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improvement: precomputed values for hash of tag #298

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improvement: precomputed values for hash of tag #298

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28 changes: 6 additions & 22 deletions onchain/src/bip340.cairo
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Original file line number Diff line number Diff line change
Expand Up @@ -41,28 +41,12 @@ const p: u256 = 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFC
/// `sha256(tag) || sha256(tag) || bytes(rx) || bytes(px) || m` as u256 where tag =
/// "BIP0340/challenge".
fn hash_challenge(rx: u256, px: u256, m: ByteArray) -> u256 {
// sha256(tag)
let [x0, x1, x2, x3, x4, x5, x6, x7] = compute_sha256_byte_array(@"BIP0340/challenge");

let mut ba = Default::default();
// sha256(tag)
ba.append_word(x0.into(), 4);
ba.append_word(x1.into(), 4);
ba.append_word(x2.into(), 4);
ba.append_word(x3.into(), 4);
ba.append_word(x4.into(), 4);
ba.append_word(x5.into(), 4);
ba.append_word(x6.into(), 4);
ba.append_word(x7.into(), 4);
// sha256(tag)
ba.append_word(x0.into(), 4);
ba.append_word(x1.into(), 4);
ba.append_word(x2.into(), 4);
ba.append_word(x3.into(), 4);
ba.append_word(x4.into(), 4);
ba.append_word(x5.into(), 4);
ba.append_word(x6.into(), 4);
ba.append_word(x7.into(), 4);
//Precomputed values -> tag = 'compute_sha256_byte_array(@"BIP0340/challenge")'
// sha256(tag) || sha256(tag)
let mut ba: ByteArray = Default::default();
ba.append_word(0x7bb52d7a9fef58323eb1bf7a407db382d2f3f2d81bb1224f49fe518f6d48d3, 31);
ba.append_word(0x7c7bb52d7a9fef58323eb1bf7a407db382d2f3f2d81bb1224f49fe518f6d48, 31);
ba.append_word(0xd37c, 2);
// bytes(rx)
ba.append_word(rx.high.into(), 16);
ba.append_word(rx.low.into(), 16);
Expand Down