linux/crypto/cfb.c

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//SPDX-License-Identifier: GPL-2.0
/*
* CFB: Cipher FeedBack mode
*
* Copyright (c) 2018 James.Bottomley@HansenPartnership.com
*
* CFB is a stream cipher mode which is layered on to a block
* encryption scheme. It works very much like a one time pad where
* the pad is generated initially from the encrypted IV and then
* subsequently from the encrypted previous block of ciphertext. The
* pad is XOR'd into the plain text to get the final ciphertext.
*
* The scheme of CFB is best described by wikipedia:
*
* https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#CFB
*
* Note that since the pad for both encryption and decryption is
* generated by an encryption operation, CFB never uses the block
* decryption function.
*/
#include <crypto/algapi.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>
#include <linux/string.h>
#include <linux/types.h>
struct crypto_cfb_ctx {
struct crypto_cipher *child;
};
static unsigned int crypto_cfb_bsize(struct crypto_skcipher *tfm)
{
struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(tfm);
struct crypto_cipher *child = ctx->child;
return crypto_cipher_blocksize(child);
}
static void crypto_cfb_encrypt_one(struct crypto_skcipher *tfm,
const u8 *src, u8 *dst)
{
struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(tfm);
crypto_cipher_encrypt_one(ctx->child, dst, src);
}
/* final encrypt and decrypt is the same */
static void crypto_cfb_final(struct skcipher_walk *walk,
struct crypto_skcipher *tfm)
{
const unsigned long alignmask = crypto_skcipher_alignmask(tfm);
u8 tmp[MAX_CIPHER_BLOCKSIZE + MAX_CIPHER_ALIGNMASK];
u8 *stream = PTR_ALIGN(tmp + 0, alignmask + 1);
u8 *src = walk->src.virt.addr;
u8 *dst = walk->dst.virt.addr;
u8 *iv = walk->iv;
unsigned int nbytes = walk->nbytes;
crypto_cfb_encrypt_one(tfm, iv, stream);
crypto_xor_cpy(dst, stream, src, nbytes);
}
static int crypto_cfb_encrypt_segment(struct skcipher_walk *walk,
struct crypto_skcipher *tfm)
{
const unsigned int bsize = crypto_cfb_bsize(tfm);
unsigned int nbytes = walk->nbytes;
u8 *src = walk->src.virt.addr;
u8 *dst = walk->dst.virt.addr;
u8 *iv = walk->iv;
do {
crypto_cfb_encrypt_one(tfm, iv, dst);
crypto_xor(dst, src, bsize);
memcpy(iv, dst, bsize);
src += bsize;
dst += bsize;
} while ((nbytes -= bsize) >= bsize);
return nbytes;
}
static int crypto_cfb_encrypt_inplace(struct skcipher_walk *walk,
struct crypto_skcipher *tfm)
{
const unsigned int bsize = crypto_cfb_bsize(tfm);
unsigned int nbytes = walk->nbytes;
u8 *src = walk->src.virt.addr;
u8 *iv = walk->iv;
u8 tmp[MAX_CIPHER_BLOCKSIZE];
do {
crypto_cfb_encrypt_one(tfm, iv, tmp);
crypto_xor(src, tmp, bsize);
iv = src;
src += bsize;
} while ((nbytes -= bsize) >= bsize);
memcpy(walk->iv, iv, bsize);
return nbytes;
}
static int crypto_cfb_encrypt(struct skcipher_request *req)
{
struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
struct skcipher_walk walk;
unsigned int bsize = crypto_cfb_bsize(tfm);
int err;
err = skcipher_walk_virt(&walk, req, false);
while (walk.nbytes >= bsize) {
if (walk.src.virt.addr == walk.dst.virt.addr)
err = crypto_cfb_encrypt_inplace(&walk, tfm);
else
err = crypto_cfb_encrypt_segment(&walk, tfm);
err = skcipher_walk_done(&walk, err);
}
if (walk.nbytes) {
crypto_cfb_final(&walk, tfm);
err = skcipher_walk_done(&walk, 0);
}
return err;
}
static int crypto_cfb_decrypt_segment(struct skcipher_walk *walk,
struct crypto_skcipher *tfm)
{
const unsigned int bsize = crypto_cfb_bsize(tfm);
unsigned int nbytes = walk->nbytes;
u8 *src = walk->src.virt.addr;
u8 *dst = walk->dst.virt.addr;
u8 *iv = walk->iv;
do {
crypto_cfb_encrypt_one(tfm, iv, dst);
crypto_xor(dst, src, bsize);
iv = src;
src += bsize;
dst += bsize;
} while ((nbytes -= bsize) >= bsize);
memcpy(walk->iv, iv, bsize);
return nbytes;
}
static int crypto_cfb_decrypt_inplace(struct skcipher_walk *walk,
struct crypto_skcipher *tfm)
{
const unsigned int bsize = crypto_cfb_bsize(tfm);
unsigned int nbytes = walk->nbytes;
u8 *src = walk->src.virt.addr;
u8 *iv = walk->iv;
u8 tmp[MAX_CIPHER_BLOCKSIZE];
do {
crypto_cfb_encrypt_one(tfm, iv, tmp);
