diff --git a/library/bignum_mod.c b/library/bignum_mod.c
new file mode 100644
index 0000000..63f9172
--- /dev/null
+++ b/library/bignum_mod.c
@@ -0,0 +1,153 @@
+/**
+ *  Internal bignum functions
+ *
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may
+ *  not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+#include "common.h"
+
+#if defined(MBEDTLS_BIGNUM_C)
+
+#include <string.h>
+
+#include "mbedtls/platform_util.h"
+#include "mbedtls/error.h"
+#include "mbedtls/bignum.h"
+
+#if defined(MBEDTLS_PLATFORM_C)
+#include "mbedtls/platform.h"
+#else
+#include <stdio.h>
+#include <stdlib.h>
+#define mbedtls_printf      printf
+#define mbedtls_calloc      calloc
+#define mbedtls_free        free
+#endif
+
+#include "bignum_core.h"
+#include "bignum_mod.h"
+#include "bignum_mod_raw.h"
+#include "constant_time_internal.h"
+
+int mbedtls_mpi_mod_residue_setup( mbedtls_mpi_mod_residue *r,
+                                   mbedtls_mpi_mod_modulus *m,
+                                   mbedtls_mpi_uint *p,
+                                   size_t pn )
+{
+    if( p == NULL || m == NULL || r == NULL )
+        return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
+
+    if( pn < m->n || !mbedtls_mpi_core_lt_ct( m->p, p, pn ) )
+        return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
+
+    r->n = m->n;
+    r->p = p;
+
+    return( 0 );
+}
+
+void mbedtls_mpi_mod_residue_release( mbedtls_mpi_mod_residue *r )
+{
+    if ( r == NULL )
+        return;
+
+    r->n = 0;
+    r->p = NULL;
+}
+
+void mbedtls_mpi_mod_modulus_init( mbedtls_mpi_mod_modulus *m )
+{
+    if ( m == NULL )
+        return;
+
+    m->p = NULL;
+    m->n = 0;
+    m->plen = 0;
+    m->ext_rep = MBEDTLS_MPI_MOD_EXT_REP_INVALID;
+    m->int_rep = MBEDTLS_MPI_MOD_REP_INVALID;
+}
+
+void mbedtls_mpi_mod_modulus_free( mbedtls_mpi_mod_modulus *m )
+{
+    if ( m == NULL )
+        return;
+
+    switch( m->int_rep )
+    {
+        case MBEDTLS_MPI_MOD_REP_MONTGOMERY:
+            mbedtls_free( m->rep.mont ); break;
+        case MBEDTLS_MPI_MOD_REP_OPT_RED:
+            mbedtls_free( m->rep.ored ); break;
+        default:
+            break;
+    }
+
+    m->p = NULL;
+    m->n = 0;
+    m->plen = 0;
+    m->ext_rep = MBEDTLS_MPI_MOD_EXT_REP_INVALID;
+    m->int_rep = MBEDTLS_MPI_MOD_REP_INVALID;
+}
+
+int mbedtls_mpi_mod_modulus_setup( mbedtls_mpi_mod_modulus *m,
+                                   mbedtls_mpi_uint *p,
+                                   size_t pn,
+                                   int ext_rep,
+                                   int int_rep )
+{
+    int ret = 0;
+
+    if ( p == NULL || m == NULL )
+        return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
+
+    m->p = p;
+    m->n = pn;
+    m->plen = mbedtls_mpi_core_bitlen( p, pn );
+
+    switch( ext_rep )
+    {
+        case MBEDTLS_MPI_MOD_EXT_REP_LE:
+        case MBEDTLS_MPI_MOD_EXT_REP_BE:
+            m->ext_rep = ext_rep; break;
+        default:
+            ret = MBEDTLS_ERR_MPI_BAD_INPUT_DATA;
+            goto exit;
+    }
+
+    switch( int_rep )
+    {
+        case MBEDTLS_MPI_MOD_REP_MONTGOMERY:
+            m->int_rep = int_rep;
+            m->rep.mont = NULL; break;
+        case MBEDTLS_MPI_MOD_REP_OPT_RED:
+            m->int_rep = int_rep;
+            m->rep.ored = NULL; break;
+        default:
+            ret = MBEDTLS_ERR_MPI_BAD_INPUT_DATA;
+            goto exit;
+    }
+
+exit:
+
+    if( ret != 0 )
+    {
+        mbedtls_mpi_mod_modulus_free( m );
+    }
+
+    return( ret );
+}
+
+#endif /* MBEDTLS_BIGNUM_C */