diff --git a/library/bignum_mod.h b/library/bignum_mod.h
new file mode 100644
index 0000000..378c58d
--- /dev/null
+++ b/library/bignum_mod.h
@@ -0,0 +1,68 @@
+/**
+ *  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.
+ */
+
+#ifndef MBEDTLS_BIGNUM_MOD_H
+#define MBEDTLS_BIGNUM_MOD_H
+
+#include "common.h"
+
+#if defined(MBEDTLS_BIGNUM_C)
+#include "mbedtls/bignum.h"
+#endif
+
+
+typedef struct
+{
+    size_t n;
+    mbedtls_mpi_uint *p;
+} mbedtls_mpi_mod_residue;
+
+typedef void* mbedtls_mpi_mont_struct;
+typedef void* mbedtls_mpi_opt_red_struct;
+
+typedef struct {
+    mbedtls_mpi_uint *p;
+    size_t n;       // number of limbs
+    size_t plen;    // bitlen of p
+    int ext_rep;    // signals external representation (eg. byte order)
+    int int_rep;    // selector to signal the active member of the union
+    union rep
+    {
+        mbedtls_mpi_mont_struct mont;
+        mbedtls_mpi_opt_red_struct ored;
+    } rep;
+} mbedtls_mpi_mod_modulus;
+
+void mbedtls_mpi_mod_residue_release( mbedtls_mpi_mod_residue *r );
+
+int mbedtls_mpi_mod_residue_setup( mbedtls_mpi_mod_residue *r,
+                                   mbedtls_mpi_mod_modulus *m,
+                                   mbedtls_mpi_uint *p );
+
+void mbedtls_mpi_mod_modulus_init( mbedtls_mpi_mod_modulus *m );
+
+void mbedtls_mpi_mod_modulus_init( mbedtls_mpi_mod_modulus *m );
+
+int mbedtls_mpi_mod_modulus_setup( mbedtls_mpi_mod_modulus *m,
+                                   mbedtls_mpi_uint *p,
+                                   size_t n,
+                                   int ext_rep,
+                                   int int_rep );
+
+#endif /* MBEDTLS_BIGNUM_MOD_H */