/*

 * Copyright 2002-2018 The OpenSSL Project Authors. All Rights Reserved.

 * Copyright (c) 2002, Oracle and/or its affiliates. All rights reserved

 *

 * Licensed under the OpenSSL license (the "License").  You may not use

 * this file except in compliance with the License.  You can obtain a copy

 * in the file LICENSE in the source distribution or at

 * https://www.openssl.org/source/license.html

 */

#include <assert.h>

#include <limits.h>

#include <stdio.h>

#include "internal/cryptlib.h"

#include "bn_lcl.h"

#ifndef OPENSSL_NO_EC2M

/*

 * Maximum number of iterations before BN_GF2m_mod_solve_quad_arr should

 * fail.

 */

# define MAX_ITERATIONS 50

# define SQR_nibble(w)   ((((w) & 8) << 3) \

                       |  (((w) & 4) << 2) \

                       |  (((w) & 2) << 1) \

                       |   ((w) & 1))

/* Platform-specific macros to accelerate squaring. */

# if defined(SIXTY_FOUR_BIT) || defined(SIXTY_FOUR_BIT_LONG)

#  define SQR1(w) \

    SQR_nibble((w) >> 60) << 56 | SQR_nibble((w) >> 56) << 48 | \

    SQR_nibble((w) >> 52) << 40 | SQR_nibble((w) >> 48) << 32 | \

    SQR_nibble((w) >> 44) << 24 | SQR_nibble((w) >> 40) << 16 | \

    SQR_nibble((w) >> 36) <<  8 | SQR_nibble((w) >> 32)

#  define SQR0(w) \

    SQR_nibble((w) >> 28) << 56 | SQR_nibble((w) >> 24) << 48 | \

    SQR_nibble((w) >> 20) << 40 | SQR_nibble((w) >> 16) << 32 | \

    SQR_nibble((w) >> 12) << 24 | SQR_nibble((w) >>  8) << 16 | \

    SQR_nibble((w) >>  4) <<  8 | SQR_nibble((w)      )

# endif

# ifdef THIRTY_TWO_BIT

#  define SQR1(w) \

    SQR_nibble((w) >> 28) << 24 | SQR_nibble((w) >> 24) << 16 | \

    SQR_nibble((w) >> 20) <<  8 | SQR_nibble((w) >> 16)

#  define SQR0(w) \

    SQR_nibble((w) >> 12) << 24 | SQR_nibble((w) >>  8) << 16 | \

    SQR_nibble((w) >>  4) <<  8 | SQR_nibble((w)      )

# endif

# if !defined(OPENSSL_BN_ASM_GF2m)

/*

 * Product of two polynomials a, b each with degree < BN_BITS2 - 1, result is

 * a polynomial r with degree < 2 * BN_BITS - 1 The caller MUST ensure that

 * the variables have the right amount of space allocated.

 */

#  ifdef THIRTY_TWO_BIT

static void bn_GF2m_mul_1x1(BN_ULONG *r1, BN_ULONG *r0, const BN_ULONG a,

                            const BN_ULONG b)

{

    register BN_ULONG h, l, s;

    BN_ULONG tab[8], top2b = a >> 30;

    register BN_ULONG a1, a2, a4;

    a1 = a & (0x3FFFFFFF);

    a2 = a1 << 1;

    a4 = a2 << 1;

    tab[0] = 0;

    tab[1] = a1;

    tab[2] = a2;

    tab[3] = a1 ^ a2;

    tab[4] = a4;

    tab[5] = a1 ^ a4;

    tab[6] = a2 ^ a4;

    tab[7] = a1 ^ a2 ^ a4;

    s = tab[b & 0x7];

    l = s;

    s = tab[b >> 3 & 0x7];

    l ^= s << 3;

    h = s >> 29;

    s = tab[b >> 6 & 0x7];

    l ^= s << 6;

    h ^= s >> 26;

    s = tab[b >> 9 & 0x7];

    l ^= s << 9;

    h ^= s >> 23;

    s = tab[b >> 12 & 0x7];

    l ^= s << 12;

    h ^= s >> 20;

    s = tab[b >> 15 & 0x7];

    l ^= s << 15;

    h ^= s >> 17;

    s = tab[b >> 18 & 0x7];

    l ^= s << 18;

    h ^= s >> 14;

    s = tab[b >> 21 & 0x7];

    l ^= s << 21;

    h ^= s >> 11;

    s = tab[b >> 24 & 0x7];

    l ^= s << 24;

    h ^= s >> 8;

    s = tab[b >> 27 & 0x7];

    l ^= s << 27;

    h ^= s >> 5;

    s = tab[b >> 30];

    l ^= s << 30;

    h ^= s >> 2;

