Merge pull request #106 from kcalvinalvin/2024-01-08-bip340

chaincfg: bip340

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.