inbound_group_session.c 15.4 KB
Newer Older
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
/* 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/inbound_group_session.h"

#include <string.h>

#include "olm/base64.h"
#include "olm/cipher.h"
Richard van der Hoff's avatar
Richard van der Hoff committed
22
#include "olm/crypto.h"
23
24
#include "olm/error.h"
#include "olm/megolm.h"
25
#include "olm/memory.h"
26
#include "olm/message.h"
27
28
29
#include "olm/pickle.h"
#include "olm/pickle_encoding.h"

30
31

#define OLM_PROTOCOL_VERSION     3
32
#define GROUP_SESSION_ID_LENGTH  ED25519_PUBLIC_KEY_LENGTH
33
#define PICKLE_VERSION           2
34
#define SESSION_KEY_VERSION      2
35
#define SESSION_EXPORT_VERSION   1
36
37
38
39
40
41
42
43

struct OlmInboundGroupSession {
    /** our earliest known ratchet value */
    Megolm initial_ratchet;

    /** The most recent ratchet value */
    Megolm latest_ratchet;

Richard van der Hoff's avatar
Richard van der Hoff committed
44
45
46
    /** The ed25519 signing key */
    struct _olm_ed25519_public_key signing_key;

47
48
49
    /**
     * Have we ever seen any evidence that this is a valid session?
     * (either because the original session share was signed, or because we
50
     * have subsequently successfully decrypted a message)
51
52
53
54
55
56
57
     *
     * (We don't do anything with this currently, but we may want to bear it in
     * mind when we consider handling key-shares for sessions we already know
     * about.)
     */
    int signing_key_verified;

58
59
60
    enum OlmErrorCode last_error;
};

manuroe's avatar
manuroe committed
61
size_t olm_inbound_group_session_size(void) {
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
    return sizeof(OlmInboundGroupSession);
}

OlmInboundGroupSession * olm_inbound_group_session(
    void *memory
) {
    OlmInboundGroupSession *session = memory;
    olm_clear_inbound_group_session(session);
    return session;
}

const char *olm_inbound_group_session_last_error(
    const OlmInboundGroupSession *session
) {
    return _olm_error_to_string(session->last_error);
}

size_t olm_clear_inbound_group_session(
    OlmInboundGroupSession *session
) {
82
    _olm_unset(session, sizeof(OlmInboundGroupSession));
83
84
85
    return sizeof(OlmInboundGroupSession);
}

86
87
88
#define SESSION_EXPORT_RAW_LENGTH \
    (1 + 4 + MEGOLM_RATCHET_LENGTH + ED25519_PUBLIC_KEY_LENGTH)

Richard van der Hoff's avatar
Richard van der Hoff committed
89
#define SESSION_KEY_RAW_LENGTH \
90
91
    (1 + 4 + MEGOLM_RATCHET_LENGTH + ED25519_PUBLIC_KEY_LENGTH\
        + ED25519_SIGNATURE_LENGTH)
Richard van der Hoff's avatar
Richard van der Hoff committed
92
93
94

static size_t _init_group_session_keys(
    OlmInboundGroupSession *session,
95
96
    const uint8_t *key_buf,
    int export_format
Richard van der Hoff's avatar
Richard van der Hoff committed
97
) {
98
99
    const uint8_t expected_version =
        (export_format ? SESSION_EXPORT_VERSION : SESSION_KEY_VERSION);
Richard van der Hoff's avatar
Richard van der Hoff committed
100
101
102
    const uint8_t *ptr = key_buf;
    size_t version = *ptr++;

103
    if (version != expected_version) {
Richard van der Hoff's avatar
Richard van der Hoff committed
104
105
106
107
        session->last_error = OLM_BAD_SESSION_KEY;
        return (size_t)-1;
    }

108
    uint32_t counter = 0;
109
110
111
112
    // Decode counter as a big endian 32-bit number.
    for (unsigned i = 0; i < 4; i++) {
        counter <<= 8; counter |= *ptr++;
    }
113
114
115
116

    megolm_init(&session->initial_ratchet, ptr, counter);
    megolm_init(&session->latest_ratchet, ptr, counter);