    /* compensate for the top two bits of a */

    if (top2b & 01) {

        l ^= b << 30;

        h ^= b >> 2;

    }

    if (top2b & 02) {

        l ^= b << 31;

        h ^= b >> 1;

    }

    *r1 = h;

    *r0 = l;

}

#  endif

#  if defined(SIXTY_FOUR_BIT) || defined(SIXTY_FOUR_BIT_LONG)

static void bn_GF2m_mul_1x1(BN_ULONG *r1, BN_ULONG *r0, const BN_ULONG a,

                            const BN_ULONG b)

{

    register BN_ULONG h, l, s;

    BN_ULONG tab[16], top3b = a >> 61;

    register BN_ULONG a1, a2, a4, a8;

    a1 = a & (0x1FFFFFFFFFFFFFFFULL);

    a2 = a1 << 1;

    a4 = a2 << 1;

    a8 = a4 << 1;

    tab[0] = 0;

    tab[1] = a1;

    tab[2] = a2;

    tab[3] = a1 ^ a2;

    tab[4] = a4;

    tab[5] = a1 ^ a4;

    tab[6] = a2 ^ a4;

    tab[7] = a1 ^ a2 ^ a4;

    tab[8] = a8;

    tab[9] = a1 ^ a8;

    tab[10] = a2 ^ a8;

    tab[11] = a1 ^ a2 ^ a8;

    tab[12] = a4 ^ a8;

    tab[13] = a1 ^ a4 ^ a8;

    tab[14] = a2 ^ a4 ^ a8;

    tab[15] = a1 ^ a2 ^ a4 ^ a8;

    s = tab[b & 0xF];

    l = s;

    s = tab[b >> 4 & 0xF];

    l ^= s << 4;

    h = s >> 60;

    s = tab[b >> 8 & 0xF];

    l ^= s << 8;

    h ^= s >> 56;

    s = tab[b >> 12 & 0xF];

    l ^= s << 12;

    h ^= s >> 52;

    s = tab[b >> 16 & 0xF];

    l ^= s << 16;

    h ^= s >> 48;

    s = tab[b >> 20 & 0xF];

    l ^= s << 20;

    h ^= s >> 44;

    s = tab[b >> 24 & 0xF];

    l ^= s << 24;

    h ^= s >> 40;

    s = tab[b >> 28 & 0xF];

    l ^= s << 28;

    h ^= s >> 36;

    s = tab[b >> 32 & 0xF];

    l ^= s << 32;

    h ^= s >> 32;

    s = tab[b >> 36 & 0xF];

    l ^= s << 36;

    h ^= s >> 28;

    s = tab[b >> 40 & 0xF];

    l ^= s << 40;

    h ^= s >> 24;

    s = tab[b >> 44 & 0xF];

    l ^= s << 44;

    h ^= s >> 20;

    s = tab[b >> 48 & 0xF];

    l ^= s << 48;

    h ^= s >> 16;

    s = tab[b >> 52 & 0xF];

    l ^= s << 52;

    h ^= s >> 12;

    s = tab[b >> 56 & 0xF];

    l ^= s << 56;

    h ^= s >> 8;

    s = tab[b >> 60];

    l ^= s << 60;

    h ^= s >> 4;

    /* compensate for the top three bits of a */

    if (top3b & 01) {

        l ^= b << 61;

        h ^= b >> 3;

    }

    if (top3b & 02) {

        l ^= b << 62;

        h ^= b >> 2;

    }

    if (top3b & 04) {

        l ^= b << 63;

        h ^= b >> 1;

    }

    *r1 = h;

    *r0 = l;

}

#  endif

/*

 * Product of two polynomials a, b each with degree < 2 * BN_BITS2 - 1,

 * result is a polynomial r with degree < 4 * BN_BITS2 - 1 The caller MUST

 * ensure that the variables have the right amount of space allocated.

