/*
* 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
__be64 A;
__be64 R;
};
/*
* 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;
struct crypto_kw_block block;
struct scatterlist *lsrc, *ldst;
u64 t = 6 * ((nbytes) >> 3);
unsigned int i;
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++) {
struct scatter_walk src_walk, dst_walk;
unsigned int tmp_nbytes = nbytes;
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: modify IV with counter */
block.A ^= cpu_to_be64(t);
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 (block.A != cpu_to_be64(0xa6a6a6a6a6a6a6a6ULL))
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;
struct crypto_kw_block block;
struct scatterlist *lsrc, *ldst;
u64 t = 1;
unsigned int i;
/*
* 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.
*/
block.A = cpu_to_be64(0xa6a6a6a6a6a6a6a6ULL);
/*
* 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++) {
struct scatter_walk src_walk, dst_walk;
unsigned int tmp_nbytes = nbytes;
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: modify IV with counter */
block.A ^= cpu_to_be64(t);
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");
