linux/crypto/ofb.c
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   1// SPDX-License-Identifier: GPL-2.0
   2
   3/*
   4 * OFB: Output FeedBack mode
   5 *
   6 * Copyright (C) 2018 ARM Limited or its affiliates.
   7 * All rights reserved.
   8 */
   9
  10#include <crypto/algapi.h>
  11#include <crypto/internal/cipher.h>
  12#include <crypto/internal/skcipher.h>
  13#include <linux/err.h>
  14#include <linux/init.h>
  15#include <linux/kernel.h>
  16#include <linux/module.h>
  17
  18static int crypto_ofb_crypt(struct skcipher_request *req)
  19{
  20        struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
  21        struct crypto_cipher *cipher = skcipher_cipher_simple(tfm);
  22        const unsigned int bsize = crypto_cipher_blocksize(cipher);
  23        struct skcipher_walk walk;
  24        int err;
  25
  26        err = skcipher_walk_virt(&walk, req, false);
  27
  28        while (walk.nbytes >= bsize) {
  29                const u8 *src = walk.src.virt.addr;
  30                u8 *dst = walk.dst.virt.addr;
  31                u8 * const iv = walk.iv;
  32                unsigned int nbytes = walk.nbytes;
  33
  34                do {
  35                        crypto_cipher_encrypt_one(cipher, iv, iv);
  36                        crypto_xor_cpy(dst, src, iv, bsize);
  37                        dst += bsize;
  38                        src += bsize;
  39                } while ((nbytes -= bsize) >= bsize);
  40
  41                err = skcipher_walk_done(&walk, nbytes);
  42        }
  43
  44        if (walk.nbytes) {
  45                crypto_cipher_encrypt_one(cipher, walk.iv, walk.iv);
  46                crypto_xor_cpy(walk.dst.virt.addr, walk.src.virt.addr, walk.iv,
  47                               walk.nbytes);
  48                err = skcipher_walk_done(&walk, 0);
  49        }
  50        return err;
  51}
  52
  53static int crypto_ofb_create(struct crypto_template *tmpl, struct rtattr **tb)
  54{
  55        struct skcipher_instance *inst;
  56        struct crypto_alg *alg;
  57        int err;
  58
  59        inst = skcipher_alloc_instance_simple(tmpl, tb);
  60        if (IS_ERR(inst))
  61                return PTR_ERR(inst);
  62
  63        alg = skcipher_ialg_simple(inst);
  64
  65        /* OFB mode is a stream cipher. */
  66        inst->alg.base.cra_blocksize = 1;
  67
  68        /*
  69         * To simplify the implementation, configure the skcipher walk to only
  70         * give a partial block at the very end, never earlier.
  71         */
  72        inst->alg.chunksize = alg->cra_blocksize;
  73
  74        inst->alg.encrypt = crypto_ofb_crypt;
  75        inst->alg.decrypt = crypto_ofb_crypt;
  76
  77        err = skcipher_register_instance(tmpl, inst);
  78        if (err)
  79                inst->free(inst);
  80
  81        return err;
  82}
  83
  84static struct crypto_template crypto_ofb_tmpl = {
  85        .name = "ofb",
  86        .create = crypto_ofb_create,
  87        .module = THIS_MODULE,
  88};
  89
  90static int __init crypto_ofb_module_init(void)
  91{
  92        return crypto_register_template(&crypto_ofb_tmpl);
  93}
  94
  95static void __exit crypto_ofb_module_exit(void)
  96{
  97        crypto_unregister_template(&crypto_ofb_tmpl);
  98}
  99
 100subsys_initcall(crypto_ofb_module_init);
 101module_exit(crypto_ofb_module_exit);
 102
 103MODULE_LICENSE("GPL");
 104MODULE_DESCRIPTION("OFB block cipher mode of operation");
 105MODULE_ALIAS_CRYPTO("ofb");
 106MODULE_IMPORT_NS(CRYPTO_INTERNAL);
 107
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