diff --git a/library/rsa_internal.c b/library/rsa_internal.c
new file mode 100644
index 0000000..a46b7f4
--- /dev/null
+++ b/library/rsa_internal.c
@@ -0,0 +1,487 @@
+/*
+ *  Helper functions for the RSA module
+ *
+ *  Copyright (C) 2006-2017, ARM Limited, All Rights Reserved
+ *  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.
+ *
+ *  This file is part of Mbed Crypto (https://tls.mbed.org)
+ *
+ */
+
+#if !defined(MBEDCRYPTO_CONFIG_FILE)
+#include "mbedcrypto/config.h"
+#else
+#include MBEDCRYPTO_CONFIG_FILE
+#endif
+
+#if defined(MBEDCRYPTO_RSA_C)
+
+#include "mbedcrypto/rsa.h"
+#include "mbedcrypto/bignum.h"
+#include "mbedcrypto/rsa_internal.h"
+
+/*
+ * Compute RSA prime factors from public and private exponents
+ *
+ * Summary of algorithm:
+ * Setting F := lcm(P-1,Q-1), the idea is as follows:
+ *
+ * (a) For any 1 <= X < N with gcd(X,N)=1, we have X^F = 1 modulo N, so X^(F/2)
+ *     is a square root of 1 in Z/NZ. Since Z/NZ ~= Z/PZ x Z/QZ by CRT and the
+ *     square roots of 1 in Z/PZ and Z/QZ are +1 and -1, this leaves the four
+ *     possibilities X^(F/2) = (+-1, +-1). If it happens that X^(F/2) = (-1,+1)
+ *     or (+1,-1), then gcd(X^(F/2) + 1, N) will be equal to one of the prime
+ *     factors of N.
+ *
+ * (b) If we don't know F/2 but (F/2) * K for some odd (!) K, then the same
+ *     construction still applies since (-)^K is the identity on the set of
+ *     roots of 1 in Z/NZ.
+ *
+ * The public and private key primitives (-)^E and (-)^D are mutually inverse
+ * bijections on Z/NZ if and only if (-)^(DE) is the identity on Z/NZ, i.e.
+ * if and only if DE - 1 is a multiple of F, say DE - 1 = F * L.
+ * Splitting L = 2^t * K with K odd, we have
+ *
+ *   DE - 1 = FL = (F/2) * (2^(t+1)) * K,
+ *
+ * so (F / 2) * K is among the numbers
+ *
+ *   (DE - 1) >> 1, (DE - 1) >> 2, ..., (DE - 1) >> ord
+ *
+ * where ord is the order of 2 in (DE - 1).
+ * We can therefore iterate through these numbers apply the construction
+ * of (a) and (b) above to attempt to factor N.
+ *
+ */
+int mbedcrypto_rsa_deduce_primes( mbedcrypto_mpi const *N,
+                     mbedcrypto_mpi const *E, mbedcrypto_mpi const *D,
+                     mbedcrypto_mpi *P, mbedcrypto_mpi *Q )
+{
+    int ret = 0;
+
+    uint16_t attempt;  /* Number of current attempt  */
+    uint16_t iter;     /* Number of squares computed in the current attempt */
+
+    uint16_t order;    /* Order of 2 in DE - 1 */
+
+    mbedcrypto_mpi T;  /* Holds largest odd divisor of DE - 1     */
+    mbedcrypto_mpi K;  /* Temporary holding the current candidate */
+
+    const unsigned char primes[] = { 2,
+           3,    5,    7,   11,   13,   17,   19,   23,
+          29,   31,   37,   41,   43,   47,   53,   59,
+          61,   67,   71,   73,   79,   83,   89,   97,
+         101,  103,  107,  109,  113,  127,  131,  137,
+         139,  149,  151,  157,  163,  167,  173,  179,
+         181,  191,  193,  197,  199,  211,  223,  227,
+         229,  233,  239,  241,  251
+    };
+
+    const size_t num_primes = sizeof( primes ) / sizeof( *primes );
+
+    if( P == NULL || Q == NULL || P->p != NULL || Q->p != NULL )
+        return( MBEDCRYPTO_ERR_MPI_BAD_INPUT_DATA );
+
+    if( mbedcrypto_mpi_cmp_int( N, 0 ) <= 0 ||
+        mbedcrypto_mpi_cmp_int( D, 1 ) <= 0 ||
+        mbedcrypto_mpi_cmp_mpi( D, N ) >= 0 ||
+        mbedcrypto_mpi_cmp_int( E, 1 ) <= 0 ||
+        mbedcrypto_mpi_cmp_mpi( E, N ) >= 0 )
+    {
+        return( MBEDCRYPTO_ERR_MPI_BAD_INPUT_DATA );
+    }
+
+    /*
+     * Initializations and temporary changes
+     */
+
+    mbedcrypto_mpi_init( &K );
+    mbedcrypto_mpi_init( &T );
+
+    /* T := DE - 1 */
+    MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_mul_mpi( &T, D,  E ) );
+    MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_sub_int( &T, &T, 1 ) );
+
+    if( ( order = (uint16_t) mbedcrypto_mpi_lsb( &T ) ) == 0 )
+    {
+        ret = MBEDCRYPTO_ERR_MPI_BAD_INPUT_DATA;
+        goto cleanup;
+    }
+
+    /* After this operation, T holds the largest odd divisor of DE - 1. */
+    MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_shift_r( &T, order ) );
+
+    /*
+     * Actual work
+     */
+
+    /* Skip trying 2 if N == 1 mod 8 */
+    attempt = 0;
+    if( N->p[0] % 8 == 1 )
+        attempt = 1;
+
+    for( ; attempt < num_primes; ++attempt )
+    {
+        mbedcrypto_mpi_lset( &K, primes[attempt] );
+
+        /* Check if gcd(K,N) = 1 */
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_gcd( P, &K, N ) );
+        if( mbedcrypto_mpi_cmp_int( P, 1 ) != 0 )
+            continue;
+
+        /* Go through K^T + 1, K^(2T) + 1, K^(4T) + 1, ...
