diff --git a/library/CMakeLists.txt b/library/CMakeLists.txt
index 19ba315..bef0dbf 100644
--- a/library/CMakeLists.txt
+++ b/library/CMakeLists.txt
@@ -19,6 +19,7 @@
     base64.c
     bignum.c
     bignum_new.c
+    bignum_core.c
     camellia.c
     ccm.c
     chacha20.c
diff --git a/library/Makefile b/library/Makefile
index ac8f331..a1c4bb9 100644
--- a/library/Makefile
+++ b/library/Makefile
@@ -84,6 +84,7 @@
 	     base64.o \
 	     bignum.o \
 	     bignum_new.o \
+	     bignum_core.o \
 	     camellia.o \
 	     ccm.o \
 	     chacha20.o \
diff --git a/library/bignum_core.c b/library/bignum_core.c
new file mode 100644
index 0000000..35173b9
--- /dev/null
+++ b/library/bignum_core.c
@@ -0,0 +1,353 @@
+/*
+ *  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 <string.h>
+
+#include "mbedtls/error.h"
+#include "mbedtls/platform_util.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"
+
+#define MPI_VALIDATE_RET( cond )                                       \
+    MBEDTLS_INTERNAL_VALIDATE_RET( cond, MBEDTLS_ERR_MPI_BAD_INPUT_DATA )
+#define MPI_VALIDATE( cond )                                           \
+    MBEDTLS_INTERNAL_VALIDATE( cond )
+
+#define ciL    (sizeof(mbedtls_mpi_uint))   /* chars in limb  */
+#define biL    (ciL << 3)                   /* bits  in limb  */
+#define biH    (ciL << 2)                   /* half limb size */
+
+/*
+ * Convert between bits/chars and number of limbs
+ * Divide first in order to avoid potential overflows
+ */
+#define BITS_TO_LIMBS(i)  ( (i) / biL + ( (i) % biL != 0 ) )
+#define CHARS_TO_LIMBS(i) ( (i) / ciL + ( (i) % ciL != 0 ) )
+/* Get a specific byte, without range checks. */
+#define GET_BYTE( X, i )                                \
+    ( ( ( X )[( i ) / ciL] >> ( ( ( i ) % ciL ) * 8 ) ) & 0xff )
+
+/*
+ * Count leading zero bits in a given integer
+ */
+size_t mbedtls_mpi_core_clz( const mbedtls_mpi_uint x )
+{
+    size_t j;
+    mbedtls_mpi_uint mask = (mbedtls_mpi_uint) 1 << (biL - 1);
+
+    for( j = 0; j < biL; j++ )
+    {
+        if( x & mask ) break;
+
+        mask >>= 1;
+    }
+
+    return j;
+}
+
+/*
+ * Return the number of bits
+ */
+size_t mbedtls_mpi_core_bitlen( const mbedtls_mpi_uint *X, size_t nx )
+{
+    size_t i, j;
+
+    if( nx == 0 )
+        return( 0 );
+
+    for( i = nx - 1; i > 0; i-- )
+        if( X[i] != 0 )
+            break;
+
+    j = biL - mbedtls_mpi_core_clz( X[i] );
+
+    return( ( i * biL ) + j );
+}
+
+/* Check X to have at least n limbs and set it to 0. */
+static int mpi_core_clear( mbedtls_mpi_uint *X,
+                           size_t nx,
+                           size_t limbs )
+{
+    if( nx < limbs )
+        return( MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL );
+
+    if( X != NULL )
+        memset( X, 0, nx * ciL );
+
+    return( 0 );
+}
+
+/* Convert a big-endian byte array aligned to the size of mbedtls_mpi_uint
+ * into the storage form used by mbedtls_mpi. */
+static mbedtls_mpi_uint mpi_bigendian_to_host_c( mbedtls_mpi_uint x )
+{
+    uint8_t i;
+    unsigned char *x_ptr;
+    mbedtls_mpi_uint tmp = 0;
+
+    for( i = 0, x_ptr = (unsigned char*) &x; i < ciL; i++, x_ptr++ )
+    {
+        tmp <<= CHAR_BIT;
+        tmp |= (mbedtls_mpi_uint) *x_ptr;
+    }
+
+    return( tmp );
+}
+
+static mbedtls_mpi_uint mpi_bigendian_to_host( mbedtls_mpi_uint x )
+{
+#if defined(__BYTE_ORDER__)
+
+/* Nothing to do on bigendian systems. */
+#if ( __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ )
+    return( x );
+#endif /* __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ */
+
+#if ( __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ )
+
+/* For GCC and Clang, have builtins for byte swapping. */
+#if defined(__GNUC__) && defined(__GNUC_PREREQ)
+#if __GNUC_PREREQ(4,3)
+#define have_bswap
+#endif
+#endif
+
+#if defined(__clang__) && defined(__has_builtin)
+#if __has_builtin(__builtin_bswap32)  &&                 \
+    __has_builtin(__builtin_bswap64)
+#define have_bswap
+#endif
+#endif
+
+#if defined(have_bswap)
+    /* The compiler is hopefully able to statically evaluate this! */
