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Experiment with hybrid KEM.
Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>
This commit is contained in:
NIIBE Yutaka
parent
068bb5b6f9
commit
c9f71ba8ee
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@ -171,6 +171,302 @@ reverse_buffer (unsigned char *buffer, unsigned int length)
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}
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}
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static gpg_error_t
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agent_hybrid_kem_decap (ctrl_t ctrl, const char *desc_text, int kemid,
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gcry_sexp_t s_cipher, membuf_t *outbuf)
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{
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gcry_sexp_t s_skey0 = NULL;
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gcry_sexp_t s_skey1 = NULL;
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unsigned char *shadow_info = NULL;
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gpg_error_t err = 0;
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int no_shadow_info = 0;
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unsigned int nbits;
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const unsigned char *p;
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size_t len;
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gcry_mpi_t encrypted_sessionkey_mpi;
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const unsigned char *encrypted_sessionkey;
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size_t encrypted_sessionkey_len;
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gcry_mpi_t ecc_sk_mpi;
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unsigned char ecc_sk[32];
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gcry_mpi_t ecc_pk_mpi;
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unsigned char ecc_pk[32];
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gcry_mpi_t ecc_ct_mpi;
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const unsigned char *ecc_ct;
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size_t ecc_ct_len;
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unsigned char ecc_ecdh[32];
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unsigned char ecc_ss[32];
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gcry_mpi_t mlkem_sk_mpi;
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gcry_mpi_t mlkem_ct_mpi;
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const unsigned char *mlkem_sk;
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const unsigned char *mlkem_ct;
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unsigned char mlkem_ss[GCRY_KEM_MLKEM768_SHARED_LEN];
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gcry_buffer_t iov[13];
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unsigned char head136[2];
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unsigned char headK[2];
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const unsigned char pad[95] = { 0 };
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unsigned char right_encode_L[3];
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unsigned char kekkey[16];
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size_t kekkeylen = 16; /* AES, perhaps */
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gcry_cipher_hd_t hd;
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unsigned char sessionkey_encoded[256];
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size_t sessionkey_encoded_len;
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const unsigned char fixedinfo[1] = { 105 };
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(void)kemid; /* For now, only PGP. */
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/*
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(enc-val(pqc(s%m)(e%m)(k%m))))
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*/
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err = agent_key_from_file (ctrl, NULL, desc_text,
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NULL, &shadow_info,
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CACHE_MODE_NORMAL, NULL, &s_skey0, NULL, NULL);
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if (gpg_err_code (err) == GPG_ERR_NO_SECKEY)
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no_shadow_info = 1;
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else if (err)
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{
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log_error ("failed to read the secret key\n");
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goto leave;
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}
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if (shadow_info || no_shadow_info)
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{ /* divert operation to the smartcard */
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err = gpg_error (GPG_ERR_NO_SECKEY); /* Not implemented yet. */
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goto leave;
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}
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err = agent_key_from_file (ctrl, NULL, desc_text,
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NULL, &shadow_info,
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CACHE_MODE_NORMAL, NULL, &s_skey1, NULL, NULL);
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if (gpg_err_code (err) == GPG_ERR_NO_SECKEY)
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no_shadow_info = 1;
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else if (err)
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{
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log_error ("failed to read the secret key\n");
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goto leave;
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}
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if (shadow_info || no_shadow_info)
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{ /* divert operation to the smartcard */
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err = gpg_error (GPG_ERR_NO_SECKEY); /* Not implemented yet. */
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goto leave;
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}
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/* No smartcard, but private keys */
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gcry_sexp_extract_param (s_cipher, NULL, "/e/k/s",
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&ecc_ct_mpi,
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&mlkem_ct_mpi,
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&encrypted_sessionkey_mpi, NULL);
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encrypted_sessionkey = gcry_mpi_get_opaque (encrypted_sessionkey_mpi, &nbits);
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encrypted_sessionkey_len = (nbits+7)/8;
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encrypted_sessionkey_len--;
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if (encrypted_sessionkey[0] != encrypted_sessionkey_len)
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{
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err = GPG_ERR_INV_DATA;
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goto leave;
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}
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encrypted_sessionkey++;
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/* Fistly, ECC. */
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gcry_sexp_extract_param (s_skey0, NULL, "/q/d",
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&ecc_pk_mpi, &ecc_sk_mpi, NULL);
