/*
 * This code is based on an OpenSSL implementation of chacha20. 
 * Hence, the copyright below applies.
 * 
 */
/* ====================================================================
 * Copyright (c) 2011-2013 The OpenSSL Project.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. 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.
 *
 * 3. All advertising materials mentioning features or use of this
 *    software must display the following acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
 *    for use in the OpenSSL Toolkit. (http://www.OpenSSL.org/)"
 *
 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission. For written permission, please contact
 *    licensing@OpenSSL.org.
 *
 * 5. Products derived from this software may not be called "OpenSSL"
 *    nor may "OpenSSL" appear in their names without prior written
 *    permission of the OpenSSL Project.
 *
 * 6. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
 *    for use in the OpenSSL Toolkit (http://www.OpenSSL.org/)"
 *
 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
 * EXPRESSED 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 OpenSSL PROJECT OR
 * ITS 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.
 * ====================================================================
 */

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

#include <stdint.h>
#include <string.h>
#include "chacha.h"

/* sigma contains the ChaCha constants, which happen to be an ASCII string. */
static const char sigma[16] = "expand 32-byte k";

#define ROTATE(v, n) (((v) << (n)) | ((v) >> (32 - (n))))
#define XOR(v, w) ((v) ^ (w))
#define PLUS(x, y) ((x) + (y))
#define PLUSONE(v) (PLUS((v), 1))

#define U32TO8_LITTLE(p, v) \
	{ (p)[0] = (v >>  0) & 0xff; (p)[1] = (v >>  8) & 0xff; \
	  (p)[2] = (v >> 16) & 0xff; (p)[3] = (v >> 24) & 0xff; }
#define U8TO32_LITTLE(p)   \
	(((uint32_t)((p)[0])      ) | ((uint32_t)((p)[1]) <<  8) | \
	 ((uint32_t)((p)[2]) << 16) | ((uint32_t)((p)[3]) << 24)   )

/* QUARTERROUND updates a, b, c, d with a ChaCha "quarter" round. */
#define QUARTERROUND(a,b,c,d) \
  x[a] = PLUS(x[a],x[b]); x[d] = ROTATE(XOR(x[d],x[a]),16); \
  x[c] = PLUS(x[c],x[d]); x[b] = ROTATE(XOR(x[b],x[c]),12); \
  x[a] = PLUS(x[a],x[b]); x[d] = ROTATE(XOR(x[d],x[a]), 8); \
  x[c] = PLUS(x[c],x[d]); x[b] = ROTATE(XOR(x[b],x[c]), 7);

/* chacha_core performs |num_rounds| rounds of ChaCha20 on the input words in
 * |input| and writes the 64 output bytes to |output|. */
static void chacha_core(unsigned char output[64], const uint32_t input[16],
			int num_rounds)
	{
	uint32_t x[16];
	int i;

	memcpy(x, input, sizeof(uint32_t) * 16);
	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)
		}

	for (i = 0; i < 16; ++i)
		x[i] = PLUS(x[i], input[i]);
	for (i = 0; i < 16; ++i)
		U32TO8_LITTLE(output + 4 * i, x[i]);
	}

void CRYPTO_chacha_20(unsigned char *out,
		      const unsigned char *in, size_t in_len,
		      const unsigned char key[32],
		      const unsigned char nonce[12],
		      uint32_t counter)
	{
	uint32_t input[16];
	unsigned char buf[64];
	size_t todo, i;

	input[0] = U8TO32_LITTLE(sigma + 0);
	input[1] = U8TO32_LITTLE(sigma + 4);
	input[2] = U8TO32_LITTLE(sigma + 8);
	input[3] = U8TO32_LITTLE(sigma + 12);

	input[4] = U8TO32_LITTLE(key + 0);
	input[5] = U8TO32_LITTLE(key + 4);
	input[6] = U8TO32_LITTLE(key + 8);
	input[7] = U8TO32_LITTLE(key + 12);

	input[8] = U8TO32_LITTLE(key + 16);
	input[9] = U8TO32_LITTLE(key + 20);
	input[10] = U8TO32_LITTLE(key + 24);
	input[11] = U8TO32_LITTLE(key + 28);

	input[12] = counter;
	input[13] = U8TO32_LITTLE(nonce + 0);
	input[14] = U8TO32_LITTLE(nonce + 4);
	input[15] = U8TO32_LITTLE(nonce + 8);

	while (in_len > 0)
		{
		todo = sizeof(buf);
		if (in_len < todo)
			todo = in_len;

		chacha_core(buf, input, 20);
		for (i = 0; i < todo; i++)
			out[i] = in[i] ^ buf[i];

		out += todo;
		in += todo;
		in_len -= todo;

		input[12]++;
		if (input[12] == 0)
			input[13]++;
		}
	}
	
void CRYPTO_chacha_20_keystream(unsigned char *out,
		      size_t out_len,
		      const unsigned char key[32],
		      const unsigned char nonce[12],
		      uint32_t counter)
	{
	uint32_t input[16];
	unsigned char buf[64];
	size_t todo, i;

	input[0] = U8TO32_LITTLE(sigma + 0);
	input[1] = U8TO32_LITTLE(sigma + 4);
	input[2] = U8TO32_LITTLE(sigma + 8);
	input[3] = U8TO32_LITTLE(sigma + 12);

	input[4] = U8TO32_LITTLE(key + 0);
	input[5] = U8TO32_LITTLE(key + 4);
	input[6] = U8TO32_LITTLE(key + 8);
	input[7] = U8TO32_LITTLE(key + 12);

	input[8] = U8TO32_LITTLE(key + 16);
	input[9] = U8TO32_LITTLE(key + 20);
	input[10] = U8TO32_LITTLE(key + 24);
	input[11] = U8TO32_LITTLE(key + 28);

	input[12] = counter;
	input[13] = U8TO32_LITTLE(nonce + 0);
	input[14] = U8TO32_LITTLE(nonce + 4);
	input[15] = U8TO32_LITTLE(nonce + 8);

	while (out_len > 0)
		{
		todo = sizeof(buf);
		if (out_len < todo)
			todo = out_len;

		chacha_core(buf, input, 20);
		for (i = 0; i < todo; i++)
			out[i] = buf[i];

		out += todo;
		out_len -= todo;

		input[12]++;
		if (input[12] == 0)
			input[13]++;
		}
	}