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

Original change by @jpeletier

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))