commit 28b61074d105e1551f6980609b850a49f58266bc
author TRodziewicz <rodziewicz@gmail.com> Wed Feb 24 14:01:40 2021 +0100
committer TRodziewicz <rodziewicz@gmail.com> Thu Feb 25 11:02:16 2021 +0100
tree fc3ca8cca5a3e1d3462d925be15d51bdd664bf2e
parent 5068b061ac1c396300048a4b315c879e51b14552

Adding shortcut for all-bits-zero payloads (mbedtls_ecp_mul_shortcuts()) and returning proper error code (MBEDTLS_ERR_ECP_INVALID_KEY) for that case (ecjpake_zkp_read()).

Signed-off-by: TRodziewicz <rodziewicz@gmail.com>

library/ecjpake.c

diff --git a/library/ecjpake.c b/library/ecjpake.c
index bd47169..b835ac1 100644
--- a/library/ecjpake.c
+++ b/library/ecjpake.c
@@ -286,6 +286,13 @@
      * Verification
      */
     MBEDTLS_MPI_CHK( ecjpake_hash( md_info, grp, pf, G, &V, X, id, &h ) );
+
+    if( mbedtls_mpi_cmp_int( &r,0 ) == 0 )
+    {
+        ret = MBEDTLS_ERR_ECP_INVALID_KEY;
+        goto cleanup;
+    }
+
     MBEDTLS_MPI_CHK( mbedtls_ecp_muladd( (mbedtls_ecp_group *) grp,
                      &VV, &h, X, &r, G ) );
 

library/ecp.c

diff --git a/library/ecp.c b/library/ecp.c
index 3b68e8e..d229a0a 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -2795,7 +2795,7 @@
 
 #if defined(MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED)
 /*
- * R = m * P with shortcuts for m == 1 and m == -1
+ * R = m * P with shortcuts for m == 0, m == 1 and m == -1
  * NOT constant-time - ONLY for short Weierstrass!
  */
 static int mbedtls_ecp_mul_shortcuts( mbedtls_ecp_group *grp,
@@ -2806,7 +2806,11 @@
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
 
-    if( mbedtls_mpi_cmp_int( m, 1 ) == 0 )
+    if( mbedtls_mpi_cmp_int( m, 0 ) == 0 )
+    {
+        MBEDTLS_MPI_CHK( mbedtls_ecp_set_zero( R ) );
+    }
+    else if( mbedtls_mpi_cmp_int( m, 1 ) == 0 )
     {
         MBEDTLS_MPI_CHK( mbedtls_ecp_copy( R, P ) );
     }