2 * CTS: Cipher Text Stealing mode
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19 * THIS SOFTWARE IS PROVIDED AS IS, WITHOUT REPRESENTATION
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33 /* Derived from various:
34 * Copyright (c) 2006 Herbert Xu <herbert@gondor.apana.org.au>
38 * This is the Cipher Text Stealing mode as described by
39 * Section 8 of rfc2040 and referenced by rfc3962.
40 * rfc3962 includes errata information in its Appendix A.
43 #include <crypto/algapi.h>
44 #include <linux/err.h>
45 #include <linux/init.h>
46 #include <linux/kernel.h>
47 #include <linux/log2.h>
48 #include <linux/module.h>
49 #include <linux/scatterlist.h>
50 #include <crypto/scatterwalk.h>
51 #include <linux/slab.h>
53 struct crypto_cts_ctx {
54 struct crypto_blkcipher *child;
57 static int crypto_cts_setkey(struct crypto_tfm *parent, const u8 *key,
60 struct crypto_cts_ctx *ctx = crypto_tfm_ctx(parent);
61 struct crypto_blkcipher *child = ctx->child;
64 crypto_blkcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
65 crypto_blkcipher_set_flags(child, crypto_tfm_get_flags(parent) &
67 err = crypto_blkcipher_setkey(child, key, keylen);
68 crypto_tfm_set_flags(parent, crypto_blkcipher_get_flags(child) &
73 static int cts_cbc_encrypt(struct crypto_cts_ctx *ctx,
74 struct blkcipher_desc *desc,
75 struct scatterlist *dst,
76 struct scatterlist *src,
80 int bsize = crypto_blkcipher_blocksize(desc->tfm);
81 u8 tmp[bsize], tmp2[bsize];
82 struct blkcipher_desc lcldesc;
83 struct scatterlist sgsrc[1], sgdst[1];
84 int lastn = nbytes - bsize;
86 u8 s[bsize * 2], d[bsize * 2];
92 sg_init_table(sgsrc, 1);
93 sg_init_table(sgdst, 1);
95 memset(s, 0, sizeof(s));
96 scatterwalk_map_and_copy(s, src, offset, nbytes, 0);
98 memcpy(iv, desc->info, bsize);
100 lcldesc.tfm = ctx->child;
102 lcldesc.flags = desc->flags;
104 sg_set_buf(&sgsrc[0], s, bsize);
105 sg_set_buf(&sgdst[0], tmp, bsize);
106 err = crypto_blkcipher_encrypt_iv(&lcldesc, sgdst, sgsrc, bsize);
108 memcpy(d + bsize, tmp, lastn);
112 sg_set_buf(&sgsrc[0], s + bsize, bsize);
113 sg_set_buf(&sgdst[0], tmp2, bsize);
114 err = crypto_blkcipher_encrypt_iv(&lcldesc, sgdst, sgsrc, bsize);
116 memcpy(d, tmp2, bsize);
118 scatterwalk_map_and_copy(d, dst, offset, nbytes, 1);
120 memcpy(desc->info, tmp2, bsize);
125 static int crypto_cts_encrypt(struct blkcipher_desc *desc,
126 struct scatterlist *dst, struct scatterlist *src,
129 struct crypto_cts_ctx *ctx = crypto_blkcipher_ctx(desc->tfm);
130 int bsize = crypto_blkcipher_blocksize(desc->tfm);
131 int tot_blocks = (nbytes + bsize - 1) / bsize;
132 int cbc_blocks = tot_blocks > 2 ? tot_blocks - 2 : 0;
133 struct blkcipher_desc lcldesc;
136 lcldesc.tfm = ctx->child;
137 lcldesc.info = desc->info;
138 lcldesc.flags = desc->flags;
140 if (tot_blocks == 1) {
141 err = crypto_blkcipher_encrypt_iv(&lcldesc, dst, src, bsize);
142 } else if (nbytes <= bsize * 2) {
143 err = cts_cbc_encrypt(ctx, desc, dst, src, 0, nbytes);
145 /* do normal function for tot_blocks - 2 */
146 err = crypto_blkcipher_encrypt_iv(&lcldesc, dst, src,
149 /* do cts for final two blocks */
150 err = cts_cbc_encrypt(ctx, desc, dst, src,
152 nbytes - (cbc_blocks * bsize));
159 static int cts_cbc_decrypt(struct crypto_cts_ctx *ctx,
160 struct blkcipher_desc *desc,
161 struct scatterlist *dst,
162 struct scatterlist *src,
166 int bsize = crypto_blkcipher_blocksize(desc->tfm);
168 struct blkcipher_desc lcldesc;
169 struct scatterlist sgsrc[1], sgdst[1];
170 int lastn = nbytes - bsize;
172 u8 s[bsize * 2], d[bsize * 2];
178 sg_init_table(sgsrc, 1);
179 sg_init_table(sgdst, 1);
181 scatterwalk_map_and_copy(s, src, offset, nbytes, 0);
183 lcldesc.tfm = ctx->child;
185 lcldesc.flags = desc->flags;
187 /* 1. Decrypt Cn-1 (s) to create Dn (tmp)*/
188 memset(iv, 0, sizeof(iv));
189 sg_set_buf(&sgsrc[0], s, bsize);
190 sg_set_buf(&sgdst[0], tmp, bsize);
191 err = crypto_blkcipher_decrypt_iv(&lcldesc, sgdst, sgsrc, bsize);
194 /* 2. Pad Cn with zeros at the end to create C of length BB */
195 memset(iv, 0, sizeof(iv));
196 memcpy(iv, s + bsize, lastn);
197 /* 3. Exclusive-or Dn (tmp) with C (iv) to create Xn (tmp) */
