message.cpp 8.1 KB
Newer Older
Mark Haines's avatar
Mark Haines committed
1
2
3
4
5
6
7
8
9
10
11
12
13
14
/* Copyright 2015 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.
 */
Mark Haines's avatar
Mark Haines committed
15
16
17
18
19
20
21
22
23
#include "axolotl/message.hh"

namespace {

template<typename T>
std::size_t varint_length(
    T value
) {
    std::size_t result = 1;
24
    while (value >= 128U) {
Mark Haines's avatar
Mark Haines committed
25
26
27
28
29
30
31
32
33
34
35
36
        ++result;
        value >>= 7;
    }
    return result;
}


template<typename T>
std::uint8_t * varint_encode(
    std::uint8_t * output,
    T value
) {
37
    while (value >= 128U) {
Mark Haines's avatar
Mark Haines committed
38
        *(output++) = (0x7F & value) | 0x80;
39
        value >>= 7;
Mark Haines's avatar
Mark Haines committed
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
    }
    (*output++) = value;
    return output;
}


template<typename T>
T varint_decode(
    std::uint8_t const * varint_start,
    std::uint8_t const * varint_end
) {
    T value = 0;
    do {
        value <<= 7;
        value |= 0x7F & *(--varint_end);
    } while (varint_end != varint_start);
    return value;
}


std::uint8_t const * varint_skip(
    std::uint8_t const * input,
    std::uint8_t const * input_end
) {
    while (input != input_end) {
        std::uint8_t tmp = *(input++);
        if ((tmp & 0x80) == 0) {
            return input;
        }
    }
    return input;
}


std::size_t varstring_length(
    std::size_t string_length
) {
    return varint_length(string_length) + string_length;
}

static std::size_t const VERSION_LENGTH = 1;
static std::uint8_t const RATCHET_KEY_TAG = 012;
static std::uint8_t const COUNTER_TAG = 020;
static std::uint8_t const CIPHERTEXT_TAG = 042;

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
std::uint8_t * encode(
    std::uint8_t * pos,
    std::uint8_t tag,
    std::uint32_t value
) {
    *(pos++) = tag;
    return varint_encode(pos, value);
}

std::uint8_t * encode(
    std::uint8_t * pos,
    std::uint8_t tag,
    std::uint8_t * & value, std::size_t value_length
) {
    *(pos++) = tag;
    pos = varint_encode(pos, value_length);
    value = pos;
    return pos + value_length;
}

std::uint8_t const * decode(
    std::uint8_t const * pos, std::uint8_t const * end,
    std::uint8_t tag,
    std::uint32_t & value, bool & has_value
) {
    if (pos != end && *pos == tag) {
        ++pos;
        std::uint8_t const * value_start = pos;
        pos = varint_skip(pos, end);
        value = varint_decode<std::uint32_t>(value_start, pos);
        has_value = true;
    }
    return pos;
}


std::uint8_t const * decode(
    std::uint8_t const * pos, std::uint8_t const * end,
    std::uint8_t tag,
    std::uint8_t const * & value, std::size_t & value_length
) {
    if (pos != end && *pos == tag) {
        ++pos;
        std::uint8_t const * len_start = pos;
        pos = varint_skip(pos, end);
        std::size_t len = varint_decode<std::size_t>(len_start, pos);
        if (len > end - pos) return end;
        value = pos;
        value_length = len;
        pos += len;
    }
    return pos;
}

std::uint8_t const * skip_unknown(
    std::uint8_t const * pos, std::uint8_t const * end
) {
    if (pos != end) {
        uint8_t tag = *pos;
144
        if ((tag & 0x7) == 0) {
145
146
            pos = varint_skip(pos, end);
            pos = varint_skip(pos, end);
147
        } else if ((tag & 0x7) == 2) {
148
149
150
151
152
153
154
155
156
157
158
159
160
            pos = varint_skip(pos, end);
            std::uint8_t const * len_start = pos;
            pos = varint_skip(pos, end);
            std::size_t len = varint_decode<std::size_t>(len_start, pos);
            if (len > end - pos) return end;
            pos += len;
        } else {
            return end;
        }
    }
    return pos;
}

Mark Haines's avatar
Mark Haines committed
161
162
163
164
165
166
167
168
169
170
171
172
173
} // namespace


std::size_t axolotl::encode_message_length(
    std::uint32_t counter,
    std::size_t ratchet_key_length,
    std::size_t ciphertext_length,
    std::size_t mac_length
) {
    std::size_t length = VERSION_LENGTH;
    length += 1 + varstring_length(ratchet_key_length);
    length += 1 + varint_length(counter);
    length += 1 + varstring_length(ciphertext_length);
174
175
    length += mac_length;
    return length;
Mark Haines's avatar
Mark Haines committed
176
177
178
}


