1/*
2 * Copyright 2008-2016 The OpenSSL Project Authors. All Rights Reserved.
3 *
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
8 */
9
10#include <string.h>
11#include <openssl/crypto.h>
12#include "crypto/modes.h"
13
14/*
15 * NOTE: the IV/counter CTR mode is big-endian. The code itself is
16 * endian-neutral.
17 */
18
19/* increment counter (128-bit int) by 1 */
20static void ctr128_inc(unsigned char *counter)
21{
22 u32 n = 16, c = 1;
23
24 do {
25 --n;
26 c += counter[n];
27 counter[n] = (u8)c;
28 c >>= 8;
29 } while (n);
30}
31
32#if !defined(OPENSSL_SMALL_FOOTPRINT)
33static void ctr128_inc_aligned(unsigned char *counter)
34{
35 size_t *data, c, d, n;
36 const union {
37 long one;
38 char little;
39 } is_endian = {
40 1
41 };
42
43 if (is_endian.little || ((size_t)counter % sizeof(size_t)) != 0) {
44 ctr128_inc(counter);
45 return;
46 }
47
48 data = (size_t *)counter;
49 c = 1;
50 n = 16 / sizeof(size_t);
51 do {
52 --n;
53 d = data[n] += c;
54 /* did addition carry? */
55 c = ((d - c) & ~d) >> (sizeof(size_t) * 8 - 1);
56 } while (n);
57}
58#endif
59
60/*
61 * The input encrypted as though 128bit counter mode is being used. The
62 * extra state information to record how much of the 128bit block we have
63 * used is contained in *num, and the encrypted counter is kept in
64 * ecount_buf. Both *num and ecount_buf must be initialised with zeros
65 * before the first call to CRYPTO_ctr128_encrypt(). This algorithm assumes
66 * that the counter is in the x lower bits of the IV (ivec), and that the
67 * application has full control over overflow and the rest of the IV. This
68 * implementation takes NO responsibility for checking that the counter
69 * doesn't overflow into the rest of the IV when incremented.
70 */
71void CRYPTO_ctr128_encrypt(const unsigned char *in, unsigned char *out,
72 size_t len, const void *key,
73 unsigned char ivec[16],
74 unsigned char ecount_buf[16], unsigned int *num,
75 block128_f block)
76{
77 unsigned int n;
78 size_t l = 0;
79
80 n = *num;
81
82#if !defined(OPENSSL_SMALL_FOOTPRINT)
83 if (16 % sizeof(size_t) == 0) { /* always true actually */
84 do {
85 while (n && len) {
86 *(out++) = *(in++) ^ ecount_buf[n];
87 --len;
88 n = (n + 1) % 16;
89 }
90
91# if defined(STRICT_ALIGNMENT)
92 if (((size_t)in | (size_t)out | (size_t)ecount_buf)
93 % sizeof(size_t) != 0)
94 break;
95# endif
96 while (len >= 16) {
97 (*block) (ivec, ecount_buf, key);
98 ctr128_inc_aligned(ivec);
99 for (n = 0; n < 16; n += sizeof(size_t))
100 *(size_t *)(out + n) =
101 *(size_t *)(in + n) ^ *(size_t *)(ecount_buf + n);
102 len -= 16;
103 out += 16;
104 in += 16;
105 n = 0;
106 }
107 if (len) {
108 (*block) (ivec, ecount_buf, key);
109 ctr128_inc_aligned(ivec);
110 while (len--) {
111 out[n] = in[n] ^ ecount_buf[n];
112 ++n;
113 }
114 }
115 *num = n;
116 return;
117 } while (0);
118 }
119 /* the rest would be commonly eliminated by x86* compiler */
120#endif
121 while (l < len) {
122 if (n == 0) {
123 (*block) (ivec, ecount_buf, key);
124 ctr128_inc(ivec);
125 }
126 out[l] = in[l] ^ ecount_buf[n];
127 ++l;
128 n = (n + 1) % 16;
129 }
130
131 *num = n;
132}
133
134/* increment upper 96 bits of 128-bit counter by 1 */
135static void ctr96_inc(unsigned char *counter)
136{
137 u32 n = 12, c = 1;
138
139 do {
140 --n;
141 c += counter[n];
142 counter[n] = (u8)c;
143 c >>= 8;
144 } while (n);
145}
146
147void CRYPTO_ctr128_encrypt_ctr32(const unsigned char *in, unsigned char *out,
148 size_t len, const void *key,
149 unsigned char ivec[16],
150 unsigned char ecount_buf[16],
151 unsigned int *num, ctr128_f func)
152{
153 unsigned int n, ctr32;
154
155 n = *num;
156
157 while (n && len) {
158 *(out++) = *(in++) ^ ecount_buf[n];
159 --len;
160 n = (n + 1) % 16;
161 }
162
163 ctr32 = GETU32(ivec + 12);
164 while (len >= 16) {
165 size_t blocks = len / 16;
166 /*
167 * 1<<28 is just a not-so-small yet not-so-large number...
168 * Below condition is practically never met, but it has to
169 * be checked for code correctness.
170 */
171 if (sizeof(size_t) > sizeof(unsigned int) && blocks > (1U << 28))
172 blocks = (1U << 28);
173 /*
174 * As (*func) operates on 32-bit counter, caller
175 * has to handle overflow. 'if' below detects the
176 * overflow, which is then handled by limiting the
177 * amount of blocks to the exact overflow point...
178 */
179 ctr32 += (u32)blocks;
180 if (ctr32 < blocks) {
181 blocks -= ctr32;
182 ctr32 = 0;
183 }
184 (*func) (in, out, blocks, key, ivec);
185 /* (*ctr) does not update ivec, caller does: */
186 PUTU32(ivec + 12, ctr32);
187 /* ... overflow was detected, propagate carry. */
188 if (ctr32 == 0)
189 ctr96_inc(ivec);
190 blocks *= 16;
191 len -= blocks;
192 out += blocks;
193 in += blocks;
194 }
195 if (len) {
196 memset(ecount_buf, 0, 16);
197 (*func) (ecount_buf, ecount_buf, 1, key, ivec);
198 ++ctr32;
199 PUTU32(ivec + 12, ctr32);
200 if (ctr32 == 0)
201 ctr96_inc(ivec);
202 while (len--) {
203 out[n] = in[n] ^ ecount_buf[n];
204 ++n;
205 }
206 }
207
208 *num = n;
209}
210