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![Herbert Xu](/assets/img/avatar_default.png)
This patch introduces the skcipher_ialg_simple helper which fetches the crypto_alg structure from a simple skcipher instance's spawn. This allows us to remove the third argument from the function skcipher_alloc_instance_simple. In doing so the reference count to the algorithm is now maintained by the Crypto API and the caller no longer needs to drop the alg refcount. Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
252 lines
6.1 KiB
C
252 lines
6.1 KiB
C
//SPDX-License-Identifier: GPL-2.0
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/*
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* CFB: Cipher FeedBack mode
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*
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* Copyright (c) 2018 James.Bottomley@HansenPartnership.com
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*
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* CFB is a stream cipher mode which is layered on to a block
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* encryption scheme. It works very much like a one time pad where
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* the pad is generated initially from the encrypted IV and then
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* subsequently from the encrypted previous block of ciphertext. The
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* pad is XOR'd into the plain text to get the final ciphertext.
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*
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* The scheme of CFB is best described by wikipedia:
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*
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* https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#CFB
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*
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* Note that since the pad for both encryption and decryption is
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* generated by an encryption operation, CFB never uses the block
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* decryption function.
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*/
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#include <crypto/algapi.h>
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#include <crypto/internal/skcipher.h>
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#include <linux/err.h>
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#include <linux/init.h>
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/string.h>
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static unsigned int crypto_cfb_bsize(struct crypto_skcipher *tfm)
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{
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return crypto_cipher_blocksize(skcipher_cipher_simple(tfm));
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}
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static void crypto_cfb_encrypt_one(struct crypto_skcipher *tfm,
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const u8 *src, u8 *dst)
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{
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crypto_cipher_encrypt_one(skcipher_cipher_simple(tfm), dst, src);
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}
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/* final encrypt and decrypt is the same */
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static void crypto_cfb_final(struct skcipher_walk *walk,
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struct crypto_skcipher *tfm)
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{
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const unsigned long alignmask = crypto_skcipher_alignmask(tfm);
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u8 tmp[MAX_CIPHER_BLOCKSIZE + MAX_CIPHER_ALIGNMASK];
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u8 *stream = PTR_ALIGN(tmp + 0, alignmask + 1);
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u8 *src = walk->src.virt.addr;
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u8 *dst = walk->dst.virt.addr;
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u8 *iv = walk->iv;
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unsigned int nbytes = walk->nbytes;
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crypto_cfb_encrypt_one(tfm, iv, stream);
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crypto_xor_cpy(dst, stream, src, nbytes);
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}
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static int crypto_cfb_encrypt_segment(struct skcipher_walk *walk,
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struct crypto_skcipher *tfm)
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{
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const unsigned int bsize = crypto_cfb_bsize(tfm);
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unsigned int nbytes = walk->nbytes;
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u8 *src = walk->src.virt.addr;
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u8 *dst = walk->dst.virt.addr;
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u8 *iv = walk->iv;
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do {
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crypto_cfb_encrypt_one(tfm, iv, dst);
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crypto_xor(dst, src, bsize);
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iv = dst;
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src += bsize;
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dst += bsize;
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} while ((nbytes -= bsize) >= bsize);
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memcpy(walk->iv, iv, bsize);
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return nbytes;
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}
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static int crypto_cfb_encrypt_inplace(struct skcipher_walk *walk,
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struct crypto_skcipher *tfm)
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{
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const unsigned int bsize = crypto_cfb_bsize(tfm);
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unsigned int nbytes = walk->nbytes;
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u8 *src = walk->src.virt.addr;
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u8 *iv = walk->iv;
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u8 tmp[MAX_CIPHER_BLOCKSIZE];
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do {
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crypto_cfb_encrypt_one(tfm, iv, tmp);
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crypto_xor(src, tmp, bsize);
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iv = src;
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src += bsize;
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} while ((nbytes -= bsize) >= bsize);
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memcpy(walk->iv, iv, bsize);
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return nbytes;
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}
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static int crypto_cfb_encrypt(struct skcipher_request *req)
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{
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struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
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struct skcipher_walk walk;
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unsigned int bsize = crypto_cfb_bsize(tfm);
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int err;
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err = skcipher_walk_virt(&walk, req, false);
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while (walk.nbytes >= bsize) {
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if (walk.src.virt.addr == walk.dst.virt.addr)
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err = crypto_cfb_encrypt_inplace(&walk, tfm);
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else
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err = crypto_cfb_encrypt_segment(&walk, tfm);
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err = skcipher_walk_done(&walk, err);
