/*
   * Salsa20: Salsa20 stream cipher algorithm
   *
   * Copyright (c) 2007 Tan Swee Heng <thesweeheng@gmail.com>
   *
   * Derived from:
   * - salsa20.c: Public domain C code by Daniel J. Bernstein <djb@cr.yp.to>
   *
   * Salsa20 is a stream cipher candidate in eSTREAM, the ECRYPT Stream
   * Cipher Project. It is designed by Daniel J. Bernstein <djb@cr.yp.to>.
   * More information about eSTREAM and Salsa20 can be found here:

   *   https://www.ecrypt.eu.org/stream/
   *   https://cr.yp.to/snuffle.html

   *
   * This program is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License as published by the Free
   * Software Foundation; either version 2 of the License, or (at your option)
   * any later version.
   *
   */

  #include <asm/unaligned.h>
  #include <crypto/internal/skcipher.h>

  #include <linux/module.h>

  #define SALSA20_IV_SIZE        8
  #define SALSA20_MIN_KEY_SIZE  16
  #define SALSA20_MAX_KEY_SIZE  32
  #define SALSA20_BLOCK_SIZE    64
  
  struct salsa20_ctx {
  	u32 initial_state[16];
  };

  static void salsa20_block(u32 *state, __le32 *stream)

  {
  	u32 x[16];
  	int i;

  	memcpy(x, state, sizeof(x));
  
  	for (i = 0; i < 20; i += 2) {

  		x[ 4] ^= rol32((x[ 0] + x[12]),  7);
  		x[ 8] ^= rol32((x[ 4] + x[ 0]),  9);
  		x[12] ^= rol32((x[ 8] + x[ 4]), 13);
  		x[ 0] ^= rol32((x[12] + x[ 8]), 18);
  		x[ 9] ^= rol32((x[ 5] + x[ 1]),  7);
  		x[13] ^= rol32((x[ 9] + x[ 5]),  9);
  		x[ 1] ^= rol32((x[13] + x[ 9]), 13);
  		x[ 5] ^= rol32((x[ 1] + x[13]), 18);
  		x[14] ^= rol32((x[10] + x[ 6]),  7);
  		x[ 2] ^= rol32((x[14] + x[10]),  9);
  		x[ 6] ^= rol32((x[ 2] + x[14]), 13);
  		x[10] ^= rol32((x[ 6] + x[ 2]), 18);
  		x[ 3] ^= rol32((x[15] + x[11]),  7);
  		x[ 7] ^= rol32((x[ 3] + x[15]),  9);
  		x[11] ^= rol32((x[ 7] + x[ 3]), 13);
  		x[15] ^= rol32((x[11] + x[ 7]), 18);
  		x[ 1] ^= rol32((x[ 0] + x[ 3]),  7);
  		x[ 2] ^= rol32((x[ 1] + x[ 0]),  9);
  		x[ 3] ^= rol32((x[ 2] + x[ 1]), 13);
  		x[ 0] ^= rol32((x[ 3] + x[ 2]), 18);
  		x[ 6] ^= rol32((x[ 5] + x[ 4]),  7);
  		x[ 7] ^= rol32((x[ 6] + x[ 5]),  9);
  		x[ 4] ^= rol32((x[ 7] + x[ 6]), 13);
  		x[ 5] ^= rol32((x[ 4] + x[ 7]), 18);
  		x[11] ^= rol32((x[10] + x[ 9]),  7);
  		x[ 8] ^= rol32((x[11] + x[10]),  9);
  		x[ 9] ^= rol32((x[ 8] + x[11]), 13);
  		x[10] ^= rol32((x[ 9] + x[ 8]), 18);
  		x[12] ^= rol32((x[15] + x[14]),  7);
  		x[13] ^= rol32((x[12] + x[15]),  9);
  		x[14] ^= rol32((x[13] + x[12]), 13);
  		x[15] ^= rol32((x[14] + x[13]), 18);

  	}

  	for (i = 0; i < 16; i++)
  		stream[i] = cpu_to_le32(x[i] + state[i]);
  
  	if (++state[8] == 0)
  		state[9]++;
  }

  static void salsa20_docrypt(u32 *state, u8 *dst, const u8 *src,
  			    unsigned int bytes)

  {

  	__le32 stream[SALSA20_BLOCK_SIZE / sizeof(__le32)];

  	while (bytes >= SALSA20_BLOCK_SIZE) {
  		salsa20_block(state, stream);

  		crypto_xor_cpy(dst, src, (const u8 *)stream,
  			       SALSA20_BLOCK_SIZE);

  		bytes -= SALSA20_BLOCK_SIZE;
  		dst += SALSA20_BLOCK_SIZE;

  		src += SALSA20_BLOCK_SIZE;