 */

static void bn_GF2m_mul_2x2(BN_ULONG *r, const BN_ULONG a1, const BN_ULONG a0,

                            const BN_ULONG b1, const BN_ULONG b0)

{

    BN_ULONG m1, m0;

    /* r[3] = h1, r[2] = h0; r[1] = l1; r[0] = l0 */

    bn_GF2m_mul_1x1(r + 3, r + 2, a1, b1);

    bn_GF2m_mul_1x1(r + 1, r, a0, b0);

    bn_GF2m_mul_1x1(&m1, &m0, a0 ^ a1, b0 ^ b1);

    /* Correction on m1 ^= l1 ^ h1; m0 ^= l0 ^ h0; */

    r[2] ^= m1 ^ r[1] ^ r[3];   /* h0 ^= m1 ^ l1 ^ h1; */

    r[1] = r[3] ^ r[2] ^ r[0] ^ m1 ^ m0; /* l1 ^= l0 ^ h0 ^ m0; */

}

# else

void bn_GF2m_mul_2x2(BN_ULONG *r, BN_ULONG a1, BN_ULONG a0, BN_ULONG b1,

                     BN_ULONG b0);

# endif

/*

 * Add polynomials a and b and store result in r; r could be a or b, a and b

 * could be equal; r is the bitwise XOR of a and b.

 */

int BN_GF2m_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)

{

    int i;

    const BIGNUM *at, *bt;

    bn_check_top(a);

    bn_check_top(b);

    if (a->top < b->top) {

        at = b;

        bt = a;

    } else {

        at = a;

        bt = b;

    }

    if (bn_wexpand(r, at->top) == NULL)

        return 0;

    for (i = 0; i < bt->top; i++) {

        r->d[i] = at->d[i] ^ bt->d[i];

    }

    for (; i < at->top; i++) {

        r->d[i] = at->d[i];

    }

    r->top = at->top;

    bn_correct_top(r);

    return 1;

}

/*-

 * Some functions allow for representation of the irreducible polynomials

 * as an int[], say p.  The irreducible f(t) is then of the form:

 *     t^p[0] + t^p[1] + ... + t^p[k]

 * where m = p[0] > p[1] > ... > p[k] = 0.

 */

/* Performs modular reduction of a and store result in r.  r could be a. */

int BN_GF2m_mod_arr(BIGNUM *r, const BIGNUM *a, const int p[])

{

    int j, k;

    int n, dN, d0, d1;

    BN_ULONG zz, *z;

    bn_check_top(a);

    if (!p[0]) {

        /* reduction mod 1 => return 0 */

        BN_zero(r);

        return 1;

    }

    /*

     * Since the algorithm does reduction in the r value, if a != r, copy the

     * contents of a into r so we can do reduction in r.

     */

    if (a != r) {

        if (!bn_wexpand(r, a->top))

            return 0;

        for (j = 0; j < a->top; j++) {

            r->d[j] = a->d[j];

        }

        r->top = a->top;

    }

    z = r->d;

    /* start reduction */

    dN = p[0] / BN_BITS2;

    for (j = r->top - 1; j > dN;) {

        zz = z[j];

        if (z[j] == 0) {

            j--;

            continue;

        }

        z[j] = 0;

        for (k = 1; p[k] != 0; k++) {

            /* reducing component t^p[k] */

            n = p[0] - p[k];

            d0 = n % BN_BITS2;

            d1 = BN_BITS2 - d0;

            n /= BN_BITS2;

            z[j - n] ^= (zz >> d0);

            if (d0)

                z[j - n - 1] ^= (zz << d1);

        }

        /* reducing component t^0 */

        n = dN;

        d0 = p[0] % BN_BITS2;

        d1 = BN_BITS2 - d0;

        z[j - n] ^= (zz >> d0);

        if (d0)

            z[j - n - 1] ^= (zz << d1);

    }

    /* final round of reduction */

    while (j == dN) {

        d0 = p[0] % BN_BITS2;

        zz = z[dN] >> d0;

        if (zz == 0)

            break;

        d1 = BN_BITS2 - d0;

        /* clear up the top d1 bits */

        if (d0)

            z[dN] = (z[dN] << d1) >> d1;

        else

            z[dN] = 0;

        z[0] ^= zz;             /* reduction t^0 component */

        for (k = 1; p[k] != 0; k++) {

            BN_ULONG tmp_ulong;

            /* reducing component t^p[k] */

            n = p[k] / BN_BITS2;

            d0 = p[k] % BN_BITS2;

            d1 = BN_BITS2 - d0;

            z[n] ^= (zz << d0);

            if (d0 && (tmp_ulong = zz >> d1))

                z[n + 1] ^= tmp_ulong;

        }

    }

    bn_correct_top(r);

    return 1;

}

/*

 * Performs modular reduction of a by p and store result in r.  r could be a.

