Rework LuCI build system

 * Rename subdirectories to their repective OpenWrt package names
 * Make each LuCI module its own standalone package
 * Deploy a shared luci.mk which is used by each module Makefile

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

1 files changed, 1575 insertions, 0 deletions

diff --git a/libs/luci-lib-nixio/axTLS/crypto/bigint.c b/libs/luci-lib-nixio/axTLS/crypto/bigint.c
new file mode 100644
index 0000000000..53a5839293
--- /dev/null
+++ b/libs/luci-lib-nixio/axTLS/crypto/bigint.c
@@ -0,0 +1,1575 @@
+/*
+ * Copyright (c) 2007, Cameron Rich
+ * 
+ * All rights reserved.
+ * 
+ * Redistribution and use in source and binary forms, with or without 
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * * Redistributions of source code must retain the above copyright notice, 
+ *   this list of conditions and the following disclaimer.
+ * * Redistributions in binary form must reproduce the above copyright notice, 
+ *   this list of conditions and the following disclaimer in the documentation 
+ *   and/or other materials provided with the distribution.
+ * * Neither the name of the axTLS project nor the names of its contributors 
+ *   may be used to endorse or promote products derived from this software 
+ *   without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/**
+ * @defgroup bigint_api Big Integer API
+ * @brief The bigint implementation as used by the axTLS project.
+ *
+ * The bigint library is for RSA encryption/decryption as well as signing.
+ * This code tries to minimise use of malloc/free by maintaining a small 
+ * cache. A bigint context may maintain state by being made "permanent". 
+ * It be be later released with a bi_depermanent() and bi_free() call.
+ *
+ * It supports the following reduction techniques:
+ * - Classical
+ * - Barrett
+ * - Montgomery
+ *
+ * It also implements the following:
+ * - Karatsuba multiplication
+ * - Squaring
+ * - Sliding window exponentiation
+ * - Chinese Remainder Theorem (implemented in rsa.c).
+ *
+ * All the algorithms used are pretty standard, and designed for different
+ * data bus sizes. Negative numbers are not dealt with at all, so a subtraction
+ * may need to be tested for negativity.
+ *
+ * This library steals some ideas from Jef Poskanzer
+ * <http://cs.marlboro.edu/term/cs-fall02/algorithms/crypto/RSA/bigint>
+ * and GMP <http://www.swox.com/gmp>. It gets most of its implementation
+ * detail from "The Handbook of Applied Cryptography"
+ * <http://www.cacr.math.uwaterloo.ca/hac/about/chap14.pdf>
+ * @{
+ */
+
+#include <stdlib.h>
+#include <limits.h>
+#include <string.h>
+#include <stdio.h>
+#include <time.h>
+#include "bigint.h"
+
+#define V1      v->comps[v->size-1]                 /**< v1 for division */
+#define V2      v->comps[v->size-2]                 /**< v2 for division */
+#define U(j)    tmp_u->comps[tmp_u->size-j-1]       /**< uj for division */
+#define Q(j)    quotient->comps[quotient->size-j-1] /**< qj for division */
+
+static bigint *bi_int_multiply(BI_CTX *ctx, bigint *bi, comp i);
+static bigint *bi_int_divide(BI_CTX *ctx, bigint *biR, comp denom);
+static bigint *alloc(BI_CTX *ctx, int size);
+static bigint *trim(bigint *bi);
+static void more_comps(bigint *bi, int n);
+#if defined(CONFIG_BIGINT_KARATSUBA) || defined(CONFIG_BIGINT_BARRETT) || \
+    defined(CONFIG_BIGINT_MONTGOMERY)
+static bigint *comp_right_shift(bigint *biR, int num_shifts);
+static bigint *comp_left_shift(bigint *biR, int num_shifts);
+#endif
+
+#ifdef CONFIG_BIGINT_CHECK_ON
+static void check(const bigint *bi);
+#else
+#define check(A)                /**< disappears in normal production mode */
+#endif
+
+
+/**
+ * @brief Start a new bigint context.
+ * @return A bigint context.
+ */
+BI_CTX *bi_initialize(void)
+{
+    /* calloc() sets everything to zero */
+    BI_CTX *ctx = (BI_CTX *)calloc(1, sizeof(BI_CTX));
+   
+    /* the radix */
+    ctx->bi_radix = alloc(ctx, 2); 
+    ctx->bi_radix->comps[0] = 0;
+    ctx->bi_radix->comps[1] = 1;
+    bi_permanent(ctx->bi_radix);
+    return ctx;
+}
+
+/**
+ * @brief Close the bigint context and free any resources.
+ *
+ * Free up any used memory - a check is done if all objects were not 
+ * properly freed.
+ * @param ctx [in]   The bigint session context.
+ */
+void bi_terminate(BI_CTX *ctx)
+{
+    bi_depermanent(ctx->bi_radix); 
+    bi_free(ctx, ctx->bi_radix);
+
+    if (ctx->active_count != 0)
+    {
+#ifdef CONFIG_SSL_FULL_MODE
+        printf("bi_terminate: there were %d un-freed bigints\n",
+                       ctx->active_count);
+#endif
+        abort();
+    }
+
+    bi_clear_cache(ctx);
+    free(ctx);
+}
+
+/**
+ *@brief Clear the memory cache.
+ */
+void bi_clear_cache(BI_CTX *ctx)
+{
+    bigint *p, *pn;
+
+    if (ctx->free_list == NULL)
+        return;
+    
+    for (p = ctx->free_list; p != NULL; p = pn)
+    {
+        pn = p->next;
+        free(p->comps);
+        free(p);
+    }
+
+    ctx->free_count = 0;
+    ctx->free_list = NULL;
+}
+
+/**
+ * @brief Increment the number of references to this object. 
+ * It does not do a full copy.
+ * @param bi [in]   The bigint to copy.
+ * @return A reference to the same bigint.
+ */
+bigint *bi_copy(bigint *bi)
+{
+    check(bi);
+    if (bi->refs != PERMANENT)
+        bi->refs++;
+    return bi;
+}
+
+/**
+ * @brief Simply make a bigint object "unfreeable" if bi_free() is called on it.
+ *
+ * For this object to be freed, bi_depermanent() must be called.
+ * @param bi [in]   The bigint to be made permanent.