Richard van der Hoff's avatar
Richard van der Hoff committed
117
118
119
120
121
    ptr += MEGOLM_RATCHET_LENGTH;
    memcpy(
        session->signing_key.public_key, ptr, ED25519_PUBLIC_KEY_LENGTH
    );
    ptr += ED25519_PUBLIC_KEY_LENGTH;
122

123
124
125
126
127
128
129
130
131
    if (!export_format) {
        if (!_olm_crypto_ed25519_verify(&session->signing_key, key_buf,
                                        ptr - key_buf, ptr)) {
            session->last_error = OLM_BAD_SIGNATURE;
            return (size_t)-1;
        }

        /* signed keyshare */
        session->signing_key_verified = 1;
132
    }
Richard van der Hoff's avatar
Richard van der Hoff committed
133
134
135
    return 0;
}

136
137
138
139
size_t olm_init_inbound_group_session(
    OlmInboundGroupSession *session,
    const uint8_t * session_key, size_t session_key_length
) {
Richard van der Hoff's avatar
Richard van der Hoff committed
140
    uint8_t key_buf[SESSION_KEY_RAW_LENGTH];
141
    size_t raw_length = _olm_decode_base64_length(session_key_length);
Richard van der Hoff's avatar
Richard van der Hoff committed
142
    size_t result;
143
144
145
146
147
148

    if (raw_length == (size_t)-1) {
        session->last_error = OLM_INVALID_BASE64;
        return (size_t)-1;
    }

Richard van der Hoff's avatar
Richard van der Hoff committed
149
    if (raw_length != SESSION_KEY_RAW_LENGTH) {
150
        session->last_error = OLM_BAD_SESSION_KEY;
151
152
153
154
        return (size_t)-1;
    }

    _olm_decode_base64(session_key, session_key_length, key_buf);
155
    result = _init_group_session_keys(session, key_buf, 0);
Richard van der Hoff's avatar
Richard van der Hoff committed
156
157
    _olm_unset(key_buf, SESSION_KEY_RAW_LENGTH);
    return result;
158
159
}

160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
size_t olm_import_inbound_group_session(
    OlmInboundGroupSession *session,
    const uint8_t * session_key, size_t session_key_length
) {
    uint8_t key_buf[SESSION_EXPORT_RAW_LENGTH];
    size_t raw_length = _olm_decode_base64_length(session_key_length);
    size_t result;

    if (raw_length == (size_t)-1) {
        session->last_error = OLM_INVALID_BASE64;
        return (size_t)-1;
    }

    if (raw_length != SESSION_EXPORT_RAW_LENGTH) {
        session->last_error = OLM_BAD_SESSION_KEY;
        return (size_t)-1;
    }

    _olm_decode_base64(session_key, session_key_length, key_buf);
    result = _init_group_session_keys(session, key_buf, 1);
    _olm_unset(key_buf, SESSION_EXPORT_RAW_LENGTH);
    return result;
}

184
185
186
187
188
189
190
static size_t raw_pickle_length(
    const OlmInboundGroupSession *session
) {
    size_t length = 0;
    length += _olm_pickle_uint32_length(PICKLE_VERSION);
    length += megolm_pickle_length(&session->initial_ratchet);
    length += megolm_pickle_length(&session->latest_ratchet);
Richard van der Hoff's avatar
Richard van der Hoff committed
191
    length += _olm_pickle_ed25519_public_key_length(&session->signing_key);
192
    length += _olm_pickle_bool_length(session->signing_key_verified);
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
    return length;
}

size_t olm_pickle_inbound_group_session_length(
    const OlmInboundGroupSession *session
) {
    return _olm_enc_output_length(raw_pickle_length(session));
}

size_t olm_pickle_inbound_group_session(
    OlmInboundGroupSession *session,
    void const * key, size_t key_length,
    void * pickled, size_t pickled_length
) {
    size_t raw_length = raw_pickle_length(session);
    uint8_t *pos;

