diff --git a/library/bignum_new.c b/library/bignum_new.c
new file mode 100644
index 0000000..29c1212
--- /dev/null
+++ b/library/bignum_new.c
@@ -0,0 +1,126 @@
+/*
+ *  Multi-precision integer library
+ *
+ *  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 "mbedtls/bignum.h"
+#include "bignum_core.h"
+#include "bn_mul.h"
+
+#include <string.h>
+
+void MPI_CORE(montmul)( mbedtls_mpi_uint *X,
+                        const mbedtls_mpi_uint *A,
+                        const mbedtls_mpi_uint *B,
+                        size_t B_len,
+                        const mbedtls_mpi_uint *N,
+                        size_t n,
+                        mbedtls_mpi_uint mm,
+                        mbedtls_mpi_uint *T )
+{
+    memset( T, 0, (2*n+1)*ciL );
+
+    for( size_t i = 0; i < n; i++, T++ )
+    {
+        mbedtls_mpi_uint u0, u1;
+        /* T = (T + u0*B + u1*N) / 2^biL */
+        u0 = A[i];
+        u1 = ( T[0] + u0 * B[0] ) * mm;
+
+        (void) MPI_CORE(mla)( T, n + 2, B, B_len, u0 );
+        (void) MPI_CORE(mla)( T, n + 2, N, n, u1 );
+    }
+
+    mbedtls_mpi_uint carry, borrow, fixup;
+
+    carry  = T[n];
+    borrow = MPI_CORE(sub)( X, T, N, n );
+    fixup  = carry < borrow;
+    (void) MPI_CORE(add_if)( X, N, n, fixup );
+}
+
+mbedtls_mpi_uint MPI_CORE(mla)( mbedtls_mpi_uint *d, size_t d_len,
+                                const mbedtls_mpi_uint *s, size_t s_len,
+                                mbedtls_mpi_uint b )
+{
+    mbedtls_mpi_uint c = 0; /* carry */
+    if( d_len < s_len )
+        s_len = d_len;
+    size_t excess_len = d_len - s_len;
+    size_t steps_x8 = s_len / 8;
+    size_t steps_x1 = s_len & 7;
+
+    while( steps_x8-- )
+    {
+        MULADDC_X8_INIT
+        MULADDC_X8_CORE
+        MULADDC_X8_STOP
+    }
+
+    while( steps_x1-- )
+    {
+        MULADDC_X1_INIT
+        MULADDC_X1_CORE
+        MULADDC_X1_STOP
+    }
+
+    while( excess_len-- )
+    {
+        *d += c; c = ( *d < c ); d++;
+    }
+
+    return( c );
+}
+
+mbedtls_mpi_uint MPI_CORE(sub)( mbedtls_mpi_uint *d,
+                                const mbedtls_mpi_uint *l,
+                                const mbedtls_mpi_uint *r,
+                                size_t n )
+{
+    mbedtls_mpi_uint c = 0, t, z;
+
+    for( size_t i = 0; i < n; i++ )
+    {
+        z = ( l[i] <  c );    t = l[i] - c;
+        c = ( t < r[i] ) + z; d[i] = t - r[i];
+    }
+
+    return( c );
+}
+
+mbedtls_mpi_uint MPI_CORE(add_if)( mbedtls_mpi_uint *d,
+                                   const mbedtls_mpi_uint *r,
+                                   size_t n,
+                                   unsigned cond )
+{
+    mbedtls_mpi_uint c = 0, t;
+    for( size_t i = 0; i < n; i++ )
+    {
+        mbedtls_mpi_uint add = cond * r[i];
+        t  = c;
+        t += d[i]; c  = ( t < d[i] );
+        t += add;  c += ( t < add  );
+        d[i] = t;
+    }
+    return( c );
+}
+
+#endif /* MBEDTLS_BIGNUM_C */