+ */
+void bi_permanent(bigint *bi)
+{
+    check(bi);
+    if (bi->refs != 1)
+    {
+#ifdef CONFIG_SSL_FULL_MODE
+        printf("bi_permanent: refs was not 1\n");
+#endif
+        abort();
+    }
+
+    bi->refs = PERMANENT;
+}
+
+/**
+ * @brief Take a permanent object and make it eligible for freedom.
+ * @param bi [in]   The bigint to be made back to temporary.
+ */
+void bi_depermanent(bigint *bi)
+{
+    check(bi);
+    if (bi->refs != PERMANENT)
+    {
+#ifdef CONFIG_SSL_FULL_MODE
+        printf("bi_depermanent: bigint was not permanent\n");
+#endif
+        abort();
+    }
+
+    bi->refs = 1;
+}
+
+/**
+ * @brief Free a bigint object so it can be used again. 
+ *
+ * The memory itself it not actually freed, just tagged as being available 
+ * @param ctx [in]   The bigint session context.
+ * @param bi [in]    The bigint to be freed.
+ */
+void bi_free(BI_CTX *ctx, bigint *bi)
+{
+    check(bi);
+    if (bi->refs == PERMANENT)
+    {
+        return;
+    }
+
+    if (--bi->refs > 0)
+    {
+        return;
+    }
+
+    bi->next = ctx->free_list;
+    ctx->free_list = bi;
+    ctx->free_count++;
+
+    if (--ctx->active_count < 0)
+    {
+#ifdef CONFIG_SSL_FULL_MODE
+        printf("bi_free: active_count went negative "
+                "- double-freed bigint?\n");
+#endif
+        abort();
+    }
+}
+
+/**
+ * @brief Convert an (unsigned) integer into a bigint.
+ * @param ctx [in]   The bigint session context.
+ * @param i [in]     The (unsigned) integer to be converted.
+ * 
+ */
+bigint *int_to_bi(BI_CTX *ctx, comp i)
+{
+    bigint *biR = alloc(ctx, 1);
+    biR->comps[0] = i;
+    return biR;
+}
+
+/**
+ * @brief Do a full copy of the bigint object.
+ * @param ctx [in]   The bigint session context.
+ * @param bi  [in]   The bigint object to be copied.
+ */
+bigint *bi_clone(BI_CTX *ctx, const bigint *bi)
+{
+    bigint *biR = alloc(ctx, bi->size);
+    check(bi);
+    memcpy(biR->comps, bi->comps, bi->size*COMP_BYTE_SIZE);
+    return biR;
+}
+
+/**
+ * @brief Perform an addition operation between two bigints.
+ * @param ctx [in]  The bigint session context.
+ * @param bia [in]  A bigint.
+ * @param bib [in]  Another bigint.
+ * @return The result of the addition.
+ */
+bigint *bi_add(BI_CTX *ctx, bigint *bia, bigint *bib)
+{
+    int n;
+    comp carry = 0;
+    comp *pa, *pb;
+
+    check(bia);
+    check(bib);
+
+    n = max(bia->size, bib->size);
+    more_comps(bia, n+1);
+    more_comps(bib, n);
+    pa = bia->comps;
+    pb = bib->comps;
+
+    do
+    {
+        comp  sl, rl, cy1;
+        sl = *pa + *pb++;
+        rl = sl + carry;
+        cy1 = sl < *pa;
+        carry = cy1 | (rl < sl);
+        *pa++ = rl;
+    } while (--n != 0);
+
+    *pa = carry;                  /* do overflow */
+    bi_free(ctx, bib);
+    return trim(bia);
+}
+
+/**
+ * @brief Perform a subtraction operation between two bigints.
+ * @param ctx [in]  The bigint session context.
+ * @param bia [in]  A bigint.
+ * @param bib [in]  Another bigint.
+ * @param is_negative [out] If defined, indicates that the result was negative.
+ * is_negative may be null.
+ * @return The result of the subtraction. The result is always positive.
+ */
+bigint *bi_subtract(BI_CTX *ctx, 
+        bigint *bia, bigint *bib, int *is_negative)
+{
+    int n = bia->size;
+    comp *pa, *pb, carry = 0;
+
+    check(bia);
+    check(bib);
+
+    more_comps(bib, n);
+    pa = bia->comps;
+    pb = bib->comps;
+
+    do 
+    {
+        comp sl, rl, cy1;
+        sl = *pa - *pb++;
+        rl = sl - carry;
+        cy1 = sl > *pa;
+        carry = cy1 | (rl > sl);
+        *pa++ = rl;
+    } while (--n != 0);
+
+    if (is_negative)    /* indicate a negative result */
+    {
+        *is_negative = carry;
+    }
+
+    bi_free(ctx, trim(bib));    /* put bib back to the way it was */
+    return trim(bia);
+}
+
+/**
+ * Perform a multiply between a bigint an an (unsigned) integer
+ */
+static bigint *bi_int_multiply(BI_CTX *ctx, bigint *bia, comp b)
+{
+    int j = 0, n = bia->size;
+    bigint *biR = alloc(ctx, n + 1);
+    comp carry = 0;
+    comp *r = biR->comps;
+    comp *a = bia->comps;
+
+    check(bia);
+
+    /* clear things to start with */
+    memset(r, 0, ((n+1)*COMP_BYTE_SIZE));
+
+    do
+    {
+        long_comp tmp = *r + (long_comp)a[j]*b + carry;
+        *r++ = (comp)tmp;              /* downsize */
+        carry = (comp)(tmp >> COMP_BIT_SIZE);
+    } while (++j < n);
+
+    *r = carry;
+    bi_free(ctx, bia);
+    return trim(biR);
+}
+
+/**
+ * @brief Does both division and modulo calculations. 
+ *
+ * Used extensively when doing classical reduction.
+ * @param ctx [in]  The bigint session context.
+ * @param u [in]    A bigint which is the numerator.
+ * @param v [in]    Either the denominator or the modulus depending on the mode.
+ * @param is_mod [n] Determines if this is a normal division (0) or a reduction
+ * (1).
+ * @return  The result of the division/reduction.