 * This function calls down to the BN_GF2m_mod_arr implementation; this wrapper

 * function is only provided for convenience; for best performance, use the

 * BN_GF2m_mod_arr function.

 */

int BN_GF2m_mod(BIGNUM *r, const BIGNUM *a, const BIGNUM *p)

{

    int ret = 0;

    int arr[6];

    bn_check_top(a);

    bn_check_top(p);

    ret = BN_GF2m_poly2arr(p, arr, OSSL_NELEM(arr));

    if (!ret || ret > (int)OSSL_NELEM(arr)) {

        BNerr(BN_F_BN_GF2M_MOD, BN_R_INVALID_LENGTH);

        return 0;

    }

    ret = BN_GF2m_mod_arr(r, a, arr);

    bn_check_top(r);

    return ret;

}

/*

 * Compute the product of two polynomials a and b, reduce modulo p, and store

 * the result in r.  r could be a or b; a could be b.

 */

int BN_GF2m_mod_mul_arr(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,

                        const int p[], BN_CTX *ctx)

{

    int zlen, i, j, k, ret = 0;

    BIGNUM *s;

    BN_ULONG x1, x0, y1, y0, zz[4];

    bn_check_top(a);

    bn_check_top(b);

    if (a == b) {

        return BN_GF2m_mod_sqr_arr(r, a, p, ctx);

    }

    BN_CTX_start(ctx);

    if ((s = BN_CTX_get(ctx)) == NULL)

        goto err;

    zlen = a->top + b->top + 4;

    if (!bn_wexpand(s, zlen))

        goto err;

    s->top = zlen;

    for (i = 0; i < zlen; i++)

        s->d[i] = 0;

    for (j = 0; j < b->top; j += 2) {

        y0 = b->d[j];

        y1 = ((j + 1) == b->top) ? 0 : b->d[j + 1];

        for (i = 0; i < a->top; i += 2) {

            x0 = a->d[i];

            x1 = ((i + 1) == a->top) ? 0 : a->d[i + 1];

            bn_GF2m_mul_2x2(zz, x1, x0, y1, y0);

            for (k = 0; k < 4; k++)

                s->d[i + j + k] ^= zz[k];

        }

    }

    bn_correct_top(s);

    if (BN_GF2m_mod_arr(r, s, p))

        ret = 1;

    bn_check_top(r);

 err:

    BN_CTX_end(ctx);

    return ret;

}

/*

 * Compute the product of two polynomials a and b, reduce modulo p, and store

 * the result in r.  r could be a or b; a could equal b. This function calls

 * down to the BN_GF2m_mod_mul_arr implementation; this wrapper function is

 * only provided for convenience; for best performance, use the

 * BN_GF2m_mod_mul_arr function.

 */

int BN_GF2m_mod_mul(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,

                    const BIGNUM *p, BN_CTX *ctx)

{

    int ret = 0;

    const int max = BN_num_bits(p) + 1;

    int *arr = NULL;

    bn_check_top(a);

    bn_check_top(b);

    bn_check_top(p);

    if ((arr = OPENSSL_malloc(sizeof(*arr) * max)) == NULL)

        goto err;

    ret = BN_GF2m_poly2arr(p, arr, max);

    if (!ret || ret > max) {

        BNerr(BN_F_BN_GF2M_MOD_MUL, BN_R_INVALID_LENGTH);

        goto err;

    }

    ret = BN_GF2m_mod_mul_arr(r, a, b, arr, ctx);

    bn_check_top(r);

 err:

    OPENSSL_free(arr);

    return ret;

}

/* Square a, reduce the result mod p, and store it in a.  r could be a. */

int BN_GF2m_mod_sqr_arr(BIGNUM *r, const BIGNUM *a, const int p[],

                        BN_CTX *ctx)

{

    int i, ret = 0;

    BIGNUM *s;

    bn_check_top(a);