+         * and check whether they have nontrivial GCD with N. */
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_exp_mod( &K, &K, &T, N,
+                             Q /* temporarily use Q for storing Montgomery
+                                * multiplication helper values */ ) );
+
+        for( iter = 1; iter <= order; ++iter )
+        {
+            /* If we reach 1 prematurely, there's no point
+             * in continuing to square K */
+            if( mbedcrypto_mpi_cmp_int( &K, 1 ) == 0 )
+                break;
+
+            MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_add_int( &K, &K, 1 ) );
+            MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_gcd( P, &K, N ) );
+
+            if( mbedcrypto_mpi_cmp_int( P, 1 ) ==  1 &&
+                mbedcrypto_mpi_cmp_mpi( P, N ) == -1 )
+            {
+                /*
+                 * Have found a nontrivial divisor P of N.
+                 * Set Q := N / P.
+                 */
+
+                MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_div_mpi( Q, NULL, N, P ) );
+                goto cleanup;
+            }
+
+            MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_sub_int( &K, &K, 1 ) );
+            MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_mul_mpi( &K, &K, &K ) );
+            MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_mod_mpi( &K, &K, N ) );
+        }
+
+        /*
+         * If we get here, then either we prematurely aborted the loop because
+         * we reached 1, or K holds primes[attempt]^(DE - 1) mod N, which must
+         * be 1 if D,E,N were consistent.
+         * Check if that's the case and abort if not, to avoid very long,
+         * yet eventually failing, computations if N,D,E were not sane.
+         */
+        if( mbedcrypto_mpi_cmp_int( &K, 1 ) != 0 )
+        {
+            break;
+        }
+    }
+
+    ret = MBEDCRYPTO_ERR_MPI_BAD_INPUT_DATA;
+
+cleanup:
+
+    mbedcrypto_mpi_free( &K );
+    mbedcrypto_mpi_free( &T );
+    return( ret );
+}
+
+/*
+ * Given P, Q and the public exponent E, deduce D.
+ * This is essentially a modular inversion.
+ */
+int mbedcrypto_rsa_deduce_private_exponent( mbedcrypto_mpi const *P,
+                                         mbedcrypto_mpi const *Q,
+                                         mbedcrypto_mpi const *E,
+                                         mbedcrypto_mpi *D )
+{
+    int ret = 0;
+    mbedcrypto_mpi K, L;
+
+    if( D == NULL || mbedcrypto_mpi_cmp_int( D, 0 ) != 0 )
+        return( MBEDCRYPTO_ERR_MPI_BAD_INPUT_DATA );
+
+    if( mbedcrypto_mpi_cmp_int( P, 1 ) <= 0 ||
+        mbedcrypto_mpi_cmp_int( Q, 1 ) <= 0 ||
+        mbedcrypto_mpi_cmp_int( E, 0 ) == 0 )
+    {
+        return( MBEDCRYPTO_ERR_MPI_BAD_INPUT_DATA );
+    }
+
+    mbedcrypto_mpi_init( &K );
+    mbedcrypto_mpi_init( &L );
+
+    /* Temporarily put K := P-1 and L := Q-1 */
+    MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_sub_int( &K, P, 1 ) );
+    MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_sub_int( &L, Q, 1 ) );
+
+    /* Temporarily put D := gcd(P-1, Q-1) */
+    MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_gcd( D, &K, &L ) );
+
+    /* K := LCM(P-1, Q-1) */
+    MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_mul_mpi( &K, &K, &L ) );
+    MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_div_mpi( &K, NULL, &K, D ) );
+
+    /* Compute modular inverse of E in LCM(P-1, Q-1) */
+    MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_inv_mod( D, E, &K ) );
+
+cleanup:
+
+    mbedcrypto_mpi_free( &K );
+    mbedcrypto_mpi_free( &L );
+
+    return( ret );
+}
+
+/*
+ * Check that RSA CRT parameters are in accordance with core parameters.
