crypto: keywrap - add key wrapping block chaining mode

/*

 * Key Wrapping: RFC3394 / NIST SP800-38F

 *

 * Copyright (C) 2015, Stephan Mueller <smueller@chronox.de>

 *

 * 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, and the entire permission notice in its entirety,

 *    including the disclaimer of warranties.

 * 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. The name of the author may not be used to endorse or promote

 *    products derived from this software without specific prior

 *    written permission.

 *

 * ALTERNATIVELY, this product may be distributed under the terms of

 * the GNU General Public License, in which case the provisions of the GPL2

 * are required INSTEAD OF the above restrictions.  (This clause is

 * necessary due to a potential bad interaction between the GPL and

 * the restrictions contained in a BSD-style copyright.)

 *

 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED

 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES

 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF

 * WHICH ARE HEREBY DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR 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 NOT ADVISED OF THE POSSIBILITY OF SUCH

 * DAMAGE.

 */

/*

 * Note for using key wrapping:

 *

 *	* The result of the encryption operation is the ciphertext starting

 *	  with the 2nd semiblock. The first semiblock is provided as the IV.

 *	  The IV used to start the encryption operation is the default IV.

 *

 *	* The input for the decryption is the first semiblock handed in as an

 *	  IV. The ciphertext is the data starting with the 2nd semiblock. The

 *	  return code of the decryption operation will be EBADMSG in case an

 *	  integrity error occurs.

 *

 * To obtain the full result of an encryption as expected by SP800-38F, the

 * caller must allocate a buffer of plaintext + 8 bytes:

 *

 *	unsigned int datalen = ptlen + crypto_skcipher_ivsize(tfm);

 *	u8 data[datalen];

 *	u8 *iv = data;

 *	u8 *pt = data + crypto_skcipher_ivsize(tfm);

 *		<ensure that pt contains the plaintext of size ptlen>

 *	sg_init_one(&sg, ptdata, ptlen);

 *	skcipher_request_set_crypt(req, &sg, &sg, ptlen, iv);

 *

 *	==> After encryption, data now contains full KW result as per SP800-38F.

 *

 * In case of decryption, ciphertext now already has the expected length

 * and must be segmented appropriately:

 *

 *	unsigned int datalen = CTLEN;

 *	u8 data[datalen];

 *		<ensure that data contains full ciphertext>

 *	u8 *iv = data;

 *	u8 *ct = data + crypto_skcipher_ivsize(tfm);

 *	unsigned int ctlen = datalen - crypto_skcipher_ivsize(tfm);

 *	sg_init_one(&sg, ctdata, ctlen);

 *	skcipher_request_set_crypt(req, &sg, &sg, ptlen, iv);

 *

 *	==> After decryption (which hopefully does not return EBADMSG), the ct

 *	pointer now points to the plaintext of size ctlen.

 *

 * Note 2: KWP is not implemented as this would defy in-place operation.

 *	   If somebody wants to wrap non-aligned data, he should simply pad

 *	   the input with zeros to fill it up to the 8 byte boundary.

 */

#include <linux/module.h>

#include <linux/crypto.h>

#include <linux/scatterlist.h>

#include <crypto/scatterwalk.h>

#include <crypto/internal/skcipher.h>

struct crypto_kw_ctx {

	struct crypto_cipher *child;

};

struct crypto_kw_block {

#define SEMIBSIZE 8

	u8 A[SEMIBSIZE];

	u8 R[SEMIBSIZE];

};

/* convert 64 bit integer into its string representation */

static inline void crypto_kw_cpu_to_be64(u64 val, u8 *buf)

{

	__be64 *a = (__be64 *)buf;

	*a = cpu_to_be64(val);

}

/*

 * Fast forward the SGL to the "end" length minus SEMIBSIZE.

 * The start in the SGL defined by the fast-forward is returned with

 * the walk variable

 */

static void crypto_kw_scatterlist_ff(struct scatter_walk *walk,

				     struct scatterlist *sg,

				     unsigned int end)

{

	unsigned int skip = 0;

	/* The caller should only operate on full SEMIBLOCKs. */

	BUG_ON(end < SEMIBSIZE);

	skip = end - SEMIBSIZE;

	while (sg) {

		if (sg->length > skip) {

			scatterwalk_start(walk, sg);

			scatterwalk_advance(walk, skip);

			break;

		} else

			skip -= sg->length;

		sg = sg_next(sg);

	}

}

static int crypto_kw_decrypt(struct blkcipher_desc *desc,

			     struct scatterlist *dst, struct scatterlist *src,

			     unsigned int nbytes)

{

	struct crypto_blkcipher *tfm = desc->tfm;

	struct crypto_kw_ctx *ctx = crypto_blkcipher_ctx(tfm);

	struct crypto_cipher *child = ctx->child;

	unsigned long alignmask = max_t(unsigned long, SEMIBSIZE,

					crypto_cipher_alignmask(child));

	unsigned int i;

	u8 blockbuf[sizeof(struct crypto_kw_block) + alignmask];

	struct crypto_kw_block *block = (struct crypto_kw_block *)

					PTR_ALIGN(blockbuf + 0, alignmask + 1);

	u64 t = 6 * ((nbytes) >> 3);

	struct scatterlist *lsrc, *ldst;

	int ret = 0;

	/*

	 * Require at least 2 semiblocks (note, the 3rd semiblock that is

	 * required by SP800-38F is the IV.

