common/bitutil: deprecate XORBytes in favor of stdlib crypto/subtle (#33331)

XORBytes was added to package crypto/subtle in Go 1.20, and it's faster 
than our bitutil.XORBytes. There is only one use of this function
across go-ethereum so we can simply deprecate the custom implementation.

---------

Co-authored-by: Felix Lange <fjl@twurst.com>

common/bitutil/bitutil.go

@@ -8,6 +8,7 @@
 package bitutil
 
 import (
+	"crypto/subtle"
 	"runtime"
 	"unsafe"
 )
@@ -17,46 +18,16 @@ const supportsUnaligned = runtime.GOARCH == "386" || runtime.GOARCH == "amd64" |
 
 // XORBytes xors the bytes in a and b. The destination is assumed to have enough
 // space. Returns the number of bytes xor'd.
+//
+// If dst does not have length at least n,
+// XORBytes panics without writing anything to dst.
+//
+// dst and x or y may overlap exactly or not at all,
+// otherwise XORBytes may panic.
+//
+// Deprecated: use crypto/subtle.XORBytes
 func XORBytes(dst, a, b []byte) int {
-	if supportsUnaligned {
-		return fastXORBytes(dst, a, b)
-	}
-	return safeXORBytes(dst, a, b)
-}
-
-// fastXORBytes xors in bulk. It only works on architectures that support
-// unaligned read/writes.
-func fastXORBytes(dst, a, b []byte) int {
-	n := len(a)
-	if len(b) < n {
-		n = len(b)
-	}
-	w := n / wordSize
-	if w > 0 {
-		dw := *(*[]uintptr)(unsafe.Pointer(&dst))
-		aw := *(*[]uintptr)(unsafe.Pointer(&a))
-		bw := *(*[]uintptr)(unsafe.Pointer(&b))
-		for i := 0; i < w; i++ {
-			dw[i] = aw[i] ^ bw[i]
-		}
-	}
-	for i := n - n%wordSize; i < n; i++ {
-		dst[i] = a[i] ^ b[i]
-	}
-	return n
-}
-
-// safeXORBytes xors one by one. It works on all architectures, independent if
-// it supports unaligned read/writes or not.
-func safeXORBytes(dst, a, b []byte) int {
-	n := len(a)
-	if len(b) < n {
-		n = len(b)
-	}
-	for i := 0; i < n; i++ {
-		dst[i] = a[i] ^ b[i]
-	}
-	return n
+	return subtle.XORBytes(dst, a, b)
 }
 
 // ANDBytes ands the bytes in a and b. The destination is assumed to have enough

common/bitutil/bitutil_test.go

@@ -29,7 +29,7 @@ func TestXOR(t *testing.T) {
 				d2 := make([]byte, 1023+alignD)[alignD:]
 
 				XORBytes(d1, p, q)
-				safeXORBytes(d2, p, q)
+				naiveXOR(d2, p, q)
 				if !bytes.Equal(d1, d2) {
 					t.Error("not equal", d1, d2)
 				}
@@ -38,6 +38,18 @@ func TestXOR(t *testing.T) {
 	}
 }
 
+// naiveXOR xors bytes one by one.
+func naiveXOR(dst, a, b []byte) int {
+	n := len(a)
+	if len(b) < n {
+		n = len(b)
+	}
+	for i := 0; i < n; i++ {
+		dst[i] = a[i] ^ b[i]
+	}
+	return n
+}
+
 // Tests that bitwise AND works for various alignments.
 func TestAND(t *testing.T) {
 	for alignP := 0; alignP < 2; alignP++ {
@@ -134,7 +146,7 @@ func benchmarkBaseXOR(b *testing.B, size int) {
 	p, q := make([]byte, size), make([]byte, size)
 
 	for i := 0; i < b.N; i++ {
-		safeXORBytes(p, p, q)
+		naiveXOR(p, p, q)
 	}
 }
 

p2p/rlpx/rlpx.go

@@ -24,6 +24,7 @@ import (
 	"crypto/ecdsa"
 	"crypto/hmac"
 	"crypto/rand"
+	"crypto/subtle"
 	"encoding/binary"
 	"errors"
 	"fmt"
@@ -33,7 +34,6 @@ import (
 	"net"
 	"time"
 
-	"github.com/ethereum/go-ethereum/common/bitutil"
 	"github.com/ethereum/go-ethereum/crypto"
 	"github.com/ethereum/go-ethereum/crypto/ecies"
 	"github.com/ethereum/go-ethereum/rlp"
@@ -677,6 +677,6 @@ func exportPubkey(pub *ecies.PublicKey) []byte {
 
 func xor(one, other []byte) (xor []byte) {
 	xor = make([]byte, len(one))
-	bitutil.XORBytes(xor, one, other)
+	subtle.XORBytes(xor, one, other)
 	return xor
 }