+ */
+bigint *bi_divide(BI_CTX *ctx, bigint *u, bigint *v, int is_mod)
+{
+    int n = v->size, m = u->size-n;
+    int j = 0, orig_u_size = u->size;
+    uint8_t mod_offset = ctx->mod_offset;
+    comp d;
+    bigint *quotient, *tmp_u;
+    comp q_dash;
+
+    check(u);
+    check(v);
+
+    /* if doing reduction and we are < mod, then return mod */
+    if (is_mod && bi_compare(v, u) > 0)
+    {
+        bi_free(ctx, v);
+        return u;
+    }
+
+    quotient = alloc(ctx, m+1);
+    tmp_u = alloc(ctx, n+1);
+    v = trim(v);        /* make sure we have no leading 0's */
+    d = (comp)((long_comp)COMP_RADIX/(V1+1));
+
+    /* clear things to start with */
+    memset(quotient->comps, 0, ((quotient->size)*COMP_BYTE_SIZE));
+
+    /* normalise */
+    if (d > 1)
+    {
+        u = bi_int_multiply(ctx, u, d);
+
+        if (is_mod)
+        {
+            v = ctx->bi_normalised_mod[mod_offset];
+        }
+        else
+        {
+            v = bi_int_multiply(ctx, v, d);
+        }
+    }
+
+    if (orig_u_size == u->size)  /* new digit position u0 */
+    {
+        more_comps(u, orig_u_size + 1);
+    }
+
+    do
+    {
+        /* get a temporary short version of u */
+        memcpy(tmp_u->comps, &u->comps[u->size-n-1-j], (n+1)*COMP_BYTE_SIZE);
+
+        /* calculate q' */
+        if (U(0) == V1)
+        {
+            q_dash = COMP_RADIX-1;
+        }
+        else
+        {
+            q_dash = (comp)(((long_comp)U(0)*COMP_RADIX + U(1))/V1);
+        }
+
+        if (v->size > 1 && V2)
+        {
+            /* we are implementing the following:
+            if (V2*q_dash > (((U(0)*COMP_RADIX + U(1) - 
+                    q_dash*V1)*COMP_RADIX) + U(2))) ... */
+            comp inner = (comp)((long_comp)COMP_RADIX*U(0) + U(1) - 
+                                        (long_comp)q_dash*V1);
+            if ((long_comp)V2*q_dash > (long_comp)inner*COMP_RADIX + U(2))
+            {
+                q_dash--;
+            }
+        }
+
+        /* multiply and subtract */
+        if (q_dash)
+        {
+            int is_negative;
+            tmp_u = bi_subtract(ctx, tmp_u, 
+                    bi_int_multiply(ctx, bi_copy(v), q_dash), &is_negative);
+            more_comps(tmp_u, n+1);
+
+            Q(j) = q_dash; 
+
+            /* add back */
+            if (is_negative)
+            {
+                Q(j)--;
+                tmp_u = bi_add(ctx, tmp_u, bi_copy(v));
+
+                /* lop off the carry */
+                tmp_u->size--;
+                v->size--;
+            }
+        }
+        else
+        {
+            Q(j) = 0; 
+        }
+
+        /* copy back to u */
+        memcpy(&u->comps[u->size-n-1-j], tmp_u->comps, (n+1)*COMP_BYTE_SIZE);
+    } while (++j <= m);
+
+    bi_free(ctx, tmp_u);
+    bi_free(ctx, v);
+
+    if (is_mod)     /* get the remainder */
+    {
+        bi_free(ctx, quotient);
+        return bi_int_divide(ctx, trim(u), d);
+    }
+    else            /* get the quotient */
+    {
+        bi_free(ctx, u);
+        return trim(quotient);
+    }
+}
+
+/*
+ * Perform an integer divide on a bigint.
+ */
+static bigint *bi_int_divide(BI_CTX *ctx, bigint *biR, comp denom)
+{
+    int i = biR->size - 1;
+    long_comp r = 0;
+
+    check(biR);
+
+    do
+    {
+        r = (r<<COMP_BIT_SIZE) + biR->comps[i];
+        biR->comps[i] = (comp)(r / denom);
+        r %= denom;
+    } while (--i >= 0);
+
+    return trim(biR);
+}
+
+#ifdef CONFIG_BIGINT_MONTGOMERY
+/**
+ * There is a need for the value of integer N' such that B^-1(B-1)-N^-1N'=1, 
+ * where B^-1(B-1) mod N=1. Actually, only the least significant part of 
+ * N' is needed, hence the definition N0'=N' mod b. We reproduce below the 
+ * simple algorithm from an article by Dusse and Kaliski to efficiently 
+ * find N0' from N0 and b */
+static comp modular_inverse(bigint *bim)
+{
+    int i;
+    comp t = 1;
+    comp two_2_i_minus_1 = 2;   /* 2^(i-1) */
+    long_comp two_2_i = 4;      /* 2^i */
+    comp N = bim->comps[0];
+
+    for (i = 2; i <= COMP_BIT_SIZE; i++)
+    {
+        if ((long_comp)N*t%two_2_i >= two_2_i_minus_1)
+        {
+            t += two_2_i_minus_1;
+        }
+
+        two_2_i_minus_1 <<= 1;
+        two_2_i <<= 1;
+    }
+
+    return (comp)(COMP_RADIX-t);
+}
+#endif
+
+#if defined(CONFIG_BIGINT_KARATSUBA) || defined(CONFIG_BIGINT_BARRETT) || \
+    defined(CONFIG_BIGINT_MONTGOMERY)
+/**
+ * Take each component and shift down (in terms of components) 
+ */
+static bigint *comp_right_shift(bigint *biR, int num_shifts)
+{
+    int i = biR->size-num_shifts;
+    comp *x = biR->comps;
+    comp *y = &biR->comps[num_shifts];
+
+    check(biR);
+
+    if (i <= 0)     /* have we completely right shifted? */
+    {
+        biR->comps[0] = 0;  /* return 0 */
+        biR->size = 1;
+        return biR;
+    }
+
+    do
+    {
+        *x++ = *y++;
+    } while (--i > 0);
+
+    biR->size -= num_shifts;
+    return biR;
+}
+
+/**
+ * Take each component and shift it up (in terms of components) 
+ */
+static bigint *comp_left_shift(bigint *biR, int num_shifts)
+{
+    int i = biR->size-1;
+    comp *x, *y;
+
+    check(biR);
+
+    if (num_shifts <= 0)
+    {
+        return biR;
+    }
+
+    more_comps(biR, biR->size + num_shifts);
+
+    x = &biR->comps[i+num_shifts];
+    y = &biR->comps[i];
+
+    do
+    {
+        *x-- = *y--;
+    } while (i--);
+
+    memset(biR->comps, 0, num_shifts*COMP_BYTE_SIZE); /* zero LS comps */
+    return biR;
+}
+#endif
+
+/**
+ * @brief Allow a binary sequence to be imported as a bigint.
