mldsa,slhdsa: crypto.Signer assertion

Author: emmansun

mldsa/field.go

@@ -243,3 +243,19 @@ func vectorCountOnes(a []ringElement) int {
 	}
 	return oneCount
 }
+
+func constantTimeEqualRingElement(a, b ringElement) int {
+    var res int32
+    for i := range a {
+        res |= int32(a[i] ^ b[i])
+    }
+    return subtle.ConstantTimeByteEq(byte(res|(-res)>>31), 0)
+}
+
+func constantTimeEqualRingElementArray(a, b []ringElement) int {
+    eq := 1
+    for i := range a {
+        eq &= constantTimeEqualRingElement(a[i], b[i])
+    }
+    return eq
+}

mldsa/mldsa44.go

@@ -101,6 +101,9 @@ const (
 	sigEncodedLen87 = lambda256/4 + encodingSize20*l87 + omega75 + k87
 )
 
+var _ crypto.Signer = (*PrivateKey44)(nil)
+var _ crypto.Signer = (*Key44)(nil)
+
 // A PrivateKey44 is the private key for the ML-DSA-44 signature scheme.
 type PrivateKey44 struct {
 	rho        [32]byte         // public random seed
@@ -118,10 +121,10 @@ type PrivateKey44 struct {
 	t1Once     sync.Once
 }
 
-// PublicKey returns the public key corresponding to the private key.
+// Public returns the public key corresponding to the private key.
 // Although we can derive the public key from the private key,
 // but we do NOT need to derive it at most of the time.
-func (sk *PrivateKey44) PublicKey() crypto.PublicKey {
+func (sk *PrivateKey44) Public() crypto.PublicKey {
 	sk.ensureT1()
 	return &PublicKey44{
 		rho: sk.rho,
@@ -187,9 +190,9 @@ type PublicKey44 struct {
 	nttOnce   sync.Once
 }
 
-// PublicKey generates and returns the corresponding public key for the given
+// Public generates and returns the corresponding public key for the given
 // Key44 instance.
-func (sk *Key44) PublicKey() *PublicKey44 {
+func (sk *Key44) Public() crypto.PublicKey {
 	return &PublicKey44{
 		rho: sk.rho,
 		t1:  sk.t1,
@@ -210,9 +213,9 @@ func (pk *PublicKey44) Equal(x crypto.PublicKey) bool {
 	if !ok {
 		return false
 	}
-	b1 := pk.Bytes()
-	b2 := xx.Bytes()
-	return subtle.ConstantTimeCompare(b1, b2) == 1
+	eq := subtle.ConstantTimeCompare(pk.rho[:], xx.rho[:]) &
+		constantTimeEqualRingElementArray(pk.t1[:], xx.t1[:])
+	return eq == 1
 }
 
 // Bytes converts the PublicKey44 instance into a byte slice.
@@ -271,9 +274,13 @@ func (sk *PrivateKey44) Equal(x any) bool {
 	if !ok {
 		return false
 	}
-	b1 := sk.Bytes()
-	b2 := xx.Bytes()
-	return subtle.ConstantTimeCompare(b1, b2) == 1
+	eq := subtle.ConstantTimeCompare(sk.rho[:], xx.rho[:]) &
+		subtle.ConstantTimeCompare(sk.k[:], xx.k[:]) &
+		subtle.ConstantTimeCompare(sk.tr[:], xx.tr[:]) &
+		constantTimeEqualRingElementArray(sk.s1[:], xx.s1[:]) &
+		constantTimeEqualRingElementArray(sk.s2[:], xx.s2[:]) &
+		constantTimeEqualRingElementArray(sk.t0[:], xx.t0[:])
+	return eq == 1
 }
 
 // GenerateKey44 generates a new Key44 (ML-DSA-44) using the provided random source.
@@ -363,7 +370,7 @@ func dsaKeyGen44(sk *Key44, xi *[32]byte) {
 		}
 	}
 	H.Reset()
-	ek := sk.PublicKey().Bytes()
+	ek := sk.Public().(*PublicKey44).Bytes()
 	H.Write(ek)
 	H.Read(sk.tr[:])
 }

mldsa/mldsa44_test.go

@@ -46,7 +46,7 @@ func TestKeyGen44(t *testing.T) {
 		if err != nil {
 			t.Fatalf("NewPrivateKey44 failed: %v", err)
 		}
-		pub := priv.PublicKey()
+		pub := priv.Public().(*PublicKey44)
 		pubBytes := pub.Bytes()
 		if !bytes.Equal(pubBytes, pk) {
 			t.Errorf("Public key mismatch: got %x, want %x", pubBytes, pk)
@@ -70,7 +70,7 @@ func TestKeyGen44(t *testing.T) {
 		if !priv.Equal(priv2) {
 			t.Errorf("Private key not equal: got %x, want %x", privBytes, priv2.Bytes())
 		}
-		pub3 := priv2.PublicKey()
+		pub3 := priv2.Public()
 		if !pub.Equal(pub3) {
 			t.Errorf("Public key from private key not equal")
 		}
@@ -127,6 +127,7 @@ func TestSign44(t *testing.T) {
 		if err != nil {
 			t.Fatalf("NewPrivateKey44 failed: %v", err)
 		}
+
 		sig2, err := priv.signInternal(seed[:], mu)
 		if err != nil {
 			t.Fatalf("failed to sign: %v", err)