    BN_CTX_start(ctx);

    if ((s = BN_CTX_get(ctx)) == NULL)

        goto err;

    if (!bn_wexpand(s, 2 * a->top))

        goto err;

    for (i = a->top - 1; i >= 0; i--) {

        s->d[2 * i + 1] = SQR1(a->d[i]);

        s->d[2 * i] = SQR0(a->d[i]);

    }

    s->top = 2 * a->top;

    bn_correct_top(s);

    if (!BN_GF2m_mod_arr(r, s, p))

        goto err;

    bn_check_top(r);

    ret = 1;

 err:

    BN_CTX_end(ctx);

    return ret;

}

/*

 * Square a, reduce the result mod p, and store it in a.  r could be a. This

 * function calls down to the BN_GF2m_mod_sqr_arr implementation; this

 * wrapper function is only provided for convenience; for best performance,

 * use the BN_GF2m_mod_sqr_arr function.

 */

int BN_GF2m_mod_sqr(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)

{

    int ret = 0;

    const int max = BN_num_bits(p) + 1;

    int *arr = NULL;

    bn_check_top(a);

    bn_check_top(p);

    if ((arr = OPENSSL_malloc(sizeof(*arr) * max)) == NULL)

        goto err;

    ret = BN_GF2m_poly2arr(p, arr, max);

    if (!ret || ret > max) {

        BNerr(BN_F_BN_GF2M_MOD_SQR, BN_R_INVALID_LENGTH);

        goto err;

    }

    ret = BN_GF2m_mod_sqr_arr(r, a, arr, ctx);

    bn_check_top(r);

 err:

    OPENSSL_free(arr);

    return ret;

}

/*

 * Invert a, reduce modulo p, and store the result in r. r could be a. Uses

 * Modified Almost Inverse Algorithm (Algorithm 10) from Hankerson, D.,

 * Hernandez, J.L., and Menezes, A.  "Software Implementation of Elliptic

 * Curve Cryptography Over Binary Fields".

 */

static int BN_GF2m_mod_inv_vartime(BIGNUM *r, const BIGNUM *a,

                                   const BIGNUM *p, BN_CTX *ctx)

{

    BIGNUM *b, *c = NULL, *u = NULL, *v = NULL, *tmp;

    int ret = 0;

    bn_check_top(a);

    bn_check_top(p);

    BN_CTX_start(ctx);

    b = BN_CTX_get(ctx);

    c = BN_CTX_get(ctx);

    u = BN_CTX_get(ctx);

    v = BN_CTX_get(ctx);

    if (v == NULL)

        goto err;

    if (!BN_GF2m_mod(u, a, p))

        goto err;

    if (BN_is_zero(u))

        goto err;

    if (!BN_copy(v, p))

        goto err;

# if 0

    if (!BN_one(b))

        goto err;

    while (1) {

        while (!BN_is_odd(u)) {

            if (BN_is_zero(u))

                goto err;

            if (!BN_rshift1(u, u))

                goto err;

            if (BN_is_odd(b)) {

                if (!BN_GF2m_add(b, b, p))

                    goto err;

            }

            if (!BN_rshift1(b, b))

                goto err;

        }

        if (BN_abs_is_word(u, 1))

            break;

        if (BN_num_bits(u) < BN_num_bits(v)) {

            tmp = u;

            u = v;

            v = tmp;

            tmp = b;

            b = c;

            c = tmp;

        }

        if (!BN_GF2m_add(u, u, v))

            goto err;

        if (!BN_GF2m_add(b, b, c))

            goto err;

    }

# else

    {

        int i;

        int ubits = BN_num_bits(u);

        int vbits = BN_num_bits(v); /* v is copy of p */

        int top = p->top;

        BN_ULONG *udp, *bdp, *vdp, *cdp;

        if (!bn_wexpand(u, top))

            goto err;

        udp = u->d;

        for (i = u->top; i < top; i++)

            udp[i] = 0;

        u->top = top;

        if (!bn_wexpand(b, top))

          goto err;

        bdp = b->d;

        bdp[0] = 1;

        for (i = 1; i < top; i++)

            bdp[i] = 0;

        b->top = top;

        if (!bn_wexpand(c, top))

          goto err;

        cdp = c->d;

        for (i = 0; i < top; i++)

            cdp[i] = 0;

        c->top = top;

        vdp = v->d;             /* It pays off to "cache" *->d pointers,

                                 * because it allows optimizer to be more

                                 * aggressive. But we don't have to "cache"

