text: /*
   * ChaCha and XChaCha stream ciphers, including ChaCha20 (RFC7539)
   *
   * Copyright (C) 2015 Martin Willi
   * Copyright (C) 2018 Google LLC
   *
   * 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/algapi.h>
  #include <crypto/chacha.h>
  #include <crypto/internal/skcipher.h>
  #include <linux/module.h>
  
  static void chacha_docrypt(u32 *state, u8 *dst, const u8 *src,
  			   unsigned int bytes, int nrounds)
  {
  	/* aligned to potentially speed up crypto_xor() */
  	u8 stream[CHACHA_BLOCK_SIZE] __aligned(sizeof(long));
  
  	if (dst != src)
  		memcpy(dst, src, bytes);
  
  	while (bytes >= CHACHA_BLOCK_SIZE) {
  		chacha_block(state, stream, nrounds);
  		crypto_xor(dst, stream, CHACHA_BLOCK_SIZE);
  		bytes -= CHACHA_BLOCK_SIZE;
  		dst += CHACHA_BLOCK_SIZE;
  	}
  	if (bytes) {
  		chacha_block(state, stream, nrounds);
  		crypto_xor(dst, stream, bytes);
  	}
  }
  
  static int chacha_stream_xor(struct skcipher_request *req,
  			     struct chacha_ctx *ctx, u8 *iv)
  {
  	struct skcipher_walk walk;
  	u32 state[16];
  	int err;
  
  	err = skcipher_walk_virt(&walk, req, false);
  
  	crypto_chacha_init(state, ctx, iv);
  
  	while (walk.nbytes > 0) {
  		unsigned int nbytes = walk.nbytes;
  
  		if (nbytes < walk.total)
  			nbytes = round_down(nbytes, walk.stride);
  
  		chacha_docrypt(state, walk.dst.virt.addr, walk.src.virt.addr,
  			       nbytes, ctx->nrounds);
  		err = skcipher_walk_done(&walk, walk.nbytes - nbytes);
  	}
  
  	return err;
  }
  
  void crypto_chacha_init(u32 *state, struct chacha_ctx *ctx, u8 *iv)
  {
  	state[0]  = 0x61707865; /* "expa" */
  	state[1]  = 0x3320646e; /* "nd 3" */
  	state[2]  = 0x79622d32; /* "2-by" */
  	state[3]  = 0x6b206574; /* "te k" */
  	state[4]  = ctx->key[0];
  	state[5]  = ctx->key[1];
  	state[6]  = ctx->key[2];
  	state[7]  = ctx->key[3];
  	state[8]  = ctx->key[4];
  	state[9]  = ctx->key[5];
  	state[10] = ctx->key[6];
  	state[11] = ctx->key[7];
  	state[12] = get_unaligned_le32(iv +  0);
  	state[13] = get_unaligned_le32(iv +  4);
  	state[14] = get_unaligned_le32(iv +  8);
  	state[15] = get_unaligned_le32(iv + 12);
  }
  EXPORT_SYMBOL_GPL(crypto_chacha_init);
  
  static int chacha_setkey(struct crypto_skcipher *tfm, const u8 *key,
  			 unsigned int keysize, int nrounds)
  {
  	struct chacha_ctx *ctx = crypto_skcipher_ctx(tfm);
  	int i;
  
  	if (keysize != CHACHA_KEY_SIZE)
  		return -EINVAL;
  
  	for (i = 0; i < ARRAY_SIZE(ctx->key); i++)
  		ctx->key[i] = get_unaligned_le32(key + i * sizeof(u32));
  
  	ctx->nrounds = nrounds;
  	return 0;
  }
  
  int crypto_chacha20_setkey(struct crypto_skcipher *tfm, const u8 *key,
  			   unsigned int keysize)
  {
  	return chacha_setkey(tfm, key, keysize, 20);
  }
  EXPORT_SYMBOL_GPL(crypto_chacha20_setkey);
  
  int crypto_chacha12_setkey(struct crypto_skcipher *tfm, const u8 *key,
  			   unsigned int keysize)
  {
  	return chacha_setkey(tfm, key, keysize, 12);
  }
  EXPORT_SYMBOL_GPL(crypto_chacha12_setkey);
  
  int crypto_chacha_crypt(struct skcipher_request *req)
  {
  	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
  	struct chacha_ctx *ctx = crypto_skcipher_ctx(tfm);
  
  	return chacha_stream_xor(req, ctx, req->iv);
  }
  EXPORT_SYMBOL_GPL(crypto_chacha_crypt);
  
  int crypto_xchacha_crypt(struct skcipher_request *req)
  {
  	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
  	struct chacha_ctx *ctx = crypto_skcipher_ctx(tfm);
  	struct chacha_ctx subctx;
  	u32 state[16];
  	u8 real_iv[16];
  