memcpy(iv, src, bsize);
crypto_xor(src, tmp, bsize);
src += bsize;
} while ((nbytes -= bsize) >= bsize);
memcpy(walk->iv, iv, bsize);
return nbytes;
}
static int crypto_cfb_decrypt_blocks(struct skcipher_walk *walk,
struct crypto_skcipher *tfm)
{
if (walk->src.virt.addr == walk->dst.virt.addr)
return crypto_cfb_decrypt_inplace(walk, tfm);
else
return crypto_cfb_decrypt_segment(walk, tfm);
}
static int crypto_cfb_setkey(struct crypto_skcipher *parent, const u8 *key,
unsigned int keylen)
{
struct crypto_cfb_ctx *ctx = crypto_skcipher_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_skcipher_get_flags(parent) &
CRYPTO_TFM_REQ_MASK);
err = crypto_cipher_setkey(child, key, keylen);
crypto_skcipher_set_flags(parent, crypto_cipher_get_flags(child) &
CRYPTO_TFM_RES_MASK);
return err;
}
static int crypto_cfb_decrypt(struct skcipher_request *req)
{
struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
struct skcipher_walk walk;
const unsigned int bsize = crypto_cfb_bsize(tfm);
int err;
err = skcipher_walk_virt(&walk, req, false);
while (walk.nbytes >= bsize) {
err = crypto_cfb_decrypt_blocks(&walk, tfm);
err = skcipher_walk_done(&walk, err);
}
if (walk.nbytes) {
crypto_cfb_final(&walk, tfm);
err = skcipher_walk_done(&walk, 0);
}
return err;
}
static int crypto_cfb_init_tfm(struct crypto_skcipher *tfm)
{
struct skcipher_instance *inst = skcipher_alg_instance(tfm);
struct crypto_spawn *spawn = skcipher_instance_ctx(inst);
struct crypto_cfb_ctx *ctx = crypto_skcipher_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_cfb_exit_tfm(struct crypto_skcipher *tfm)
{
struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(tfm);
crypto_free_cipher(ctx->child);
}
static void crypto_cfb_free(struct skcipher_instance *inst)
{
crypto_drop_skcipher(skcipher_instance_ctx(inst));
kfree(inst);
}
static int crypto_cfb_create(struct crypto_template *tmpl, struct rtattr **tb)
{
struct skcipher_instance *inst;
struct crypto_attr_type *algt;
struct crypto_spawn *spawn;
struct crypto_alg *alg;
u32 mask;
int err;
err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SKCIPHER);
if (err)
return err;
inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL);
if (!inst)
return -ENOMEM;
algt = crypto_get_attr_type(tb);
err = PTR_ERR(algt);
if (IS_ERR(algt))
goto err_free_inst;
mask = CRYPTO_ALG_TYPE_MASK |
crypto_requires_off(algt->type, algt->mask,
CRYPTO_ALG_NEED_FALLBACK);
alg = crypto_get_attr_alg(tb, CRYPTO_ALG_TYPE_CIPHER, mask);
err = PTR_ERR(alg);
if (IS_ERR(alg))
goto err_free_inst;
spawn = skcipher_instance_ctx(inst);
err = crypto_init_spawn(spawn, alg, skcipher_crypto_instance(inst),
CRYPTO_ALG_TYPE_MASK);
if (err)
goto err_put_alg;
err = crypto_inst_setname(skcipher_crypto_instance(inst), "cfb", alg);
if (err)
goto err_drop_spawn;
inst->alg.base.cra_priority = alg->cra_priority;
/* we're a stream cipher independend of the crypto cra_blocksize */
inst->alg.base.cra_blocksize = 1;
inst->alg.base.cra_alignmask = alg->cra_alignmask;
inst->alg.ivsize = alg->cra_blocksize;
inst->alg.min_keysize = alg->cra_cipher.cia_min_keysize;
inst->alg.max_keysize = alg->cra_cipher.cia_max_keysize;
inst->alg.base.cra_ctxsize = sizeof(struct crypto_cfb_ctx);
inst->alg.init = crypto_cfb_init_tfm;
inst->alg.exit = crypto_cfb_exit_tfm;
inst->alg.setkey = crypto_cfb_setkey;
inst->alg.encrypt = crypto_cfb_encrypt;
inst->alg.decrypt = crypto_cfb_decrypt;
inst->free = crypto_cfb_free;
err = skcipher_register_instance(tmpl, inst);
if (err)
goto err_drop_spawn;
crypto_mod_put(alg);
out:
return err;
err_drop_spawn:
crypto_drop_spawn(spawn);
err_put_alg:
crypto_mod_put(alg);
err_free_inst:
kfree(inst);
goto out;
}
static struct crypto_template crypto_cfb_tmpl = {
.name = "cfb",
.create = crypto_cfb_create,
.module = THIS_MODULE,
};
static int __init crypto_cfb_module_init(void)
{
return crypto_register_template(&crypto_cfb_tmpl);
}
static void __exit crypto_cfb_module_exit(void)
{
crypto_unregister_template(&crypto_cfb_tmpl);
}
module_init(crypto_cfb_module_init);
module_exit(crypto_cfb_module_exit);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("CFB block cipher algorithm");
MODULE_ALIAS_CRYPTO("cfb");