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 18 static 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 53 static 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 84 static struct crypto_template crypto_ofb_tmpl = { 85 .name = "ofb", 86 .create = crypto_ofb_create, 87 .module = THIS_MODULE, 88 }; 89 90 static int __init crypto_ofb_module_init(void) 91 { 92 return crypto_register_template(&crypto_ofb_tmpl); 93 } 94 95 static void __exit crypto_ofb_module_exit(void) 96 { 97 crypto_unregister_template(&crypto_ofb_tmpl); 98 } 99 100 subsys_initcall(crypto_ofb_module_init); 101 module_exit(crypto_ofb_module_exit); 102 103 MODULE_LICENSE("GPL"); 104 MODULE_DESCRIPTION("OFB block cipher mode of operation"); 105 MODULE_ALIAS_CRYPTO("ofb"); 106 MODULE_IMPORT_NS(CRYPTO_INTERNAL); 107