    if (pickled_length < _olm_enc_output_length(raw_length)) {
        session->last_error = OLM_OUTPUT_BUFFER_TOO_SMALL;
        return (size_t)-1;
    }

    pos = _olm_enc_output_pos(pickled, raw_length);
    pos = _olm_pickle_uint32(pos, PICKLE_VERSION);
    pos = megolm_pickle(&session->initial_ratchet, pos);
    pos = megolm_pickle(&session->latest_ratchet, pos);
Richard van der Hoff's avatar
Richard van der Hoff committed
219
    pos = _olm_pickle_ed25519_public_key(pos, &session->signing_key);
220
    pos = _olm_pickle_bool(pos, session->signing_key_verified);
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243

    return _olm_enc_output(key, key_length, pickled, raw_length);
}

size_t olm_unpickle_inbound_group_session(
    OlmInboundGroupSession *session,
    void const * key, size_t key_length,
    void * pickled, size_t pickled_length
) {
    const uint8_t *pos;
    const uint8_t *end;
    uint32_t pickle_version;

    size_t raw_length = _olm_enc_input(
        key, key_length, pickled, pickled_length, &(session->last_error)
    );
    if (raw_length == (size_t)-1) {
        return raw_length;
    }

    pos = pickled;
    end = pos + raw_length;
    pos = _olm_unpickle_uint32(pos, end, &pickle_version);
244
    if (pickle_version < 1 || pickle_version > PICKLE_VERSION) {
245
246
247
248
249
        session->last_error = OLM_UNKNOWN_PICKLE_VERSION;
        return (size_t)-1;
    }
    pos = megolm_unpickle(&session->initial_ratchet, pos, end);
    pos = megolm_unpickle(&session->latest_ratchet, pos, end);
Richard van der Hoff's avatar
Richard van der Hoff committed
250
    pos = _olm_unpickle_ed25519_public_key(pos, end, &session->signing_key);
251

252
253
254
255
256
257
258
259
    if (pickle_version == 1) {
        /* pickle v1 had no signing_key_verified field (all keyshares were
         * verified at import time) */
        session->signing_key_verified = 1;
    } else {
        pos = _olm_unpickle_bool(pos, end, &(session->signing_key_verified));
    }

260
261
262
263
264
265
266
267
268
    if (end != pos) {
        /* We had the wrong number of bytes in the input. */
        session->last_error = OLM_CORRUPTED_PICKLE;
        return (size_t)-1;
    }

    return pickled_length;
}

269
270
271
272
/**
 * get the max plaintext length in an un-base64-ed message
 */
static size_t _decrypt_max_plaintext_length(
273
274
275
276
277
278
279
    OlmInboundGroupSession *session,
    uint8_t * message, size_t message_length
) {
    struct _OlmDecodeGroupMessageResults decoded_results;

    _olm_decode_group_message(
        message, message_length,
280
        megolm_cipher->ops->mac_length(megolm_cipher),
Richard van der Hoff's avatar
Richard van der Hoff committed
281
        ED25519_SIGNATURE_LENGTH,
282
283
284
285
286
287
288
289
290
291
292
293
        &decoded_results);

    if (decoded_results.version != OLM_PROTOCOL_VERSION) {
        session->last_error = OLM_BAD_MESSAGE_VERSION;
        return (size_t)-1;
    }

    if (!decoded_results.ciphertext) {
        session->last_error = OLM_BAD_MESSAGE_FORMAT;
        return (size_t)-1;
    }

294
295
    return megolm_cipher->ops->decrypt_max_plaintext_length(
        megolm_cipher, decoded_results.ciphertext_length);
296
297
}

298
299
300
301
302
size_t olm_group_decrypt_max_plaintext_length(
    OlmInboundGroupSession *session,
    uint8_t * message, size_t message_length
) {
    size_t raw_length;
303

