[linux.git] / crypto / xctr.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * XCTR: XOR Counter mode - Adapted from ctr.c
 *
 * (C) Copyright IBM Corp. 2007 - Joy Latten <[email protected]>
 * Copyright 2021 Google LLC
 */

/*
 * XCTR mode is a blockcipher mode of operation used to implement HCTR2. XCTR is
 * closely related to the CTR mode of operation; the main difference is that CTR
 * generates the keystream using E(CTR + IV) whereas XCTR generates the
 * keystream using E(CTR ^ IV). This allows implementations to avoid dealing
 * with multi-limb integers (as is required in CTR mode). XCTR is also specified
 * using little-endian arithmetic which makes it slightly faster on LE machines.
 *
 * See the HCTR2 paper for more details:
 *	Length-preserving encryption with HCTR2
 *      (https://eprint.iacr.org/2021/1441.pdf)
 */

#include <crypto/algapi.h>
#include <crypto/internal/cipher.h>
#include <crypto/internal/skcipher.h>
#include <linux/err.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/slab.h>

/* For now this implementation is limited to 16-byte blocks for simplicity */
#define XCTR_BLOCKSIZE 16

static void crypto_xctr_crypt_final(struct skcipher_walk *walk,
				   struct crypto_cipher *tfm, u32 byte_ctr)
{
	u8 keystream[XCTR_BLOCKSIZE];
	const u8 *src = walk->src.virt.addr;
	u8 *dst = walk->dst.virt.addr;
	unsigned int nbytes = walk->nbytes;
	__le32 ctr32 = cpu_to_le32(byte_ctr / XCTR_BLOCKSIZE + 1);

	crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));
	crypto_cipher_encrypt_one(tfm, keystream, walk->iv);
	crypto_xor_cpy(dst, keystream, src, nbytes);
	crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));
}

static int crypto_xctr_crypt_segment(struct skcipher_walk *walk,
				    struct crypto_cipher *tfm, u32 byte_ctr)
{
	void (*fn)(struct crypto_tfm *, u8 *, const u8 *) =
		   crypto_cipher_alg(tfm)->cia_encrypt;
	const u8 *src = walk->src.virt.addr;
	u8 *dst = walk->dst.virt.addr;
	unsigned int nbytes = walk->nbytes;
	__le32 ctr32 = cpu_to_le32(byte_ctr / XCTR_BLOCKSIZE + 1);

	do {
		crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));
		fn(crypto_cipher_tfm(tfm), dst, walk->iv);
		crypto_xor(dst, src, XCTR_BLOCKSIZE);
		crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));

		le32_add_cpu(&ctr32, 1);

		src += XCTR_BLOCKSIZE;
		dst += XCTR_BLOCKSIZE;
	} while ((nbytes -= XCTR_BLOCKSIZE) >= XCTR_BLOCKSIZE);

	return nbytes;
}

static int crypto_xctr_crypt_inplace(struct skcipher_walk *walk,
				    struct crypto_cipher *tfm, u32 byte_ctr)
{
	void (*fn)(struct crypto_tfm *, u8 *, const u8 *) =
		   crypto_cipher_alg(tfm)->cia_encrypt;
	unsigned long alignmask = crypto_cipher_alignmask(tfm);
	unsigned int nbytes = walk->nbytes;
	u8 *data = walk->src.virt.addr;
	u8 tmp[XCTR_BLOCKSIZE + MAX_CIPHER_ALIGNMASK];
	u8 *keystream = PTR_ALIGN(tmp + 0, alignmask + 1);
	__le32 ctr32 = cpu_to_le32(byte_ctr / XCTR_BLOCKSIZE + 1);

	do {
		crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));
		fn(crypto_cipher_tfm(tfm), keystream, walk->iv);
		crypto_xor(data, keystream, XCTR_BLOCKSIZE);
		crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));

		le32_add_cpu(&ctr32, 1);

		data += XCTR_BLOCKSIZE;
	} while ((nbytes -= XCTR_BLOCKSIZE) >= XCTR_BLOCKSIZE);

	return nbytes;
}

static int crypto_xctr_crypt(struct skcipher_request *req)
{
	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
	struct crypto_cipher *cipher = skcipher_cipher_simple(tfm);
	struct skcipher_walk walk;
	unsigned int nbytes;
	int err;
	u32 byte_ctr = 0;

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

	while (walk.nbytes >= XCTR_BLOCKSIZE) {
		if (walk.src.virt.addr == walk.dst.virt.addr)
			nbytes = crypto_xctr_crypt_inplace(&walk, cipher,
							   byte_ctr);
		else
			nbytes = crypto_xctr_crypt_segment(&walk, cipher,
							   byte_ctr);

		byte_ctr += walk.nbytes - nbytes;
		err = skcipher_walk_done(&walk, nbytes);
	}

	if (walk.nbytes) {
		crypto_xctr_crypt_final(&walk, cipher, byte_ctr);
		err = skcipher_walk_done(&walk, 0);
	}

	return err;
}

static int crypto_xctr_create(struct crypto_template *tmpl, struct rtattr **tb)
{
	struct skcipher_instance *inst;
	struct crypto_alg *alg;
	int err;

	inst = skcipher_alloc_instance_simple(tmpl, tb);
	if (IS_ERR(inst))
		return PTR_ERR(inst);

	alg = skcipher_ialg_simple(inst);

