2 * Copyright 2020-2021 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 128 bit CBC CTS ciphers (Currently AES and Camellia).
13 * The function dispatch tables are embedded into cipher_aes.c
14 * and cipher_camellia.c using cipher_aes_cts.inc and cipher_camellia_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 "prov/ciphercommon.h"
52 #include "internal/nelem.h"
53 #include "cipher_cts.h"
55 /* The value assigned to 0 is the default */
60 #define CTS_BLOCK_SIZE 16
64 unsigned char c[CTS_BLOCK_SIZE];
67 typedef struct cts_mode_name2id_st {
72 static CTS_MODE_NAME2ID cts_modes[] =
74 { CTS_CS1, OSSL_CIPHER_CTS_MODE_CS1 },
75 { CTS_CS2, OSSL_CIPHER_CTS_MODE_CS2 },
76 { CTS_CS3, OSSL_CIPHER_CTS_MODE_CS3 },
79 const char *ossl_cipher_cbc_cts_mode_id2name(unsigned int id)
83 for (i = 0; i < OSSL_NELEM(cts_modes); ++i) {
84 if (cts_modes[i].id == id)
85 return cts_modes[i].name;
90 int ossl_cipher_cbc_cts_mode_name2id(const char *name)
94 for (i = 0; i < OSSL_NELEM(cts_modes); ++i) {
95 if (strcasecmp(name, cts_modes[i].name) == 0)
96 return (int)cts_modes[i].id;
101 static size_t cts128_cs1_encrypt(PROV_CIPHER_CTX *ctx, const unsigned char *in,
102 unsigned char *out, size_t len)
104 aligned_16bytes tmp_in;
107 residue = len % CTS_BLOCK_SIZE;
109 if (!ctx->hw->cipher(ctx, out, in, len))
118 memset(tmp_in.c, 0, sizeof(tmp_in));
119 memcpy(tmp_in.c, in, residue);
120 if (!ctx->hw->cipher(ctx, out - CTS_BLOCK_SIZE + residue, tmp_in.c,
123 return len + residue;
126 static void do_xor(const unsigned char *in1, const unsigned char *in2,
127 size_t len, unsigned char *out)
131 for (i = 0; i < len; ++i)
132 out[i] = in1[i] ^ in2[i];
135 static size_t cts128_cs1_decrypt(PROV_CIPHER_CTX *ctx, const unsigned char *in,
136 unsigned char *out, size_t len)
138 aligned_16bytes mid_iv, ct_mid, cn, pt_last;
141 residue = len % CTS_BLOCK_SIZE;
143 /* If there are no partial blocks then it is the same as CBC mode */
144 if (!ctx->hw->cipher(ctx, out, in, len))
148 /* Process blocks at the start - but leave the last 2 blocks */
149 len -= CTS_BLOCK_SIZE + residue;
151 if (!ctx->hw->cipher(ctx, out, in, len))
156 /* Save the iv that will be used by the second last block */
157 memcpy(mid_iv.c, ctx->iv, CTS_BLOCK_SIZE);
158 /* Save the C(n) block */
159 memcpy(cn.c, in + residue, CTS_BLOCK_SIZE);
161 /* Decrypt the last block first using an iv of zero */
162 memset(ctx->iv, 0, CTS_BLOCK_SIZE);
163 if (!ctx->hw->cipher(ctx, pt_last.c, in + residue, CTS_BLOCK_SIZE))
167 * Rebuild the ciphertext of the second last block as a combination of
168 * the decrypted last block + replace the start with the ciphertext bytes
169 * of the partial second last block.
171 memcpy(ct_mid.c, in, residue);
172 memcpy(ct_mid.c + residue, pt_last.c + residue, CTS_BLOCK_SIZE - residue);
174 * Restore the last partial ciphertext block.
175 * Now that we have the cipher text of the second last block, apply
176 * that to the partial plaintext end block. We have already decrypted the
177 * block using an IV of zero. For decryption the IV is just XORed after
178 * doing an Cipher CBC block - so just XOR in the cipher text.
180 do_xor(ct_mid.c, pt_last.c, residue, out + CTS_BLOCK_SIZE);
182 /* Restore the iv needed by the second last block */
183 memcpy(ctx->iv, mid_iv.c, CTS_BLOCK_SIZE);
186 * Decrypt the second last plaintext block now that we have rebuilt the
189 if (!ctx->hw->cipher(ctx, out, ct_mid.c, CTS_BLOCK_SIZE))
192 /* The returned iv is the C(n) block */
193 memcpy(ctx->iv, cn.c, CTS_BLOCK_SIZE);
194 return len + CTS_BLOCK_SIZE + residue;
197 static size_t cts128_cs3_encrypt(PROV_CIPHER_CTX *ctx, const unsigned char *in,
198 unsigned char *out, size_t len)
200 aligned_16bytes tmp_in;
203 if (len < CTS_BLOCK_SIZE) /* CS3 requires at least one block */
206 /* If we only have one block then just process the aligned block */
207 if (len == CTS_BLOCK_SIZE)
208 return ctx->hw->cipher(ctx, out, in, len) ? len : 0;
210 residue = len % CTS_BLOCK_SIZE;
212 residue = CTS_BLOCK_SIZE;
215 if (!ctx->hw->cipher(ctx, out, in, len))
221 memset(tmp_in.c, 0, sizeof(tmp_in));
222 memcpy(tmp_in.c, in, residue);
223 memcpy(out, out - CTS_BLOCK_SIZE, residue);
224 if (!ctx->hw->cipher(ctx, out - CTS_BLOCK_SIZE, tmp_in.c, CTS_BLOCK_SIZE))
226 return len + residue;
231 * The cipher text (in) is of the form C(0), C(1), ., C(n), C(n-1)* where
232 * C(n) is a full block and C(n-1)* can be a partial block
233 * (but could be a full block).