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p = gcry_mpi_get_opaque (ecc_pk_mpi, &nbits);
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len = (nbits+7)/8;
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memcpy (ecc_pk, p+1, 32);
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p = gcry_mpi_get_opaque (ecc_sk_mpi, &nbits);
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len = (nbits+7)/8;
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memset (ecc_sk, 0, 32);
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memcpy (ecc_sk + 32 - len, p, len);
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reverse_buffer (ecc_sk, 32);
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mpi_release (ecc_pk_mpi);
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mpi_release (ecc_sk_mpi);
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ecc_ct = gcry_mpi_get_opaque (ecc_ct_mpi, &nbits);
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ecc_ct_len = (nbits+7)/8;
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/* Remove the 0x40 prefix*/
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ecc_ct++;
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ecc_ct_len--;
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/*FIXME make sure the lengths are all correct. */
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/*FIXME: check the internal of optional to determine the KEK-algo and KEKKEYLEN. */
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err = gcry_kem_decap (GCRY_KEM_RAW_X25519,
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ecc_sk, 32,
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ecc_ct, ecc_ct_len,
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ecc_ecdh, 32,
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NULL, 0);
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mpi_release (ecc_ct_mpi);
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iov[0].data = ecc_ecdh;
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iov[0].off = 0;
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iov[0].len = 32;
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iov[1].data = (unsigned char *)ecc_ct;
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iov[1].off = 0;
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iov[1].len = 32;
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iov[2].data = ecc_pk;
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iov[2].off = 0;
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iov[2].len = 32;
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gcry_md_hash_buffers (GCRY_MD_SHA3_256, 0, ecc_ss, iov, 3);
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/* Secondly, ML-KEM */
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gcry_sexp_extract_param (s_skey1, NULL, "/s", &mlkem_sk_mpi, NULL);
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mlkem_sk = gcry_mpi_get_opaque (mlkem_sk_mpi, &nbits);
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len = (nbits+7)/8;
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mlkem_ct = gcry_mpi_get_opaque (mlkem_ct_mpi, &nbits);
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len = (nbits+7)/8;
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err = gcry_kem_decap (GCRY_KEM_MLKEM768,
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mlkem_sk, GCRY_KEM_MLKEM768_SECKEY_LEN,
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mlkem_ct, GCRY_KEM_MLKEM768_ENCAPS_LEN,
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mlkem_ss, GCRY_KEM_MLKEM768_SHARED_LEN,
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NULL, 0);
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mpi_release (mlkem_sk_mpi);
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mpi_release (mlkem_ct_mpi);
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/* Then, combine two shared secrets into one */
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// multiKeyCombine(eccKeyShare, eccCipherText,
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// mlkemKeyShare, mlkemCipherText,
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// fixedInfo, oBits)
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//
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// Input:
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// eccKeyShare - the ECC key share encoded as an octet string
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// eccCipherText - the ECC ciphertext encoded as an octet string
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// mlkemKeyShare - the ML-KEM key share encoded as an octet string
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// mlkemCipherText - the ML-KEM ciphertext encoded as an octet string
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// fixedInfo - the fixed information octet string
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// oBits - the size of the output keying material in bits
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//
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// Constants:
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// domSeparation - the UTF-8 encoding of the string
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// "OpenPGPCompositeKeyDerivationFunction"
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// counter - the 4 byte value 00 00 00 01
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// customizationString - the UTF-8 encoding of the string "KDF"
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//
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// eccData = eccKeyShare || eccCipherText
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// mlkemData = mlkemKeyShare || mlkemCipherText
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// encData = counter || eccData || mlkemData || fixedInfo
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//
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// KEK = KMAC256(domSeparation, encData, oBits, customizationString)
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// return KEK
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//
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// fixedInfo = algID (105 for ML-KEM-768-x25519kem)
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//
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// KMAC256(K,X,L,S):
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// newX = bytepad(encode_string(K), 136) || X || right_encode(L)
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// cSHAKE256(newX,L,"KMAC",S)
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len = 4 + 32 + 32 + GCRY_KEM_MLKEM768_SHARED_LEN + GCRY_KEM_MLKEM768_ENCAPS_LEN;
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iov[0].data = "KMAC";
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iov[0].off = 0;
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iov[0].len = 4;
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iov[1].data = "KDF";
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iov[1].off = 0;
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iov[1].len = 3;
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head136[0] = 1;
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head136[1] = 136;
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iov[2].data = head136;
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iov[2].off = 0;
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iov[2].len = 2;
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headK[0] = 1;
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headK[1] = 37;
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iov[3].data = headK;
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iov[3].off = 0;
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iov[3].len = 2;
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iov[4].data = "OpenPGPCompositeKeyDerivationFunction";
