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package hybrid
import (
"encoding/hex"
"testing"
"github.com/cloudflare/circl/kem"
)
func mustDecodeString(s string) []byte {
b, err := hex.DecodeString(s)
if err != nil {
panic(err)
}
return b
}
// patchHybridWithLowOrderX25519 replaces the last half of the given ciphertext
// or public key by a 32-byte Curve25519 public key with a point of low order.
func patchHybridWithLowOrderX25519(hybridKey []byte) {
// order 8
xPub := mustDecodeString("e0eb7a7c3b41b8ae1656e3faf19fc46ada098deb9c32b1fd866205165f49b800")
copy(hybridKey[len(hybridKey)-len(xPub):], xPub)
}
func patchHybridPublicKeyWithLowOrderX25519(pub kem.PublicKey) (kem.PublicKey, error) {
packed, err := pub.MarshalBinary()
if err != nil {
return nil, err
}
patchHybridWithLowOrderX25519(packed)
return pub.Scheme().UnmarshalBinaryPublicKey(packed)
}
func TestLowOrderX25519PointEncapsulate(t *testing.T) {
scheme := X25519MLKEM768()
pk, _, err := scheme.GenerateKeyPair()
if err != nil {
t.Fatalf("X25519MLKEM768 keygen: %s", err)
}
badPk, err := patchHybridPublicKeyWithLowOrderX25519(pk)
if err != nil {
t.Fatalf("patching X25519 key failed: %s", err)
}
_, _, err = scheme.Encapsulate(badPk)
want := kem.ErrPubKey
if err != want {
t.Fatalf("Encapsulate error: expected %v; got %v", want, err)
}
}
func TestLowOrderX25519PointDecapsulate(t *testing.T) {
scheme := X25519MLKEM768()
pk, sk, err := scheme.GenerateKeyPair()
if err != nil {
t.Fatalf("X25519MLKEM768 keygen: %s", err)
}
ct, _, err := scheme.Encapsulate(pk)
if err != nil {
t.Fatalf("Encapsulate failed: %s", err)
}
patchHybridWithLowOrderX25519(ct)
_, err = scheme.Decapsulate(sk, ct)
want := kem.ErrPubKey
if err != want {
t.Fatalf("Decapsulate error: expected %v; got %v", want, err)
}
}
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