mldsa/mldsa65.go

@@ -46,7 +46,7 @@ func TestKeyGen65(t *testing.T) {
 		if err != nil {
 			t.Fatalf("NewPrivateKey65 failed: %v", err)
 		}
-		pub := priv.PublicKey()
+		pub := priv.Public().(*PublicKey65)
 		pubBytes := pub.Bytes()
 		if !bytes.Equal(pubBytes, pk) {
 			t.Errorf("Public key mismatch: got %x, want %x", pubBytes, pk)
@@ -70,7 +70,7 @@ func TestKeyGen65(t *testing.T) {
 		if !priv.Equal(priv2) {
 			t.Errorf("Private key not equal: got %x, want %x", privBytes, priv2.Bytes())
 		}
-		pub3 := priv2.PublicKey()
+		pub3 := priv2.Public()
 		if !pub.Equal(pub3) {
 			t.Errorf("Public key from private key not equal")
 		}

mldsa/mldsa65_test.go

@@ -46,7 +46,7 @@ func TestKeyGen87(t *testing.T) {
 		if err != nil {
 			t.Fatalf("NewPrivateKey65 failed: %v", err)
 		}
-		pub := priv.PublicKey()
+		pub := priv.Public().(*PublicKey87)
 		pubBytes := pub.Bytes()
 		if !bytes.Equal(pubBytes, pk) {
 			t.Errorf("Public key mismatch: got %x, want %x", pubBytes, pk)
@@ -70,7 +70,7 @@ func TestKeyGen87(t *testing.T) {
 		if !priv.Equal(priv2) {
 			t.Errorf("Private key not equal: got %x, want %x", privBytes, priv2.Bytes())
 		}
-		pub3 := priv2.PublicKey()
+		pub3 := priv2.Public()
 		if !pub.Equal(pub3) {
 			t.Errorf("Public key from private key not equal")
 		}

mldsa/mldsa87.go

@@ -7,18 +7,42 @@
 package slhdsa
 
 import (
+	"crypto"
 	"errors"
+	"io"
 )
 
+var _ crypto.Signer = (*PrivateKey)(nil)
+
+type Options struct {
+	Context []byte
+	AddRand []byte // optional randomness to be added to the signature. If nil, the signature is deterministic.
+}
+
+func (opts *Options) HashFunc() crypto.Hash {
+	return crypto.Hash(0)
+}
+
+// Sign produces a signature of the message using the private key.
+// It is a wrapper around the SignMessage method, implementing the crypto.Signer interface.
+func (sk *PrivateKey) Sign(rand io.Reader, message []byte, opts crypto.SignerOpts) ([]byte, error) {
+	return sk.SignMessage(rand, message, opts)
+}
+
 // Sign generates a pure SLH-DSA signature for the given message.
 // The signature is deterministic if the addRand parameter is nil.
 // If addRand is not nil, it must be of the same length as n.
 //
 // See FIPS 205 Algorithm 22 slh_sign
-func (sk *PrivateKey) Sign(message, context, addRand []byte) ([]byte, error) {
+func (sk *PrivateKey) SignMessage(rand io.Reader, message []byte, opts crypto.SignerOpts) ([]byte, error) {
 	if len(message) == 0 {
 		return nil, errors.New("slhdsa: empty message")
 	}
+	var context, addRand []byte
+	if opts, ok := opts.(*Options); ok {
+		context = opts.Context
+		addRand = opts.AddRand
+	}
 	if len(addRand) > 0 && len(addRand) != int(sk.params.n) {
 		return nil, errors.New("slhdsa: addrnd should be nil (deterministic variant) or of length n")
 	}
@@ -85,10 +109,14 @@ func (sk *PrivateKey) signInternal(msgPrefix, message, addRand []byte) ([]byte,
 // Verify verifies a pure SLH-DSA signature for the given message.
 //
 // See FIPS 205 Algorithm 24 slh_verify
-func (pk *PublicKey) Verify(signature, message, context []byte) bool {
+func (pk *PublicKey) VerifyWithOptions(signature, message []byte, opts crypto.SignerOpts) bool {
 	if len(message) == 0 {
 		return false
 	}
+	var context []byte
+	if opts, ok := opts.(*Options); ok {
+		context = opts.Context
+	}
 	if len(context) > maxContextLen {
 		return false
 	}

mldsa/mldsa87_test.go

@@ -75,7 +75,7 @@ func testData(t *testing.T, filename string, tc *slhtest) {
 	if err != nil {
 		t.Fatalf("%v NewPrivateKey(%x) = %v", filename, skBytes, err)
 	}
-	sig2, err := privKey.Sign(message, context, addRand)
+	sig2, err := privKey.Sign(nil, message, &Options{context, addRand})
 	if err != nil {
 		t.Fatalf("%v Sign(%x,%x) = %v", filename, message, context, err)
 	}
@@ -104,7 +104,7 @@ func testData(t *testing.T, filename string, tc *slhtest) {
 	if err != nil {
 		t.Fatalf("%v NewPublicKey(%x) = %v", filename, pkBytes, err)
 	}
-	if !pub.Verify(sigOriginal, message, context) {
+	if !pub.VerifyWithOptions(sigOriginal, message, &Options{Context: context}) {
 		t.Errorf("%v Verify() = false, want true", filename)
 	}
 }

slhdsa/dsa.go

@@ -7,6 +7,7 @@
 package slhdsa
 
 import (
+	"crypto"
 	"crypto/sha256"
 	"crypto/sha3"
 	"crypto/sha512"
@@ -69,7 +70,7 @@ func (sk *PrivateKey) Bytes() []byte {
 }
 
 // Public returns the public key of the private key.
-func (sk *PrivateKey) Public() *PublicKey {
+func (sk *PrivateKey) Public() crypto.PublicKey {
 	return &sk.PublicKey
 }