304
305
306
307
308
309
310
311
312
313
314
    raw_length = _olm_decode_base64(message, message_length, message);
    if (raw_length == (size_t)-1) {
        session->last_error = OLM_INVALID_BASE64;
        return (size_t)-1;
    }

    return _decrypt_max_plaintext_length(
        session, message, raw_length
    );
}

315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
/**
 * get a copy of the megolm ratchet, advanced
 * to the relevant index. Returns 0 on success, -1 on error
 */
static size_t _get_megolm(
    OlmInboundGroupSession *session, uint32_t message_index, Megolm *result
) {
    /* pick a megolm instance to use. If we're at or beyond the latest ratchet
     * value, use that */
    if ((message_index - session->latest_ratchet.counter) < (1U << 31)) {
        megolm_advance_to(&session->latest_ratchet, message_index);
        *result = session->latest_ratchet;
        return 0;
    } else if ((message_index - session->initial_ratchet.counter) >= (1U << 31)) {
        /* the counter is before our intial ratchet - we can't decode this. */
        session->last_error = OLM_UNKNOWN_MESSAGE_INDEX;
        return (size_t)-1;
    } else {
        /* otherwise, start from the initial megolm. Take a copy so that we
         * don't overwrite the initial megolm */
        *result = session->initial_ratchet;
        megolm_advance_to(result, message_index);
        return 0;
    }
}

341
342
343
344
/**
 * decrypt an un-base64-ed message
 */
static size_t _decrypt(
345
346
    OlmInboundGroupSession *session,
    uint8_t * message, size_t message_length,
347
348
    uint8_t * plaintext, size_t max_plaintext_length,
    uint32_t * message_index
349
350
) {
    struct _OlmDecodeGroupMessageResults decoded_results;
351
    size_t max_length, r;
352
    Megolm megolm;
353
354

    _olm_decode_group_message(
355
        message, message_length,
356
        megolm_cipher->ops->mac_length(megolm_cipher),
Richard van der Hoff's avatar
Richard van der Hoff committed
357
        ED25519_SIGNATURE_LENGTH,
358
359
360
361
362
363
364
        &decoded_results);

    if (decoded_results.version != OLM_PROTOCOL_VERSION) {
        session->last_error = OLM_BAD_MESSAGE_VERSION;
        return (size_t)-1;
    }

Richard van der Hoff's avatar
Richard van der Hoff committed
365
    if (!decoded_results.has_message_index || !decoded_results.ciphertext) {
366
367
368
369
        session->last_error = OLM_BAD_MESSAGE_FORMAT;
        return (size_t)-1;
    }

370
371
372
    if (message_index != NULL) {
        *message_index = decoded_results.message_index;
    }
373

Richard van der Hoff's avatar
Richard van der Hoff committed
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
    /* verify the signature. We could do this before decoding the message, but
     * we allow for the possibility of future protocol versions which use a
     * different signing mechanism; we would rather throw "BAD_MESSAGE_VERSION"
     * than "BAD_SIGNATURE" in this case.
     */
    message_length -= ED25519_SIGNATURE_LENGTH;
    r = _olm_crypto_ed25519_verify(
        &session->signing_key,
        message, message_length,
        message + message_length
    );
    if (!r) {
        session->last_error = OLM_BAD_SIGNATURE;
        return (size_t)-1;
    }

390
391
    max_length = megolm_cipher->ops->decrypt_max_plaintext_length(
        megolm_cipher,
392
393
394
395
396
397
398
        decoded_results.ciphertext_length
    );
    if (max_plaintext_length < max_length) {
        session->last_error = OLM_OUTPUT_BUFFER_TOO_SMALL;
        return (size_t)-1;
    }

399
400
401
    r = _get_megolm(session, decoded_results.message_index, &megolm);
    if (r == (size_t)-1) {
        return r;
402
403
404
    }

