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btcec+chaincfg: use pre-computed tag hash values

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In this commit, we optimize our signature implementation slightly, by
defining pre-computed sha256(tag) variables for the commonly used
values.  If a tag matches this, then we'll use that hash value to avoid
an extra round of hashing.
This commit is contained in:
Olaoluwa Osuntokun 2022-01-31 14:54:12 -08:00
parent 973fb37600
commit b7a4622a6b
No known key found for this signature in database
GPG Key ID: 3BBD59E99B280306
2 changed files with 31 additions and 15 deletions
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18
btcec/schnorr/signature.go
View File

@ -22,14 +22,6 @@ const (
scalarSize = 32
)
var (
tagHashAux = []byte("BIP0340/aux")
tagHashNonce = []byte("BIP0340/nonce")
tagHashChallenge = []byte("BIP0340/challenge")
)
var (
// rfc6979ExtraDataV0 is the extra data to feed to RFC6979 when
// generating the deterministic nonce for the BIP-340 scheme. This
@ -183,7 +175,7 @@ func schnorrVerify(sig *Signature, hash []byte, pubKeyBytes []byte) error {
pBytes := SerializePubKey(pubKey)
commitment := chainhash.TaggedHash(
tagHashChallenge, rBytes[:], pBytes, hash,
chainhash.TagBIP0340Challenge, rBytes[:], pBytes, hash,
)
var e btcec.ModNScalar
@ -325,7 +317,7 @@ func schnorrSign(privKey, nonce *btcec.ModNScalar, pubKey *btcec.PublicKey, hash
pBytes := SerializePubKey(pubKey)
commitment := chainhash.TaggedHash(
tagHashChallenge, rBytes[:], pBytes, hash,
chainhash.TagBIP0340Challenge, rBytes[:], pBytes, hash,
)
var e btcec.ModNScalar
@ -492,7 +484,9 @@ func Sign(privKey *btcec.PrivateKey, hash []byte,
//
// t = bytes(d) xor tagged_hash("BIP0340/aux", a)
privBytes := privKeyScalar.Bytes()
t := chainhash.TaggedHash(tagHashAux, (*opts.authNonce)[:])
t := chainhash.TaggedHash(
chainhash.TagBIP0340Aux, (*opts.authNonce)[:],
)
for i := 0; i < len(t); i++ {
t[i] ^= privBytes[i]
}
@ -504,7 +498,7 @@ func Sign(privKey *btcec.PrivateKey, hash []byte,
// We snip off the first byte of the serialized pubkey, as we
// only need the x coordinate and not the market byte.
rand := chainhash.TaggedHash(
tagHashNonce, t[:], pubKeyBytes[1:], hash,
chainhash.TagBIP0340Nonce, t[:], pubKeyBytes[1:], hash,
)
// Step 8.

28
chaincfg/chainhash/hash.go
View File

@ -17,6 +17,25 @@ const HashSize = 32
// MaxHashStringSize is the maximum length of a Hash hash string.
const MaxHashStringSize = HashSize * 2
var (
// TagBIP0340Challenge is the BIP-0340 tag for challenges.
TagBIP0340Challenge = []byte("BIP0340/challenge")
// TagBIP0340Aux is the BIP-0340 tag for aux data.
TagBIP0340Aux = []byte("BIP0340/aux")
// TagBIP0340Nonce is the BIP-0340 tag for nonces.
TagBIP0340Nonce = []byte("BIP0340/nonce")
// precomputedTags is a map containing the SHA-256 hash of the BIP-0340
// tags.
precomputedTags = map[string]Hash{
string(TagBIP0340Challenge): sha256.Sum256(TagBIP0340Challenge),
string(TagBIP0340Aux): sha256.Sum256(TagBIP0340Aux),
string(TagBIP0340Nonce): sha256.Sum256(TagBIP0340Nonce),
}
)
// ErrHashStrSize describes an error that indicates the caller specified a hash
// string that has too many characters.
var ErrHashStrSize = fmt.Errorf("max hash string length is %v bytes", MaxHashStringSize)
@ -84,10 +103,13 @@ func NewHash(newHash []byte) (*Hash, error) {
// TaggedHash implements the tagged hash scheme described in BIP-340. We use
// sha-256 to bind a message hash to a specific context using a tag:
// sha256(sha256(tag) || sha256(tag) || msg).
//
// TODO(roasbeef): add fast paths for common known tags
func TaggedHash(tag []byte, msgs ...[]byte) *Hash {
shaTag := sha256.Sum256(tag)
// Check to see if we've already pre-computed the hash of the tag. If
// so then this'll save us an extra sha256 hash.
shaTag, ok := precomputedTags[string(tag)]
if !ok {
shaTag = sha256.Sum256(tag)
}
// h = sha256(sha256(tag) || sha256(tag) || msg)
h := sha256.New()