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PQC: Update key KEM combiner to latest draft #253

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PQC: Update key KEM combiner to latest draft #253

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d188e97
feat: Update key KEM combiner to latest draft
lubux Nov 29, 2024
c4b9f84
chore: Update pqc test vector
lubux Dec 4, 2024
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21 changes: 9 additions & 12 deletions openpgp/mlkem_ecdh/mlkem_ecdh.go
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@ import (
const (
maxSessionKeyLength = 64
MlKemSeedLen = 64
kdfContext = "OpenPGPCompositeKDFv1"
)

type PublicKey struct {
Expand Down Expand Up @@ -138,16 +139,11 @@ func Decrypt(priv *PrivateKey, kEphemeral, ecEphemeral, ciphertext []byte) (msg
return keywrap.Unwrap(kek, ciphertext)
}

// buildKey implements the composite KDF 2a from
// https://mailarchive.ietf.org/arch/msg/openpgp/NMTCy707LICtxIhP3Xt1U5C8MF0/
// buildKey implements the composite KDF from
// https://github.com/openpgp-pqc/draft-openpgp-pqc/pull/161
func buildKey(pub *PublicKey, eccSecretPoint, eccEphemeral, eccPublicKey, mlkemKeyShare, mlkemEphemeral []byte, mlkemPublicKey kem.PublicKey) ([]byte, error) {
h := sha3.New256()

// SHA3 never returns error
_, _ = h.Write(eccSecretPoint)
_, _ = h.Write(eccEphemeral)
_, _ = h.Write(eccPublicKey)
eccKeyShare := h.Sum(nil)
/// Set the output `ecdhKeyShare` to `eccSecretPoint`
eccKeyShare := eccSecretPoint

serializedMlkemPublicKey, err := mlkemPublicKey.MarshalBinary()
if err != nil {
Expand All @@ -162,16 +158,17 @@ func buildKey(pub *PublicKey, eccSecretPoint, eccEphemeral, eccPublicKey, mlkemK
// eccEphemeral - the ECDH ciphertext encoded as an octet string
// eccPublicKey - The ECDH public key of the recipient as an octet string

// 2a. SHA3-256(mlkemKeyShare || eccKeyShare || eccEphemeral || eccPublicKey || Domain)
// where Domain is "Domain" for LAMPS, and "mlkemEphemeral || mlkemPublicKey || algId" for OpenPGP
h.Reset()
// SHA3-256(mlkemKeyShare || eccKeyShare || eccEphemeral || eccPublicKey ||
// mlkemEphemeral || mlkemPublicKey || algId || "OpenPGPCompositeKDFv1")
h := sha3.New256()
_, _ = h.Write(mlkemKeyShare)
_, _ = h.Write(eccKeyShare)
_, _ = h.Write(eccEphemeral)
_, _ = h.Write(eccPublicKey)
_, _ = h.Write(mlkemEphemeral)
_, _ = h.Write(serializedMlkemPublicKey)
_, _ = h.Write([]byte{pub.AlgId})
_, _ = h.Write([]byte(kdfContext))
return h.Sum(nil), nil
}

Expand Down
15 changes: 7 additions & 8 deletions openpgp/read_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -967,13 +967,12 @@ var pqcDraftVectors = map[string]struct {
fingerprints []string
armoredMessages []string
}{
// Update with fresh vectors
//"v6_Ed25519_ML-KEM-768+X25519": {
// v6Ed25519Mlkem768X25519PrivateTestVector,
// v6Ed25519Mlkem768X25519PublicTestVector,
// []string{"52343242345254050219ceff286e9c8e479ec88757f95354388984a02d7d0b59", "263e34b69938e753dc67ca8ee37652795135e0e16e48887103c11d7307df40ed"},
// []string{v6Ed25519Mlkem768X25519PrivateMessageTestVector},
//},
"v6_Ed25519_ML-KEM-768+X25519": {
v6Ed25519Mlkem768X25519PrivateTestVector,
v6Ed25519Mlkem768X25519PublicTestVector,
[]string{"bf262b24177002ac8ae5dc6da47c056d22ab9906d47d07952b75c358021901ca", "48b94bce2f9771788f5feb74122d599989c400cc0f49108bc98e0ea7945e4838"},
[]string{v6Ed25519Mlkem768X25519PrivateMessageTestVector},
},
}

func TestPqcDraftVectors(t *testing.T) {
Expand Down Expand Up @@ -1040,7 +1039,7 @@ func TestPqcDraftVectors(t *testing.T) {
return
}

if string(contents) != "Testing\n" {
if string(contents) != "Testing\r\n" {
t.Fatalf("Decrypted message is wrong: %s", contents)
}
})
Expand Down
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