                                 * p->d, because *p is declared 'const'... */

        while (1) {

            while (ubits && !(udp[0] & 1)) {

                BN_ULONG u0, u1, b0, b1, mask;

                u0 = udp[0];

                b0 = bdp[0];

                mask = (BN_ULONG)0 - (b0 & 1);

                b0 ^= p->d[0] & mask;

                for (i = 0; i < top - 1; i++) {

                    u1 = udp[i + 1];

                    udp[i] = ((u0 >> 1) | (u1 << (BN_BITS2 - 1))) & BN_MASK2;

                    u0 = u1;

                    b1 = bdp[i + 1] ^ (p->d[i + 1] & mask);

                    bdp[i] = ((b0 >> 1) | (b1 << (BN_BITS2 - 1))) & BN_MASK2;

                    b0 = b1;

                }

                udp[i] = u0 >> 1;

                bdp[i] = b0 >> 1;

                ubits--;

            }

            if (ubits <= BN_BITS2) {

                if (udp[0] == 0) /* poly was reducible */

                    goto err;

                if (udp[0] == 1)

                    break;

            }

            if (ubits < vbits) {

                i = ubits;

                ubits = vbits;

                vbits = i;

                tmp = u;

                u = v;

                v = tmp;

                tmp = b;

                b = c;

                c = tmp;

                udp = vdp;

                vdp = v->d;

                bdp = cdp;

                cdp = c->d;

            }

            for (i = 0; i < top; i++) {

                udp[i] ^= vdp[i];

                bdp[i] ^= cdp[i];

            }

            if (ubits == vbits) {

                BN_ULONG ul;

                int utop = (ubits - 1) / BN_BITS2;

                while ((ul = udp[utop]) == 0 && utop)

                    utop--;

                ubits = utop * BN_BITS2 + BN_num_bits_word(ul);

            }

        }

        bn_correct_top(b);

    }

# endif

    if (!BN_copy(r, b))

        goto err;

    bn_check_top(r);

    ret = 1;

 err:

# ifdef BN_DEBUG                /* BN_CTX_end would complain about the

                                 * expanded form */

    bn_correct_top(c);

    bn_correct_top(u);

    bn_correct_top(v);

# endif

    BN_CTX_end(ctx);

    return ret;

}

/*-

 * Wrapper for BN_GF2m_mod_inv_vartime that blinds the input before calling.

 * This is not constant time.

 * But it does eliminate first order deduction on the input.

 */

int BN_GF2m_mod_inv(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)

{

    BIGNUM *b = NULL;

    int ret = 0;

    BN_CTX_start(ctx);

    if ((b = BN_CTX_get(ctx)) == NULL)

        goto err;

    /* generate blinding value */

    do {

        if (!BN_priv_rand(b, BN_num_bits(p) - 1,

                          BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY))

            goto err;

    } while (BN_is_zero(b));

    /* r := a * b */

    if (!BN_GF2m_mod_mul(r, a, b, p, ctx))

        goto err;

    /* r := 1/(a * b) */

    if (!BN_GF2m_mod_inv_vartime(r, r, p, ctx))

        goto err;

    /* r := b/(a * b) = 1/a */

    if (!BN_GF2m_mod_mul(r, r, b, p, ctx))

        goto err;

    ret = 1;

 err:

    BN_CTX_end(ctx);

    return ret;

}

/*

 * Invert xx, reduce modulo p, and store the result in r. r could be xx.

 * This function calls down to the BN_GF2m_mod_inv implementation; this

 * wrapper function is only provided for convenience; for best performance,

 * use the BN_GF2m_mod_inv function.

 */

int BN_GF2m_mod_inv_arr(BIGNUM *r, const BIGNUM *xx, const int p[],

                        BN_CTX *ctx)

{

    BIGNUM *field;

    int ret = 0;

    bn_check_top(xx);

    BN_CTX_start(ctx);

    if ((field = BN_CTX_get(ctx)) == NULL)

        goto err;

    if (!BN_GF2m_arr2poly(p, field))

        goto err;

    ret = BN_GF2m_mod_inv(r, xx, field, ctx);

    bn_check_top(r);

 err:

    BN_CTX_end(ctx);

    return ret;

}

/*

 * Divide y by x, reduce modulo p, and store the result in r. r could be x

 * or y, x could equal y.

