2 * Copyright 2020 The OpenSSL Project Authors. All Rights Reserved.
4 * Licensed under the Apache License 2.0 (the "License"). You may not use
5 * this file except in compliance with the License. You can obtain a copy
6 * in the file LICENSE in the source distribution or at
7 * https://www.openssl.org/source/license.html
11 * Helper functions for AES CBC CTS ciphers.
13 * The function dispatch tables are embedded into cipher_aes.c
14 * using cipher_aes_cts.inc
18 * Refer to SP800-38A-Addendum
20 * Ciphertext stealing encrypts plaintext using a block cipher, without padding
21 * the message to a multiple of the block size, so the ciphertext is the same
22 * size as the plaintext.
23 * It does this by altering processing of the last two blocks of the message.
24 * The processing of all but the last two blocks is unchanged, but a portion of
25 * the second-last block's ciphertext is "stolen" to pad the last plaintext
26 * block. The padded final block is then encrypted as usual.
27 * The final ciphertext for the last two blocks, consists of the partial block
28 * (with the "stolen" portion omitted) plus the full final block,
29 * which are the same size as the original plaintext.
30 * Decryption requires decrypting the final block first, then restoring the
31 * stolen ciphertext to the partial block, which can then be decrypted as usual.
33 * AES_CBC_CTS has 3 variants:
34 * (1) CS1 The NIST variant.
35 * If the length is a multiple of the blocksize it is the same as CBC mode.
36 * otherwise it produces C1||C2||(C(n-1))*||Cn.
37 * Where C(n-1)* is a partial block.
39 * If the length is a multiple of the blocksize it is the same as CBC mode.
40 * otherwise it produces C1||C2||Cn||(C(n-1))*.
41 * Where C(n-1)* is a partial block.
42 * (3) CS3 The Kerberos5 variant.
43 * Produces C1||C2||Cn||(C(n-1))* regardless of the length.
44 * If the length is a multiple of the blocksize it looks similar to CBC mode
45 * with the last 2 blocks swapped.
46 * Otherwise it is the same as CS2.
49 #include "e_os.h" /* strcasecmp */
50 #include <openssl/core_names.h>
51 #include <openssl/aes.h>
52 #include "prov/ciphercommon.h"
53 #include "internal/nelem.h"
54 #include "cipher_aes_cts.h"
56 /* The value assigned to 0 is the default */
63 unsigned char c
[AES_BLOCK_SIZE
];
66 typedef struct cts_mode_name2id_st
{
71 static CTS_MODE_NAME2ID cts_modes
[] =
73 { CTS_CS1
, OSSL_CIPHER_CTS_MODE_CS1
},
74 { CTS_CS2
, OSSL_CIPHER_CTS_MODE_CS2
},
75 { CTS_CS3
, OSSL_CIPHER_CTS_MODE_CS3
},
78 const char *ossl_aes_cbc_cts_mode_id2name(unsigned int id
)
82 for (i
= 0; i
< OSSL_NELEM(cts_modes
); ++i
) {
83 if (cts_modes
[i
].id
== id
)
84 return cts_modes
[i
].name
;
89 int ossl_aes_cbc_cts_mode_name2id(const char *name
)
93 for (i
= 0; i
< OSSL_NELEM(cts_modes
); ++i
) {
94 if (strcasecmp(name
, cts_modes
[i
].name
) == 0)
95 return (int)cts_modes
[i
].id
;
100 static size_t cts128_cs1_encrypt(PROV_CIPHER_CTX
*ctx
, const unsigned char *in
,
101 unsigned char *out
, size_t len
)
103 aligned_16bytes tmp_in
;
106 residue
= len
% AES_BLOCK_SIZE
;
108 if (!ctx
->hw
->cipher(ctx
, out
, in
, len
))
117 memset(tmp_in
.c
, 0, sizeof(tmp_in
));
118 memcpy(tmp_in
.c
, in
, residue
);
119 if (!ctx
->hw
->cipher(ctx
, out
- AES_BLOCK_SIZE
+ residue
, tmp_in
.c
,
122 return len
+ residue
;
125 static void do_xor(const unsigned char *in1
, const unsigned char *in2
,
126 size_t len
, unsigned char *out
)
130 for (i
= 0; i
< len
; ++i
)
131 out
[i
] = in1
[i
] ^ in2
[i
];
134 static size_t cts128_cs1_decrypt(PROV_CIPHER_CTX
*ctx
, const unsigned char *in
,
135 unsigned char *out
, size_t len
)
137 aligned_16bytes mid_iv
, ct_mid
, pt_last
;
140 residue
= len
% AES_BLOCK_SIZE
;
142 /* If there are no partial blocks then it is the same as CBC mode */
143 if (!ctx
->hw
->cipher(ctx
, out
, in
, len
))
147 /* Process blocks at the start - but leave the last 2 blocks */
148 len
-= AES_BLOCK_SIZE
+ residue
;
150 if (!ctx
->hw
->cipher(ctx
, out
, in
, len
))
155 /* Save the iv that will be used by the second last block */
156 memcpy(mid_iv
.c
, ctx
->iv
, AES_BLOCK_SIZE
);
158 /* Decrypt the last block first using an iv of zero */
159 memset(ctx
->iv
, 0, AES_BLOCK_SIZE
);
160 if (!ctx
->hw
->cipher(ctx
, pt_last
.c
, in
+ residue
, AES_BLOCK_SIZE
))
164 * Rebuild the ciphertext of the second last block as a combination of
165 * the decrypted last block + replace the start with the ciphertext bytes
166 * of the partial second last block.
