crypto: add SignatureLength constant and use it everywhere (#19996)

Original change by @jpeletier 

3 files changed, 18 insertions, 9 deletions

diff --git a/crypto/crypto.go b/crypto/crypto.go
index 4567fafc7..2869b4c19 100644
--- a/crypto/crypto.go
+++ b/crypto/crypto.go
@@ -34,6 +34,15 @@ import (
 	"golang.org/x/crypto/sha3"
 )
 
+//SignatureLength indicates the byte length required to carry a signature with recovery id.
+const SignatureLength = 64 + 1 // 64 bytes ECDSA signature + 1 byte recovery id
+
+// RecoveryIDOffset points to the byte offset within the signature that contains the recovery id.
+const RecoveryIDOffset = 64
+
+// DigestLength sets the signature digest exact length
+const DigestLength = 32
+
 var (
 	secp256k1N, _  = new(big.Int).SetString("fffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141", 16)
 	secp256k1halfN = new(big.Int).Div(secp256k1N, big.NewInt(2))
diff --git a/crypto/signature_cgo.go b/crypto/signature_cgo.go
index aadf028d2..1fe84509e 100644
--- a/crypto/signature_cgo.go
+++ b/crypto/signature_cgo.go
@@ -47,24 +47,24 @@ func SigToPub(hash, sig []byte) (*ecdsa.PublicKey, error) {
 //
 // This function is susceptible to chosen plaintext attacks that can leak
 // information about the private key that is used for signing. Callers must
-// be aware that the given hash cannot be chosen by an adversery. Common
+// be aware that the given digest cannot be chosen by an adversery. Common
 // solution is to hash any input before calculating the signature.
 //
 // The produced signature is in the [R || S || V] format where V is 0 or 1.
-func Sign(hash []byte, prv *ecdsa.PrivateKey) (sig []byte, err error) {
-	if len(hash) != 32 {
-		return nil, fmt.Errorf("hash is required to be exactly 32 bytes (%d)", len(hash))
+func Sign(digestHash []byte, prv *ecdsa.PrivateKey) (sig []byte, err error) {
+	if len(digestHash) != DigestLength {
+		return nil, fmt.Errorf("hash is required to be exactly %d bytes (%d)", DigestLength, len(digestHash))
 	}
 	seckey := math.PaddedBigBytes(prv.D, prv.Params().BitSize/8)
 	defer zeroBytes(seckey)
-	return secp256k1.Sign(hash, seckey)
+	return secp256k1.Sign(digestHash, seckey)
 }
 
-// VerifySignature checks that the given public key created signature over hash.
+// VerifySignature checks that the given public key created signature over digest.
 // The public key should be in compressed (33 bytes) or uncompressed (65 bytes) format.
 // The signature should have the 64 byte [R || S] format.
-func VerifySignature(pubkey, hash, signature []byte) bool {
-	return secp256k1.VerifySignature(pubkey, hash, signature)
+func VerifySignature(pubkey, digestHash, signature []byte) bool {
+	return secp256k1.VerifySignature(pubkey, digestHash, signature)
 }
 
 // DecompressPubkey parses a public key in the 33-byte compressed format.
diff --git a/crypto/signature_nocgo.go b/crypto/signature_nocgo.go
index 90d072cda..067d32e13 100644
--- a/crypto/signature_nocgo.go
+++ b/crypto/signature_nocgo.go
@@ -41,7 +41,7 @@ func Ecrecover(hash, sig []byte) ([]byte, error) {
 // SigToPub returns the public key that created the given signature.
 func SigToPub(hash, sig []byte) (*ecdsa.PublicKey, error) {
 	// Convert to btcec input format with 'recovery id' v at the beginning.
-	btcsig := make([]byte, 65)
+	btcsig := make([]byte, SignatureLength)
 	btcsig[0] = sig[64] + 27
 	copy(btcsig[1:], sig)