47 lines
1.8 KiB
Text
47 lines
1.8 KiB
Text
import "hashes/sha256/1024bitPadded.code" as sha256
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import "ecc/edwardsScalarMult.code" as scalarMult
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import "ecc/edwardsAdd.code" as add
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import "utils/pack/unpack256.code" as unpack256
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import "ecc/edwardsOnCurve.code" as onCurve
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import "ecc/edwardsOrderCheck.code" as orderCheck
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/// Verifies an EdDSA Signature.
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///
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/// Checks the correctness of a given EdDSA Signature (R,S) for the provided
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/// public key A and message (M0, M1).
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/// For more information see:
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/// https://en.wikipedia.org/wiki/EdDSA
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/// https://eprint.iacr.org/2015/677.pdf
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///
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/// Arguments:
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/// R: Curve point. Hidden version of the per-message nonce.
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/// S: Field element. Signature to be verified.
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/// A: Curve point. Public part of the key used to create S.
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/// M0: 256bit array. First 256bits of the message used to create S .
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/// M1: 256bit array. Trailing 256bits of the message used to create S .
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/// context: Curve parameters used to create S.
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///
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/// Returns:
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/// Return 1 for S being a valid EdDSA Signature, 0 otherwise.
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def main(private field[2] R, private field S, field[2] A, field[256] M0, field[256] M1, field[10] context) -> (field):
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field[2] G = [context[4], context[5]]
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// Check if R is on curve and if it is not in a small subgroup. A is public input and can be checked offline
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field isOnCurve = onCurve(R, context) // throws if R is not on curve
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field isPrimeOrder = orderCheck(R, context)
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1 == isPrimeOrder
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field[256] Rx = unpack256(R[0])
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field[256] Ax = unpack256(A[0])
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field[256] hRAM = sha256(Rx, Ax, M0, M1)
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field[256] sBits = unpack256(S)
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field[2] lhs = scalarMult(sBits, G, context)
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field[2] AhRAM = scalarMult(hRAM, A, context)
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field[2] rhs = add(R, AhRAM, context)
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field out = if rhs[0] == lhs[0] && rhs[1] == lhs[1] then 1 else 0 fi
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return out
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