168 memcpy(ct_mid
.c
, in
, residue
);
169 memcpy(ct_mid
.c
+ residue
, pt_last
.c
+ residue
, AES_BLOCK_SIZE
- residue
);
171 * Restore the last partial ciphertext block.
172 * Now that we have the cipher text of the second last block, apply
173 * that to the partial plaintext end block. We have already decrypted the
174 * block using an IV of zero. For decryption the IV is just XORed after
175 * doing an AES block - so just XOR in the cipher text.
177 do_xor(ct_mid
.c
, pt_last
.c
, residue
, out
+ AES_BLOCK_SIZE
);
179 /* Restore the iv needed by the second last block */
180 memcpy(ctx
->iv
, mid_iv
.c
, AES_BLOCK_SIZE
);
182 * Decrypt the second last plaintext block now that we have rebuilt the
185 if (!ctx
->hw
->cipher(ctx
, out
, ct_mid
.c
, AES_BLOCK_SIZE
))
188 return len
+ AES_BLOCK_SIZE
+ residue
;
191 static size_t cts128_cs3_encrypt(PROV_CIPHER_CTX
*ctx
, const unsigned char *in
,
192 unsigned char *out
, size_t len
)
194 aligned_16bytes tmp_in
;
197 if (len
<= AES_BLOCK_SIZE
) /* CS3 requires 2 blocks */
200 residue
= len
% AES_BLOCK_SIZE
;
202 residue
= AES_BLOCK_SIZE
;
205 if (!ctx
->hw
->cipher(ctx
, out
, in
, len
))
211 memset(tmp_in
.c
, 0, sizeof(tmp_in
));
212 memcpy(tmp_in
.c
, in
, residue
);
213 memcpy(out
, out
- AES_BLOCK_SIZE
, residue
);
214 if (!ctx
->hw
->cipher(ctx
, out
- AES_BLOCK_SIZE
, tmp_in
.c
, AES_BLOCK_SIZE
))
216 return len
+ residue
;
221 * The cipher text (in) is of the form C(0), C(1), ., C(n), C(n-1)* where
222 * C(n) is a full block and C(n-1)* can be a partial block
223 * (but could be a full block).
224 * This means that the output plaintext (out) needs to swap the plaintext of
225 * the last two decoded ciphertext blocks.
227 static size_t cts128_cs3_decrypt(PROV_CIPHER_CTX
*ctx
, const unsigned char *in
,
228 unsigned char *out
, size_t len
)
230 aligned_16bytes mid_iv
, ct_mid
, pt_last
;
233 if (len
<= AES_BLOCK_SIZE
) /* CS3 requires 2 blocks */
236 /* Process blocks at the start - but leave the last 2 blocks */
237 residue
= len
% AES_BLOCK_SIZE
;
239 residue
= AES_BLOCK_SIZE
;
240 len
-= AES_BLOCK_SIZE
+ residue
;
243 if (!ctx
->hw
->cipher(ctx
, out
, in
, len
))
248 /* Save the iv that will be used by the second last block */
249 memcpy(mid_iv
.c
, ctx
->iv
, AES_BLOCK_SIZE
);
251 /* Decrypt the Cn block first using an iv of zero */
252 memset(ctx
->iv
, 0, AES_BLOCK_SIZE
);
253 if (!ctx
->hw
->cipher(ctx
, pt_last
.c
, in
, AES_BLOCK_SIZE
))
257 * Rebuild the ciphertext of C(n-1) as a combination of
258 * the decrypted C(n) block + replace the start with the ciphertext bytes
259 * of the partial last block.