234 * This means that the output plaintext (out) needs to swap the plaintext of
235 * the last two decoded ciphertext blocks.
237 static size_t cts128_cs3_decrypt(PROV_CIPHER_CTX *ctx, const unsigned char *in,
238 unsigned char *out, size_t len)
240 aligned_16bytes mid_iv, ct_mid, cn, pt_last;
243 if (len < CTS_BLOCK_SIZE) /* CS3 requires at least one block */
246 /* If we only have one block then just process the aligned block */
247 if (len == CTS_BLOCK_SIZE)
248 return ctx->hw->cipher(ctx, out, in, len) ? len : 0;
250 /* Process blocks at the start - but leave the last 2 blocks */
251 residue = len % CTS_BLOCK_SIZE;
253 residue = CTS_BLOCK_SIZE;
254 len -= CTS_BLOCK_SIZE + residue;
257 if (!ctx->hw->cipher(ctx, out, in, len))
262 /* Save the iv that will be used by the second last block */
263 memcpy(mid_iv.c, ctx->iv, CTS_BLOCK_SIZE);
264 /* Save the C(n) block : For CS3 it is C(1)||...||C(n-2)||C(n)||C(n-1)* */
265 memcpy(cn.c, in, CTS_BLOCK_SIZE);
267 /* Decrypt the C(n) block first using an iv of zero */
268 memset(ctx->iv, 0, CTS_BLOCK_SIZE);
269 if (!ctx->hw->cipher(ctx, pt_last.c, in, CTS_BLOCK_SIZE))
273 * Rebuild the ciphertext of C(n-1) as a combination of
274 * the decrypted C(n) block + replace the start with the ciphertext bytes
275 * of the partial last block.
277 memcpy(ct_mid.c, in + CTS_BLOCK_SIZE, residue);
278 if (residue != CTS_BLOCK_SIZE)
279 memcpy(ct_mid.c + residue, pt_last.c + residue, CTS_BLOCK_SIZE - residue);
281 * Restore the last partial ciphertext block.
282 * Now that we have the cipher text of the second last block, apply
283 * that to the partial plaintext end block. We have already decrypted the
284 * block using an IV of zero. For decryption the IV is just XORed after
285 * doing an AES block - so just XOR in the ciphertext.
287 do_xor(ct_mid.c, pt_last.c, residue, out + CTS_BLOCK_SIZE);
289 /* Restore the iv needed by the second last block */
290 memcpy(ctx->iv, mid_iv.c, CTS_BLOCK_SIZE);
292 * Decrypt the second last plaintext block now that we have rebuilt the
295 if (!ctx->hw->cipher(ctx, out, ct_mid.c, CTS_BLOCK_SIZE))
298 /* The returned iv is the C(n) block */
299 memcpy(ctx->iv, cn.c, CTS_BLOCK_SIZE);
300 return len + CTS_BLOCK_SIZE + residue;
303 static size_t cts128_cs2_encrypt(PROV_CIPHER_CTX *ctx, const unsigned char *in,
304 unsigned char *out, size_t len)
306 if (len % CTS_BLOCK_SIZE == 0) {
307 /* If there are no partial blocks then it is the same as CBC mode */
308 if (!ctx->hw->cipher(ctx, out, in, len))
312 /* For partial blocks CS2 is equivalent to CS3 */
313 return cts128_cs3_encrypt(ctx, in, out, len);
316 static size_t cts128_cs2_decrypt(PROV_CIPHER_CTX *ctx, const unsigned char *in,
317 unsigned char *out, size_t len)
319 if (len % CTS_BLOCK_SIZE == 0) {
320 /* If there are no partial blocks then it is the same as CBC mode */
321 if (!ctx->hw->cipher(ctx, out, in, len))
325 /* For partial blocks CS2 is equivalent to CS3 */
326 return cts128_cs3_decrypt(ctx, in, out, len);
329 int ossl_cipher_cbc_cts_block_update(void *vctx, unsigned char *out, size_t *outl,
330 size_t outsize, const unsigned char *in,
333 PROV_CIPHER_CTX *ctx = (PROV_CIPHER_CTX *)vctx;
336 if (inl < CTS_BLOCK_SIZE) /* There must be at least one block for CTS mode */
346 * Return an error if the update is called multiple times, only one shot
349 if (ctx->updated == 1)
353 if (ctx->cts_mode == CTS_CS1)
354 sz = cts128_cs1_encrypt(ctx, in, out, inl);
355 else if (ctx->cts_mode == CTS_CS2)
356 sz = cts128_cs2_encrypt(ctx, in, out, inl);
357 else if (ctx->cts_mode == CTS_CS3)
358 sz = cts128_cs3_encrypt(ctx, in, out, inl);
360 if (ctx->cts_mode == CTS_CS1)
361 sz = cts128_cs1_decrypt(ctx, in, out, inl);
362 else if (ctx->cts_mode == CTS_CS2)
363 sz = cts128_cs2_decrypt(ctx, in, out, inl);
364 else if (ctx->cts_mode == CTS_CS3)
365 sz = cts128_cs3_decrypt(ctx, in, out, inl);
369 ctx->updated = 1; /* Stop multiple updates being allowed */
374 int ossl_cipher_cbc_cts_block_final(void *vctx, unsigned char *out, size_t *outl,