+ * @param ctx [in]  The bigint session context.
+ * @param data [in] The data to be converted.
+ * @param size [in] The number of bytes of data.
+ * @return A bigint representing this data.
+ */
+bigint *bi_import(BI_CTX *ctx, const uint8_t *data, int size)
+{
+    bigint *biR = alloc(ctx, (size+COMP_BYTE_SIZE-1)/COMP_BYTE_SIZE);
+    int i, j = 0, offset = 0;
+
+    memset(biR->comps, 0, biR->size*COMP_BYTE_SIZE);
+
+    for (i = size-1; i >= 0; i--)
+    {
+        biR->comps[offset] += data[i] << (j*8);
+
+        if (++j == COMP_BYTE_SIZE)
+        {
+            j = 0;
+            offset ++;
+        }
+    }
+
+    return trim(biR);
+}
+
+#ifdef CONFIG_SSL_FULL_MODE
+/**
+ * @brief The testharness uses this code to import text hex-streams and 
+ * convert them into bigints.
+ * @param ctx [in]  The bigint session context.
+ * @param data [in] A string consisting of hex characters. The characters must
+ * be in upper case.
+ * @return A bigint representing this data.
+ */
+bigint *bi_str_import(BI_CTX *ctx, const char *data)
+{
+    int size = strlen(data);
+    bigint *biR = alloc(ctx, (size+COMP_NUM_NIBBLES-1)/COMP_NUM_NIBBLES);
+    int i, j = 0, offset = 0;
+    memset(biR->comps, 0, biR->size*COMP_BYTE_SIZE);
+
+    for (i = size-1; i >= 0; i--)
+    {
+        int num = (data[i] <= '9') ? (data[i] - '0') : (data[i] - 'A' + 10);
+        biR->comps[offset] += num << (j*4);
+
+        if (++j == COMP_NUM_NIBBLES)
+        {
+            j = 0;
+            offset ++;
+        }
+    }
+
+    return biR;
+}
+
+void bi_print(const char *label, bigint *x)
+{
+    int i, j;
+
+    if (x == NULL)
+    {
+        printf("%s: (null)\n", label);
+        return;
+    }
+
+    printf("%s: (size %d)\n", label, x->size);
+    for (i = x->size-1; i >= 0; i--)
+    {
+        for (j = COMP_NUM_NIBBLES-1; j >= 0; j--)
+        {
+            comp mask = 0x0f << (j*4);
+            comp num = (x->comps[i] & mask) >> (j*4);
+            putc((num <= 9) ? (num + '0') : (num + 'A' - 10), stdout);
+        }
+    }  
+
+    printf("\n");
+}
+#endif
+
+/**
+ * @brief Take a bigint and convert it into a byte sequence. 
+ *
+ * This is useful after a decrypt operation.
+ * @param ctx [in]  The bigint session context.
+ * @param x [in]  The bigint to be converted.
+ * @param data [out] The converted data as a byte stream.
+ * @param size [in] The maximum size of the byte stream. Unused bytes will be
+ * zeroed.
+ */
+void bi_export(BI_CTX *ctx, bigint *x, uint8_t *data, int size)
+{
+    int i, j, k = size-1;
+
+    check(x);
+    memset(data, 0, size);  /* ensure all leading 0's are cleared */
+
+    for (i = 0; i < x->size; i++)
+    {
+        for (j = 0; j < COMP_BYTE_SIZE; j++)
+        {
+            comp mask = 0xff << (j*8);
+            int num = (x->comps[i] & mask) >> (j*8);
+            data[k--] = num;
+
+            if (k < 0)
+            {
+                break;
+            }
+        }
+    }
+
+    bi_free(ctx, x);
+}
+
+/**
+ * @brief Pre-calculate some of the expensive steps in reduction. 
+ *
+ * This function should only be called once (normally when a session starts).
+ * When the session is over, bi_free_mod() should be called. bi_mod_power()
+ * relies on this function being called.
+ * @param ctx [in]  The bigint session context.
+ * @param bim [in]  The bigint modulus that will be used.
+ * @param mod_offset [in] There are three moduluii that can be stored - the
+ * standard modulus, and its two primes p and q. This offset refers to which
+ * modulus we are referring to.
+ * @see bi_free_mod(), bi_mod_power().
+ */
+void bi_set_mod(BI_CTX *ctx, bigint *bim, int mod_offset)
+{
+    int k = bim->size;
+    comp d = (comp)((long_comp)COMP_RADIX/(bim->comps[k-1]+1));
+#ifdef CONFIG_BIGINT_MONTGOMERY
+    bigint *R, *R2;
+#endif
+
+    ctx->bi_mod[mod_offset] = bim;
+    bi_permanent(ctx->bi_mod[mod_offset]);
+    ctx->bi_normalised_mod[mod_offset] = bi_int_multiply(ctx, bim, d);
+    bi_permanent(ctx->bi_normalised_mod[mod_offset]);
+
+#if defined(CONFIG_BIGINT_MONTGOMERY)
+    /* set montgomery variables */
+    R = comp_left_shift(bi_clone(ctx, ctx->bi_radix), k-1);     /* R */
+    R2 = comp_left_shift(bi_clone(ctx, ctx->bi_radix), k*2-1);  /* R^2 */
+    ctx->bi_RR_mod_m[mod_offset] = bi_mod(ctx, R2);             /* R^2 mod m */
+    ctx->bi_R_mod_m[mod_offset] = bi_mod(ctx, R);               /* R mod m */
+
+    bi_permanent(ctx->bi_RR_mod_m[mod_offset]);
+    bi_permanent(ctx->bi_R_mod_m[mod_offset]);
+
+    ctx->N0_dash[mod_offset] = modular_inverse(ctx->bi_mod[mod_offset]);
+
+#elif defined (CONFIG_BIGINT_BARRETT)
+    ctx->bi_mu[mod_offset] = 
+        bi_divide(ctx, comp_left_shift(
+            bi_clone(ctx, ctx->bi_radix), k*2-1), ctx->bi_mod[mod_offset], 0);
+    bi_permanent(ctx->bi_mu[mod_offset]);
+#endif
+}
+
+/**
+ * @brief Used when cleaning various bigints at the end of a session.
+ * @param ctx [in]  The bigint session context.
+ * @param mod_offset [in] The offset to use.
+ * @see bi_set_mod().