 */

int BN_GF2m_mod_div(BIGNUM *r, const BIGNUM *y, const BIGNUM *x,

                    const BIGNUM *p, BN_CTX *ctx)

{

    BIGNUM *xinv = NULL;

    int ret = 0;

    bn_check_top(y);

    bn_check_top(x);

    bn_check_top(p);

    BN_CTX_start(ctx);

    xinv = BN_CTX_get(ctx);

    if (xinv == NULL)

        goto err;

    if (!BN_GF2m_mod_inv(xinv, x, p, ctx))

        goto err;

    if (!BN_GF2m_mod_mul(r, y, xinv, p, ctx))

        goto err;

    bn_check_top(r);

    ret = 1;

 err:

    BN_CTX_end(ctx);

    return ret;

}

/*

 * Divide yy by xx, reduce modulo p, and store the result in r. r could be xx

 * * or yy, xx could equal yy. This function calls down to the

 * BN_GF2m_mod_div implementation; this wrapper function is only provided for

 * convenience; for best performance, use the BN_GF2m_mod_div function.

 */

int BN_GF2m_mod_div_arr(BIGNUM *r, const BIGNUM *yy, const BIGNUM *xx,

                        const int p[], BN_CTX *ctx)

{

    BIGNUM *field;

    int ret = 0;

    bn_check_top(yy);

    bn_check_top(xx);

    BN_CTX_start(ctx);

    if ((field = BN_CTX_get(ctx)) == NULL)

        goto err;

    if (!BN_GF2m_arr2poly(p, field))

        goto err;

    ret = BN_GF2m_mod_div(r, yy, xx, field, ctx);

    bn_check_top(r);

 err:

    BN_CTX_end(ctx);

    return ret;

}

/*

 * Compute the bth power of a, reduce modulo p, and store the result in r.  r

 * could be a. Uses simple square-and-multiply algorithm A.5.1 from IEEE

 * P1363.

 */

int BN_GF2m_mod_exp_arr(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,

                        const int p[], BN_CTX *ctx)

{

    int ret = 0, i, n;

    BIGNUM *u;

    bn_check_top(a);

    bn_check_top(b);

    if (BN_is_zero(b))

        return BN_one(r);

    if (BN_abs_is_word(b, 1))

        return (BN_copy(r, a) != NULL);

    BN_CTX_start(ctx);

    if ((u = BN_CTX_get(ctx)) == NULL)

        goto err;

    if (!BN_GF2m_mod_arr(u, a, p))

        goto err;

    n = BN_num_bits(b) - 1;

    for (i = n - 1; i >= 0; i--) {

        if (!BN_GF2m_mod_sqr_arr(u, u, p, ctx))

            goto err;

        if (BN_is_bit_set(b, i)) {

            if (!BN_GF2m_mod_mul_arr(u, u, a, p, ctx))

                goto err;

        }

    }

    if (!BN_copy(r, u))

        goto err;

    bn_check_top(r);

    ret = 1;

 err:

    BN_CTX_end(ctx);

    return ret;

}

/*

 * Compute the bth power of a, reduce modulo p, and store the result in r.  r

 * could be a. This function calls down to the BN_GF2m_mod_exp_arr

 * implementation; this wrapper function is only provided for convenience;

 * for best performance, use the BN_GF2m_mod_exp_arr function.

 */

int BN_GF2m_mod_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,

                    const BIGNUM *p, BN_CTX *ctx)

{

    int ret = 0;

    const int max = BN_num_bits(p) + 1;

    int *arr = NULL;

    bn_check_top(a);

    bn_check_top(b);

    bn_check_top(p);

    if ((arr = OPENSSL_malloc(sizeof(*arr) * max)) == NULL)

        goto err;

    ret = BN_GF2m_poly2arr(p, arr, max);

    if (!ret || ret > max) {

        BNerr(BN_F_BN_GF2M_MOD_EXP, BN_R_INVALID_LENGTH);

        goto err;

    }

    ret = BN_GF2m_mod_exp_arr(r, a, b, arr, ctx);

    bn_check_top(r);

 err:

    OPENSSL_free(arr);

    return ret;

}

/*

 * Compute the square root of a, reduce modulo p, and store the result in r.