commit 50cd4b842b02c1a6d3052121f64e7b6b7dce6fd4
author Janos Follath <janos.follath@arm.com> Thu Nov 24 17:08:13 2022 +0000
committer Janos Follath <janos.follath@arm.com> Fri Nov 25 17:55:00 2022 +0000
tree cd916c200f47237c3dcb60e0abf65dedb2acd626
parent b62bad442e6afc863829d130f3cb5e5b5bacdf61

Bignum Mod: Restrict residue setup

In theory we could allow residues to have more allocated limbs than the
modulus, but we might or might not need it in the end.

Go for the simpler option for now and we can extend it later if we
really need it.

Signed-off-by: Janos Follath <janos.follath@arm.com>

library/bignum_mod.c

diff --git a/library/bignum_mod.c b/library/bignum_mod.c
index 1b3aff6..4303efe 100644
--- a/library/bignum_mod.c
+++ b/library/bignum_mod.c
@@ -39,7 +39,7 @@
                                    mbedtls_mpi_uint *p,
                                    size_t p_limbs )
 {
-    if( p_limbs < m->limbs || !mbedtls_mpi_core_lt_ct( p, m->p, m->limbs ) )
+    if( p_limbs != m->limbs || !mbedtls_mpi_core_lt_ct( p, m->p, m->limbs ) )
         return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
 
     r->limbs = m->limbs;

tests/suites/test_suite_bignum_mod.data

diff --git a/tests/suites/test_suite_bignum_mod.data b/tests/suites/test_suite_bignum_mod.data
index 02bc9f7..ba7d577 100644
--- a/tests/suites/test_suite_bignum_mod.data
+++ b/tests/suites/test_suite_bignum_mod.data
@@ -56,17 +56,17 @@
 Test mbedtls_mpi_residue_setup #2 r == m - 1
 mpi_residue_setup:"ff":"fe":0
 
-Test mbedtls_mpi_residue_setup #3 m->limbs > r-> limbs && m > r
-mpi_residue_setup:"000000000000000000000000000000007dfe5c6beb35a2d6":"fe":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
+Test mbedtls_mpi_residue_setup #3 m->limbs = r-> limbs && m > r
+mpi_residue_setup:"7dfe5c6":"fe":0
 
 Test mbedtls_mpi_residue_setup #4 m->limbs = r-> limbs && m > r
 mpi_residue_setup:"7ffffffffffffffffffffffffffffffffffffffffffffff1":"0000000000000000000000000000000000000000000000fe":0
 
-Test mbedtls_mpi_residue_setup #5 m->limbs < r-> limbs && m > r
-mpi_residue_setup:"7ffffffff0000000":"000000000000000fe":0
+Test mbedtls_mpi_residue_setup #5 m->limbs > r-> limbs && m > r
+mpi_residue_setup:"7ffffffff00000000":"fe":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
 
 Test mbedtls_mpi_residue_setup #6 m->limbs < r-> limbs && m > r
-mpi_residue_setup:"ff":"000000000000000000000000000000000000000000000001":0
+mpi_residue_setup:"ff":"000000000000000000000000000000000000000000000001":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
 
 Test mbedtls_mpi_residue_setup #7 r == m
 mpi_residue_setup:"fe":"fe":-4