179
180
void axolotl::encode_message(
    axolotl::MessageWriter & writer,
Mark Haines's avatar
Mark Haines committed
181
182
183
184
185
186
187
188
    std::uint8_t version,
    std::uint32_t counter,
    std::size_t ratchet_key_length,
    std::size_t ciphertext_length,
    std::uint8_t * output
) {
    std::uint8_t * pos = output;
    *(pos++) = version;
189
190
191
    pos = encode(pos, RATCHET_KEY_TAG, writer.ratchet_key, ratchet_key_length);
    pos = encode(pos, COUNTER_TAG, counter);
    pos = encode(pos, CIPHERTEXT_TAG, writer.ciphertext, ciphertext_length);
Mark Haines's avatar
Mark Haines committed
192
193
194
}


195
void axolotl::decode_message(
196
    axolotl::MessageReader & reader,
Mark Haines's avatar
Mark Haines committed
197
198
199
200
201
    std::uint8_t const * input, std::size_t input_length,
    std::size_t mac_length
) {
    std::uint8_t const * pos = input;
    std::uint8_t const * end = input + input_length - mac_length;
202
    std::uint8_t const * unknown = nullptr;
203
204

    if (pos == end) return;
205
    reader.version = *(pos++);
206
207
208
    reader.input = input;
    reader.input_length = input_length;
    reader.has_counter = false;
209
210
    reader.ratchet_key = nullptr;
    reader.ciphertext = nullptr;
211

Mark Haines's avatar
Mark Haines committed
212
    while (pos != end) {
213
214
215
216
217
218
219
220
221
222
223
224
225
        pos = decode(
            pos, end, RATCHET_KEY_TAG,
            reader.ratchet_key, reader.ratchet_key_length
        );
        pos = decode(
            pos, end, COUNTER_TAG,
            reader.counter, reader.has_counter
        );
        pos = decode(
            pos, end, CIPHERTEXT_TAG,
            reader.ciphertext, reader.ciphertext_length
        );
        if (unknown == pos) {
226
            pos = skip_unknown(pos, end);
Mark Haines's avatar
Mark Haines committed
227
        }
228
        unknown = pos;
Mark Haines's avatar
Mark Haines committed
229
    }
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
}


namespace {

static std::uint8_t const ONE_TIME_KEY_ID_TAG = 010;
static std::uint8_t const BASE_KEY_TAG = 022;
static std::uint8_t const IDENTITY_KEY_TAG = 032;
static std::uint8_t const MESSAGE_TAG = 042;

} // namespace


std::size_t axolotl::encode_one_time_key_message_length(
    std::uint32_t one_time_key_id,
    std::size_t identity_key_length,
    std::size_t base_key_length,
    std::size_t message_length
) {
    std::size_t length = VERSION_LENGTH;
    length += 1 + varint_length(one_time_key_id);
    length += 1 + varstring_length(identity_key_length);
    length += 1 + varstring_length(base_key_length);
    length += 1 + varstring_length(message_length);
    return length;
}


void axolotl::encode_one_time_key_message(
    axolotl::PreKeyMessageWriter & writer,
    std::uint8_t version,
    std::uint32_t one_time_key_id,
    std::size_t identity_key_length,
    std::size_t base_key_length,
    std::size_t message_length,
    std::uint8_t * output
) {
    std::uint8_t * pos = output;
    *(pos++) = version;
    pos = encode(pos, ONE_TIME_KEY_ID_TAG, one_time_key_id);
    pos = encode(pos, BASE_KEY_TAG, writer.base_key, base_key_length);
    pos = encode(pos, IDENTITY_KEY_TAG, writer.identity_key, identity_key_length);
    pos = encode(pos, MESSAGE_TAG, writer.message, message_length);
}


void axolotl::decode_one_time_key_message(
    PreKeyMessageReader & reader,
    std::uint8_t const * input, std::size_t input_length
) {
    std::uint8_t const * pos = input;
    std::uint8_t const * end = input + input_length;
282
    std::uint8_t const * unknown = nullptr;
283
284
285
286

    if (pos == end) return;
    reader.version = *(pos++);
    reader.has_one_time_key_id = false;
287
288
289
    reader.identity_key = nullptr;
    reader.base_key = nullptr;
    reader.message = nullptr;
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308

    while (pos != end) {
        pos = decode(
            pos, end, ONE_TIME_KEY_ID_TAG,
            reader.one_time_key_id, reader.has_one_time_key_id
        );
        pos = decode(
            pos, end, BASE_KEY_TAG,
            reader.base_key, reader.base_key_length
        );
        pos = decode(
            pos, end, IDENTITY_KEY_TAG,
            reader.identity_key, reader.identity_key_length
        );
        pos = decode(
            pos, end, MESSAGE_TAG,
            reader.message, reader.message_length
        );
        if (unknown == pos) {
309
            pos = skip_unknown(pos, end);
310
311
        }
        unknown = pos;
Mark Haines's avatar
Mark Haines committed
312
313
    }
}