198 crypto_xor(tmp, iv, bsize);
199 /* 4. Select the first Ln bytes of Xn (tmp) to create Pn */
200 memcpy(d + bsize, tmp, lastn);
202 /* 5. Append the tail (BB - Ln) bytes of Xn (tmp) to Cn to create En */
203 memcpy(s + bsize + lastn, tmp + lastn, bsize - lastn);
204 /* 6. Decrypt En to create Pn-1 */
205 memzero_explicit(iv, sizeof(iv));
207 sg_set_buf(&sgsrc[0], s + bsize, bsize);
208 sg_set_buf(&sgdst[0], d, bsize);
209 err = crypto_blkcipher_decrypt_iv(&lcldesc, sgdst, sgsrc, bsize);
211 /* XOR with previous block */
212 crypto_xor(d, desc->info, bsize);
214 scatterwalk_map_and_copy(d, dst, offset, nbytes, 1);
216 memcpy(desc->info, s, bsize);
220 static int crypto_cts_decrypt(struct blkcipher_desc *desc,
221 struct scatterlist *dst, struct scatterlist *src,
224 struct crypto_cts_ctx *ctx = crypto_blkcipher_ctx(desc->tfm);
225 int bsize = crypto_blkcipher_blocksize(desc->tfm);
226 int tot_blocks = (nbytes + bsize - 1) / bsize;
227 int cbc_blocks = tot_blocks > 2 ? tot_blocks - 2 : 0;
228 struct blkcipher_desc lcldesc;
231 lcldesc.tfm = ctx->child;
232 lcldesc.info = desc->info;
233 lcldesc.flags = desc->flags;
235 if (tot_blocks == 1) {
236 err = crypto_blkcipher_decrypt_iv(&lcldesc, dst, src, bsize);
237 } else if (nbytes <= bsize * 2) {
238 err = cts_cbc_decrypt(ctx, desc, dst, src, 0, nbytes);
240 /* do normal function for tot_blocks - 2 */
241 err = crypto_blkcipher_decrypt_iv(&lcldesc, dst, src,
244 /* do cts for final two blocks */
245 err = cts_cbc_decrypt(ctx, desc, dst, src,
247 nbytes - (cbc_blocks * bsize));
253 static int crypto_cts_init_tfm(struct crypto_tfm *tfm)
255 struct crypto_instance *inst = (void *)tfm->__crt_alg;
256 struct crypto_spawn *spawn = crypto_instance_ctx(inst);
257 struct crypto_cts_ctx *ctx = crypto_tfm_ctx(tfm);
258 struct crypto_blkcipher *cipher;
260 cipher = crypto_spawn_blkcipher(spawn);
262 return PTR_ERR(cipher);
268 static void crypto_cts_exit_tfm(struct crypto_tfm *tfm)
270 struct crypto_cts_ctx *ctx = crypto_tfm_ctx(tfm);
271 crypto_free_blkcipher(ctx->child);
274 static struct crypto_instance *crypto_cts_alloc(struct rtattr **tb)
276 struct crypto_instance *inst;
277 struct crypto_alg *alg;
280 err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_BLKCIPHER);
284 alg = crypto_attr_alg(tb[1], CRYPTO_ALG_TYPE_BLKCIPHER,
285 CRYPTO_ALG_TYPE_MASK);
287 return ERR_CAST(alg);
289 inst = ERR_PTR(-EINVAL);
290 if (!is_power_of_2(alg->cra_blocksize))
293 if (strncmp(alg->cra_name, "cbc(", 4))
296 inst = crypto_alloc_instance("cts", alg);
300 inst->alg.cra_flags = CRYPTO_ALG_TYPE_BLKCIPHER;
301 inst->alg.cra_priority = alg->cra_priority;
302 inst->alg.cra_blocksize = alg->cra_blocksize;
303 inst->alg.cra_alignmask = alg->cra_alignmask;
304 inst->alg.cra_type = &crypto_blkcipher_type;
306 /* We access the data as u32s when xoring. */
307 inst->alg.cra_alignmask |= __alignof__(u32) - 1;
309 inst->alg.cra_blkcipher.ivsize = alg->cra_blocksize;
310 inst->alg.cra_blkcipher.min_keysize = alg->cra_blkcipher.min_keysize;
311 inst->alg.cra_blkcipher.max_keysize = alg->cra_blkcipher.max_keysize;
313 inst->alg.cra_ctxsize = sizeof(struct crypto_cts_ctx);
315 inst->alg.cra_init = crypto_cts_init_tfm;
316 inst->alg.cra_exit = crypto_cts_exit_tfm;
318 inst->alg.cra_blkcipher.setkey = crypto_cts_setkey;
319 inst->alg.cra_blkcipher.encrypt = crypto_cts_encrypt;
320 inst->alg.cra_blkcipher.decrypt = crypto_cts_decrypt;
327 static void crypto_cts_free(struct crypto_instance *inst)
329 crypto_drop_spawn(crypto_instance_ctx(inst));
333 static struct crypto_template crypto_cts_tmpl = {
335 .alloc = crypto_cts_alloc,
336 .free = crypto_cts_free,
337 .module = THIS_MODULE,
340 static int __init crypto_cts_module_init(void)
342 return crypto_register_template(&crypto_cts_tmpl);
345 static void __exit crypto_cts_module_exit(void)
347 crypto_unregister_template(&crypto_cts_tmpl);
350 module_init(crypto_cts_module_init);
351 module_exit(crypto_cts_module_exit);
353 MODULE_LICENSE("Dual BSD/GPL");
354 MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC");
355 MODULE_ALIAS_CRYPTO("cts");