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 17 static 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 52 static 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, &alg); 59 if (IS_ERR(inst)) 60 return PTR_ERR(inst); 61 62 /* OFB mode is a stream cipher. */ 63 inst->alg.base.cra_blocksize = 1; 64 65 /* 66 * To simplify the implementation, configure the skcipher walk to only 67 * give a partial block at the very end, never earlier. 68 */ 69 inst->alg.chunksize = alg->cra_blocksize; 70 71 inst->alg.encrypt = crypto_ofb_crypt; 72 inst->alg.decrypt = crypto_ofb_crypt; 73 74 err = skcipher_register_instance(tmpl, inst); 75 if (err) 76 inst->free(inst); 77 78 crypto_mod_put(alg); 79 return err; 80 } 81 82 static struct crypto_template crypto_ofb_tmpl = { 83 .name = "ofb", 84 .create = crypto_ofb_create, 85 .module = THIS_MODULE, 86 }; 87 88 static int __init crypto_ofb_module_init(void) 89 { 90 return crypto_register_template(&crypto_ofb_tmpl); 91 } 92 93 static void __exit crypto_ofb_module_exit(void) 94 { 95 crypto_unregister_template(&crypto_ofb_tmpl); 96 } 97 98 module_init(crypto_ofb_module_init); 99 module_exit(crypto_ofb_module_exit); 100 101 MODULE_LICENSE("GPL"); 102 MODULE_DESCRIPTION("OFB block cipher mode of operation"); 103 MODULE_ALIAS_CRYPTO("ofb"); 104