+    switch( sizeof(mbedtls_mpi_uint) )
+    {
+        case 4:
+            return( __builtin_bswap32(x) );
+        case 8:
+            return( __builtin_bswap64(x) );
+    }
+#endif
+#endif /* __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ */
+#endif /* __BYTE_ORDER__ */
+
+    /* Fall back to C-based reordering if we don't know the byte order
+     * or we couldn't use a compiler-specific builtin. */
+    return( mpi_bigendian_to_host_c( x ) );
+}
+
+void mbedtls_mpi_core_bigendian_to_host( mbedtls_mpi_uint * const X,
+                                         size_t limbs )
+{
+    mbedtls_mpi_uint *cur_limb_left;
+    mbedtls_mpi_uint *cur_limb_right;
+    if( limbs == 0 )
+        return;
+
+    /*
+     * Traverse limbs and
+     * - adapt byte-order in each limb
+     * - swap the limbs themselves.
+     * For that, simultaneously traverse the limbs from left to right
+     * and from right to left, as long as the left index is not bigger
+     * than the right index (it's not a problem if limbs is odd and the
+     * indices coincide in the last iteration).
+     */
+    for( cur_limb_left = X, cur_limb_right = X + ( limbs - 1 );
+         cur_limb_left <= cur_limb_right;
+         cur_limb_left++, cur_limb_right-- )
+    {
+        mbedtls_mpi_uint tmp;
+        /* Note that if cur_limb_left == cur_limb_right,
+         * this code effectively swaps the bytes only once. */
+        tmp             = mpi_bigendian_to_host( *cur_limb_left  );
+        *cur_limb_left  = mpi_bigendian_to_host( *cur_limb_right );
+        *cur_limb_right = tmp;
+    }
+}
+
+/*
+ * Import X from unsigned binary data, little endian
+ *
+ * The MPI needs to have enough limbs to store the full value (in particular,
+ * this function does not skip 0s in the input).
+ */
+int mbedtls_mpi_core_read_le( mbedtls_mpi_uint *X,
+                              size_t nx,
+                              const unsigned char *buf,
+                              size_t buflen )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    size_t i;
+    size_t const limbs = CHARS_TO_LIMBS( buflen );
+
+    /* Ensure that target MPI has at least the necessary number of limbs */
+    MBEDTLS_MPI_CHK( mpi_core_clear( X, nx, limbs ) );
+
+    for( i = 0; i < buflen; i++ )
+        X[i / ciL] |= ((mbedtls_mpi_uint) buf[i]) << ((i % ciL) << 3);
+
+cleanup:
+    return( ret );
+}
+
+/*
+ * Import X from unsigned binary data, big endian
+ *
+ * The MPI needs to have enough limbs to store the full value (in particular,
+ * this function does not skip 0s in the input).
+ */
+int mbedtls_mpi_core_read_be( mbedtls_mpi_uint *X,
+                              size_t nx,
+                              const unsigned char *buf,
+                              size_t buflen )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    size_t const limbs = CHARS_TO_LIMBS( buflen );
+    size_t overhead;
+    unsigned char *Xp;
+
+    MPI_VALIDATE_RET( X != NULL );
+    MPI_VALIDATE_RET( buflen == 0 || buf != NULL );
+
+    /* Ensure that target MPI has at least the necessary number of limbs */
+    MBEDTLS_MPI_CHK( mpi_core_clear( X, nx, limbs ) );
+
+    overhead = ( nx * ciL ) - buflen;
+
+    /* Avoid calling `memcpy` with NULL source or destination argument,
+     * even if buflen is 0. */
+    if( buflen != 0 )
+    {
+        Xp = (unsigned char*) X;
+        memcpy( Xp + overhead, buf, buflen );
+
+        mbedtls_mpi_core_bigendian_to_host( X, nx );
+    }
+
+cleanup:
+    return( ret );
+}
+
+/*
+ * Export X into unsigned binary data, little endian
+ */
+int mbedtls_mpi_core_write_le( const mbedtls_mpi_uint *X,
+                               size_t nx,
+                               unsigned char *buf,
+                               size_t buflen )
+{
+    size_t stored_bytes = nx * ciL;
+    size_t bytes_to_copy;
+    size_t i;
+
+    if( stored_bytes < buflen )
+    {
+        bytes_to_copy = stored_bytes;
+    }
+    else
+    {
+        bytes_to_copy = buflen;
+
+        /* The output buffer is smaller than the allocated size of X.
