diff --git a/chaincfg/chainhash/hash.go b/chaincfg/chainhash/hash.go index 2d38c095..02513236 100644 --- a/chaincfg/chainhash/hash.go +++ b/chaincfg/chainhash/hash.go @@ -6,6 +6,7 @@ package chainhash import ( + "crypto/sha256" "encoding/binary" "encoding/hex" "encoding/json" @@ -19,6 +20,25 @@ 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) @@ -103,6 +123,35 @@ func NewHash(newHash []byte) (*Hash, error) { return &sh, err } +// 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). +func TaggedHash(tag []byte, msgs ...[]byte) *Hash { + // 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() + h.Write(shaTag[:]) + h.Write(shaTag[:]) + + for _, msg := range msgs { + h.Write(msg) + } + + taggedHash := h.Sum(nil) + + // The function can't error out since the above hash is guaranteed to + // be 32 bytes. + hash, _ := NewHash(taggedHash) + + return hash +} + // NewHashFromStr creates a Hash from a hash string. The string should be // the hexadecimal string of a byte-reversed hash, but any missing characters // result in zero padding at the end of the Hash.