kem: add P-256 + Kyber768Draft00 hybrid

Author: bwesterb

kem/hybrid/ckem.go

@@ -0,0 +1,211 @@
+package hybrid
+
+// TODO move over to crypto/ecdh once we can assume Go 1.20.
+
+import (
+	"bytes"
+	"crypto/elliptic"
+	cryptoRand "crypto/rand"
+	"crypto/subtle"
+	"math/big"
+
+	"github.com/cloudflare/circl/kem"
+	"github.com/cloudflare/circl/xof"
+)
+
+type cPublicKey struct {
+	scheme *cScheme
+	x, y   *big.Int
+}
+type cPrivateKey struct {
+	scheme *cScheme
+	key    []byte
+}
+type cScheme struct {
+	curve elliptic.Curve
+}
+
+var p256Kem = &cScheme{elliptic.P256()}
+
+func (sch *cScheme) scSize() int {
+	return (sch.curve.Params().N.BitLen() + 7) / 8
+}
+
+func (sch *cScheme) ptSize() int {
+	return (sch.curve.Params().BitSize + 7) / 8
+}
+
+func (sch *cScheme) Name() string {
+	return sch.curve.Params().Name
+}
+
+func (sch *cScheme) PublicKeySize() int {
+	return 2*sch.ptSize() + 1
+}
+
+func (sch *cScheme) PrivateKeySize() int {
+	return sch.scSize()
+}
+
+func (sch *cScheme) SeedSize() int {
+	return sch.PrivateKeySize()
+}
+
+func (sch *cScheme) SharedKeySize() int {
+	return sch.ptSize()
+}
+
+func (sch *cScheme) CiphertextSize() int {
+	return sch.PublicKeySize()
+}
+
+func (sch *cScheme) EncapsulationSeedSize() int {
+	return sch.SeedSize()
+}
+
+func (sk *cPrivateKey) Scheme() kem.Scheme { return sk.scheme }
+func (pk *cPublicKey) Scheme() kem.Scheme  { return pk.scheme }
+
+func (sk *cPrivateKey) MarshalBinary() ([]byte, error) {
+	ret := make([]byte, len(sk.key))
+	copy(ret, sk.key)
+	return ret, nil
+}
+
+func (sk *cPrivateKey) Equal(other kem.PrivateKey) bool {
+	oth, ok := other.(*cPrivateKey)
+	if !ok {
+		return false
+	}
+	if oth.scheme != sk.scheme {
+		return false
+	}
+	return subtle.ConstantTimeCompare(oth.key, sk.key) == 1
+}
+
+func (sk *cPrivateKey) Public() kem.PublicKey {
+	x, y := sk.scheme.curve.ScalarBaseMult(sk.key)
+	return &cPublicKey{
+		sk.scheme,
+		x,
+		y,
+	}
+}
+
+func (pk *cPublicKey) Equal(other kem.PublicKey) bool {
+	oth, ok := other.(*cPublicKey)
+	if !ok {
+		return false
+	}
+	if oth.scheme != pk.scheme {
+		return false
+	}
+	return oth.x.Cmp(pk.x) == 0 && oth.y.Cmp(pk.y) == 0
+}
+
+func (pk *cPublicKey) MarshalBinary() ([]byte, error) {
+	return elliptic.Marshal(pk.scheme.curve, pk.x, pk.y), nil
+}
+
+func (sch *cScheme) GenerateKeyPair() (kem.PublicKey, kem.PrivateKey, error) {
+	seed := make([]byte, sch.SeedSize())
+	_, err := cryptoRand.Read(seed)
+	if err != nil {
+		return nil, nil, err
+	}
+	pk, sk := sch.DeriveKeyPair(seed)
+	return pk, sk, nil
+}
+
+func (sch *cScheme) DeriveKeyPair(seed []byte) (kem.PublicKey, kem.PrivateKey) {
+	if len(seed) != sch.SeedSize() {
+		panic(kem.ErrSeedSize)
+	}
+	h := xof.SHAKE256.New()
+	_, _ = h.Write(seed)
+	buf := make([]byte, sch.PrivateKeySize())
+	_, _ = h.Read(buf)
+	rnd := bytes.NewReader(buf)
+	key, x, y, err := elliptic.GenerateKey(sch.curve, rnd)
+	if err != nil {
+		panic(err)
+	}
+
+	sk := cPrivateKey{scheme: sch, key: key}
+	pk := cPublicKey{scheme: sch, x: x, y: y}
+
+	return &pk, &sk
+}
+
+func (sch *cScheme) Encapsulate(pk kem.PublicKey) (ct, ss []byte, err error) {
+	seed := make([]byte, sch.EncapsulationSeedSize())
+	_, err = cryptoRand.Read(seed)
+	if err != nil {
+		return
+	}
+	return sch.EncapsulateDeterministically(pk, seed)
+}
+
+func (pk *cPublicKey) X(sk *cPrivateKey) []byte {
+	if pk.scheme != sk.scheme {
+		panic(kem.ErrTypeMismatch)
+	}
+
+	sharedKey := make([]byte, pk.scheme.SharedKeySize())
+	xShared, _ := pk.scheme.curve.ScalarMult(pk.x, pk.y, sk.key)
+	xShared.FillBytes(sharedKey)
+	return sharedKey
+}
+
+func (sch *cScheme) EncapsulateDeterministically(
+	pk kem.PublicKey, seed []byte,
+) (ct, ss []byte, err error) {
+	if len(seed) != sch.EncapsulationSeedSize() {
+		return nil, nil, kem.ErrSeedSize
+	}
+	pub, ok := pk.(*cPublicKey)
+	if !ok || pub.scheme != sch {
+		return nil, nil, kem.ErrTypeMismatch
+	}
+
+	pk2, sk2 := sch.DeriveKeyPair(seed)
+	ss = pub.X(sk2.(*cPrivateKey))
+	ct, _ = pk2.MarshalBinary()
+	return
+}
+
+func (sch *cScheme) Decapsulate(sk kem.PrivateKey, ct []byte) ([]byte, error) {
+	if len(ct) != sch.CiphertextSize() {
+		return nil, kem.ErrCiphertextSize
+	}
+
+	priv, ok := sk.(*cPrivateKey)
+	if !ok || priv.scheme != sch {
+		return nil, kem.ErrTypeMismatch
+	}
+
+	pk, err := sch.UnmarshalBinaryPublicKey(ct)
+	if err != nil {
+		return nil, err
+	}
+
+	ss := pk.(*cPublicKey).X(priv)
+	return ss, nil
+}
+
+func (sch *cScheme) UnmarshalBinaryPublicKey(buf []byte) (kem.PublicKey, error) {
+	if len(buf) != sch.PublicKeySize() {
+		return nil, kem.ErrPubKeySize
+	}
+	x, y := elliptic.Unmarshal(sch.curve, buf)
+	return &cPublicKey{sch, x, y}, nil
+}
+
+func (sch *cScheme) UnmarshalBinaryPrivateKey(buf []byte) (kem.PrivateKey, error) {
+	if len(buf) != sch.PrivateKeySize() {
+		return nil, kem.ErrPrivKeySize
+	}
+	ret := cPrivateKey{sch, make([]byte, sch.PrivateKeySize())}
+	copy(ret.key, buf)
+	return &ret, nil
+}

