add letsencrypt to Gitea (#4189)

vendor/golang.org/x/crypto/ed25519/ed25519.go

@@ -171,9 +171,16 @@ func Verify(publicKey PublicKey, message, sig []byte) bool {
 	edwards25519.ScReduce(&hReduced, &digest)
 
 	var R edwards25519.ProjectiveGroupElement
-	var b [32]byte
-	copy(b[:], sig[32:])
-	edwards25519.GeDoubleScalarMultVartime(&R, &hReduced, &A, &b)
+	var s [32]byte
+	copy(s[:], sig[32:])
+
+	// https://tools.ietf.org/html/rfc8032#section-5.1.7 requires that s be in
+	// the range [0, order) in order to prevent signature malleability.
+	if !edwards25519.ScMinimal(&s) {
+		return false
+	}
+
+	edwards25519.GeDoubleScalarMultVartime(&R, &hReduced, &A, &s)
 
 	var checkR [32]byte
 	R.ToBytes(&checkR)

vendor/golang.org/x/crypto/ed25519/internal/edwards25519/edwards25519.go

@@ -4,6 +4,8 @@
 
 package edwards25519
 
+import "encoding/binary"
+
 // This code is a port of the public domain, “ref10” implementation of ed25519
 // from SUPERCOP.
 
@@ -1769,3 +1771,23 @@ func ScReduce(out *[32]byte, s *[64]byte) {
 	out[30] = byte(s11 >> 9)
 	out[31] = byte(s11 >> 17)
 }
+
+// order is the order of Curve25519 in little-endian form.
+var order = [4]uint64{0x5812631a5cf5d3ed, 0x14def9dea2f79cd6, 0, 0x1000000000000000}
+
+// ScMinimal returns true if the given scalar is less than the order of the
+// curve.
+func ScMinimal(scalar *[32]byte) bool {
+	for i := 3; ; i-- {
+		v := binary.LittleEndian.Uint64(scalar[i*8:])
+		if v > order[i] {
+			return false
+		} else if v < order[i] {
+			break
+		} else if i == 0 {
+			return false
+		}
+	}
+
+	return true
+}