From 480235ae6a9b6fb1bedd84b27ad450cd2a773909 Mon Sep 17 00:00:00 2001
From: yjwxfq <112159687+yjwxfq@users.noreply.github.com>
Date: Mon, 2 Sep 2024 10:21:04 +0800
Subject: [PATCH] Modify the function of SignCanonical in btcec, do makeCompact
 after isCanonicalSig.
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Since function recoverKeyFromSignature is called inside function makeCompact, the performance loss calculated by function recoverKeyFromSignature is relatively large.
So do makeCompact after isCanonicalSig can reduce the number of times it is executed, when isCanonicalSig is false then continue the next loop.
The average performance improvement after modification is nearly 40%－50%.
---
 btcsuite/btcd/btcec/privkey.go | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/btcsuite/btcd/btcec/privkey.go b/btcsuite/btcd/btcec/privkey.go
index d8c6417f..ed794c7d 100644
--- a/btcsuite/btcd/btcec/privkey.go
+++ b/btcsuite/btcd/btcec/privkey.go
@@ -65,6 +65,7 @@ func (p *PrivateKey) Sign(hash []byte) (*Signature, error) {
 
 // SignCanonical goes through signatures and returns only a canonical
 // representations.  This matches the EOS blockchain expectations.
+// do isCanonical before compactSig, for performance improvement
 func (p *PrivateKey) SignCanonical(curve *KoblitzCurve, hash []byte) ([]byte, error) {
 	for i := 0; i < 25; i++ {
 		sig, err := signRFC6979(p, hash, i)
@@ -72,14 +73,15 @@ func (p *PrivateKey) SignCanonical(curve *KoblitzCurve, hash []byte) ([]byte, er
 			return nil, err
 		}
 
-		compactSig, err := makeCompact(curve, sig, p, hash, true)
-		if err != nil {
+		if !isCanonicalSig(sig.R.Bytes(), sig.S.Bytes()) {
 			continue
 		}
 
-		if isCanonical(compactSig) {
-			return compactSig, nil
+		compactSig, err := makeCompact(curve, sig, p, hash, true)
+		if err != nil {
+			continue
 		}
+		return compactSig, nil
 	}
 	return nil, errors.New("couldn't find a canonical signature")
 }
@@ -110,3 +112,14 @@ func isCanonical(compactSig []byte) bool {
 	t4 := !(d[33] == 0 && ((d[34] & 0x80) == 0))
 	return t1 && t2 && t3 && t4
 }
+
+// add function for original signature, do isCanonical before compactSig
+func isCanonicalSig(r []byte, s []byte) bool {
+	rlen := len(r)
+	slen := len(s)
+	t1 := rlen < 32 || (r[0] & 0x80) == 0
+	t2 := !( (rlen < 32 || r[0] == 0) && ((rlen >= 31 && (r[rlen-31] & 0x80) == 0) || rlen < 31) )
+	t3 := slen < 32 || (s[0] & 0x80) == 0
+	t4 := !( (slen < 32 || s[0] == 0) && ((slen >= 31 && (s[slen-31] & 0x80) == 0) || slen < 31) )
+	return t1 && t2 && t3 && t4
+}