kem/hybrid/hybrid.go

@@ -42,18 +42,27 @@ import (
 
 var ErrUninitialized = errors.New("public or private key not initialized")
 
-// Returns the hybrid KEM of Kyber512 and X25519.
+// Returns the hybrid KEM of Kyber512Draft00 and X25519.
 func Kyber512X25519() kem.Scheme { return kyber512X }
 
-// Returns the hybrid KEM of Kyber768 and X25519.
+// Returns the hybrid KEM of Kyber768Draft00 and X25519.
 func Kyber768X25519() kem.Scheme { return kyber768X }
 
-// Returns the hybrid KEM of Kyber768 and X448.
+// Returns the hybrid KEM of Kyber768Draft00 and X448.
 func Kyber768X448() kem.Scheme { return kyber768X4 }
 
-// Returns the hybrid KEM of Kyber1024 and X448.
+// Returns the hybrid KEM of Kyber1024Draft00 and X448.
 func Kyber1024X448() kem.Scheme { return kyber1024X }
 
+// Returns the hybrid KEM of Kyber768Draft00 and P-256.
+func P256Kyber768Draft00() kem.Scheme { return p256Kyber768Draft00 }
+
+var p256Kyber768Draft00 kem.Scheme = &scheme{
+	"P256Kyber768Draft00",
+	p256Kem,
+	kyber768.Scheme(),
+}
+
 var kyber512X kem.Scheme = &scheme{
 	"Kyber512-X25519",
 	x25519Kem,

kem/schemes/schemes.go

@@ -42,6 +42,7 @@ var allSchemes = [...]kem.Scheme{
 	hybrid.Kyber768X25519(),
 	hybrid.Kyber768X448(),
 	hybrid.Kyber1024X448(),
+	hybrid.P256Kyber768Draft00(),
 }
 
 var allSchemeNames map[string]kem.Scheme

kem/schemes/schemes_test.go

@@ -159,4 +159,5 @@ func Example_schemes() {
 	// Kyber768-X25519
 	// Kyber768-X448
 	// Kyber1024-X448
+	// P256Kyber768Draft00
 }