+ */
+void bi_free_mod(BI_CTX *ctx, int mod_offset)
+{
+    bi_depermanent(ctx->bi_mod[mod_offset]);
+    bi_free(ctx, ctx->bi_mod[mod_offset]);
+#if defined (CONFIG_BIGINT_MONTGOMERY)
+    bi_depermanent(ctx->bi_RR_mod_m[mod_offset]);
+    bi_depermanent(ctx->bi_R_mod_m[mod_offset]);
+    bi_free(ctx, ctx->bi_RR_mod_m[mod_offset]);
+    bi_free(ctx, ctx->bi_R_mod_m[mod_offset]);
+#elif defined(CONFIG_BIGINT_BARRETT)
+    bi_depermanent(ctx->bi_mu[mod_offset]); 
+    bi_free(ctx, ctx->bi_mu[mod_offset]);
+#endif
+    bi_depermanent(ctx->bi_normalised_mod[mod_offset]); 
+    bi_free(ctx, ctx->bi_normalised_mod[mod_offset]);
+}
+
+/** 
+ * Perform a standard multiplication between two bigints.
+ */
+static bigint *regular_multiply(BI_CTX *ctx, bigint *bia, bigint *bib)
+{
+    int i, j, i_plus_j;
+    int n = bia->size; 
+    int t = bib->size;
+    bigint *biR = alloc(ctx, n + t);
+    comp *sr = biR->comps;
+    comp *sa = bia->comps;
+    comp *sb = bib->comps;
+
+    check(bia);
+    check(bib);
+
+    /* clear things to start with */
+    memset(biR->comps, 0, ((n+t)*COMP_BYTE_SIZE));
+    i = 0;
+
+    do 
+    {
+        comp carry = 0;
+        comp b = *sb++;
+        i_plus_j = i;
+        j = 0;
+
+        do
+        {
+            long_comp tmp = sr[i_plus_j] + (long_comp)sa[j]*b + carry;
+            sr[i_plus_j++] = (comp)tmp;              /* downsize */
+            carry = (comp)(tmp >> COMP_BIT_SIZE);
+        } while (++j < n);
+
+        sr[i_plus_j] = carry;
+    } while (++i < t);
+
+    bi_free(ctx, bia);
+    bi_free(ctx, bib);
+    return trim(biR);
+}
+
+#ifdef CONFIG_BIGINT_KARATSUBA
+/*
+ * Karatsuba improves on regular multiplication due to only 3 multiplications 
+ * being done instead of 4. The additional additions/subtractions are O(N) 
+ * rather than O(N^2) and so for big numbers it saves on a few operations 
+ */
+static bigint *karatsuba(BI_CTX *ctx, bigint *bia, bigint *bib, int is_square)
+{
+    bigint *x0, *x1;
+    bigint *p0, *p1, *p2;
+    int m;
+
+    if (is_square)
+    {
+        m = (bia->size + 1)/2;
+    }
+    else
+    {
+        m = (max(bia->size, bib->size) + 1)/2;
+    }
+
+    x0 = bi_clone(ctx, bia);
+    x0->size = m;
+    x1 = bi_clone(ctx, bia);
+    comp_right_shift(x1, m);
+    bi_free(ctx, bia);
+
+    /* work out the 3 partial products */
+    if (is_square)
+    {
+        p0 = bi_square(ctx, bi_copy(x0));
+        p2 = bi_square(ctx, bi_copy(x1));
+        p1 = bi_square(ctx, bi_add(ctx, x0, x1));
+    }
+    else /* normal multiply */
+    {
+        bigint *y0, *y1;
+        y0 = bi_clone(ctx, bib);
+        y0->size = m;
+        y1 = bi_clone(ctx, bib);
+        comp_right_shift(y1, m);
+        bi_free(ctx, bib);
+
+        p0 = bi_multiply(ctx, bi_copy(x0), bi_copy(y0));
+        p2 = bi_multiply(ctx, bi_copy(x1), bi_copy(y1));
+        p1 = bi_multiply(ctx, bi_add(ctx, x0, x1), bi_add(ctx, y0, y1));
+    }
+
+    p1 = bi_subtract(ctx, 
+            bi_subtract(ctx, p1, bi_copy(p2), NULL), bi_copy(p0), NULL);
+
+    comp_left_shift(p1, m);
+    comp_left_shift(p2, 2*m);
+    return bi_add(ctx, p1, bi_add(ctx, p0, p2));
+}
+#endif
+
+/**
+ * @brief Perform a multiplication operation between two bigints.
+ * @param ctx [in]  The bigint session context.
+ * @param bia [in]  A bigint.
+ * @param bib [in]  Another bigint.
+ * @return The result of the multiplication.
+ */
+bigint *bi_multiply(BI_CTX *ctx, bigint *bia, bigint *bib)
+{
+    check(bia);
+    check(bib);
+
+#ifdef CONFIG_BIGINT_KARATSUBA
+    if (min(bia->size, bib->size) < MUL_KARATSUBA_THRESH)
+    {
+        return regular_multiply(ctx, bia, bib);
+    }
+
+    return karatsuba(ctx, bia, bib, 0);
+#else
+    return regular_multiply(ctx, bia, bib);
+#endif
+}
+
+#ifdef CONFIG_BIGINT_SQUARE
+/*
+ * Perform the actual square operion. It takes into account overflow.
+ */
+static bigint *regular_square(BI_CTX *ctx, bigint *bi)
+{
+    int t = bi->size;
+    int i = 0, j;
+    bigint *biR = alloc(ctx, t*2);
+    comp *w = biR->comps;
+    comp *x = bi->comps;
+    comp carry;
+
+    memset(w, 0, biR->size*COMP_BYTE_SIZE);
+
+    do
+    {
+        long_comp tmp = w[2*i] + (long_comp)x[i]*x[i];
+        comp u = 0;
+        w[2*i] = (comp)tmp;
+        carry = (comp)(tmp >> COMP_BIT_SIZE);
+
+        for (j = i+1; j < t; j++)
+        {
+            long_comp xx = (long_comp)x[i]*x[j];
+            long_comp xx2 = 2*xx;
+            long_comp blob = (long_comp)w[i+j]+carry;
+
+            if (u)                  /* previous overflow */
+            {
+                blob += COMP_RADIX;
+            }
+
+
+            u = 0;
+            tmp = xx2 + blob;
+
+            /* check for overflow */
+            if ((COMP_MAX-xx) < xx  || (COMP_MAX-xx2) < blob)
+            {
+                u = 1;
+            }
+
+            w[i+j] = (comp)tmp;
+            carry = (comp)(tmp >> COMP_BIT_SIZE);
+        }
+
+        w[i+t] += carry;
+
+        if (u)
+        {
+            w[i+t+1] = 1;   /* add carry */
+        }
+    } while (++i < t);
+
+    bi_free(ctx, bi);
+    return trim(biR);
+}
+
+/**
+ * @brief Perform a square operation on a bigint.
