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cosi: fix bug in signing code, make tests pass

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This commit is contained in:
matejcik 2018-10-02 16:09:12 +02:00
parent 4ff5fb4492
commit a66cf99b74
1 changed files with 4 additions and 3 deletions
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7
trezorlib/cosi.py
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@ -94,12 +94,13 @@ def sign_with_privkey(
"""
b = _ed25519.b
h = _ed25519.H(privkey)
a = int.from_bytes(h, "little")
# curvepoint preparation:
# 1. clear lowest three and highest bit
# 1. take lowest b bits of h
a = int.from_bytes(h[: b // 8], "little")
# 2. clear lowest three and highest bit
bitmask = 1 + 2 + 4 + (1 << b - 1)
a &= ~bitmask
# 2. set next-highest bit
# 3. set next-highest bit
a |= 1 << b - 2
S = (nonce + _ed25519.Hint(global_commit + global_pubkey + digest) * a) % _ed25519.l