  	}
  	if (bytes) {
  		salsa20_block(state, stream);

  		crypto_xor_cpy(dst, src, (const u8 *)stream, bytes);

  	}

  }

  static void salsa20_init(u32 *state, const struct salsa20_ctx *ctx,

  			 const u8 *iv)

  {

  	memcpy(state, ctx->initial_state, sizeof(ctx->initial_state));
  	state[6] = get_unaligned_le32(iv + 0);
  	state[7] = get_unaligned_le32(iv + 4);

  }

  static int salsa20_setkey(struct crypto_skcipher *tfm, const u8 *key,

  			  unsigned int keysize)

  {

  	static const char sigma[16] = "expand 32-byte k";
  	static const char tau[16] = "expand 16-byte k";
  	struct salsa20_ctx *ctx = crypto_skcipher_ctx(tfm);
  	const char *constants;

  	if (keysize != SALSA20_MIN_KEY_SIZE &&
  	    keysize != SALSA20_MAX_KEY_SIZE)
  		return -EINVAL;

  	ctx->initial_state[1] = get_unaligned_le32(key + 0);
  	ctx->initial_state[2] = get_unaligned_le32(key + 4);
  	ctx->initial_state[3] = get_unaligned_le32(key + 8);
  	ctx->initial_state[4] = get_unaligned_le32(key + 12);
  	if (keysize == 32) { /* recommended */
  		key += 16;
  		constants = sigma;
  	} else { /* keysize == 16 */
  		constants = tau;

  	}

  	ctx->initial_state[11] = get_unaligned_le32(key + 0);
  	ctx->initial_state[12] = get_unaligned_le32(key + 4);
  	ctx->initial_state[13] = get_unaligned_le32(key + 8);
  	ctx->initial_state[14] = get_unaligned_le32(key + 12);
  	ctx->initial_state[0]  = get_unaligned_le32(constants + 0);
  	ctx->initial_state[5]  = get_unaligned_le32(constants + 4);
  	ctx->initial_state[10] = get_unaligned_le32(constants + 8);
  	ctx->initial_state[15] = get_unaligned_le32(constants + 12);
  
  	/* space for the nonce; it will be overridden for each request */
  	ctx->initial_state[6] = 0;
  	ctx->initial_state[7] = 0;
  
  	/* initial block number */
  	ctx->initial_state[8] = 0;
  	ctx->initial_state[9] = 0;

  	return 0;
  }

  static int salsa20_crypt(struct skcipher_request *req)

  {

  	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
  	const struct salsa20_ctx *ctx = crypto_skcipher_ctx(tfm);
  	struct skcipher_walk walk;
  	u32 state[16];

  	int err;

  	err = skcipher_walk_virt(&walk, req, false);

  	salsa20_init(state, ctx, req->iv);

  	while (walk.nbytes > 0) {
  		unsigned int nbytes = walk.nbytes;

  		if (nbytes < walk.total)
  			nbytes = round_down(nbytes, walk.stride);
  
  		salsa20_docrypt(state, walk.dst.virt.addr, walk.src.virt.addr,
  				nbytes);
  		err = skcipher_walk_done(&walk, walk.nbytes - nbytes);

  	}

  	return err;
  }

  static struct skcipher_alg alg = {
  	.base.cra_name		= "salsa20",
  	.base.cra_driver_name	= "salsa20-generic",
  	.base.cra_priority	= 100,
  	.base.cra_blocksize	= 1,
  	.base.cra_ctxsize	= sizeof(struct salsa20_ctx),
  	.base.cra_module	= THIS_MODULE,
  
  	.min_keysize		= SALSA20_MIN_KEY_SIZE,
  	.max_keysize		= SALSA20_MAX_KEY_SIZE,
  	.ivsize			= SALSA20_IV_SIZE,
  	.chunksize		= SALSA20_BLOCK_SIZE,

  	.setkey			= salsa20_setkey,

  	.encrypt		= salsa20_crypt,
  	.decrypt		= salsa20_crypt,

  };

  static int __init salsa20_generic_mod_init(void)

  {

  	return crypto_register_skcipher(&alg);

  }

  static void __exit salsa20_generic_mod_fini(void)

  {

  	crypto_unregister_skcipher(&alg);

  }

  subsys_initcall(salsa20_generic_mod_init);

  module_exit(salsa20_generic_mod_fini);

  
  MODULE_LICENSE("GPL");
  MODULE_DESCRIPTION ("Salsa20 stream cipher algorithm");

  MODULE_ALIAS_CRYPTO("salsa20");

  MODULE_ALIAS_CRYPTO("salsa20-generic");