mlkem768,xwing: add SeedSize

FiloSottile · Feb 21, 2024 · 5ce9162 · 5ce9162
1 parent b43add9
commit 5ce9162
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Showing 2 changed files with 7 additions and 5 deletions.
diff --git a/mlkem768.go b/mlkem768.go
@@ -63,6 +63,7 @@ const (
 	EncapsulationKeySize = encryptionKeySize
 	DecapsulationKeySize = decryptionKeySize + encryptionKeySize + 32 + 32
 	SharedKeySize        = 32
+	SeedSize             = 32 + 32
 )
 
 // GenerateKey generates an encapsulation key and a corresponding decapsulation
@@ -86,10 +87,10 @@ func GenerateKey() (encapsulationKey, decapsulationKey []byte, err error) {
 // corresponding decapsulation key from a 64-byte seed. The seed must be
 // uniformly random.
 func NewKeyFromSeed(seed []byte) (encapsulationKey, decapsulationKey []byte, err error) {
-	if len(seed) != 64 {
+	if len(seed) != SeedSize {
 		return nil, nil, errors.New("mlkem768: invalid seed length")
 	}
-	ek, dk := kemKeyGen(seed[0:32], seed[32:64])
+	ek, dk := kemKeyGen(seed[:32], seed[32:])
 	return ek, dk, nil
 }
 

diff --git a/xwing/xwing.go b/xwing/xwing.go
@@ -22,6 +22,7 @@ const (
 	EncapsulationKeySize = mlkem768.EncapsulationKeySize + 32
 	DecapsulationKeySize = mlkem768.DecapsulationKeySize + 32 + 32
 	SharedKeySize        = 32
+	SeedSize             = mlkem768.SeedSize + 32
 )
 
 // GenerateKey generates an encapsulation key and a corresponding decapsulation
@@ -48,18 +49,18 @@ func GenerateKey() (encapsulationKey, decapsulationKey []byte, err error) {
 // corresponding decapsulation key from a 96-byte seed. The seed must be
 // uniformly random.
 func NewKeyFromSeed(seed []byte) (encapsulationKey, decapsulationKey []byte, err error) {
-	if len(seed) != 96 {
+	if len(seed) != SeedSize {
 		return nil, nil, errors.New("xwing: invalid seed length")
 	}
 
-	skX := seed[64:96]
+	skX := seed[mlkem768.SeedSize:]
 	x, err := ecdh.X25519().NewPrivateKey(skX)
 	if err != nil {
 		return nil, nil, err
 	}
 	pkX := x.PublicKey().Bytes()
 
-	pkM, skM, err := mlkem768.NewKeyFromSeed(seed[0:64])
+	pkM, skM, err := mlkem768.NewKeyFromSeed(seed[:mlkem768.SeedSize])
 	if err != nil {
 		return nil, nil, err
 	}