crypto/cbc.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * CBC: Cipher Block Chaining mode
   4  *
   5  * Copyright (c) 2006-2016 Herbert Xu <herbert@gondor.apana.org.au>
   6  */
   7
   8 #include <crypto/internal/skcipher.h>
   9 #include <linux/err.h>
  10 #include <linux/init.h>
  11 #include <linux/kernel.h>
  12 #include <linux/log2.h>
  13 #include <linux/module.h>
  14
  15 static int crypto_cbc_encrypt_segment(struct crypto_lskcipher *tfm,
  16                                       const u8 *src, u8 *dst, unsigned nbytes,
  17                                       u8 *iv)
  18 {
  19         unsigned int bsize = crypto_lskcipher_blocksize(tfm);
  20
  21         for (; nbytes >= bsize; src += bsize, dst += bsize, nbytes -= bsize) {
  22                 crypto_xor(iv, src, bsize);
  23                 crypto_lskcipher_encrypt(tfm, iv, dst, bsize, NULL);
  24                 memcpy(iv, dst, bsize);
  25         }
  26
  27         return nbytes;
  28 }
  29
  30 static int crypto_cbc_encrypt_inplace(struct crypto_lskcipher *tfm,
  31                                       u8 *src, unsigned nbytes, u8 *oiv)
  32 {
  33         unsigned int bsize = crypto_lskcipher_blocksize(tfm);
  34         u8 *iv = oiv;
  35
  36         if (nbytes < bsize)
  37                 goto out;
  38
  39         do {
  40                 crypto_xor(src, iv, bsize);
  41                 crypto_lskcipher_encrypt(tfm, src, src, bsize, NULL);
  42                 iv = src;
  43
  44                 src += bsize;
  45         } while ((nbytes -= bsize) >= bsize);
  46
  47         memcpy(oiv, iv, bsize);
  48
  49 out:
  50         return nbytes;
  51 }
  52
  53 static int crypto_cbc_encrypt(struct crypto_lskcipher *tfm, const u8 *src,
  54                               u8 *dst, unsigned len, u8 *iv, bool final)
  55 {
  56         struct crypto_lskcipher **ctx = crypto_lskcipher_ctx(tfm);
  57         struct crypto_lskcipher *cipher = *ctx;
  58         int rem;
  59
  60         if (src == dst)
  61                 rem = crypto_cbc_encrypt_inplace(cipher, dst, len, iv);
  62         else
  63                 rem = crypto_cbc_encrypt_segment(cipher, src, dst, len, iv);
  64
  65         return rem && final ? -EINVAL : rem;
  66 }
  67
  68 static int crypto_cbc_decrypt_segment(struct crypto_lskcipher *tfm,
  69                                       const u8 *src, u8 *dst, unsigned nbytes,
  70                                       u8 *oiv)
  71 {
  72         unsigned int bsize = crypto_lskcipher_blocksize(tfm);
  73         const u8 *iv = oiv;
  74
  75         if (nbytes < bsize)
  76                 goto out;
  77
  78         do {
  79                 crypto_lskcipher_decrypt(tfm, src, dst, bsize, NULL);
  80                 crypto_xor(dst, iv, bsize);
  81                 iv = src;
  82
  83                 src += bsize;
  84                 dst += bsize;
  85         } while ((nbytes -= bsize) >= bsize);
  86
  87         memcpy(oiv, iv, bsize);
  88
  89 out:
  90         return nbytes;
  91 }
  92
  93 static int crypto_cbc_decrypt_inplace(struct crypto_lskcipher *tfm,
  94                                       u8 *src, unsigned nbytes, u8 *iv)
  95 {
  96         unsigned int bsize = crypto_lskcipher_blocksize(tfm);
  97         u8 last_iv[MAX_CIPHER_BLOCKSIZE];
  98
  99         if (nbytes < bsize)
 100                 goto out;
 101
 102         /* Start of the last block. */
 103         src += nbytes - (nbytes & (bsize - 1)) - bsize;
 104         memcpy(last_iv, src, bsize);
 105
 106         for (;;) {
 107                 crypto_lskcipher_decrypt(tfm, src, src, bsize, NULL);
 108                 if ((nbytes -= bsize) < bsize)
 109                         break;
 110                 crypto_xor(src, src - bsize, bsize);
 111                 src -= bsize;
 112         }
 113
 114         crypto_xor(src, iv, bsize);
 115         memcpy(iv, last_iv, bsize);
 116
 117 out:
 118         return nbytes;
 119 }
 120
 121 static int crypto_cbc_decrypt(struct crypto_lskcipher *tfm, const u8 *src,
 122                               u8 *dst, unsigned len, u8 *iv, bool final)
 123 {
 124         struct crypto_lskcipher **ctx = crypto_lskcipher_ctx(tfm);
 125         struct crypto_lskcipher *cipher = *ctx;
 126         int rem;
 127
 128         if (src == dst)
 129                 rem = crypto_cbc_decrypt_inplace(cipher, dst, len, iv);
 130         else
 131                 rem = crypto_cbc_decrypt_segment(cipher, src, dst, len, iv);
 132
 133         return rem && final ? -EINVAL : rem;
 134 }
 135
 136 static int crypto_cbc_create(struct crypto_template *tmpl, struct rtattr **tb)
 137 {
 138         struct lskcipher_instance *inst;
 139         int err;
 140
 141         inst = lskcipher_alloc_instance_simple(tmpl, tb);
 142         if (IS_ERR(inst))
 143                 return PTR_ERR(inst);
 144
 145         err = -EINVAL;
 146         if (!is_power_of_2(inst->alg.co.base.cra_blocksize))
 147                 goto out_free_inst;
 148
 149         inst->alg.encrypt = crypto_cbc_encrypt;
 150         inst->alg.decrypt = crypto_cbc_decrypt;
 151
 152         err = lskcipher_register_instance(tmpl, inst);
 153         if (err) {
 154 out_free_inst:
 155                 inst->free(inst);
 156         }
 157
 158         return err;
 159 }
 160
 161 static struct crypto_template crypto_cbc_tmpl = {
 162         .name = "cbc",
 163         .create = crypto_cbc_create,
 164         .module = THIS_MODULE,
 165 };
 166
 167 static int __init crypto_cbc_module_init(void)
 168 {
 169         return crypto_register_template(&crypto_cbc_tmpl);
 170 }
 171
 172 static void __exit crypto_cbc_module_exit(void)
 173 {
 174         crypto_unregister_template(&crypto_cbc_tmpl);
 175 }
 176
 177 subsys_initcall(crypto_cbc_module_init);
 178 module_exit(crypto_cbc_module_exit);
 179
 180 MODULE_LICENSE("GPL");
 181 MODULE_DESCRIPTION("CBC block cipher mode of operation");
 182 MODULE_ALIAS_CRYPTO("cbc");