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Implement and test mbedtls_ecp_write_key

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mbedtls_ecp_write_key is a mirror function to mbedtls_ecp_read_key, which
writes a private key back into a byte buffer in the correct format.
This is a helpful convenience function, since the byte order is defined
differently between Montgomery and Weierstrass curves. Since this difference
is accounted for in mbedtls_ecp_read_key, it made sense to add
mbedtls_ecp_write_key for the purpose of abstracting this away such that
psa_export_key doesn't need to take byte order into account.

Signed-off-by: Steven Cooreman <steven.cooreman@silabs.com>
This commit is contained in:
Steven Cooreman 2020-06-09 19:55:26 +02:00
parent 0af1560919
commit de8593f2fe
4 changed files with 133 additions and 17 deletions
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47
library/ecp.c
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@ -2996,6 +2996,53 @@ cleanup:
return( ret );
}
/*
* Write a private key.
*/
int mbedtls_ecp_write_key( mbedtls_ecp_group_id grp_id, mbedtls_ecp_keypair *key,
size_t *olen, unsigned char *buf, size_t buflen )
{
int ret = 0;
ECP_VALIDATE_RET( key != NULL );
ECP_VALIDATE_RET( buf != NULL );
ECP_VALIDATE_RET( olen != NULL );
if( ( ret = mbedtls_ecp_group_load( &key->grp, grp_id ) ) != 0 )
return( ret );
ret = MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE;
#if defined(ECP_MONTGOMERY)
if( mbedtls_ecp_get_type( &key->grp ) == MBEDTLS_ECP_TYPE_MONTGOMERY )
{
if( grp_id == MBEDTLS_ECP_DP_CURVE25519 )
{
if( buflen < ECP_CURVE25519_KEY_SIZE )
return MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL;
MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary_le( &key->d, buf, buflen ) );
*olen = ECP_CURVE25519_KEY_SIZE;
}
else
ret = MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE;
}
#endif
#if defined(ECP_SHORTWEIERSTRASS)
if( mbedtls_ecp_get_type( &key->grp ) == MBEDTLS_ECP_TYPE_SHORT_WEIERSTRASS )
{
MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &key->d, buf, buflen ) );
*olen = mbedtls_mpi_size( &key->d );
}
#endif
cleanup:
return( ret );
}
/*
* Check a public-private key pair
*/