LXR linux/crypto/ofb.c

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