inbound_group_session.c 5.82 KB
Newer Older
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
146
147
148
149
150
151
152
153
154
155
156
157
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
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
/* 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"
#include "olm/error.h"
#include "olm/megolm.h"
#include "olm/message.h"

#define OLM_PROTOCOL_VERSION     3

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

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

    enum OlmErrorCode last_error;
};

size_t olm_inbound_group_session_size() {
    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
) {
    memset(session, 0, sizeof(OlmInboundGroupSession));
    return sizeof(OlmInboundGroupSession);
}

size_t olm_init_inbound_group_session(
    OlmInboundGroupSession *session,
    uint32_t message_index,
    const uint8_t * session_key, size_t session_key_length
) {
    uint8_t key_buf[MEGOLM_RATCHET_LENGTH];
    size_t raw_length = _olm_decode_base64_length(session_key_length);

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

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

    _olm_decode_base64(session_key, session_key_length, key_buf);
    megolm_init(&session->initial_ratchet, key_buf, message_index);
    megolm_init(&session->latest_ratchet, key_buf, message_index);
    memset(key_buf, 0, MEGOLM_RATCHET_LENGTH);

    return 0;
}

size_t olm_group_decrypt_max_plaintext_length(
    OlmInboundGroupSession *session,
    uint8_t * message, size_t message_length
) {
    size_t r;
    const struct _olm_cipher *cipher = megolm_cipher();
    struct _OlmDecodeGroupMessageResults decoded_results;

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

    _olm_decode_group_message(
        message, message_length,
        cipher->ops->mac_length(cipher),
        &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;
    }

    return cipher->ops->decrypt_max_plaintext_length(
        cipher, decoded_results.ciphertext_length);
}


size_t olm_group_decrypt(
    OlmInboundGroupSession *session,
    uint8_t * message, size_t message_length,
    uint8_t * plaintext, size_t max_plaintext_length
) {
    struct _OlmDecodeGroupMessageResults decoded_results;
    const struct _olm_cipher *cipher = megolm_cipher();
    size_t max_length, raw_message_length, r;
    Megolm *megolm;
    Megolm tmp_megolm;

    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;
    }

    _olm_decode_group_message(
        message, raw_message_length,
        cipher->ops->mac_length(cipher),
        &decoded_results);

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

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

    max_length = cipher->ops->decrypt_max_plaintext_length(
        cipher,
        decoded_results.ciphertext_length
    );
    if (max_plaintext_length < max_length) {
        session->last_error = OLM_OUTPUT_BUFFER_TOO_SMALL;
        return (size_t)-1;
    }

    /* pick a megolm instance to use. If we're at or beyond the latest ratchet
     * value, use that */
    if ((int32_t)(decoded_results.chain_index - session->latest_ratchet.counter) >= 0) {
        megolm = &session->latest_ratchet;
    } else if ((int32_t)(decoded_results.chain_index - session->initial_ratchet.counter) < 0) {
        /* the counter is before our intial ratchet - we can't decode this. */
        session->last_error = OLM_BAD_CHAIN_INDEX;
        return (size_t)-1;
    } else {
        /* otherwise, start from the initial megolm. Take a copy so that we
         * don't overwrite the initial megolm */
        tmp_megolm = session->initial_ratchet;
        megolm = &tmp_megolm;
    }

    megolm_advance_to(megolm, decoded_results.chain_index);

    /* now try checking the mac, and decrypting */
    r = cipher->ops->decrypt(
        cipher,
        megolm_get_data(megolm), MEGOLM_RATCHET_LENGTH,
        message, raw_message_length,
        decoded_results.ciphertext, decoded_results.ciphertext_length,
        plaintext, max_plaintext_length
    );

    memset(&tmp_megolm, 0, sizeof(tmp_megolm));
    if (r == (size_t)-1) {
        session->last_error = OLM_BAD_MESSAGE_MAC;
        return r;
    }

    return r;
}