    /* now try checking the mac, and decrypting */
405
406
    r = megolm_cipher->ops->decrypt(
        megolm_cipher,
407
        megolm_get_data(&megolm), MEGOLM_RATCHET_LENGTH,
408
        message, message_length,
409
410
411
412
        decoded_results.ciphertext, decoded_results.ciphertext_length,
        plaintext, max_plaintext_length
    );

413
    _olm_unset(&megolm, sizeof(megolm));
414
415
416
417
418
    if (r == (size_t)-1) {
        session->last_error = OLM_BAD_MESSAGE_MAC;
        return r;
    }

419
420
421
422
    /* once we have successfully decrypted a message, set a flag to say the
     * session appears valid. */
    session->signing_key_verified = 1;

423
424
    return r;
}
425
426
427
428

size_t olm_group_decrypt(
    OlmInboundGroupSession *session,
    uint8_t * message, size_t message_length,
429
430
    uint8_t * plaintext, size_t max_plaintext_length,
    uint32_t * message_index
431
432
433
434
435
436
437
438
439
440
441
) {
    size_t raw_message_length;

    raw_message_length = _olm_decode_base64(message, message_length, message);
    if (raw_message_length == (size_t)-1) {
        session->last_error = OLM_INVALID_BASE64;
        return (size_t)-1;
    }

    return _decrypt(
        session, message, raw_message_length,
442
443
        plaintext, max_plaintext_length,
        message_index
444
445
    );
}
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465

size_t olm_inbound_group_session_id_length(
    const OlmInboundGroupSession *session
) {
    return _olm_encode_base64_length(GROUP_SESSION_ID_LENGTH);
}

size_t olm_inbound_group_session_id(
    OlmInboundGroupSession *session,
    uint8_t * id, size_t id_length
) {
    if (id_length < olm_inbound_group_session_id_length(session)) {
        session->last_error = OLM_OUTPUT_BUFFER_TOO_SMALL;
        return (size_t)-1;
    }

    return _olm_encode_base64(
        session->signing_key.public_key, GROUP_SESSION_ID_LENGTH, id
    );
}
466
467
468
469
470
471
472

uint32_t olm_inbound_group_session_first_known_index(
    const OlmInboundGroupSession *session
) {
    return session->initial_ratchet.counter;
}

473
474
475
476
477
478
int olm_inbound_group_session_is_verified(
    const OlmInboundGroupSession *session
) {
    return session->signing_key_verified;
}

479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
size_t olm_export_inbound_group_session_length(
    const OlmInboundGroupSession *session
) {
    return _olm_encode_base64_length(SESSION_EXPORT_RAW_LENGTH);
}

size_t olm_export_inbound_group_session(
    OlmInboundGroupSession *session,
    uint8_t * key, size_t key_length, uint32_t message_index
) {
    uint8_t *raw;
    uint8_t *ptr;
    Megolm megolm;
    size_t r;
    size_t encoded_length = olm_export_inbound_group_session_length(session);

    if (key_length < encoded_length) {
        session->last_error = OLM_OUTPUT_BUFFER_TOO_SMALL;
        return (size_t)-1;
    }

    r = _get_megolm(session, message_index, &megolm);
    if (r == (size_t)-1) {
        return r;
    }

    /* put the raw data at the end of the output buffer. */
    raw = ptr = key + encoded_length - SESSION_EXPORT_RAW_LENGTH;
    *ptr++ = SESSION_EXPORT_VERSION;

    // Encode message index as a big endian 32-bit number.
    for (unsigned i = 0; i < 4; i++) {
        *ptr++ = 0xFF & (message_index >> 24); message_index <<= 8;
    }

    memcpy(ptr, megolm_get_data(&megolm), MEGOLM_RATCHET_LENGTH);
    ptr += MEGOLM_RATCHET_LENGTH;

    memcpy(
        ptr, session->signing_key.public_key,
        ED25519_PUBLIC_KEY_LENGTH
    );
    ptr += ED25519_PUBLIC_KEY_LENGTH;

    return _olm_encode_base64(raw, SESSION_EXPORT_RAW_LENGTH, key);
}