Add Montgomery points to ecp_point_write_binary
The library is able to perform computations and cryptographic schemes on
curves with x coordinate ladder representation. Here we add the
capability to export such points.
diff --git a/library/ecp.c b/library/ecp.c
index 49f35af..66cf58e 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -729,7 +729,7 @@
}
/*
- * Export a point into unsigned binary data (SEC1 2.3.3)
+ * Export a point into unsigned binary data (SEC1 2.3.3 and RFC7748)
*/
int mbedtls_ecp_point_write_binary( const mbedtls_ecp_group *grp,
const mbedtls_ecp_point *P,
@@ -745,43 +745,58 @@
ECP_VALIDATE_RET( format == MBEDTLS_ECP_PF_UNCOMPRESSED ||
format == MBEDTLS_ECP_PF_COMPRESSED );
- /*
- * Common case: P == 0
- */
- if( mbedtls_mpi_cmp_int( &P->Z, 0 ) == 0 )
- {
- if( buflen < 1 )
- return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL );
-
- buf[0] = 0x00;
- *olen = 1;
-
- return( 0 );
- }
-
plen = mbedtls_mpi_size( &grp->P );
- if( format == MBEDTLS_ECP_PF_UNCOMPRESSED )
+#if defined(ECP_MONTGOMERY)
+ if( ecp_get_type( grp ) == ECP_TYPE_MONTGOMERY )
{
- *olen = 2 * plen + 1;
-
+ *olen = plen;
if( buflen < *olen )
- return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL );
+ return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL );
- buf[0] = 0x04;
- MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &P->X, buf + 1, plen ) );
- MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &P->Y, buf + 1 + plen, plen ) );
+ MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary_le( &P->X, buf, plen ) );
}
- else if( format == MBEDTLS_ECP_PF_COMPRESSED )
+#endif
+#if defined(ECP_SHORTWEIERSTRASS)
+ if( ecp_get_type( grp ) != ECP_TYPE_MONTGOMERY )
{
- *olen = plen + 1;
+ /*
+ * Common case: P == 0
+ */
+ if( mbedtls_mpi_cmp_int( &P->Z, 0 ) == 0 )
+ {
+ if( buflen < 1 )
+ return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL );
- if( buflen < *olen )
- return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL );
+ buf[0] = 0x00;
+ *olen = 1;
- buf[0] = 0x02 + mbedtls_mpi_get_bit( &P->Y, 0 );
- MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &P->X, buf + 1, plen ) );
+ return( 0 );
+ }
+
+ if( format == MBEDTLS_ECP_PF_UNCOMPRESSED )
+ {
+ *olen = 2 * plen + 1;
+
+ if( buflen < *olen )
+ return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL );
+
+ buf[0] = 0x04;
+ MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &P->X, buf + 1, plen ) );
+ MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &P->Y, buf + 1 + plen, plen ) );
+ }
+ else if( format == MBEDTLS_ECP_PF_COMPRESSED )
+ {
+ *olen = plen + 1;
+
+ if( buflen < *olen )
+ return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL );
+
+ buf[0] = 0x02 + mbedtls_mpi_get_bit( &P->Y, 0 );
+ MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &P->X, buf + 1, plen ) );
+ }
}
+#endif
cleanup:
return( ret );