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March 19, 2019 14:58
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import "hashes/sha256/1024bitPadded.code" as sha256 | |
import "ecc/edwardsScalarMult.code" as scalarMult | |
import "ecc/edwardsAdd.code" as add | |
import "utils/pack/unpack256.code" as unpack256 | |
import "ecc/edwardsOnCurve.code" as onCurve | |
import "ecc/edwardsOrderCheck.code" as orderCheck | |
/// Verifies an EdDSA Signature. | |
/// | |
/// Checks the correctness of a given EdDSA Signature (R,S) for the provided | |
/// public key A and message (M0, M1). | |
/// For more information see: | |
/// https://en.wikipedia.org/wiki/EdDSA | |
/// https://eprint.iacr.org/2015/677.pdf | |
/// | |
/// Arguments: | |
/// R: Curve point. Hidden version of the per-message nonce. | |
/// S: Field element. Signature to be verified. | |
/// A: Curve point. Public part of the key used to create S. | |
/// M0: 256bit array. First 256bits of the message used to create S . | |
/// M1: 256bit array. Trailing 256bits of the message used to create S . | |
/// context: Curve parameters used to create S. | |
/// | |
/// Returns: | |
/// Return 1 for S being a valid EdDSA Signature, 0 otherwise. | |
def main(private field[2] R, private field S, field[2] A, field[256] M0, field[256] M1, field[10] context) -> (field): | |
field[2] G = [context[4], context[5]] | |
// Check if R is on curve and in prime-order sub-group. A is public input and can be checked offline | |
field isOnCurve = onCurve(R, context) // throws if R is not on curve | |
field isPrimeOrder = orderCheck(R, context) | |
1 == isPrimeOrder | |
field[256] Rx = unpack256(R[0]) | |
field[256] Ax = unpack256(A[0]) | |
field[256] hRAM = sha256(Rx, Ax, M0, M1) | |
field[256] sBits = unpack256(S) | |
field[2] lhs = scalarMult(sBits, G, context) | |
field[2] AhRAM = scalarMult(hRAM, A, context) | |
field[2] rhs = add(R, AhRAM, context) | |
field out = if rhs[0] == lhs[0] && rhs[1] == lhs[1] then 1 else 0 fi | |
return out |
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