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}
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if (walk.nbytes) {
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crypto_cfb_final(&walk, tfm);
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err = skcipher_walk_done(&walk, 0);
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}
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return err;
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}
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static int crypto_cfb_decrypt_segment(struct skcipher_walk *walk,
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struct crypto_skcipher *tfm)
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{
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const unsigned int bsize = crypto_cfb_bsize(tfm);
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unsigned int nbytes = walk->nbytes;
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u8 *src = walk->src.virt.addr;
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u8 *dst = walk->dst.virt.addr;
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u8 *iv = walk->iv;
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do {
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crypto_cfb_encrypt_one(tfm, iv, dst);
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crypto_xor(dst, src, bsize);
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iv = src;
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src += bsize;
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dst += bsize;
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} while ((nbytes -= bsize) >= bsize);
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memcpy(walk->iv, iv, bsize);
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return nbytes;
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}
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static int crypto_cfb_decrypt_inplace(struct skcipher_walk *walk,
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struct crypto_skcipher *tfm)
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{
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const unsigned int bsize = crypto_cfb_bsize(tfm);
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unsigned int nbytes = walk->nbytes;
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u8 *src = walk->src.virt.addr;
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u8 * const iv = walk->iv;
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u8 tmp[MAX_CIPHER_BLOCKSIZE];
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do {
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crypto_cfb_encrypt_one(tfm, iv, tmp);
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memcpy(iv, src, bsize);
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crypto_xor(src, tmp, bsize);
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src += bsize;
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} while ((nbytes -= bsize) >= bsize);
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return nbytes;
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}
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static int crypto_cfb_decrypt_blocks(struct skcipher_walk *walk,
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struct crypto_skcipher *tfm)
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{
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if (walk->src.virt.addr == walk->dst.virt.addr)
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return crypto_cfb_decrypt_inplace(walk, tfm);
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else
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return crypto_cfb_decrypt_segment(walk, tfm);
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}
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static int crypto_cfb_decrypt(struct skcipher_request *req)
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{
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struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
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struct skcipher_walk walk;
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const unsigned int bsize = crypto_cfb_bsize(tfm);
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int err;
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err = skcipher_walk_virt(&walk, req, false);
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while (walk.nbytes >= bsize) {
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err = crypto_cfb_decrypt_blocks(&walk, tfm);
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err = skcipher_walk_done(&walk, err);
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}
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if (walk.nbytes) {
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crypto_cfb_final(&walk, tfm);
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err = skcipher_walk_done(&walk, 0);
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}
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return err;
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}
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static int crypto_cfb_create(struct crypto_template *tmpl, struct rtattr **tb)
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{
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struct skcipher_instance *inst;
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struct crypto_alg *alg;
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int err;
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inst = skcipher_alloc_instance_simple(tmpl, tb);
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if (IS_ERR(inst))
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return PTR_ERR(inst);
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alg = skcipher_ialg_simple(inst);
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/* CFB mode is a stream cipher. */
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inst->alg.base.cra_blocksize = 1;
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/*
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* To simplify the implementation, configure the skcipher walk to only
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* give a partial block at the very end, never earlier.
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*/
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inst->alg.chunksize = alg->cra_blocksize;
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inst->alg.encrypt = crypto_cfb_encrypt;
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inst->alg.decrypt = crypto_cfb_decrypt;
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err = skcipher_register_instance(tmpl, inst);
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if (err)
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inst->free(inst);
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return err;
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}
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static struct crypto_template crypto_cfb_tmpl = {
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.name = "cfb",
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.create = crypto_cfb_create,
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.module = THIS_MODULE,
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};
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static int __init crypto_cfb_module_init(void)
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{
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return crypto_register_template(&crypto_cfb_tmpl);
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}
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static void __exit crypto_cfb_module_exit(void)
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{
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crypto_unregister_template(&crypto_cfb_tmpl);
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}
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subsys_initcall(crypto_cfb_module_init);
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module_exit(crypto_cfb_module_exit);
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MODULE_LICENSE("GPL");
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MODULE_DESCRIPTION("CFB block cipher mode of operation");
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MODULE_ALIAS_CRYPTO("cfb");
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