  	/* Compute the subkey given the original key and first 128 nonce bits */
  	crypto_chacha_init(state, ctx, req->iv);
  	hchacha_block(state, subctx.key, ctx->nrounds);
  	subctx.nrounds = ctx->nrounds;
  
  	/* Build the real IV */
  	memcpy(&real_iv[0], req->iv + 24, 8); /* stream position */
  	memcpy(&real_iv[8], req->iv + 16, 8); /* remaining 64 nonce bits */
  
  	/* Generate the stream and XOR it with the data */
  	return chacha_stream_xor(req, &subctx, real_iv);
  }
  EXPORT_SYMBOL_GPL(crypto_xchacha_crypt);
  
  static struct skcipher_alg algs[] = {
  	{
  		.base.cra_name		= "chacha20",
  		.base.cra_driver_name	= "chacha20-generic",
  		.base.cra_priority	= 100,
  		.base.cra_blocksize	= 1,
  		.base.cra_ctxsize	= sizeof(struct chacha_ctx),
  		.base.cra_module	= THIS_MODULE,
  
  		.min_keysize		= CHACHA_KEY_SIZE,
  		.max_keysize		= CHACHA_KEY_SIZE,
  		.ivsize			= CHACHA_IV_SIZE,
  		.chunksize		= CHACHA_BLOCK_SIZE,
  		.setkey			= crypto_chacha20_setkey,
  		.encrypt		= crypto_chacha_crypt,
  		.decrypt		= crypto_chacha_crypt,
  	}, {
  		.base.cra_name		= "xchacha20",
  		.base.cra_driver_name	= "xchacha20-generic",
  		.base.cra_priority	= 100,
  		.base.cra_blocksize	= 1,
  		.base.cra_ctxsize	= sizeof(struct chacha_ctx),
  		.base.cra_module	= THIS_MODULE,
  
  		.min_keysize		= CHACHA_KEY_SIZE,
  		.max_keysize		= CHACHA_KEY_SIZE,
  		.ivsize			= XCHACHA_IV_SIZE,
  		.chunksize		= CHACHA_BLOCK_SIZE,
  		.setkey			= crypto_chacha20_setkey,
  		.encrypt		= crypto_xchacha_crypt,
  		.decrypt		= crypto_xchacha_crypt,
  	}, {
  		.base.cra_name		= "xchacha12",
  		.base.cra_driver_name	= "xchacha12-generic",
  		.base.cra_priority	= 100,
  		.base.cra_blocksize	= 1,
  		.base.cra_ctxsize	= sizeof(struct chacha_ctx),
  		.base.cra_module	= THIS_MODULE,
  
  		.min_keysize		= CHACHA_KEY_SIZE,
  		.max_keysize		= CHACHA_KEY_SIZE,
  		.ivsize			= XCHACHA_IV_SIZE,
  		.chunksize		= CHACHA_BLOCK_SIZE,
  		.setkey			= crypto_chacha12_setkey,
  		.encrypt		= crypto_xchacha_crypt,
  		.decrypt		= crypto_xchacha_crypt,
  	}
  };
  
  static int __init chacha_generic_mod_init(void)
  {
  	return crypto_register_skciphers(algs, ARRAY_SIZE(algs));
  }
  
  static void __exit chacha_generic_mod_fini(void)
  {
  	crypto_unregister_skciphers(algs, ARRAY_SIZE(algs));
  }
  
  module_init(chacha_generic_mod_init);
  module_exit(chacha_generic_mod_fini);
  
  MODULE_LICENSE("GPL");
  MODULE_AUTHOR("Martin Willi <martin@strongswan.org>");
  MODULE_DESCRIPTION("ChaCha and XChaCha stream ciphers (generic)");
  MODULE_ALIAS_CRYPTO("chacha20");
  MODULE_ALIAS_CRYPTO("chacha20-generic");
  MODULE_ALIAS_CRYPTO("xchacha20");
  MODULE_ALIAS_CRYPTO("xchacha20-generic");
  MODULE_ALIAS_CRYPTO("xchacha12");
  MODULE_ALIAS_CRYPTO("xchacha12-generic");
  