	 */

	if (nbytes < (2 * SEMIBSIZE) || nbytes % SEMIBSIZE)

		return -EINVAL;

	/* Place the IV into block A */

	memcpy(block->A, desc->info, SEMIBSIZE);

	/*

	 * src scatterlist is read-only. dst scatterlist is r/w. During the

	 * first loop, lsrc points to src and ldst to dst. For any

	 * subsequent round, the code operates on dst only.

	 */

	lsrc = src;

	ldst = dst;

	for (i = 0; i < 6; i++) {

		u8 tbe_buffer[SEMIBSIZE + alignmask];

		/* alignment for the crypto_xor and the _to_be64 operation */

		u8 *tbe = PTR_ALIGN(tbe_buffer + 0, alignmask + 1);

		unsigned int tmp_nbytes = nbytes;

		struct scatter_walk src_walk, dst_walk;

		while (tmp_nbytes) {

			/* move pointer by tmp_nbytes in the SGL */

			crypto_kw_scatterlist_ff(&src_walk, lsrc, tmp_nbytes);

			/* get the source block */

			scatterwalk_copychunks(block->R, &src_walk, SEMIBSIZE,

					       false);

			/* perform KW operation: get counter as byte string */

			crypto_kw_cpu_to_be64(t, tbe);

			/* perform KW operation: modify IV with counter */

			crypto_xor(block->A, tbe, SEMIBSIZE);

			t--;

			/* perform KW operation: decrypt block */

			crypto_cipher_decrypt_one(child, (u8*)block,

						  (u8*)block);

			/* move pointer by tmp_nbytes in the SGL */

			crypto_kw_scatterlist_ff(&dst_walk, ldst, tmp_nbytes);

			/* Copy block->R into place */

			scatterwalk_copychunks(block->R, &dst_walk, SEMIBSIZE,

					       true);

			tmp_nbytes -= SEMIBSIZE;

		}

		/* we now start to operate on the dst SGL only */

		lsrc = dst;

		ldst = dst;

	}

	/* Perform authentication check */

	if (crypto_memneq("\xA6\xA6\xA6\xA6\xA6\xA6\xA6\xA6", block->A,

			  SEMIBSIZE))

		ret = -EBADMSG;

	memzero_explicit(&block, sizeof(struct crypto_kw_block));

	return ret;

}

static int crypto_kw_encrypt(struct blkcipher_desc *desc,

			     struct scatterlist *dst, struct scatterlist *src,

			     unsigned int nbytes)

{

	struct crypto_blkcipher *tfm = desc->tfm;

	struct crypto_kw_ctx *ctx = crypto_blkcipher_ctx(tfm);

	struct crypto_cipher *child = ctx->child;

	unsigned long alignmask = max_t(unsigned long, SEMIBSIZE,

					crypto_cipher_alignmask(child));

	unsigned int i;

	u8 blockbuf[sizeof(struct crypto_kw_block) + alignmask];

	struct crypto_kw_block *block = (struct crypto_kw_block *)

					PTR_ALIGN(blockbuf + 0, alignmask + 1);

	u64 t = 1;

	struct scatterlist *lsrc, *ldst;

	/*

	 * Require at least 2 semiblocks (note, the 3rd semiblock that is

	 * required by SP800-38F is the IV that occupies the first semiblock.

	 * This means that the dst memory must be one semiblock larger than src.

	 * Also ensure that the given data is aligned to semiblock.

	 */

	if (nbytes < (2 * SEMIBSIZE) || nbytes % SEMIBSIZE)

		return -EINVAL;

	/*

	 * Place the predefined IV into block A -- for encrypt, the caller

	 * does not need to provide an IV, but he needs to fetch the final IV.

	 */

	memcpy(block->A, "\xA6\xA6\xA6\xA6\xA6\xA6\xA6\xA6", SEMIBSIZE);

	/*

	 * src scatterlist is read-only. dst scatterlist is r/w. During the

	 * first loop, lsrc points to src and ldst to dst. For any

	 * subsequent round, the code operates on dst only.