+ * @param ctx [in]  The bigint session context.
+ * @param bia [in]  A bigint.
+ * @return The result of the multiplication.
+ */
+bigint *bi_square(BI_CTX *ctx, bigint *bia)
+{
+    check(bia);
+
+#ifdef CONFIG_BIGINT_KARATSUBA
+    if (bia->size < SQU_KARATSUBA_THRESH) 
+    {
+        return regular_square(ctx, bia);
+    }
+
+    return karatsuba(ctx, bia, NULL, 1);
+#else
+    return regular_square(ctx, bia);
+#endif
+}
+#endif
+
+/**
+ * @brief Compare two bigints.
+ * @param bia [in]  A bigint.
+ * @param bib [in]  Another bigint.
+ * @return -1 if smaller, 1 if larger and 0 if equal.
+ */
+int bi_compare(bigint *bia, bigint *bib)
+{
+    int r, i;
+
+    check(bia);
+    check(bib);
+
+    if (bia->size > bib->size)
+        r = 1;
+    else if (bia->size < bib->size)
+        r = -1;
+    else
+    {
+        comp *a = bia->comps; 
+        comp *b = bib->comps; 
+
+        /* Same number of components.  Compare starting from the high end
+         * and working down. */
+        r = 0;
+        i = bia->size - 1;
+
+        do 
+        {
+            if (a[i] > b[i])
+            { 
+                r = 1;
+                break; 
+            }
+            else if (a[i] < b[i])
+            { 
+                r = -1;
+                break; 
+            }
+        } while (--i >= 0);
+    }
+
+    return r;
+}
+
+/*
+ * Allocate and zero more components.  Does not consume bi. 
+ */
+static void more_comps(bigint *bi, int n)
+{
+    if (n > bi->max_comps)
+    {
+        bi->max_comps = max(bi->max_comps * 2, n);
+        bi->comps = (comp*)realloc(bi->comps, bi->max_comps * COMP_BYTE_SIZE);
+    }
+
+    if (n > bi->size)
+    {
+        memset(&bi->comps[bi->size], 0, (n-bi->size)*COMP_BYTE_SIZE);
+    }
+
+    bi->size = n;
+}
+
+/*
+ * Make a new empty bigint. It may just use an old one if one is available.
+ * Otherwise get one off the heap.
+ */
+static bigint *alloc(BI_CTX *ctx, int size)
+{
+    bigint *biR;
+
+    /* Can we recycle an old bigint? */
+    if (ctx->free_list != NULL)
+    {
+        biR = ctx->free_list;
+        ctx->free_list = biR->next;
+        ctx->free_count--;
+
+        if (biR->refs != 0)
+        {
+#ifdef CONFIG_SSL_FULL_MODE
+            printf("alloc: refs was not 0\n");
+#endif
+            abort();    /* create a stack trace from a core dump */
+        }
+
+        more_comps(biR, size);
+    }
+    else
+    {
+        /* No free bigints available - create a new one. */
+        biR = (bigint *)malloc(sizeof(bigint));
+        biR->comps = (comp*)malloc(size * COMP_BYTE_SIZE);
+        biR->max_comps = size;  /* give some space to spare */
+    }
+
+    biR->size = size;
+    biR->refs = 1;
+    biR->next = NULL;
+    ctx->active_count++;
+    return biR;
+}
+
+/*
+ * Work out the highest '1' bit in an exponent. Used when doing sliding-window
+ * exponentiation.
+ */
+static int find_max_exp_index(bigint *biexp)
+{
+    int i = COMP_BIT_SIZE-1;
+    comp shift = COMP_RADIX/2;
+    comp test = biexp->comps[biexp->size-1];    /* assume no leading zeroes */
+
+    check(biexp);
+
+    do
+    {
+        if (test & shift)
+        {
+            return i+(biexp->size-1)*COMP_BIT_SIZE;
+        }
+
+        shift >>= 1;
+    } while (--i != 0);
+
+    return -1;      /* error - must have been a leading 0 */
+}
+
+/*
+ * Is a particular bit is an exponent 1 or 0? Used when doing sliding-window
+ * exponentiation.
+ */
+static int exp_bit_is_one(bigint *biexp, int offset)
+{
+    comp test = biexp->comps[offset / COMP_BIT_SIZE];
+    int num_shifts = offset % COMP_BIT_SIZE;
+    comp shift = 1;
+    int i;
+
+    check(biexp);
+
+    for (i = 0; i < num_shifts; i++)
+    {
+        shift <<= 1;
+    }
+
+    return test & shift;
+}
+
+#ifdef CONFIG_BIGINT_CHECK_ON
+/*
+ * Perform a sanity check on bi.
+ */
+static void check(const bigint *bi)
+{
+    if (bi->refs <= 0)
+    {
+        printf("check: zero or negative refs in bigint\n");
+        abort();
+    }
+
+    if (bi->next != NULL)
+    {
+        printf("check: attempt to use a bigint from "
+                "the free list\n");
+        abort();
+    }
+}
+#endif
+
+/*
+ * Delete any leading 0's (and allow for 0).
+ */
+static bigint *trim(bigint *bi)
+{
+    check(bi);
+
+    while (bi->comps[bi->size-1] == 0 && bi->size > 1)
+    {
+        bi->size--;
+    }
+
+    return bi;
+}
+
+#if defined(CONFIG_BIGINT_MONTGOMERY)
+/**
+ * @brief Perform a single montgomery reduction.
+ * @param ctx [in]  The bigint session context.
+ * @param bixy [in]  A bigint.
+ * @return The result of the montgomery reduction.
