2018-03-01 15:36:17 -07:00
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//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/slab.h>
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#include <linux/string.h>
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#include <linux/types.h>
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struct crypto_cfb_ctx {
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struct crypto_cipher *child;
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};
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static unsigned int crypto_cfb_bsize(struct crypto_skcipher *tfm)
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{
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struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(tfm);
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struct crypto_cipher *child = ctx->child;
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return crypto_cipher_blocksize(child);
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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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struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(tfm);
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crypto_cipher_encrypt_one(ctx->child, 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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2018-04-09 07:54:47 -06:00
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u8 tmp[MAX_CIPHER_BLOCKSIZE + MAX_CIPHER_ALIGNMASK];
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2018-03-01 15:36:17 -07:00
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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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memcpy(iv, dst, bsize);
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src += bsize;
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dst += 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_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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2018-04-09 07:54:47 -06:00
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u8 tmp[MAX_CIPHER_BLOCKSIZE];
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2018-03-01 15:36:17 -07:00
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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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2018-10-19 17:01:52 -06:00
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crypto_xor(dst, src, bsize);
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2018-03-01 15:36:17 -07:00
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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 *iv = walk->iv;
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2018-04-09 07:54:47 -06:00
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u8 tmp[MAX_CIPHER_BLOCKSIZE];
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2018-03-01 15:36:17 -07:00
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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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memcpy(walk->iv, iv, 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_setkey(struct crypto_skcipher *parent, const u8 *key,
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unsigned int keylen)
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{
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struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(parent);
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struct crypto_cipher *child = ctx->child;
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int err;
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crypto_cipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
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crypto_cipher_set_flags(child, crypto_skcipher_get_flags(parent) &
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CRYPTO_TFM_REQ_MASK);
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err = crypto_cipher_setkey(child, key, keylen);
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crypto_skcipher_set_flags(parent, crypto_cipher_get_flags(child) &
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CRYPTO_TFM_RES_MASK);
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return err;
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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_init_tfm(struct crypto_skcipher *tfm)
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{
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struct skcipher_instance *inst = skcipher_alg_instance(tfm);
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struct crypto_spawn *spawn = skcipher_instance_ctx(inst);
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struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(tfm);
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struct crypto_cipher *cipher;
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cipher = crypto_spawn_cipher(spawn);
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if (IS_ERR(cipher))
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return PTR_ERR(cipher);
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ctx->child = cipher;
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return 0;
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}
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static void crypto_cfb_exit_tfm(struct crypto_skcipher *tfm)
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{
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struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(tfm);
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crypto_free_cipher(ctx->child);
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}
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static void crypto_cfb_free(struct skcipher_instance *inst)
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{
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crypto_drop_skcipher(skcipher_instance_ctx(inst));
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kfree(inst);
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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_attr_type *algt;
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struct crypto_spawn *spawn;
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struct crypto_alg *alg;
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u32 mask;
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int err;
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err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SKCIPHER);
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if (err)
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return err;
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inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL);
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if (!inst)
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return -ENOMEM;
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algt = crypto_get_attr_type(tb);
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err = PTR_ERR(algt);
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if (IS_ERR(algt))
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goto err_free_inst;
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mask = CRYPTO_ALG_TYPE_MASK |
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crypto_requires_off(algt->type, algt->mask,
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CRYPTO_ALG_NEED_FALLBACK);
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alg = crypto_get_attr_alg(tb, CRYPTO_ALG_TYPE_CIPHER, mask);
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err = PTR_ERR(alg);
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if (IS_ERR(alg))
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goto err_free_inst;
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spawn = skcipher_instance_ctx(inst);
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err = crypto_init_spawn(spawn, alg, skcipher_crypto_instance(inst),
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CRYPTO_ALG_TYPE_MASK);
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crypto_mod_put(alg);
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if (err)
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goto err_free_inst;
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err = crypto_inst_setname(skcipher_crypto_instance(inst), "cfb", alg);
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if (err)
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goto err_drop_spawn;
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inst->alg.base.cra_priority = alg->cra_priority;
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/* we're a stream cipher independend of the crypto cra_blocksize */
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inst->alg.base.cra_blocksize = 1;
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inst->alg.base.cra_alignmask = alg->cra_alignmask;
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inst->alg.ivsize = alg->cra_blocksize;
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inst->alg.min_keysize = alg->cra_cipher.cia_min_keysize;
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inst->alg.max_keysize = alg->cra_cipher.cia_max_keysize;
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inst->alg.base.cra_ctxsize = sizeof(struct crypto_cfb_ctx);
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inst->alg.init = crypto_cfb_init_tfm;
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inst->alg.exit = crypto_cfb_exit_tfm;
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inst->alg.setkey = crypto_cfb_setkey;
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inst->alg.encrypt = crypto_cfb_encrypt;
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inst->alg.decrypt = crypto_cfb_decrypt;
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inst->free = crypto_cfb_free;
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err = skcipher_register_instance(tmpl, inst);
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if (err)
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goto err_drop_spawn;
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out:
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return err;
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err_drop_spawn:
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crypto_drop_spawn(spawn);
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err_free_inst:
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kfree(inst);
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goto out;
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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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module_init(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 algorithm");
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MODULE_ALIAS_CRYPTO("cfb");
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