 32-byte secp256k1 private key scalar (big-endian);A,B',C'are uncompressed SEC1 points (65 bytes each);ctris a single byte starting at0x00, incremented if the reduced value is0(max 256 attempts).This removes the dependency on RNG quality. Reusing
racross two proofs with different challenges leaks the private key immediately viaa = (s₁ - s₂)·(e₁ - e₂)⁻¹ mod n.Changes
cashu/core/crypto/b_dhke.py— newderive_dleq_nonce(a, A, B_, C_).step2_bob_dleqcomputesC_/Afirst, then derivespdeterministically. Thep_bytesoverride is retained for existing test vectors.tests/test_crypto.py— adds the NUT-12 deterministic-nonce test vector (asserts every fixed value pluse == hash(R1, R2, A, C_)verification), reproducibility, and context-sensitivity tests.Notes
step2_bob(used by the mint inledger.py) now emits deterministic nonces for every signature. DLEQ verification is unaffected —(e, s)remain valid proofs. No on-disk format or API change.e,s,A, andC_from the spec vector exactly.Test plan
tests/test_crypto.py— 19 passed, including the new NUT-12 vector and the two new determinism tests.make check(ruff + mypy) passes.