	/* Block size must be 16 bytes. */
	err = -EINVAL;
	if (alg->cra_blocksize != XCTR_BLOCKSIZE)
		goto out_free_inst;

	/* XCTR mode is a stream cipher. */
	inst->alg.base.cra_blocksize = 1;

	/*
	 * To simplify the implementation, configure the skcipher walk to only
	 * give a partial block at the very end, never earlier.
	 */
	inst->alg.chunksize = alg->cra_blocksize;

	inst->alg.encrypt = crypto_xctr_crypt;
	inst->alg.decrypt = crypto_xctr_crypt;

	err = skcipher_register_instance(tmpl, inst);
	if (err) {
out_free_inst:
		inst->free(inst);
	}

	return err;
}

static struct crypto_template crypto_xctr_tmpl = {
	.name = "xctr",
	.create = crypto_xctr_create,
	.module = THIS_MODULE,
};

static int __init crypto_xctr_module_init(void)
{
	return crypto_register_template(&crypto_xctr_tmpl);
}

static void __exit crypto_xctr_module_exit(void)
{
	crypto_unregister_template(&crypto_xctr_tmpl);
}

subsys_initcall(crypto_xctr_module_init);
module_exit(crypto_xctr_module_exit);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("XCTR block cipher mode of operation");
MODULE_ALIAS_CRYPTO("xctr");
MODULE_IMPORT_NS(CRYPTO_INTERNAL);
Commit	Line	Data
17fee07a NH	1	// SPDX-License-Identifier: GPL-2.0-or-later
	2	/*
	3	* XCTR: XOR Counter mode - Adapted from ctr.c
	4	*
	5	* (C) Copyright IBM Corp. 2007 - Joy Latten <[email protected]>
	6	* Copyright 2021 Google LLC
	7	*/
	8
	9	/*
	10	* XCTR mode is a blockcipher mode of operation used to implement HCTR2. XCTR is
	11	* closely related to the CTR mode of operation; the main difference is that CTR
	12	* generates the keystream using E(CTR + IV) whereas XCTR generates the
	13	* keystream using E(CTR ^ IV). This allows implementations to avoid dealing
	14	* with multi-limb integers (as is required in CTR mode). XCTR is also specified
	15	* using little-endian arithmetic which makes it slightly faster on LE machines.
	16	*
	17	* See the HCTR2 paper for more details:
	18	* Length-preserving encryption with HCTR2
	19	* (https://eprint.iacr.org/2021/1441.pdf)
	20	*/
	21
	22	#include <crypto/algapi.h>
	23	#include <crypto/internal/cipher.h>
	24	#include <crypto/internal/skcipher.h>
	25	#include <linux/err.h>
	26	#include <linux/init.h>
	27	#include <linux/kernel.h>
	28	#include <linux/module.h>
	29	#include <linux/slab.h>
	30
	31	/* For now this implementation is limited to 16-byte blocks for simplicity */
	32	#define XCTR_BLOCKSIZE 16
	33
	34	static void crypto_xctr_crypt_final(struct skcipher_walk *walk,
	35	struct crypto_cipher *tfm, u32 byte_ctr)
	36	{
	37	u8 keystream[XCTR_BLOCKSIZE];
	38	const u8 *src = walk->src.virt.addr;
	39	u8 *dst = walk->dst.virt.addr;
	40	unsigned int nbytes = walk->nbytes;
	41	__le32 ctr32 = cpu_to_le32(byte_ctr / XCTR_BLOCKSIZE + 1);
	42
	43	crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));
	44	crypto_cipher_encrypt_one(tfm, keystream, walk->iv);
	45	crypto_xor_cpy(dst, keystream, src, nbytes);
	46	crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));
	47	}
	48
	49	static int crypto_xctr_crypt_segment(struct skcipher_walk *walk,
	50	struct crypto_cipher *tfm, u32 byte_ctr)
	51	{
	52	void (fn)(struct crypto_tfm , u8 , const u8 ) =
	53	crypto_cipher_alg(tfm)->cia_encrypt;
	54	const u8 *src = walk->src.virt.addr;
	55	u8 *dst = walk->dst.virt.addr;
	56	unsigned int nbytes = walk->nbytes;
	57	__le32 ctr32 = cpu_to_le32(byte_ctr / XCTR_BLOCKSIZE + 1);
	58
	59	do {
	60	crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));
	61	fn(crypto_cipher_tfm(tfm), dst, walk->iv);
	62	crypto_xor(dst, src, XCTR_BLOCKSIZE);
