/*

 * Copyright 2015-2016 The OpenSSL Project Authors. 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

 */

/* Adapted from the public domain code by D. Bernstein from SUPERCOP. */

#include <string.h>

#include "crypto/chacha.h"

#include "crypto/ctype.h"

typedef unsigned int u32;

typedef unsigned char u8;

typedef union {

    u32 u[16];

    u8 c[64];

} chacha_buf;

# define ROTATE(v, n) (((v) << (n)) | ((v) >> (32 - (n))))

# define U32TO8_LITTLE(p, v) do { \

                                (p)[0] = (u8)(v >>  0); \

                                (p)[1] = (u8)(v >>  8); \

                                (p)[2] = (u8)(v >> 16); \

                                (p)[3] = (u8)(v >> 24); \

                                } while(0)

/* QUARTERROUND updates a, b, c, d with a ChaCha "quarter" round. */

# define QUARTERROUND(a,b,c,d) ( \

                x[a] += x[b], x[d] = ROTATE((x[d] ^ x[a]),16), \

                x[c] += x[d], x[b] = ROTATE((x[b] ^ x[c]),12), \

                x[a] += x[b], x[d] = ROTATE((x[d] ^ x[a]), 8), \

                x[c] += x[d], x[b] = ROTATE((x[b] ^ x[c]), 7)  )

/* chacha_core performs 20 rounds of ChaCha on the input words in

 * |input| and writes the 64 output bytes to |output|. */

static void chacha20_core(chacha_buf *output, const u32 input[16])

{

    u32 x[16];

    int i;

    const union {

        long one;

        char little;

    } is_endian = { 1 };

    memcpy(x, input, sizeof(x));

    for (i = 20; i > 0; i -= 2) {

        QUARTERROUND(0, 4, 8, 12);

        QUARTERROUND(1, 5, 9, 13);

        QUARTERROUND(2, 6, 10, 14);

        QUARTERROUND(3, 7, 11, 15);

        QUARTERROUND(0, 5, 10, 15);

        QUARTERROUND(1, 6, 11, 12);

        QUARTERROUND(2, 7, 8, 13);

        QUARTERROUND(3, 4, 9, 14);

    }

    if (is_endian.little) {

        for (i = 0; i < 16; ++i)

            output->u[i] = x[i] + input[i];

    } else {

        for (i = 0; i < 16; ++i)

            U32TO8_LITTLE(output->c + 4 * i, (x[i] + input[i]));

    }

}

void ChaCha20_ctr32(unsigned char *out, const unsigned char *inp,

                    size_t len, const unsigned int key[8],

                    const unsigned int counter[4])

{

    u32 input[16];

    chacha_buf buf;

    size_t todo, i;

    /* sigma constant "expand 32-byte k" in little-endian encoding */

    input[0] = ((u32)ossl_toascii('e')) | ((u32)ossl_toascii('x') << 8)

               | ((u32)ossl_toascii('p') << 16)

               | ((u32)ossl_toascii('a') << 24);

    input[1] = ((u32)ossl_toascii('n')) | ((u32)ossl_toascii('d') << 8)

               | ((u32)ossl_toascii(' ') << 16)

               | ((u32)ossl_toascii('3') << 24);

    input[2] = ((u32)ossl_toascii('2')) | ((u32)ossl_toascii('-') << 8)

               | ((u32)ossl_toascii('b') << 16)

               | ((u32)ossl_toascii('y') << 24);

    input[3] = ((u32)ossl_toascii('t')) | ((u32)ossl_toascii('e') << 8)

               | ((u32)ossl_toascii(' ') << 16)

               | ((u32)ossl_toascii('k') << 24);

    input[4] = key[0];

    input[5] = key[1];

    input[6] = key[2];

    input[7] = key[3];

    input[8] = key[4];

    input[9] = key[5];

    input[10] = key[6];

    input[11] = key[7];

    input[12] = counter[0];

    input[13] = counter[1];

    input[14] = counter[2];

    input[15] = counter[3];

    while (len > 0) {

        todo = sizeof(buf);

        if (len < todo)

            todo = len;

        chacha20_core(&buf, input);

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

            out[i] = inp[i] ^ buf.c[i];

        out += todo;

        inp += todo;

        len -= todo;

        /*

         * Advance 32-bit counter. Note that as subroutine is so to

         * say nonce-agnostic, this limited counter width doesn't

         * prevent caller from implementing wider counter. It would

         * simply take two calls split on counter overflow...

         */

        input[12]++;

    }

}