commit 1d2e2bb8cce97ed81b725e5af54ffa5b7040473b
author Archana <archana.madhavan@silabs.com> Mon Jun 07 06:13:16 2021 +0530
committer Archana <archana.madhavan@silabs.com> Mon Jul 12 08:02:54 2021 +0530
tree 02c8aa07ff3e5f1d08bfc6d03ef8ce2a558f0e00
parent ac694b9eac0722cfa1d4f01723d8ce1567a67683

Add missing Curve448 support for PSA keys

mbedtls_ecp_read_key and mbedtls_ecp_write_key are updated to include
support for Curve448 as prescribed by RFC 7748 §5.

Test suites have been updated to validate curve448 under Montgomery
curves.

Signed-off-by: Archana <archana.madhavan@silabs.com>

library/ecp.c

diff --git a/library/ecp.c b/library/ecp.c
index e8df7ff..7963665 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -3054,6 +3054,7 @@
 }
 
 #define ECP_CURVE25519_KEY_SIZE 32
+#define ECP_CURVE448_KEY_SIZE   56
 /*
  * Read a private key.
  */
@@ -3074,7 +3075,7 @@
     if( mbedtls_ecp_get_type( &key->grp ) == MBEDTLS_ECP_TYPE_MONTGOMERY )
     {
         /*
-         * If it is Curve25519 curve then mask the key as mandated by RFC7748
+         * Mask the key as mandated by RFC7748 for Curve25519 and Curve448.
          */
         if( grp_id == MBEDTLS_ECP_DP_CURVE25519 )
         {
@@ -3100,8 +3101,23 @@
                                          ECP_CURVE25519_KEY_SIZE * 8 - 2, 1 )
                     );
         }
-        else
-            ret = MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE;
+        else if( grp_id == MBEDTLS_ECP_DP_CURVE448 )
+        {
+            if( buflen != ECP_CURVE448_KEY_SIZE )
+                return MBEDTLS_ERR_ECP_INVALID_KEY;
+
+            MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary_le( &key->d, buf, buflen ) );
+
+            /* Set the two least significant bits to 0 */
+            MBEDTLS_MPI_CHK( mbedtls_mpi_set_bit( &key->d, 0, 0 ) );
+            MBEDTLS_MPI_CHK( mbedtls_mpi_set_bit( &key->d, 1, 0 ) );
+
+            /* Set the most significant bit to 1 */
+            MBEDTLS_MPI_CHK(
+                    mbedtls_mpi_set_bit( &key->d,
+                                         ECP_CURVE448_KEY_SIZE * 8 - 1, 1 )
+                    );
+        }
     }
 
 #endif
@@ -3141,12 +3157,14 @@
             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 ) );
         }
-        else
-            ret = MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE;
+        else if ( key->grp.id == MBEDTLS_ECP_DP_CURVE448 )
+        {
+            if( buflen < ECP_CURVE448_KEY_SIZE )
+                return MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL;
+        }
+        MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary_le( &key->d, buf, buflen ) );
     }
-
 #endif
 #if defined(MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED)
     if( mbedtls_ecp_get_type( &key->grp ) == MBEDTLS_ECP_TYPE_SHORT_WEIERSTRASS )