+ */
+int mbedcrypto_rsa_validate_crt( const mbedcrypto_mpi *P,  const mbedcrypto_mpi *Q,
+                              const mbedcrypto_mpi *D,  const mbedcrypto_mpi *DP,
+                              const mbedcrypto_mpi *DQ, const mbedcrypto_mpi *QP )
+{
+    int ret = 0;
+
+    mbedcrypto_mpi K, L;
+    mbedcrypto_mpi_init( &K );
+    mbedcrypto_mpi_init( &L );
+
+    /* Check that DP - D == 0 mod P - 1 */
+    if( DP != NULL )
+    {
+        if( P == NULL )
+        {
+            ret = MBEDCRYPTO_ERR_RSA_BAD_INPUT_DATA;
+            goto cleanup;
+        }
+
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_sub_int( &K, P, 1 ) );
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_sub_mpi( &L, DP, D ) );
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_mod_mpi( &L, &L, &K ) );
+
+        if( mbedcrypto_mpi_cmp_int( &L, 0 ) != 0 )
+        {
+            ret = MBEDCRYPTO_ERR_RSA_KEY_CHECK_FAILED;
+            goto cleanup;
+        }
+    }
+
+    /* Check that DQ - D == 0 mod Q - 1 */
+    if( DQ != NULL )
+    {
+        if( Q == NULL )
+        {
+            ret = MBEDCRYPTO_ERR_RSA_BAD_INPUT_DATA;
+            goto cleanup;
+        }
+
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_sub_int( &K, Q, 1 ) );
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_sub_mpi( &L, DQ, D ) );
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_mod_mpi( &L, &L, &K ) );
+
+        if( mbedcrypto_mpi_cmp_int( &L, 0 ) != 0 )
+        {
+            ret = MBEDCRYPTO_ERR_RSA_KEY_CHECK_FAILED;
+            goto cleanup;
+        }
+    }
+
+    /* Check that QP * Q - 1 == 0 mod P */
+    if( QP != NULL )
+    {
+        if( P == NULL || Q == NULL )
+        {
+            ret = MBEDCRYPTO_ERR_RSA_BAD_INPUT_DATA;
+            goto cleanup;
+        }
+
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_mul_mpi( &K, QP, Q ) );
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_sub_int( &K, &K, 1 ) );
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_mod_mpi( &K, &K, P ) );
+        if( mbedcrypto_mpi_cmp_int( &K, 0 ) != 0 )
+        {
+            ret = MBEDCRYPTO_ERR_RSA_KEY_CHECK_FAILED;
+            goto cleanup;
+        }
+    }
+
+cleanup:
+
+    /* Wrap MPI error codes by RSA check failure error code */
+    if( ret != 0 &&
+        ret != MBEDCRYPTO_ERR_RSA_KEY_CHECK_FAILED &&
+        ret != MBEDCRYPTO_ERR_RSA_BAD_INPUT_DATA )
+    {
+        ret += MBEDCRYPTO_ERR_RSA_KEY_CHECK_FAILED;
+    }
+
+    mbedcrypto_mpi_free( &K );
+    mbedcrypto_mpi_free( &L );
+
+    return( ret );
+}
+
+/*
+ * Check that core RSA parameters are sane.
+ */
+int mbedcrypto_rsa_validate_params( const mbedcrypto_mpi *N, const mbedcrypto_mpi *P,
+                                 const mbedcrypto_mpi *Q, const mbedcrypto_mpi *D,
+                                 const mbedcrypto_mpi *E,
+                                 int (*f_rng)(void *, unsigned char *, size_t),
+                                 void *p_rng )
+{
+    int ret = 0;
+    mbedcrypto_mpi K, L;
+
+    mbedcrypto_mpi_init( &K );
+    mbedcrypto_mpi_init( &L );
+
+    /*
+     * Step 1: If PRNG provided, check that P and Q are prime
+     */
+
+#if defined(MBEDCRYPTO_GENPRIME)
+    if( f_rng != NULL && P != NULL &&
+        ( ret = mbedcrypto_mpi_is_prime( P, f_rng, p_rng ) ) != 0 )
+    {
+        ret = MBEDCRYPTO_ERR_RSA_KEY_CHECK_FAILED;
+        goto cleanup;
+    }
+
+    if( f_rng != NULL && Q != NULL &&
+        ( ret = mbedcrypto_mpi_is_prime( Q, f_rng, p_rng ) ) != 0 )
+    {
+        ret = MBEDCRYPTO_ERR_RSA_KEY_CHECK_FAILED;
+        goto cleanup;
+    }
+#else
+    ((void) f_rng);
+    ((void) p_rng);
+#endif /* MBEDCRYPTO_GENPRIME */
+
+    /*
+     * Step 2: Check that 1 < N = P * Q
+     */
+
+    if( P != NULL && Q != NULL && N != NULL )
+    {
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_mul_mpi( &K, P, Q ) );
+        if( mbedcrypto_mpi_cmp_int( N, 1 )  <= 0 ||
+            mbedcrypto_mpi_cmp_mpi( &K, N ) != 0 )
+        {
+            ret = MBEDCRYPTO_ERR_RSA_KEY_CHECK_FAILED;
+            goto cleanup;
+        }
+    }
+
+    /*
+     * Step 3: Check and 1 < D, E < N if present.