261 memcpy(ct_mid
.c
, in
+ AES_BLOCK_SIZE
, residue
);
262 if (residue
!= AES_BLOCK_SIZE
)
263 memcpy(ct_mid
.c
+ residue
, pt_last
.c
+ residue
, AES_BLOCK_SIZE
- residue
);
265 * Restore the last partial ciphertext block.
266 * Now that we have the cipher text of the second last block, apply
267 * that to the partial plaintext end block. We have already decrypted the
268 * block using an IV of zero. For decryption the IV is just XORed after
269 * doing an AES block - so just XOR in the ciphertext.
271 do_xor(ct_mid
.c
, pt_last
.c
, residue
, out
+ AES_BLOCK_SIZE
);
273 /* Restore the iv needed by the second last block */
274 memcpy(ctx
->iv
, mid_iv
.c
, AES_BLOCK_SIZE
);
276 * Decrypt the second last plaintext block now that we have rebuilt the
279 if (!ctx
->hw
->cipher(ctx
, out
, ct_mid
.c
, AES_BLOCK_SIZE
))
282 return len
+ AES_BLOCK_SIZE
+ residue
;
285 static size_t cts128_cs2_encrypt(PROV_CIPHER_CTX
*ctx
, const unsigned char *in
,
286 unsigned char *out
, size_t len
)
288 if (len
% AES_BLOCK_SIZE
== 0) {
289 /* If there are no partial blocks then it is the same as CBC mode */
290 if (!ctx
->hw
->cipher(ctx
, out
, in
, len
))
294 /* For partial blocks CS2 is equivalent to CS3 */
295 return cts128_cs3_encrypt(ctx
, in
, out
, len
);
298 static size_t cts128_cs2_decrypt(PROV_CIPHER_CTX
*ctx
, const unsigned char *in
,
299 unsigned char *out
, size_t len
)
301 if (len
% AES_BLOCK_SIZE
== 0) {
302 /* If there are no partial blocks then it is the same as CBC mode */
303 if (!ctx
->hw
->cipher(ctx
, out
, in
, len
))
307 /* For partial blocks CS2 is equivalent to CS3 */
308 return cts128_cs3_decrypt(ctx
, in
, out
, len
);
311 int ossl_aes_cbc_cts_block_update(void *vctx
, unsigned char *out
, size_t *outl
,
312 size_t outsize
, const unsigned char *in
,
315 PROV_CIPHER_CTX
*ctx
= (PROV_CIPHER_CTX
*)vctx
;
318 if (inl
< AES_BLOCK_SIZE
) /* There must be at least one block for CTS mode */
328 * Return an error if the update is called multiple times, only one shot
331 if (ctx
->updated
== 1)
335 if (ctx
->cts_mode
== CTS_CS1
)
336 sz
= cts128_cs1_encrypt(ctx
, in
, out
, inl
);
337 else if (ctx
->cts_mode
== CTS_CS2
)
338 sz
= cts128_cs2_encrypt(ctx
, in
, out
, inl
);
339 else if (ctx
->cts_mode
== CTS_CS3
)
340 sz
= cts128_cs3_encrypt(ctx
, in
, out
, inl
);
342 if (ctx
->cts_mode
== CTS_CS1
)
343 sz
= cts128_cs1_decrypt(ctx
, in
, out
, inl
);
344 else if (ctx
->cts_mode
== CTS_CS2
)
345 sz
= cts128_cs2_decrypt(ctx
, in
, out
, inl
);
346 else if (ctx
->cts_mode
== CTS_CS3
)
347 sz
= cts128_cs3_decrypt(ctx
, in
, out
, inl
);
351 ctx
->updated
= 1; /* Stop multiple updates being allowed */
356 int ossl_aes_cbc_cts_block_final(void *vctx
, unsigned char *out
, size_t *outl
,