+ */
+bigint *bi_mont(BI_CTX *ctx, bigint *bixy)
+{
+    int i = 0, n;
+    uint8_t mod_offset = ctx->mod_offset;
+    bigint *bim = ctx->bi_mod[mod_offset];
+    comp mod_inv = ctx->N0_dash[mod_offset];
+
+    check(bixy);
+
+    if (ctx->use_classical)     /* just use classical instead */
+    {
+        return bi_mod(ctx, bixy);
+    }
+
+    n = bim->size;
+
+    do
+    {
+        bixy = bi_add(ctx, bixy, comp_left_shift(
+                    bi_int_multiply(ctx, bim, bixy->comps[i]*mod_inv), i));
+    } while (++i < n);
+
+    comp_right_shift(bixy, n);
+
+    if (bi_compare(bixy, bim) >= 0)
+    {
+        bixy = bi_subtract(ctx, bixy, bim, NULL);
+    }
+
+    return bixy;
+}
+
+#elif defined(CONFIG_BIGINT_BARRETT)
+/*
+ * Stomp on the most significant components to give the illusion of a "mod base
+ * radix" operation 
+ */
+static bigint *comp_mod(bigint *bi, int mod)
+{
+    check(bi);
+
+    if (bi->size > mod)
+    {
+        bi->size = mod;
+    }
+
+    return bi;
+}
+
+/*
+ * Barrett reduction has no need for some parts of the product, so ignore bits
+ * of the multiply. This routine gives Barrett its big performance
+ * improvements over Classical/Montgomery reduction methods. 
+ */
+static bigint *partial_multiply(BI_CTX *ctx, bigint *bia, bigint *bib, 
+        int inner_partial, int outer_partial)
+{
+    int i = 0, j, n = bia->size, t = bib->size;
+    bigint *biR;
+    comp carry;
+    comp *sr, *sa, *sb;
+
+    check(bia);
+    check(bib);
+
+    biR = alloc(ctx, n + t);
+    sa = bia->comps;
+    sb = bib->comps;
+    sr = biR->comps;
+
+    if (inner_partial)
+    {
+        memset(sr, 0, inner_partial*COMP_BYTE_SIZE); 
+    }
+    else    /* outer partial */
+    {
+        if (n < outer_partial || t < outer_partial) /* should we bother? */
+        {
+            bi_free(ctx, bia);
+            bi_free(ctx, bib);
+            biR->comps[0] = 0;      /* return 0 */
+            biR->size = 1;
+            return biR;
+        }
+
+        memset(&sr[outer_partial], 0, (n+t-outer_partial)*COMP_BYTE_SIZE);
+    }
+
+    do 
+    {
+        comp *a = sa;
+        comp b = *sb++;
+        long_comp tmp;
+        int i_plus_j = i;
+        carry = 0;
+        j = n;
+
+        if (outer_partial && i_plus_j < outer_partial)
+        {
+            i_plus_j = outer_partial;
+            a = &sa[outer_partial-i];
+            j = n-(outer_partial-i);
+        }
+
+        do
+        {
+            if (inner_partial && i_plus_j >= inner_partial) 
+            {
+                break;
+            }
+
+            tmp = sr[i_plus_j] + ((long_comp)*a++)*b + carry;
+            sr[i_plus_j++] = (comp)tmp;              /* downsize */
+            carry = (comp)(tmp >> COMP_BIT_SIZE);
+        } while (--j != 0);
+
+        sr[i_plus_j] = carry;
+    } while (++i < t);
+
+    bi_free(ctx, bia);
+    bi_free(ctx, bib);
+    return trim(biR);
+}
+
+/**
+ * @brief Perform a single Barrett reduction.
+ * @param ctx [in]  The bigint session context.
+ * @param bi [in]  A bigint.
+ * @return The result of the Barrett reduction.
+ */
+bigint *bi_barrett(BI_CTX *ctx, bigint *bi)
+{
+    bigint *q1, *q2, *q3, *r1, *r2, *r;
+    uint8_t mod_offset = ctx->mod_offset;
+    bigint *bim = ctx->bi_mod[mod_offset];
+    int k = bim->size;
+
+    check(bi);
+    check(bim);
+
+    /* use Classical method instead  - Barrett cannot help here */
+    if (bi->size > k*2)
+    {
+        return bi_mod(ctx, bi);
+    }
+
+    q1 = comp_right_shift(bi_clone(ctx, bi), k-1);
+
+    /* do outer partial multiply */
+    q2 = partial_multiply(ctx, q1, ctx->bi_mu[mod_offset], 0, k-1); 
+    q3 = comp_right_shift(q2, k+1);
+    r1 = comp_mod(bi, k+1);
+
+    /* do inner partial multiply */
+    r2 = comp_mod(partial_multiply(ctx, q3, bim, k+1, 0), k+1);
+    r = bi_subtract(ctx, r1, r2, NULL);
+
+    /* if (r >= m) r = r - m; */
+    if (bi_compare(r, bim) >= 0)
+    {
+        r = bi_subtract(ctx, r, bim, NULL);
+    }
+
+    return r;
+}
+#endif /* CONFIG_BIGINT_BARRETT */
+
+#ifdef CONFIG_BIGINT_SLIDING_WINDOW
+/*
+ * Work out g1, g3, g5, g7... etc for the sliding-window algorithm 
+ */
+static void precompute_slide_window(BI_CTX *ctx, int window, bigint *g1)
+{
+    int k = 1, i;
+    bigint *g2;
+
+    for (i = 0; i < window-1; i++)   /* compute 2^(window-1) */
+    {
+        k <<= 1;
+    }
+
+    ctx->g = (bigint **)malloc(k*sizeof(bigint *));
+    ctx->g[0] = bi_clone(ctx, g1);
+    bi_permanent(ctx->g[0]);
+    g2 = bi_residue(ctx, bi_square(ctx, ctx->g[0]));   /* g^2 */
+
+    for (i = 1; i < k; i++)
+    {
+        ctx->g[i] = bi_residue(ctx, bi_multiply(ctx, ctx->g[i-1], bi_copy(g2)));
+        bi_permanent(ctx->g[i]);
+    }
+
+    bi_free(ctx, g2);
+    ctx->window = k;
+}
+#endif
+
+/**
+ * @brief Perform a modular exponentiation.
+ *
+ * This function requires bi_set_mod() to have been called previously. This is 
+ * one of the optimisations used for performance.
+ * @param ctx [in]  The bigint session context.
+ * @param bi  [in]  The bigint on which to perform the mod power operation.
+ * @param biexp [in] The bigint exponent.
+ * @return The result of the mod exponentiation operation
+ * @see bi_set_mod().