	 */

	lsrc = src;

	ldst = dst;

	for (i = 0; i < 6; i++) {

		u8 tbe_buffer[SEMIBSIZE + alignmask];

		u8 *tbe = PTR_ALIGN(tbe_buffer + 0, alignmask + 1);

		unsigned int tmp_nbytes = nbytes;

		struct scatter_walk src_walk, dst_walk;

		scatterwalk_start(&src_walk, lsrc);

		scatterwalk_start(&dst_walk, ldst);

		while (tmp_nbytes) {

			/* get the source block */

			scatterwalk_copychunks(block->R, &src_walk, SEMIBSIZE,

					       false);

			/* perform KW operation: encrypt block */

			crypto_cipher_encrypt_one(child, (u8 *)block,

						  (u8 *)block);

			/* perform KW operation: get counter as byte string */

			crypto_kw_cpu_to_be64(t, tbe);

			/* perform KW operation: modify IV with counter */

			crypto_xor(block->A, tbe, SEMIBSIZE);

			t++;

			/* Copy block->R into place */

			scatterwalk_copychunks(block->R, &dst_walk, SEMIBSIZE,

					       true);

			tmp_nbytes -= SEMIBSIZE;

		}

		/* we now start to operate on the dst SGL only */

		lsrc = dst;

		ldst = dst;

	}

	/* establish the IV for the caller to pick up */

	memcpy(desc->info, block->A, SEMIBSIZE);

	memzero_explicit(&block, sizeof(struct crypto_kw_block));

	return 0;

}

static int crypto_kw_setkey(struct crypto_tfm *parent, const u8 *key,

			    unsigned int keylen)

{

	struct crypto_kw_ctx *ctx = crypto_tfm_ctx(parent);

	struct crypto_cipher *child = ctx->child;

	int err;

	crypto_cipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);

	crypto_cipher_set_flags(child, crypto_tfm_get_flags(parent) &

				       CRYPTO_TFM_REQ_MASK);

	err = crypto_cipher_setkey(child, key, keylen);

	crypto_tfm_set_flags(parent, crypto_cipher_get_flags(child) &

				     CRYPTO_TFM_RES_MASK);

	return err;

}

static int crypto_kw_init_tfm(struct crypto_tfm *tfm)

{

	struct crypto_instance *inst = crypto_tfm_alg_instance(tfm);

	struct crypto_spawn *spawn = crypto_instance_ctx(inst);

	struct crypto_kw_ctx *ctx = crypto_tfm_ctx(tfm);

	struct crypto_cipher *cipher;

	cipher = crypto_spawn_cipher(spawn);

	if (IS_ERR(cipher))

		return PTR_ERR(cipher);

	ctx->child = cipher;

	return 0;

}

static void crypto_kw_exit_tfm(struct crypto_tfm *tfm)

{

	struct crypto_kw_ctx *ctx = crypto_tfm_ctx(tfm);

	crypto_free_cipher(ctx->child);

}

static struct crypto_instance *crypto_kw_alloc(struct rtattr **tb)

{

	struct crypto_instance *inst = NULL;

	struct crypto_alg *alg = NULL;

	int err;

	err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_BLKCIPHER);

	if (err)

		return ERR_PTR(err);

	alg = crypto_get_attr_alg(tb, CRYPTO_ALG_TYPE_CIPHER,

				  CRYPTO_ALG_TYPE_MASK);

	if (IS_ERR(alg))

		return ERR_CAST(alg);

	inst = ERR_PTR(-EINVAL);

	/* Section 5.1 requirement for KW */

	if (alg->cra_blocksize != sizeof(struct crypto_kw_block))

		goto err;

	inst = crypto_alloc_instance("kw", alg);

	if (IS_ERR(inst))

		goto err;

	inst->alg.cra_flags = CRYPTO_ALG_TYPE_BLKCIPHER;

	inst->alg.cra_priority = alg->cra_priority;

	inst->alg.cra_blocksize = SEMIBSIZE;

	inst->alg.cra_alignmask = 0;

	inst->alg.cra_type = &crypto_blkcipher_type;

	inst->alg.cra_blkcipher.ivsize = SEMIBSIZE;

	inst->alg.cra_blkcipher.min_keysize = alg->cra_cipher.cia_min_keysize;

	inst->alg.cra_blkcipher.max_keysize = alg->cra_cipher.cia_max_keysize;

	inst->alg.cra_ctxsize = sizeof(struct crypto_kw_ctx);

	inst->alg.cra_init = crypto_kw_init_tfm;

	inst->alg.cra_exit = crypto_kw_exit_tfm;

	inst->alg.cra_blkcipher.setkey = crypto_kw_setkey;

	inst->alg.cra_blkcipher.encrypt = crypto_kw_encrypt;

	inst->alg.cra_blkcipher.decrypt = crypto_kw_decrypt;

err:

	crypto_mod_put(alg);

	return inst;

}

static void crypto_kw_free(struct crypto_instance *inst)

{

	crypto_drop_spawn(crypto_instance_ctx(inst));

	kfree(inst);

}

static struct crypto_template crypto_kw_tmpl = {

	.name = "kw",

	.alloc = crypto_kw_alloc,

	.free = crypto_kw_free,

	.module = THIS_MODULE,

};

static int __init crypto_kw_init(void)

{

	return crypto_register_template(&crypto_kw_tmpl);

}

static void __exit crypto_kw_exit(void)

{

	crypto_unregister_template(&crypto_kw_tmpl);

}

module_init(crypto_kw_init);

module_exit(crypto_kw_exit);

MODULE_LICENSE("Dual BSD/GPL");

MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");

MODULE_DESCRIPTION("Key Wrapping (RFC3394 / NIST SP800-38F)");

MODULE_ALIAS_CRYPTO("kw");