+         * However X may fit if its leading bytes are zero. */
+        for( i = bytes_to_copy; i < stored_bytes; i++ )
+        {
+            if( GET_BYTE( X, i ) != 0 )
+                return( MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL );
+        }
+    }
+
+    for( i = 0; i < bytes_to_copy; i++ )
+        buf[i] = GET_BYTE( X, i );
+
+    if( stored_bytes < buflen )
+    {
+        /* Write trailing 0 bytes */
+        memset( buf + stored_bytes, 0, buflen - stored_bytes );
+    }
+
+    return( 0 );
+}
+
+/*
+ * Export X into unsigned binary data, big endian
+ */
+int mbedtls_mpi_core_write_be( const mbedtls_mpi_uint *X,
+                               size_t nx,
+                               unsigned char *buf,
+                               size_t buflen )
+{
+    size_t stored_bytes;
+    size_t bytes_to_copy;
+    unsigned char *p;
+    size_t i;
+
+    MPI_VALIDATE_RET( X != NULL );
+    MPI_VALIDATE_RET( buflen == 0 || buf != NULL );
+
+    stored_bytes = nx * ciL;
+
+    if( stored_bytes < buflen )
+    {
+        /* There is enough space in the output buffer. Write initial
+         * null bytes and record the position at which to start
+         * writing the significant bytes. In this case, the execution
+         * trace of this function does not depend on the value of the
+         * number. */
+        bytes_to_copy = stored_bytes;
+        p = buf + buflen - stored_bytes;
+        memset( buf, 0, buflen - stored_bytes );
+    }
+    else
+    {
+        /* The output buffer is smaller than the allocated size of X.
+         * However X may fit if its leading bytes are zero. */
+        bytes_to_copy = buflen;
+        p = buf;
+        for( i = bytes_to_copy; i < stored_bytes; i++ )
+        {
+            if( GET_BYTE( X, i ) != 0 )
+                return( MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL );
+        }
+    }
+
+    for( i = 0; i < bytes_to_copy; i++ )
+        p[bytes_to_copy - i - 1] = GET_BYTE( X, i );
+
+    return( 0 );
+}
+
+#endif /* MBEDTLS_BIGNUM_C */
diff --git a/library/bignum_new.c b/library/bignum_new.c
index 2613941..8b23f13 100644
--- a/library/bignum_new.c
+++ b/library/bignum_new.c
@@ -41,63 +41,6 @@
 #define mbedtls_free        free
 #endif
 
-#define MPI_VALIDATE_RET( cond )                                       \
-    MBEDTLS_INTERNAL_VALIDATE_RET( cond, MBEDTLS_ERR_MPI_BAD_INPUT_DATA )
-#define MPI_VALIDATE( cond )                                           \
-    MBEDTLS_INTERNAL_VALIDATE( cond )
-
-#define ciL    (sizeof(mbedtls_mpi_uint))   /* chars in limb  */
-#define biL    (ciL << 3)                   /* bits  in limb  */
-#define biH    (ciL << 2)                   /* half limb size */
-
-/*
- * Convert between bits/chars and number of limbs
- * Divide first in order to avoid potential overflows
- */
-#define BITS_TO_LIMBS(i)  ( (i) / biL + ( (i) % biL != 0 ) )
-#define CHARS_TO_LIMBS(i) ( (i) / ciL + ( (i) % ciL != 0 ) )
-
-/*
- * Count leading zero bits in a given integer
- */
-size_t mbedtls_mpi_core_clz( const mbedtls_mpi_uint x )
-{
-    size_t j;
-    mbedtls_mpi_uint mask = (mbedtls_mpi_uint) 1 << (biL - 1);
-
-    for( j = 0; j < biL; j++ )
-    {
-        if( x & mask ) break;
-
-        mask >>= 1;
-    }
-
-    return j;
-}
-
-/*
- * Return the number of bits
- */
-size_t mbedtls_mpi_core_bitlen( const mbedtls_mpi_uint *X, size_t nx )
-{
-    size_t i, j;
-
-    if( nx == 0 )
-        return( 0 );
-
-    for( i = nx - 1; i > 0; i-- )
-        if( X[i] != 0 )
-            break;
-
-    j = biL - mbedtls_mpi_core_clz( X[i] );
-
-    return( ( i * biL ) + j );
-}
-
-/* Get a specific byte, without range checks. */
-#define GET_BYTE( X, i )                                \
