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g10: ECDH shared point format.

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* g10/ecdh.c (pk_ecdh_encrypt_with_shared_point): Improve handling of
ECDH shared point format.

--
This handles the case where the result comes from scdaemon.

Signed-off-by: Arnaud Fontaine <arnaud.fontaine at ssi.gouv.fr>
This commit is contained in:
Arnaud Fontaine 2016-10-25 13:43:08 +02:00 committed by NIIBE Yutaka
parent 75f8aaf5bc
commit b648f28f9f
1 changed files with 24 additions and 8 deletions
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24
g10/ecdh.c
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@ -132,14 +132,30 @@ pk_ecdh_encrypt_with_shared_point (int is_encrypt, gcry_mpi_t shared_mpi,
return err; return err;
} }
/* Expected size of the x component */
secret_x_size = (nbits+7)/8; secret_x_size = (nbits+7)/8;
log_assert (nbytes >= secret_x_size);
if ((nbytes & 1)) if (nbytes > secret_x_size)
{
/* Uncompressed format expected, so it must start with 04 */
if (secret_x[0] != (byte)0x04)
{
return gpg_error (GPG_ERR_BAD_DATA);
}
/* Remove the "04" prefix of non-compressed format. */ /* Remove the "04" prefix of non-compressed format. */
memmove (secret_x, secret_x+1, secret_x_size); memmove (secret_x, secret_x+1, secret_x_size);
if (nbytes - secret_x_size)
memset (secret_x+secret_x_size, 0, nbytes-secret_x_size);
/* Zeroize the y component following */
if (nbytes > secret_x_size)
memset (secret_x+secret_x_size, 0, nbytes-secret_x_size);
}
else if (nbytes < secret_x_size)
{
/* Raw share secret (x coordinate), without leading zeros */
memmove (secret_x+(secret_x_size - nbytes), secret_x, nbytes);
memset (secret_x, 0, secret_x_size - nbytes);
}
if (DBG_CRYPTO) if (DBG_CRYPTO)
log_printhex ("ECDH shared secret X is:", secret_x, secret_x_size ); log_printhex ("ECDH shared secret X is:", secret_x, secret_x_size );
} }