1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
|
/* Copyright 2016 OpenMarket Ltd
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "olm/megolm.h"
#include <string.h>
#include "olm/cipher.h"
#include "olm/crypto.h"
#include "olm/pickle.h"
static const struct _olm_cipher_aes_sha_256 MEGOLM_CIPHER =
OLM_CIPHER_INIT_AES_SHA_256("MEGOLM_KEYS");
const struct _olm_cipher *megolm_cipher = OLM_CIPHER_BASE(&MEGOLM_CIPHER);
/* the seeds used in the HMAC-SHA-256 functions for each part of the ratchet.
*/
#define HASH_KEY_SEED_LENGTH 1
static uint8_t HASH_KEY_SEEDS[MEGOLM_RATCHET_PARTS][HASH_KEY_SEED_LENGTH] = {
{0x00},
{0x01},
{0x02},
{0x03}
};
static void rehash_part(
uint8_t data[MEGOLM_RATCHET_PARTS][MEGOLM_RATCHET_PART_LENGTH],
int rehash_from_part, int rehash_to_part
) {
_olm_crypto_hmac_sha256(
data[rehash_from_part],
MEGOLM_RATCHET_PART_LENGTH,
HASH_KEY_SEEDS[rehash_to_part], HASH_KEY_SEED_LENGTH,
data[rehash_to_part]
);
}
void megolm_init(Megolm *megolm, uint8_t const *random_data, uint32_t counter) {
megolm->counter = counter;
memcpy(megolm->data, random_data, MEGOLM_RATCHET_LENGTH);
}
size_t megolm_pickle_length(const Megolm *megolm) {
size_t length = 0;
length += _olm_pickle_bytes_length(megolm_get_data(megolm), MEGOLM_RATCHET_LENGTH);
length += _olm_pickle_uint32_length(megolm->counter);
return length;
}
uint8_t * megolm_pickle(const Megolm *megolm, uint8_t *pos) {
pos = _olm_pickle_bytes(pos, megolm_get_data(megolm), MEGOLM_RATCHET_LENGTH);
pos = _olm_pickle_uint32(pos, megolm->counter);
return pos;
}
const uint8_t * megolm_unpickle(Megolm *megolm, const uint8_t *pos,
const uint8_t *end) {
pos = _olm_unpickle_bytes(pos, end, (uint8_t *)(megolm->data),
MEGOLM_RATCHET_LENGTH);
pos = _olm_unpickle_uint32(pos, end, &megolm->counter);
return pos;
}
/* simplistic implementation for a single step */
void megolm_advance(Megolm *megolm) {
uint32_t mask = 0x00FFFFFF;
int h = 0;
int i;
megolm->counter++;
/* figure out how much we need to rekey */
while (h < (int)MEGOLM_RATCHET_PARTS) {
if (!(megolm->counter & mask))
break;
h++;
mask >>= 8;
}
/* now update R(h)...R(3) based on R(h) */
for (i = MEGOLM_RATCHET_PARTS-1; i >= h; i--) {
rehash_part(megolm->data, h, i);
}
}
void megolm_advance_to(Megolm *megolm, uint32_t advance_to) {
int j;
/* starting with R0, see if we need to update each part of the hash */
for (j = 0; j < (int)MEGOLM_RATCHET_PARTS; j++) {
int shift = (MEGOLM_RATCHET_PARTS-j-1) * 8;
uint32_t mask = (~(uint32_t)0) << shift;
int k;
/* how many times do we need to rehash this part?
*
* '& 0xff' ensures we handle integer wraparound correctly
*/
unsigned int steps =
((advance_to >> shift) - (megolm->counter >> shift)) & 0xff;
if (steps == 0) {
if (advance_to < megolm->counter) {
steps = 0x100;
} else {
continue;
}
}
/* for all but the last step, we can just bump R(j) without regard
* to R(j+1)...R(3).
*/
while (steps > 1) {
rehash_part(megolm->data, j, j);
steps --;
}
/* on the last step we also need to bump R(j+1)...R(3).
*
* (Theoretically, we could skip bumping R(j+2) if we're going to bump
* R(j+1) again, but the code to figure that out is a bit baroque and
* doesn't save us much).
*/
for (k = 3; k >= j; k--) {
rehash_part(megolm->data, j, k);
}
megolm->counter = advance_to & mask;
}
}
|