+     */
+
+    if( N != NULL && D != NULL && E != NULL )
+    {
+        if ( mbedcrypto_mpi_cmp_int( D, 1 ) <= 0 ||
+             mbedcrypto_mpi_cmp_int( E, 1 ) <= 0 ||
+             mbedcrypto_mpi_cmp_mpi( D, N ) >= 0 ||
+             mbedcrypto_mpi_cmp_mpi( E, N ) >= 0 )
+        {
+            ret = MBEDCRYPTO_ERR_RSA_KEY_CHECK_FAILED;
+            goto cleanup;
+        }
+    }
+
+    /*
+     * Step 4: Check that D, E are inverse modulo P-1 and Q-1
+     */
+
+    if( P != NULL && Q != NULL && D != NULL && E != NULL )
+    {
+        if( mbedcrypto_mpi_cmp_int( P, 1 ) <= 0 ||
+            mbedcrypto_mpi_cmp_int( Q, 1 ) <= 0 )
+        {
+            ret = MBEDCRYPTO_ERR_RSA_KEY_CHECK_FAILED;
+            goto cleanup;
+        }
+
+        /* Compute DE-1 mod P-1 */
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_mul_mpi( &K, D, E ) );
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_sub_int( &K, &K, 1 ) );
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_sub_int( &L, P, 1 ) );
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_mod_mpi( &K, &K, &L ) );
+        if( mbedcrypto_mpi_cmp_int( &K, 0 ) != 0 )
+        {
+            ret = MBEDCRYPTO_ERR_RSA_KEY_CHECK_FAILED;
+            goto cleanup;
+        }
+
+        /* Compute DE-1 mod Q-1 */
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_mul_mpi( &K, D, E ) );
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_sub_int( &K, &K, 1 ) );
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_sub_int( &L, Q, 1 ) );
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_mod_mpi( &K, &K, &L ) );
+        if( mbedcrypto_mpi_cmp_int( &K, 0 ) != 0 )
+        {
+            ret = MBEDCRYPTO_ERR_RSA_KEY_CHECK_FAILED;
+            goto cleanup;
+        }
+    }
+
+cleanup:
+
+    mbedcrypto_mpi_free( &K );
+    mbedcrypto_mpi_free( &L );
+
+    /* Wrap MPI error codes by RSA check failure error code */
+    if( ret != 0 && ret != MBEDCRYPTO_ERR_RSA_KEY_CHECK_FAILED )
+    {
+        ret += MBEDCRYPTO_ERR_RSA_KEY_CHECK_FAILED;
+    }
+
+    return( ret );
+}
+
+int mbedcrypto_rsa_deduce_crt( const mbedcrypto_mpi *P, const mbedcrypto_mpi *Q,
+                            const mbedcrypto_mpi *D, mbedcrypto_mpi *DP,
+                            mbedcrypto_mpi *DQ, mbedcrypto_mpi *QP )
+{
+    int ret = 0;
+    mbedcrypto_mpi K;
+    mbedcrypto_mpi_init( &K );
+
+    /* DP = D mod P-1 */
+    if( DP != NULL )
+    {
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_sub_int( &K, P, 1  ) );
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_mod_mpi( DP, D, &K ) );
+    }
+
+    /* DQ = D mod Q-1 */
+    if( DQ != NULL )
+    {
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_sub_int( &K, Q, 1  ) );
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_mod_mpi( DQ, D, &K ) );
+    }
+
+    /* QP = Q^{-1} mod P */
+    if( QP != NULL )
+    {
+        MBEDCRYPTO_MPI_CHK( mbedcrypto_mpi_inv_mod( QP, Q, P ) );
+    }
+
+cleanup:
+    mbedcrypto_mpi_free( &K );
+
+    return( ret );
+}
+
+#endif /* MBEDCRYPTO_RSA_C */