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gpg: Clean up ECDH code path (3). 

* g10/ecdh.c (derive_kek): New.
(pk_ecdh_encrypt_with_shared_point): Use derive_kek.

Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>
This commit is contained in:
NIIBE Yutaka 2020-05-22 11:24:38 +09:00
parent a973d91138
commit 80c02d13d9
1 changed files with 52 additions and 36 deletions
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88
g10/ecdh.c
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@ -175,6 +175,41 @@ build_kdf_params (unsigned char kdf_params[256], size_t *r_size,
return err;
}
/* Derive KEK with KEK_SIZE into the memory at SECRET_X. */
static gpg_error_t
derive_kek (size_t kek_size,
int kdf_hash_algo,
byte *secret_x, int secret_x_size,
const unsigned char *kdf_params, size_t kdf_params_size)
{
gpg_error_t err;
gcry_md_hd_t h;
log_assert( gcry_md_get_algo_dlen (kdf_hash_algo) >= 32 );
err = gcry_md_open (&h, kdf_hash_algo, 0);
if (err)
{
log_error ("gcry_md_open failed for kdf_hash_algo %d: %s",
kdf_hash_algo, gpg_strerror (err));
return err;
}
gcry_md_write(h, "\x00\x00\x00\x01", 4); /* counter = 1 */
gcry_md_write(h, secret_x, secret_x_size); /* x of the point X */
gcry_md_write(h, kdf_params, kdf_params_size); /* KDF parameters */
gcry_md_final (h);
memcpy (secret_x, gcry_md_read (h, kdf_hash_algo), kek_size);
gcry_md_close (h);
/* Clean the tail before returning. */
memset (secret_x+kek_size, 0, secret_x_size - kek_size);
if (DBG_CRYPTO)
log_printhex (secret_x, kek_size, "ecdh KEK is:");
return err;
}
/* Encrypts/decrypts DATA using a key derived from the ECC shared
point SHARED_MPI using the FIPS SP 800-56A compliant method
key_derivation+key_wrapping. If IS_ENCRYPT is true the function
@ -198,6 +233,7 @@ pk_ecdh_encrypt_with_shared_point (int is_encrypt, gcry_mpi_t shared_mpi,
int kdf_encr_algo;
unsigned char kdf_params[256];
size_t kdf_params_size;
size_t kek_size;
*r_result = NULL;
@ -232,6 +268,10 @@ pk_ecdh_encrypt_with_shared_point (int is_encrypt, gcry_mpi_t shared_mpi,
&& kdf_encr_algo != CIPHER_ALGO_AES256)
return gpg_error (GPG_ERR_BAD_PUBKEY);
kek_size = gcry_cipher_get_algo_keylen (kdf_encr_algo);
if (kek_size > gcry_md_get_algo_dlen (kdf_hash_algo))
return gpg_error (GPG_ERR_BAD_PUBKEY);
/* Build kdf_params. */
err = build_kdf_params (kdf_params, &kdf_params_size, pkey, pk_fp);
if (err)
@ -242,6 +282,9 @@ pk_ecdh_encrypt_with_shared_point (int is_encrypt, gcry_mpi_t shared_mpi,
return gpg_error (GPG_ERR_TOO_SHORT);
secret_x_size = (nbits+7)/8;
if (kek_size > secret_x_size)
return gpg_error (GPG_ERR_BAD_PUBKEY);
err = extract_secret_x (&secret_x, shared_mpi,
/* pkey[1] is the public point */
(mpi_get_nbits (pkey[1])+7)/8,
@ -258,41 +301,14 @@ pk_ecdh_encrypt_with_shared_point (int is_encrypt, gcry_mpi_t shared_mpi,
* a KEK.
*/
/* Derive a KEK (key wrapping key) using KDF_PARAMS and SECRET_X. */
{
gcry_md_hd_t h;
int old_size;
err = gcry_md_open (&h, kdf_hash_algo, 0);
if (err)
{
log_error ("gcry_md_open failed for kdf_hash_algo %d: %s",
kdf_hash_algo, gpg_strerror (err));
xfree (secret_x);
return err;
}
gcry_md_write(h, "\x00\x00\x00\x01", 4); /* counter = 1 */
gcry_md_write(h, secret_x, secret_x_size); /* x of the point X */
gcry_md_write(h, kdf_params, kdf_params_size); /* KDF parameters */
gcry_md_final (h);
log_assert( gcry_md_get_algo_dlen (kdf_hash_algo) >= 32 );
memcpy (secret_x, gcry_md_read (h, kdf_hash_algo),
gcry_md_get_algo_dlen (kdf_hash_algo));
gcry_md_close (h);
old_size = secret_x_size;
log_assert( old_size >= gcry_cipher_get_algo_keylen( kdf_encr_algo ) );
secret_x_size = gcry_cipher_get_algo_keylen( kdf_encr_algo );
log_assert( secret_x_size <= gcry_md_get_algo_dlen (kdf_hash_algo) );
/* We could have allocated more, so clean the tail before returning. */
memset (secret_x+secret_x_size, 0, old_size - secret_x_size);
if (DBG_CRYPTO)
log_printhex (secret_x, secret_x_size, "ecdh KEK is:");
}
/* Derive a KEK (key wrapping key) using SECRET_X and KDF_PARAMS. */
err = derive_kek (kek_size, kdf_hash_algo, secret_x,
secret_x_size, kdf_params, kdf_params_size);
if (err)
{
xfree (secret_x);
return err;
}
/* And, finally, aeswrap with key secret_x. */
{
@ -313,7 +329,7 @@ pk_ecdh_encrypt_with_shared_point (int is_encrypt, gcry_mpi_t shared_mpi,
return err;
}
err = gcry_cipher_setkey (hd, secret_x, secret_x_size);
err = gcry_cipher_setkey (hd, secret_x, kek_size);
xfree (secret_x);
secret_x = NULL;
if (err)