	63	crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));
	64
65	le32_add_cpu(&ctr32, 1);
66
67	src += XCTR_BLOCKSIZE;
68	dst += XCTR_BLOCKSIZE;
69	} while ((nbytes -= XCTR_BLOCKSIZE) >= XCTR_BLOCKSIZE);
70
71	return nbytes;
72	}
73
74	static int crypto_xctr_crypt_inplace(struct skcipher_walk *walk,
75	struct crypto_cipher *tfm, u32 byte_ctr)
76	{
77	void (fn)(struct crypto_tfm , u8 , const u8 ) =
78	crypto_cipher_alg(tfm)->cia_encrypt;
79	unsigned long alignmask = crypto_cipher_alignmask(tfm);
80	unsigned int nbytes = walk->nbytes;
81	u8 *data = walk->src.virt.addr;
82	u8 tmp[XCTR_BLOCKSIZE + MAX_CIPHER_ALIGNMASK];
83	u8 *keystream = PTR_ALIGN(tmp + 0, alignmask + 1);
84	__le32 ctr32 = cpu_to_le32(byte_ctr / XCTR_BLOCKSIZE + 1);
85
86	do {
87	crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));
88	fn(crypto_cipher_tfm(tfm), keystream, walk->iv);
89	crypto_xor(data, keystream, XCTR_BLOCKSIZE);
90	crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));
91
92	le32_add_cpu(&ctr32, 1);
93
94	data += XCTR_BLOCKSIZE;
95	} while ((nbytes -= XCTR_BLOCKSIZE) >= XCTR_BLOCKSIZE);
96
97	return nbytes;
98	}
99
100	static int crypto_xctr_crypt(struct skcipher_request *req)
101	{
102	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
103	struct crypto_cipher *cipher = skcipher_cipher_simple(tfm);
104	struct skcipher_walk walk;
105	unsigned int nbytes;
106	int err;
107	u32 byte_ctr = 0;
108
109	err = skcipher_walk_virt(&walk, req, false);
110
111	while (walk.nbytes >= XCTR_BLOCKSIZE) {
112	if (walk.src.virt.addr == walk.dst.virt.addr)
113	nbytes = crypto_xctr_crypt_inplace(&walk, cipher,
114	byte_ctr);
115	else
116	nbytes = crypto_xctr_crypt_segment(&walk, cipher,
117	byte_ctr);
118
119	byte_ctr += walk.nbytes - nbytes;
120	err = skcipher_walk_done(&walk, nbytes);
121	}
122
123	if (walk.nbytes) {
124	crypto_xctr_crypt_final(&walk, cipher, byte_ctr);
125	err = skcipher_walk_done(&walk, 0);
126	}
127
128	return err;
129	}
130
131	static int crypto_xctr_create(struct crypto_template tmpl, struct rtattr *tb)
132	{
133	struct skcipher_instance *inst;
134	struct crypto_alg *alg;
135	int err;
136
137	inst = skcipher_alloc_instance_simple(tmpl, tb);
138	if (IS_ERR(inst))
139	return PTR_ERR(inst);
140
141	alg = skcipher_ialg_simple(inst);
142
143	/* Block size must be 16 bytes. */
144	err = -EINVAL;
145	if (alg->cra_blocksize != XCTR_BLOCKSIZE)
146	goto out_free_inst;
147
148	/* XCTR mode is a stream cipher. */
149	inst->alg.base.cra_blocksize = 1;
150
151	/*
152	* To simplify the implementation, configure the skcipher walk to only
153	* give a partial block at the very end, never earlier.
154	*/
155	inst->alg.chunksize = alg->cra_blocksize;
156
157	inst->alg.encrypt = crypto_xctr_crypt;
158	inst->alg.decrypt = crypto_xctr_crypt;
159
160	err = skcipher_register_instance(tmpl, inst);
161	if (err) {
162	out_free_inst:
163	inst->free(inst);
164	}
165
166	return err;
167	}
168
169	static struct crypto_template crypto_xctr_tmpl = {
170	.name = "xctr",
171	.create = crypto_xctr_create,
172	.module = THIS_MODULE,
173	};
174
175	static int __init crypto_xctr_module_init(void)
176	{
177	return crypto_register_template(&crypto_xctr_tmpl);
178	}
179
180	static void __exit crypto_xctr_module_exit(void)
181	{
182	crypto_unregister_template(&crypto_xctr_tmpl);
183	}
184
185	subsys_initcall(crypto_xctr_module_init);
186	module_exit(crypto_xctr_module_exit);
187
188	MODULE_LICENSE("GPL");
189	MODULE_DESCRIPTION("XCTR block cipher mode of operation");
190	MODULE_ALIAS_CRYPTO("xctr");
191	MODULE_IMPORT_NS(CRYPTO_INTERNAL);