commit 3eff425b1ae1a3f65fefbf47afcb1e868ced007a
author Gabor Mezei <gabor.mezei@arm.com> Mon Sep 26 17:26:42 2022 +0200
committer Gabor Mezei <gabor.mezei@arm.com> Fri Sep 30 13:36:40 2022 +0200
tree fe0ea56939a37830cfff6c7febb5bdd0921e3532
parent 81e57021c67a1a624fd8085ae287de50121e19bd

Use only one limb parameter for assign

Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>

library/constant_time.c

diff --git a/library/constant_time.c b/library/constant_time.c
index 7bf67f4..d01998b 100644
--- a/library/constant_time.c
+++ b/library/constant_time.c
@@ -682,11 +682,17 @@
     MPI_VALIDATE_RET( X != NULL );
     MPI_VALIDATE_RET( Y != NULL );
 
+    /* all-bits 1 if assign is 1, all-bits 0 if assign is 0 */
+    mbedtls_mpi_uint limb_mask = mbedtls_ct_mpi_uint_mask( assign );
+
     MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, Y->n ) );
 
     X->s = mbedtls_ct_cond_select_sign( assign, Y->s, X->s );
 
-    mbedtls_mpi_core_cond_assign( X->p, X->n, Y->p, Y->n, assign );
+    mbedtls_mpi_core_cond_assign( X->p, Y->p, Y->n, assign );
+
+    for( size_t i = Y->n; i < X->n; i++ )
+        X->p[i] &= ~limb_mask;
 
 cleanup:
     return( ret );