-    ( ( ( X )[( i ) / ciL] >> ( ( ( i ) % ciL ) * 8 ) ) & 0xff )
-
 int mbedtls_mpi_mod_residue_setup( mbedtls_mpi_mod_residue *r,
                                    mbedtls_mpi_mod_modulus *m,
                                    mbedtls_mpi_uint *p,
@@ -206,262 +149,6 @@
     return( ret );
 }
 
-/* Check X to have at least n limbs and set it to 0. */
-static int mpi_core_clear( mbedtls_mpi_uint *X,
-                           size_t nx,
-                           size_t limbs )
-{
-    if( nx < limbs )
-        return( MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL );
-
-    if( X != NULL )
-        memset( X, 0, nx * ciL );
-
-    return( 0 );
-}
-
-/* Convert a big-endian byte array aligned to the size of mbedtls_mpi_uint
- * into the storage form used by mbedtls_mpi. */
-static mbedtls_mpi_uint mpi_bigendian_to_host_c( mbedtls_mpi_uint x )
-{
-    uint8_t i;
-    unsigned char *x_ptr;
-    mbedtls_mpi_uint tmp = 0;
-
-    for( i = 0, x_ptr = (unsigned char*) &x; i < ciL; i++, x_ptr++ )
-    {
-        tmp <<= CHAR_BIT;
-        tmp |= (mbedtls_mpi_uint) *x_ptr;
-    }
-
-    return( tmp );
-}
-
-static mbedtls_mpi_uint mpi_bigendian_to_host( mbedtls_mpi_uint x )
-{
-#if defined(__BYTE_ORDER__)
-
-/* Nothing to do on bigendian systems. */
-#if ( __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ )
-    return( x );
-#endif /* __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ */
-
-#if ( __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ )
-
-/* For GCC and Clang, have builtins for byte swapping. */
-#if defined(__GNUC__) && defined(__GNUC_PREREQ)
-#if __GNUC_PREREQ(4,3)
-#define have_bswap
-#endif
-#endif
-
-#if defined(__clang__) && defined(__has_builtin)
-#if __has_builtin(__builtin_bswap32)  &&                 \
-    __has_builtin(__builtin_bswap64)
-#define have_bswap
-#endif
-#endif
-
-#if defined(have_bswap)
-    /* The compiler is hopefully able to statically evaluate this! */
-    switch( sizeof(mbedtls_mpi_uint) )
-    {
-        case 4:
-            return( __builtin_bswap32(x) );
-        case 8:
-            return( __builtin_bswap64(x) );
-    }
-#endif
-#endif /* __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ */
-#endif /* __BYTE_ORDER__ */
-
-    /* Fall back to C-based reordering if we don't know the byte order
-     * or we couldn't use a compiler-specific builtin. */
-    return( mpi_bigendian_to_host_c( x ) );
-}
-
-void mbedtls_mpi_core_bigendian_to_host( mbedtls_mpi_uint * const X,
-                                         size_t limbs )
-{
-    mbedtls_mpi_uint *cur_limb_left;
-    mbedtls_mpi_uint *cur_limb_right;
-    if( limbs == 0 )
-        return;
-
-    /*
-     * Traverse limbs and
-     * - adapt byte-order in each limb
-     * - swap the limbs themselves.
-     * For that, simultaneously traverse the limbs from left to right
-     * and from right to left, as long as the left index is not bigger
-     * than the right index (it's not a problem if limbs is odd and the
-     * indices coincide in the last iteration).
-     */
-    for( cur_limb_left = X, cur_limb_right = X + ( limbs - 1 );
-         cur_limb_left <= cur_limb_right;
-         cur_limb_left++, cur_limb_right-- )
-    {
-        mbedtls_mpi_uint tmp;
-        /* Note that if cur_limb_left == cur_limb_right,
-         * this code effectively swaps the bytes only once. */
-        tmp             = mpi_bigendian_to_host( *cur_limb_left  );
-        *cur_limb_left  = mpi_bigendian_to_host( *cur_limb_right );
-        *cur_limb_right = tmp;
-    }
-}
-
-/*
- * Import X from unsigned binary data, little endian
- *
- * The MPI needs to have enough limbs to store the full value (in particular,
- * this function does not skip 0s in the input).
