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psa_asymmetric_sign: consistently fill unused output with '!'

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Fill the unused part of the output buffer with '!', for consistency
with hash and mac.

On error, set the output length to the output buffer size and fill the
output buffer with '!', again for consistency with hash and mac. This
way an invalid output is more visible in a memory dump.

Restructure the error paths so that there is a single place where the
unused part of the output buffer is filled.

Also remove a redundant initialization of *signature_length to 0.
This commit is contained in:
Gilles Peskine 2018-06-28 12:21:19 +02:00 committed by itayzafrir
parent 2b450e3a01
commit a26ff6a290
1 changed files with 44 additions and 20 deletions
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64
library/psa_crypto.c
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@ -1766,7 +1766,6 @@ static psa_status_t psa_ecdsa_sign( mbedtls_ecp_keypair *ecp,
mbedtls_mpi_init( &r );
mbedtls_mpi_init( &s );
*signature_length = 0;
if( signature_size < 2 * curve_bytes )
{
ret = MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL;
@ -1802,8 +1801,6 @@ cleanup:
mbedtls_mpi_free( &s );
if( ret == 0 )
*signature_length = 2 * curve_bytes;
memset( signature + *signature_length, 0,
signature_size - *signature_length );
return( mbedtls_to_psa_error( ret ) );
}
@ -1850,28 +1847,43 @@ psa_status_t psa_asymmetric_sign( psa_key_slot_t key,
size_t *signature_length )
{
key_slot_t *slot;
*signature_length = 0;
psa_status_t status;
*signature_length = signature_size;
(void) salt;
(void) salt_length;
if( key == 0 || key > PSA_KEY_SLOT_COUNT )
return( PSA_ERROR_EMPTY_SLOT );
{
status = PSA_ERROR_EMPTY_SLOT;
goto exit;
}
slot = &global_data.key_slots[key];
if( slot->type == PSA_KEY_TYPE_NONE )
return( PSA_ERROR_EMPTY_SLOT );
{
status = PSA_ERROR_EMPTY_SLOT;
goto exit;
}
if( ! PSA_KEY_TYPE_IS_KEYPAIR( slot->type ) )
return( PSA_ERROR_INVALID_ARGUMENT );
{
status = PSA_ERROR_INVALID_ARGUMENT;
goto exit;
}
if( ! ( slot->policy.usage & PSA_KEY_USAGE_SIGN ) )
return( PSA_ERROR_NOT_PERMITTED );
{
status = PSA_ERROR_NOT_PERMITTED;
goto exit;
}
#if defined(MBEDTLS_RSA_C)
if( slot->type == PSA_KEY_TYPE_RSA_KEYPAIR )
{
return( psa_rsa_sign( slot->data.rsa,
alg,
hash, hash_length,
signature, signature_size,
signature_length ) );
status = psa_rsa_sign( slot->data.rsa,
alg,
hash, hash_length,
signature, signature_size,
signature_length );
}
else
#endif /* defined(MBEDTLS_RSA_C) */
@ -1880,22 +1892,34 @@ psa_status_t psa_asymmetric_sign( psa_key_slot_t key,
{
#if defined(MBEDTLS_ECDSA_C)
if( PSA_ALG_IS_ECDSA( alg ) )
return( psa_ecdsa_sign( slot->data.ecp,
alg,
hash, hash_length,
signature, signature_size,
signature_length ) );
status = psa_ecdsa_sign( slot->data.ecp,
alg,
hash, hash_length,
signature, signature_size,
signature_length );
else
#endif /* defined(MBEDTLS_ECDSA_C) */
{
return( PSA_ERROR_INVALID_ARGUMENT );
status = PSA_ERROR_INVALID_ARGUMENT;
}
}
else
#endif /* defined(MBEDTLS_ECP_C) */
{
return( PSA_ERROR_NOT_SUPPORTED );
status = PSA_ERROR_NOT_SUPPORTED;
}
exit:
/* Fill the unused part of the output buffer (the whole buffer on error,
* the trailing part on success) with something that isn't a valid mac
* (barring an attack on the mac and deliberately-crafted input),
* in case the caller doesn't check the return status properly. */
if( status == PSA_SUCCESS )
memset( signature + *signature_length, '!',
signature_size - *signature_length );
else
memset( signature, '!', signature_size );
return( status );
}
psa_status_t psa_asymmetric_verify( psa_key_slot_t key,