fix(zcash): correct seed_fingerprint formula in proto comments#28
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Field comments documented the formula as
BLAKE2b-256("Zcash_HD_Seed_FP", seed)
but ZIP-32 §6.1 (and the actual conforming implementations in the
upstream zip32 Rust crate, keystone3-firmware, and our own firmware)
prepend a 1-byte length:
BLAKE2b-256("Zcash_HD_Seed_FP", I2LEBSP_8(len(seed)) || seed)
A host implementer following the proto comments would compute the
wrong fingerprint and have the device reject every signing/display
request with "seed fingerprint mismatch."
Comment-only change. No wire-format impact.
4 tasks
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Summary
Comment-only fix — wire format unchanged.
The `seed_fingerprint` and `expected_seed_fingerprint` field comments documented the formula as
but the correct ZIP-32 §6.1 formula prepends a 1-byte length:
This matches the upstream `zip32` Rust crate, keystone3-firmware, and our own firmware C / python-keepkey implementations. A host implementer following the previous proto comments would compute the wrong fingerprint and have the device reject every signing/display request with "seed fingerprint mismatch."
Why this slipped through PR #27
I copied the formula from a draft and didn't catch the missing length prefix until validating the Python helper against keystone3-firmware's reference vector during the python-keepkey work — both impls produced the wrong output, then I fixed both. The proto comments stayed stale.
Reference vector (keystone3-firmware cross-check):
Test plan