1/*
  2 * ChaCha20 256-bit cipher algorithm, RFC7539
  3 *
  4 * Copyright (C) 2015 Martin Willi
  5 *
  6 * This program is free software; you can redistribute it and/or modify
  7 * it under the terms of the GNU General Public License as published by
  8 * the Free Software Foundation; either version 2 of the License, or
  9 * (at your option) any later version.
 10 */
 11
 12#include <asm/unaligned.h>
 13#include <crypto/algapi.h>
 14#include <crypto/chacha20.h>
 15#include <crypto/internal/skcipher.h>
 16#include <linux/module.h>
 17
 18static void chacha20_docrypt(u32 *state, u8 *dst, const u8 *src,
 19			     unsigned int bytes)
 20{
 21	u32 stream[CHACHA20_BLOCK_WORDS];
 22
 23	if (dst != src)
 24		memcpy(dst, src, bytes);
 25
 26	while (bytes >= CHACHA20_BLOCK_SIZE) {
 27		chacha20_block(state, stream);
 28		crypto_xor(dst, (const u8 *)stream, CHACHA20_BLOCK_SIZE);
 29		bytes -= CHACHA20_BLOCK_SIZE;
 30		dst += CHACHA20_BLOCK_SIZE;
 31	}
 32	if (bytes) {
 33		chacha20_block(state, stream);
 34		crypto_xor(dst, (const u8 *)stream, bytes);
 35	}
 36}
 37
 38void crypto_chacha20_init(u32 *state, struct chacha20_ctx *ctx, u8 *iv)
 39{
 40	state[0]  = 0x61707865; /* "expa" */
 41	state[1]  = 0x3320646e; /* "nd 3" */
 42	state[2]  = 0x79622d32; /* "2-by" */
 43	state[3]  = 0x6b206574; /* "te k" */
 44	state[4]  = ctx->key[0];
 45	state[5]  = ctx->key[1];
 46	state[6]  = ctx->key[2];
 47	state[7]  = ctx->key[3];
 48	state[8]  = ctx->key[4];
 49	state[9]  = ctx->key[5];
 50	state[10] = ctx->key[6];
 51	state[11] = ctx->key[7];
 52	state[12] = get_unaligned_le32(iv +  0);
 53	state[13] = get_unaligned_le32(iv +  4);
 54	state[14] = get_unaligned_le32(iv +  8);
 55	state[15] = get_unaligned_le32(iv + 12);
 56}
 57EXPORT_SYMBOL_GPL(crypto_chacha20_init);
 58
 59int crypto_chacha20_setkey(struct crypto_skcipher *tfm, const u8 *key,
 60			   unsigned int keysize)
 61{
 62	struct chacha20_ctx *ctx = crypto_skcipher_ctx(tfm);
 63	int i;
 64
 65	if (keysize != CHACHA20_KEY_SIZE)
 66		return -EINVAL;
 67
 68	for (i = 0; i < ARRAY_SIZE(ctx->key); i++)
 69		ctx->key[i] = get_unaligned_le32(key + i * sizeof(u32));
 70
 71	return 0;
 72}
 73EXPORT_SYMBOL_GPL(crypto_chacha20_setkey);
 74
 75int crypto_chacha20_crypt(struct skcipher_request *req)
 76{
 77	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 78	struct chacha20_ctx *ctx = crypto_skcipher_ctx(tfm);
 79	struct skcipher_walk walk;
 80	u32 state[16];
 81	int err;
 82
 83	err = skcipher_walk_virt(&walk, req, true);
 84
 85	crypto_chacha20_init(state, ctx, walk.iv);
 86
 87	while (walk.nbytes > 0) {
 88		unsigned int nbytes = walk.nbytes;
 89
 90		if (nbytes < walk.total)
 91			nbytes = round_down(nbytes, walk.stride);
 92
 93		chacha20_docrypt(state, walk.dst.virt.addr, walk.src.virt.addr,
 94				 nbytes);
 95		err = skcipher_walk_done(&walk, walk.nbytes - nbytes);
 96	}
 97
 98	return err;
 99}
100EXPORT_SYMBOL_GPL(crypto_chacha20_crypt);
101
102static struct skcipher_alg alg = {
103	.base.cra_name		= "chacha20",
104	.base.cra_driver_name	= "chacha20-generic",
105	.base.cra_priority	= 100,
106	.base.cra_blocksize	= 1,
107	.base.cra_ctxsize	= sizeof(struct chacha20_ctx),
108	.base.cra_module	= THIS_MODULE,
109
110	.min_keysize		= CHACHA20_KEY_SIZE,
111	.max_keysize		= CHACHA20_KEY_SIZE,
112	.ivsize			= CHACHA20_IV_SIZE,
113	.chunksize		= CHACHA20_BLOCK_SIZE,
114	.setkey			= crypto_chacha20_setkey,
115	.encrypt		= crypto_chacha20_crypt,
116	.decrypt		= crypto_chacha20_crypt,
117};
118
119static int __init chacha20_generic_mod_init(void)
120{
121	return crypto_register_skcipher(&alg);
122}
123
124static void __exit chacha20_generic_mod_fini(void)
125{
126	crypto_unregister_skcipher(&alg);
127}
128
129module_init(chacha20_generic_mod_init);
130module_exit(chacha20_generic_mod_fini);
131
132MODULE_LICENSE("GPL");
133MODULE_AUTHOR("Martin Willi <martin@strongswan.org>");
134MODULE_DESCRIPTION("chacha20 cipher algorithm");
135MODULE_ALIAS_CRYPTO("chacha20");
136MODULE_ALIAS_CRYPTO("chacha20-generic");