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Fix endianness and masking for Curve25519 keys handled by PSA

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Changed PSA core (and PKWrite) from reaching into MPI to using the proper
ecp function to fetch a private key.
Added changelog.

Signed-off-by: Steven Cooreman <steven.cooreman@silabs.com>
This commit is contained in:
Steven Cooreman 2020-06-11 16:50:36 +02:00
parent 6f5cc71ad1
commit e3fd39289e
3 changed files with 18 additions and 9 deletions
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10
ChangeLog.d/psa_curve25519_key_support.txt Normal file
View File

@ -0,0 +1,10 @@
Requirement changes
* Clarify and test the import/export behaviour of PSA key management APIs to
adhere to the to-be-introduced clarification. Montgomery keys
(such as Curve25519) should be imported/exported in masked form.
Bugfix
* Update and test the PSA key management against Montgomery keys, since
these need to be imported/exported in little-endian form. Added mirror
function of mbedtls_ecp_read_key called mbedtls_ecp_write_key to retrieve
a private key in the correct form.

3
library/pkwrite.c
View File

@ -166,9 +166,10 @@ static int pk_write_ec_private( unsigned char **p, unsigned char *start,
{
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
size_t byte_length = ( ec->grp.pbits + 7 ) / 8;
size_t output_length;
unsigned char tmp[MBEDTLS_ECP_MAX_BYTES];
ret = mbedtls_mpi_write_binary( &ec->d, tmp, byte_length );
ret = mbedtls_ecp_write_key( ec->grp.id, ec, &output_length, tmp, byte_length );
if( ret != 0 )
goto exit;
ret = mbedtls_asn1_write_octet_string( p, start, tmp, byte_length );

14
library/psa_crypto.c
View File

@ -670,16 +670,12 @@ static psa_status_t psa_import_ec_private_key( psa_ecc_curve_t curve,
if( status != PSA_SUCCESS )
goto exit;
/* Load the secret value. */
/* Load and validate the secret key */
status = mbedtls_to_psa_error(
mbedtls_mpi_read_binary( &ecp->d, data, data_length ) );
if( status != PSA_SUCCESS )
goto exit;
/* Validate the private key. */
status = mbedtls_to_psa_error(
mbedtls_ecp_check_privkey( &ecp->grp, &ecp->d ) );
mbedtls_ecp_read_key( ecp->grp.id, ecp, data, data_length ) );
if( status != PSA_SUCCESS )
goto exit;
/* Calculate the public key from the private key. */
status = mbedtls_to_psa_error(
mbedtls_ecp_mul( &ecp->grp, &ecp->Q, &ecp->d, &ecp->grp.G,
@ -1325,12 +1321,14 @@ static psa_status_t psa_internal_export_key( const psa_key_slot_t *slot,
if( PSA_KEY_TYPE_IS_ECC_KEY_PAIR( slot->attr.type ) && !export_public_key )
{
psa_status_t status;
size_t actual_data_size;
size_t bytes = PSA_BITS_TO_BYTES( slot->attr.bits );
if( bytes > data_size )
return( PSA_ERROR_BUFFER_TOO_SMALL );
status = mbedtls_to_psa_error(
mbedtls_mpi_write_binary( &slot->data.ecp->d, data, bytes ) );
mbedtls_ecp_write_key(slot->data.ecp->grp.id, slot->data.ecp,
&actual_data_size, data, bytes) );
if( status != PSA_SUCCESS )
return( status );
memset( data + bytes, 0, data_size - bytes );