commit 4268731b2ff5aa43fcb308d574b33316eaefe82c
author Dave Rodgman <dave.rodgman@arm.com> Wed Aug 10 11:26:24 2022 +0100
committer Dave Rodgman <dave.rodgman@arm.com> Fri Sep 23 10:42:33 2022 +0100
tree 86e8785dda30257e56c907aabe49072074000cee
parent 535dccebdcf6366d0533ec2b526c40a6ac158984

Fix ECDSA signature verification edge-case

For R and S equal to 1, ensure the public key is checked
for validity.

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>

library/ecp.c

diff --git a/library/ecp.c b/library/ecp.c
index 890f364..d6109c4 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -2797,14 +2797,17 @@
 
     if( mbedtls_mpi_cmp_int( m, 0 ) == 0 )
     {
+        MBEDTLS_MPI_CHK( mbedtls_ecp_check_pubkey( grp, P ) );
         MBEDTLS_MPI_CHK( mbedtls_ecp_set_zero( R ) );
     }
     else if( mbedtls_mpi_cmp_int( m, 1 ) == 0 )
     {
+        MBEDTLS_MPI_CHK( mbedtls_ecp_check_pubkey( grp, P ) );
         MBEDTLS_MPI_CHK( mbedtls_ecp_copy( R, P ) );
     }
     else if( mbedtls_mpi_cmp_int( m, -1 ) == 0 )
     {
+        MBEDTLS_MPI_CHK( mbedtls_ecp_check_pubkey( grp, P ) );
         MBEDTLS_MPI_CHK( mbedtls_ecp_copy( R, P ) );
         if( mbedtls_mpi_cmp_int( &R->Y, 0 ) != 0 )
             MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &R->Y, &grp->P, &R->Y ) );