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iov[4].off = 0;
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iov[4].len = 37;
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iov[5].data = (unsigned char *)pad;
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iov[5].off = 0;
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iov[5].len = sizeof (pad);
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iov[6].data = "\x00\x00\x00\x01"; /* Counter */
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iov[6].off = 0;
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iov[6].len = 4;
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iov[7].data = ecc_ss;
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iov[7].off = 0;
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iov[7].len = 32;
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iov[8].data = (unsigned char *)ecc_ct;
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iov[8].off = 0;
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iov[8].len = 32;
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iov[9].data = mlkem_ss;
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iov[9].off = 0;
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iov[9].len = GCRY_KEM_MLKEM768_SHARED_LEN;
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iov[10].data = (unsigned char *)mlkem_ct;
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iov[10].off = 0;
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iov[10].len = GCRY_KEM_MLKEM768_ENCAPS_LEN;
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iov[11].data = (unsigned char *)fixedinfo;
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iov[11].off = 0;
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iov[11].len = 1;
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right_encode_L[0] = (kekkeylen * 8);
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right_encode_L[1] = 1;
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iov[12].data = right_encode_L;
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iov[12].off = 0;
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iov[12].len = 2;
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gcry_md_hash_buffers_extract (GCRY_MD_CSHAKE256, 0, kekkey, kekkeylen,
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iov, DIM (iov));
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if (DBG_CRYPTO)
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{
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log_printhex (kekkey, kekkeylen, "KEK key: ");
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}
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/*FIXME: KEK may be AES256, for example */
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err = gcry_cipher_open (&hd, GCRY_CIPHER_AES, GCRY_CIPHER_MODE_AESWRAP, 0);
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if (err)
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{
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log_error ("ecdh failed to initialize AESWRAP: %s\n",
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gpg_strerror (err));
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mpi_release (encrypted_sessionkey_mpi);
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goto leave;
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}
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err = gcry_cipher_setkey (hd, kekkey, kekkeylen);
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sessionkey_encoded_len = encrypted_sessionkey_len - 8;
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gcry_cipher_decrypt (hd, sessionkey_encoded, sessionkey_encoded_len,
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encrypted_sessionkey, encrypted_sessionkey_len);
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gcry_cipher_close (hd);
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mpi_release (encrypted_sessionkey_mpi);
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if (err)
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{
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log_error ("KEM decap failed: %s\n", gpg_strerror (err));
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goto leave;
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}
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put_membuf_printf (outbuf, "(5:value%u:", (unsigned int)sessionkey_encoded_len);
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put_membuf (outbuf, sessionkey_encoded, sessionkey_encoded_len);
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put_membuf (outbuf, ")", 2);
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leave:
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gcry_sexp_release (s_skey0);
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gcry_sexp_release (s_skey1);
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xfree (shadow_info);
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return err;
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}
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gpg_error_t
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agent_kem_decap (ctrl_t ctrl, const char *desc_text, int kemid,
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const unsigned char *ciphertext, size_t ciphertextlen,
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@ -182,8 +478,6 @@ agent_kem_decap (ctrl_t ctrl, const char *desc_text, int kemid,
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gpg_error_t err = 0;
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int no_shadow_info = 0;
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/* IMPLEMENT: check ctrl->have_keygrip1, kem_decap, and call key combiner */
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if (!ctrl->have_keygrip)
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{
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log_error ("speculative decryption not yet supported\n");
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@ -204,6 +498,13 @@ agent_kem_decap (ctrl_t ctrl, const char *desc_text, int kemid,
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log_printhex (ctrl->keygrip, 20, "keygrip:");
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log_printhex (ciphertext, ciphertextlen, "cipher: ");
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}
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if (ctrl->have_keygrip1)
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{
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err = agent_hybrid_kem_decap (ctrl, desc_text, kemid, s_cipher, outbuf);
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goto leave;
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}
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err = agent_key_from_file (ctrl, NULL, desc_text,
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NULL, &shadow_info,
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CACHE_MODE_NORMAL, NULL, &s_skey, NULL, NULL);
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@ -217,7 +518,7 @@ agent_kem_decap (ctrl_t ctrl, const char *desc_text, int kemid,
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if (shadow_info || no_shadow_info)
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{ /* divert operation to the smartcard */
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err = gpg_error (GPG_ERR_NO_SECKEY);
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err = gpg_error (GPG_ERR_NO_SECKEY); /* Not implemented yet. */
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goto leave;
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}
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else
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