- */
-int mbedtls_mpi_core_read_le( mbedtls_mpi_uint *X,
-                              size_t nx,
-                              const unsigned char *buf,
-                              size_t buflen )
-{
-    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
-    size_t i;
-    size_t const limbs = CHARS_TO_LIMBS( buflen );
-
-    /* Ensure that target MPI has at least the necessary number of limbs */
-    MBEDTLS_MPI_CHK( mpi_core_clear( X, nx, limbs ) );
-
-    for( i = 0; i < buflen; i++ )
-        X[i / ciL] |= ((mbedtls_mpi_uint) buf[i]) << ((i % ciL) << 3);
-
-cleanup:
-    return( ret );
-}
-
-/*
- * Import X from unsigned binary data, big endian
- *
- * The MPI needs to have enough limbs to store the full value (in particular,
- * this function does not skip 0s in the input).
- */
-int mbedtls_mpi_core_read_be( mbedtls_mpi_uint *X,
-                              size_t nx,
-                              const unsigned char *buf,
-                              size_t buflen )
-{
-    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
-    size_t const limbs = CHARS_TO_LIMBS( buflen );
-    size_t overhead;
-    unsigned char *Xp;
-
-    MPI_VALIDATE_RET( X != NULL );
-    MPI_VALIDATE_RET( buflen == 0 || buf != NULL );
-
-    /* Ensure that target MPI has at least the necessary number of limbs */
-    MBEDTLS_MPI_CHK( mpi_core_clear( X, nx, limbs ) );
-
-    overhead = ( nx * ciL ) - buflen;
-
-    /* Avoid calling `memcpy` with NULL source or destination argument,
-     * even if buflen is 0. */
-    if( buflen != 0 )
-    {
-        Xp = (unsigned char*) X;
-        memcpy( Xp + overhead, buf, buflen );
-
-        mbedtls_mpi_core_bigendian_to_host( X, nx );
-    }
-
-cleanup:
-    return( ret );
-}
-
-/*
- * Export X into unsigned binary data, little endian
- */
-int mbedtls_mpi_core_write_le( const mbedtls_mpi_uint *X,
-                               size_t nx,
-                               unsigned char *buf,
-                               size_t buflen )
-{
-    size_t stored_bytes = nx * ciL;
-    size_t bytes_to_copy;
-    size_t i;
-
-    if( stored_bytes < buflen )
-    {
-        bytes_to_copy = stored_bytes;
-    }
-    else
-    {
-        bytes_to_copy = buflen;
-
-        /* The output buffer is smaller than the allocated size of X.
-         * However X may fit if its leading bytes are zero. */
-        for( i = bytes_to_copy; i < stored_bytes; i++ )
-        {
-            if( GET_BYTE( X, i ) != 0 )
-                return( MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL );
-        }
-    }
-
-    for( i = 0; i < bytes_to_copy; i++ )
-        buf[i] = GET_BYTE( X, i );
-
-    if( stored_bytes < buflen )
-    {
-        /* Write trailing 0 bytes */
-        memset( buf + stored_bytes, 0, buflen - stored_bytes );
-    }
-
-    return( 0 );
-}
-
-/*
- * Export X into unsigned binary data, big endian
- */
-int mbedtls_mpi_core_write_be( const mbedtls_mpi_uint *X,
-                               size_t nx,
-                               unsigned char *buf,
-                               size_t buflen )
-{
-    size_t stored_bytes;
-    size_t bytes_to_copy;
-    unsigned char *p;
-    size_t i;
-
-    MPI_VALIDATE_RET( X != NULL );
-    MPI_VALIDATE_RET( buflen == 0 || buf != NULL );
-
-    stored_bytes = nx * ciL;
-
-    if( stored_bytes < buflen )
-    {
-        /* There is enough space in the output buffer. Write initial
-         * null bytes and record the position at which to start
-         * writing the significant bytes. In this case, the execution
-         * trace of this function does not depend on the value of the
-         * number. */
-        bytes_to_copy = stored_bytes;
-        p = buf + buflen - stored_bytes;
-        memset( buf, 0, buflen - stored_bytes );
-    }
-    else
-    {
-        /* The output buffer is smaller than the allocated size of X.
-         * However X may fit if its leading bytes are zero. */
-        bytes_to_copy = buflen;
-        p = buf;
-        for( i = bytes_to_copy; i < stored_bytes; i++ )
-        {
-            if( GET_BYTE( X, i ) != 0 )
-                return( MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL );
-        }
-    }
-
-    for( i = 0; i < bytes_to_copy; i++ )
-        p[bytes_to_copy - i - 1] = GET_BYTE( X, i );
-
-    return( 0 );
-}
-
 int mbedtls_mpi_mod_raw_read( mbedtls_mpi_uint *X,
                               mbedtls_mpi_mod_modulus *m,
                               unsigned char *buf,