/*

 * Copyright 2008-2016 The OpenSSL Project Authors. All Rights Reserved.

 *

 * Licensed under the Apache License 2.0 (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 <string.h>

#include <openssl/crypto.h>

#include "crypto/modes.h"

/*

 * NOTE: the IV/counter CTR mode is big-endian.  The code itself is

 * endian-neutral.

 */

/* increment counter (128-bit int) by 1 */

static void ctr128_inc(unsigned char *counter)

{

    u32 n = 16, c = 1;

    do {

        --n;

        c += counter[n];

        counter[n] = (u8)c;

        c >>= 8;

    } while (n);

}

#if !defined(OPENSSL_SMALL_FOOTPRINT)

static void ctr128_inc_aligned(unsigned char *counter)

{

    size_t *data, c, d, n;

    const union {

        long one;

        char little;

    } is_endian = {

        1

    };

    if (is_endian.little || ((size_t)counter % sizeof(size_t)) != 0) {

        ctr128_inc(counter);

        return;

    }

    data = (size_t *)counter;

    c = 1;

    n = 16 / sizeof(size_t);

    do {

        --n;

        d = data[n] += c;

        /* did addition carry? */

        c = ((d - c) & ~d) >> (sizeof(size_t) * 8 - 1);

    } while (n);

}

#endif

/*

 * The input encrypted as though 128bit counter mode is being used.  The

 * extra state information to record how much of the 128bit block we have

 * used is contained in *num, and the encrypted counter is kept in

 * ecount_buf.  Both *num and ecount_buf must be initialised with zeros

 * before the first call to CRYPTO_ctr128_encrypt(). This algorithm assumes

 * that the counter is in the x lower bits of the IV (ivec), and that the

 * application has full control over overflow and the rest of the IV.  This

 * implementation takes NO responsibility for checking that the counter

 * doesn't overflow into the rest of the IV when incremented.

 */

void CRYPTO_ctr128_encrypt(const unsigned char *in, unsigned char *out,

                           size_t len, const void *key,

                           unsigned char ivec[16],

                           unsigned char ecount_buf[16], unsigned int *num,

                           block128_f block)

{

    unsigned int n;

    size_t l = 0;

    n = *num;

#if !defined(OPENSSL_SMALL_FOOTPRINT)

    if (16 % sizeof(size_t) == 0) { /* always true actually */

        do {

            while (n && len) {

                *(out++) = *(in++) ^ ecount_buf[n];

                --len;

                n = (n + 1) % 16;

            }

# if defined(STRICT_ALIGNMENT)

            if (((size_t)in | (size_t)out | (size_t)ecount_buf)

                % sizeof(size_t) != 0)

                break;

# endif

            while (len >= 16) {

                (*block) (ivec, ecount_buf, key);

                ctr128_inc_aligned(ivec);

                for (n = 0; n < 16; n += sizeof(size_t))

                    *(size_t *)(out + n) =

                        *(size_t *)(in + n) ^ *(size_t *)(ecount_buf + n);

                len -= 16;

                out += 16;

                in += 16;

                n = 0;

            }

            if (len) {

                (*block) (ivec, ecount_buf, key);

                ctr128_inc_aligned(ivec);

                while (len--) {

                    out[n] = in[n] ^ ecount_buf[n];

                    ++n;

                }

            }

            *num = n;

            return;

        } while (0);

    }

    /* the rest would be commonly eliminated by x86* compiler */

#endif

    while (l < len) {

        if (n == 0) {

            (*block) (ivec, ecount_buf, key);

            ctr128_inc(ivec);

        }

        out[l] = in[l] ^ ecount_buf[n];

        ++l;

        n = (n + 1) % 16;

    }

    *num = n;

}

/* increment upper 96 bits of 128-bit counter by 1 */

static void ctr96_inc(unsigned char *counter)

{

    u32 n = 12, c = 1;

    do {

        --n;

        c += counter[n];

        counter[n] = (u8)c;

        c >>= 8;

    } while (n);

}

void CRYPTO_ctr128_encrypt_ctr32(const unsigned char *in, unsigned char *out,

                                 size_t len, const void *key,

                                 unsigned char ivec[16],

                                 unsigned char ecount_buf[16],

                                 unsigned int *num, ctr128_f func)

{

    unsigned int n, ctr32;

    n = *num;

    while (n && len) {

        *(out++) = *(in++) ^ ecount_buf[n];

        --len;

        n = (n + 1) % 16;

    }

    ctr32 = GETU32(ivec + 12);

    while (len >= 16) {

        size_t blocks = len / 16;

        /*

         * 1<<28 is just a not-so-small yet not-so-large number...

         * Below condition is practically never met, but it has to

         * be checked for code correctness.

         */

        if (sizeof(size_t) > sizeof(unsigned int) && blocks > (1U << 28))

            blocks = (1U << 28);

        /*

         * As (*func) operates on 32-bit counter, caller

         * has to handle overflow. 'if' below detects the

         * overflow, which is then handled by limiting the

         * amount of blocks to the exact overflow point...

         */

        ctr32 += (u32)blocks;

        if (ctr32 < blocks) {

            blocks -= ctr32;

            ctr32 = 0;

        }

        (*func) (in, out, blocks, key, ivec);

        /* (*ctr) does not update ivec, caller does: */

        PUTU32(ivec + 12, ctr32);

        /* ... overflow was detected, propagate carry. */

        if (ctr32 == 0)

            ctr96_inc(ivec);

        blocks *= 16;

        len -= blocks;

        out += blocks;

        in += blocks;

    }

    if (len) {

        memset(ecount_buf, 0, 16);

        (*func) (ecount_buf, ecount_buf, 1, key, ivec);

        ++ctr32;

        PUTU32(ivec + 12, ctr32);

        if (ctr32 == 0)

            ctr96_inc(ivec);

        while (len--) {

            out[n] = in[n] ^ ecount_buf[n];

            ++n;

        }

    }

    *num = n;

}