+ */
+bigint *bi_mod_power(BI_CTX *ctx, bigint *bi, bigint *biexp)
+{
+    int i = find_max_exp_index(biexp), j, window_size = 1;
+    bigint *biR = int_to_bi(ctx, 1);
+
+#if defined(CONFIG_BIGINT_MONTGOMERY)
+    uint8_t mod_offset = ctx->mod_offset;
+    if (!ctx->use_classical)
+    {
+        /* preconvert */
+        bi = bi_mont(ctx, 
+                bi_multiply(ctx, bi, ctx->bi_RR_mod_m[mod_offset]));    /* x' */
+        bi_free(ctx, biR);
+        biR = ctx->bi_R_mod_m[mod_offset];                              /* A */
+    }
+#endif
+
+    check(bi);
+    check(biexp);
+
+#ifdef CONFIG_BIGINT_SLIDING_WINDOW
+    for (j = i; j > 32; j /= 5) /* work out an optimum size */
+        window_size++;
+
+    /* work out the slide constants */
+    precompute_slide_window(ctx, window_size, bi);
+#else   /* just one constant */
+    ctx->g = (bigint **)malloc(sizeof(bigint *));
+    ctx->g[0] = bi_clone(ctx, bi);
+    ctx->window = 1;
+    bi_permanent(ctx->g[0]);
+#endif
+
+    /* if sliding-window is off, then only one bit will be done at a time and
+     * will reduce to standard left-to-right exponentiation */
+    do
+    {
+        if (exp_bit_is_one(biexp, i))
+        {
+            int l = i-window_size+1;
+            int part_exp = 0;
+
+            if (l < 0)  /* LSB of exponent will always be 1 */
+                l = 0;
+            else
+            {
+                while (exp_bit_is_one(biexp, l) == 0)
+                    l++;    /* go back up */
+            }
+
+            /* build up the section of the exponent */
+            for (j = i; j >= l; j--)
+            {
+                biR = bi_residue(ctx, bi_square(ctx, biR));
+                if (exp_bit_is_one(biexp, j))
+                    part_exp++;
+
+                if (j != l)
+                    part_exp <<= 1;
+            }
+
+            part_exp = (part_exp-1)/2;  /* adjust for array */
+            biR = bi_residue(ctx, bi_multiply(ctx, biR, ctx->g[part_exp]));
+            i = l-1;
+        }
+        else    /* square it */
+        {
+            biR = bi_residue(ctx, bi_square(ctx, biR));
+            i--;
+        }
+    } while (i >= 0);
+     
+    /* cleanup */
+    for (i = 0; i < ctx->window; i++)
+    {
+        bi_depermanent(ctx->g[i]);
+        bi_free(ctx, ctx->g[i]);
+    }
+
+    free(ctx->g);
+    bi_free(ctx, bi);
+    bi_free(ctx, biexp);
+#if defined CONFIG_BIGINT_MONTGOMERY
+    return ctx->use_classical ? biR : bi_mont(ctx, biR); /* convert back */
+#else /* CONFIG_BIGINT_CLASSICAL or CONFIG_BIGINT_BARRETT */
+    return biR;
+#endif
+}
+
+#ifdef CONFIG_SSL_CERT_VERIFICATION
+/**
+ * @brief Perform a modular exponentiation using a temporary modulus.
+ *
+ * We need this function to check the signatures of certificates. The modulus
+ * of this function is temporary as it's just used for authentication.
+ * @param ctx [in]  The bigint session context.
+ * @param bi  [in]  The bigint to perform the exp/mod.
+ * @param bim [in]  The temporary modulus.
+ * @param biexp [in] The bigint exponent.
+ * @return The result of the mod exponentiation operation
+ * @see bi_set_mod().
+ */
+bigint *bi_mod_power2(BI_CTX *ctx, bigint *bi, bigint *bim, bigint *biexp)
+{
+    bigint *biR, *tmp_biR;
+
+    /* Set up a temporary bigint context and transfer what we need between
+     * them. We need to do this since we want to keep the original modulus
+     * which is already in this context. This operation is only called when
+     * doing peer verification, and so is not expensive :-) */
+    BI_CTX *tmp_ctx = bi_initialize();
+    bi_set_mod(tmp_ctx, bi_clone(tmp_ctx, bim), BIGINT_M_OFFSET);
+    tmp_biR = bi_mod_power(tmp_ctx, 
+                bi_clone(tmp_ctx, bi), 
+                bi_clone(tmp_ctx, biexp));
+    biR = bi_clone(ctx, tmp_biR);
+    bi_free(tmp_ctx, tmp_biR);
+    bi_free_mod(tmp_ctx, BIGINT_M_OFFSET);
+    bi_terminate(tmp_ctx);
+
+    bi_free(ctx, bi);
+    bi_free(ctx, bim);
+    bi_free(ctx, biexp);
+    return biR;
+}
+#endif
+
+#ifdef CONFIG_BIGINT_CRT
+/**
+ * @brief Use the Chinese Remainder Theorem to quickly perform RSA decrypts.
+ *
+ * @param ctx [in]  The bigint session context.
+ * @param bi  [in]  The bigint to perform the exp/mod.
+ * @param dP [in] CRT's dP bigint
+ * @param dQ [in] CRT's dQ bigint
+ * @param p [in] CRT's p bigint
+ * @param q [in] CRT's q bigint
+ * @param qInv [in] CRT's qInv bigint
+ * @return The result of the CRT operation
+ */
+bigint *bi_crt(BI_CTX *ctx, bigint *bi,
+        bigint *dP, bigint *dQ,
+        bigint *p, bigint *q, bigint *qInv)
+{
+    bigint *m1, *m2, *h;
+
+    /* Montgomery has a condition the 0 < x, y < m and these products violate
+     * that condition. So disable Montgomery when using CRT */
+#if defined(CONFIG_BIGINT_MONTGOMERY)
+    ctx->use_classical = 1;
+#endif
+    ctx->mod_offset = BIGINT_P_OFFSET;
+    m1 = bi_mod_power(ctx, bi_copy(bi), dP);
+
+    ctx->mod_offset = BIGINT_Q_OFFSET;
+    m2 = bi_mod_power(ctx, bi, dQ);
+
+    h = bi_subtract(ctx, bi_add(ctx, m1, p), bi_copy(m2), NULL);
+    h = bi_multiply(ctx, h, qInv);
+    ctx->mod_offset = BIGINT_P_OFFSET;
+    h = bi_residue(ctx, h);
+#if defined(CONFIG_BIGINT_MONTGOMERY)
+    ctx->use_classical = 0;         /* reset for any further operation */
+#endif
+    return bi_add(ctx, m2, bi_multiply(ctx, q, h));
+}
+#endif
+/** @} */