| //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/cipher.h> |
| #include <crypto/internal/skcipher.h> |
| #include <linux/err.h> |
| #include <linux/init.h> |
| #include <linux/kernel.h> |
| #include <linux/module.h> |
| #include <linux/string.h> |
| |
| static unsigned int crypto_cfb_bsize(struct crypto_skcipher *tfm) |
| { |
| return crypto_cipher_blocksize(skcipher_cipher_simple(tfm)); |
| } |
| |
| static void crypto_cfb_encrypt_one(struct crypto_skcipher *tfm, |
| const u8 *src, u8 *dst) |
| { |
| crypto_cipher_encrypt_one(skcipher_cipher_simple(tfm), 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); |
| iv = dst; |
| |
| src += bsize; |
| dst += bsize; |
| } while ((nbytes -= bsize) >= bsize); |
| |
| memcpy(walk->iv, iv, 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 * const 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); |
| |
| 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_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_create(struct crypto_template *tmpl, struct rtattr **tb) |
| { |
| struct skcipher_instance *inst; |
| struct crypto_alg *alg; |
| int err; |
| |
| inst = skcipher_alloc_instance_simple(tmpl, tb); |
| if (IS_ERR(inst)) |
| return PTR_ERR(inst); |
| |
| alg = skcipher_ialg_simple(inst); |
| |
| /* CFB mode is a stream cipher. */ |
| inst->alg.base.cra_blocksize = 1; |
| |
| /* |
| * To simplify the implementation, configure the skcipher walk to only |
| * give a partial block at the very end, never earlier. |
| */ |
| inst->alg.chunksize = alg->cra_blocksize; |
| |
| inst->alg.encrypt = crypto_cfb_encrypt; |
| inst->alg.decrypt = crypto_cfb_decrypt; |
| |
| err = skcipher_register_instance(tmpl, inst); |
| if (err) |
| inst->free(inst); |
| |
| return err; |
| } |
| |
| 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); |
| } |
| |
| subsys_initcall(crypto_cfb_module_init); |
| module_exit(crypto_cfb_module_exit); |
| |
| MODULE_LICENSE("GPL"); |
| MODULE_DESCRIPTION("CFB block cipher mode of operation"); |
| MODULE_ALIAS_CRYPTO("cfb"); |
| MODULE_IMPORT_NS(CRYPTO_INTERNAL); |