summaryrefslogtreecommitdiff
path: root/toxcore/crypto_core.c
blob: 8f7572ab8ff16c92fce1d703d4037e2463893f25 (plain)
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
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
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
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
/* net_crypto.c
 *
 * Functions for the core crypto.
 *
 * NOTE: This code has to be perfect. We don't mess around with encryption.
 *
 *  Copyright (C) 2013 Tox project All Rights Reserved.
 *
 *  This file is part of Tox.
 *
 *  Tox is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  Tox is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with Tox.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "crypto_core.h"

#if crypto_box_PUBLICKEYBYTES != 32
#error crypto_box_PUBLICKEYBYTES is required to be 32 bytes for public_key_cmp to work,
#endif

/* compare 2 public keys of length crypto_box_PUBLICKEYBYTES, not vulnerable to timing attacks.
   returns 0 if both mem locations of length are equal,
   return -1 if they are not. */
int public_key_cmp(const uint8_t *pk1, const uint8_t *pk2)
{
    return crypto_verify_32(pk1, pk2);
}

/*  return a random number.
 */
uint32_t random_int(void)
{
    uint32_t randnum;
    randombytes((uint8_t *)&randnum , sizeof(randnum));
    return randnum;
}

uint64_t random_64b(void)
{
    uint64_t randnum;
    randombytes((uint8_t *)&randnum, sizeof(randnum));
    return randnum;
}

/* Check if a Tox public key crypto_box_PUBLICKEYBYTES is valid or not.
 * This should only be used for input validation.
 *
 * return 0 if it isn't.
 * return 1 if it is.
 */
int public_key_valid(const uint8_t *public_key)
{
    if (public_key[31] >= 128) { /* Last bit of key is always zero. */
        return 0;
    }

    return 1;
}

/* Precomputes the shared key from their public_key and our secret_key.
 * This way we can avoid an expensive elliptic curve scalar multiply for each
 * encrypt/decrypt operation.
 * enc_key has to be crypto_box_BEFORENMBYTES bytes long.
 */
int encrypt_precompute(const uint8_t *public_key, const uint8_t *secret_key, uint8_t *enc_key)
{
    return crypto_box_beforenm(enc_key, public_key, secret_key);
}

int encrypt_data_symmetric(const uint8_t *secret_key, const uint8_t *nonce, const uint8_t *plain, uint32_t length,
                           uint8_t *encrypted)
{
    if (length == 0 || !secret_key || !nonce || !plain || !encrypted) {
        return -1;
    }

    uint8_t temp_plain[length + crypto_box_ZEROBYTES];
    uint8_t temp_encrypted[length + crypto_box_MACBYTES + crypto_box_BOXZEROBYTES];

    memset(temp_plain, 0, crypto_box_ZEROBYTES);
    memcpy(temp_plain + crypto_box_ZEROBYTES, plain, length); // Pad the message with 32 0 bytes.

    if (crypto_box_afternm(temp_encrypted, temp_plain, length + crypto_box_ZEROBYTES, nonce, secret_key) != 0) {
        return -1;
    }

    /* Unpad the encrypted message. */
    memcpy(encrypted, temp_encrypted + crypto_box_BOXZEROBYTES, length + crypto_box_MACBYTES);
    return length + crypto_box_MACBYTES;
}

int decrypt_data_symmetric(const uint8_t *secret_key, const uint8_t *nonce, const uint8_t *encrypted, uint32_t length,
                           uint8_t *plain)
{
    if (length <= crypto_box_BOXZEROBYTES || !secret_key || !nonce || !encrypted || !plain) {
        return -1;
    }

    uint8_t temp_plain[length + crypto_box_ZEROBYTES];
    uint8_t temp_encrypted[length + crypto_box_BOXZEROBYTES];

    memset(temp_encrypted, 0, crypto_box_BOXZEROBYTES);
    memcpy(temp_encrypted + crypto_box_BOXZEROBYTES, encrypted, length); // Pad the message with 16 0 bytes.

    if (crypto_box_open_afternm(temp_plain, temp_encrypted, length + crypto_box_BOXZEROBYTES, nonce, secret_key) != 0) {
        return -1;
    }

    memcpy(plain, temp_plain + crypto_box_ZEROBYTES, length - crypto_box_MACBYTES);
    return length - crypto_box_MACBYTES;
}

int encrypt_data(const uint8_t *public_key, const uint8_t *secret_key, const uint8_t *nonce,
                 const uint8_t *plain, uint32_t length, uint8_t *encrypted)
{
    if (!public_key || !secret_key) {
        return -1;
    }

    uint8_t k[crypto_box_BEFORENMBYTES];
    encrypt_precompute(public_key, secret_key, k);
    int ret = encrypt_data_symmetric(k, nonce, plain, length, encrypted);
    sodium_memzero(k, sizeof k);
    return ret;
}

int decrypt_data(const uint8_t *public_key, const uint8_t *secret_key, const uint8_t *nonce,
                 const uint8_t *encrypted, uint32_t length, uint8_t *plain)
{
    if (!public_key || !secret_key) {
        return -1;
    }

    uint8_t k[crypto_box_BEFORENMBYTES];
    encrypt_precompute(public_key, secret_key, k);
    int ret = decrypt_data_symmetric(k, nonce, encrypted, length, plain);
    sodium_memzero(k, sizeof k);
    return ret;
}


/* Increment the given nonce by 1. */
void increment_nonce(uint8_t *nonce)
{
    /* TODO(irungentoo): use increment_nonce_number(nonce, 1) or sodium_increment (change to little endian)
     * NOTE don't use breaks inside this loop
     * In particular, make sure, as far as possible,
     * that loop bounds and their potential underflow or overflow
     * are independent of user-controlled input (you may have heard of the Heartbleed bug).
     */
    uint32_t i = crypto_box_NONCEBYTES;
    uint_fast16_t carry = 1U;

    for (; i != 0; --i) {
        carry += (uint_fast16_t) nonce[i - 1];
        nonce[i - 1] = (uint8_t) carry;
        carry >>= 8;
    }
}
/* increment the given nonce by num */
void increment_nonce_number(uint8_t *nonce, uint32_t host_order_num)
{
    /* NOTE don't use breaks inside this loop
     * In particular, make sure, as far as possible,
     * that loop bounds and their potential underflow or overflow
     * are independent of user-controlled input (you may have heard of the Heartbleed bug).
     */
    const uint32_t big_endian_num = htonl(host_order_num);
    const uint8_t *const num_vec = (const uint8_t *) &big_endian_num;
    uint8_t num_as_nonce[crypto_box_NONCEBYTES] = {0};
    num_as_nonce[crypto_box_NONCEBYTES - 4] = num_vec[0];
    num_as_nonce[crypto_box_NONCEBYTES - 3] = num_vec[1];
    num_as_nonce[crypto_box_NONCEBYTES - 2] = num_vec[2];
    num_as_nonce[crypto_box_NONCEBYTES - 1] = num_vec[3];

    uint32_t i = crypto_box_NONCEBYTES;
    uint_fast16_t carry = 0U;

    for (; i != 0; --i) {
        carry += (uint_fast16_t) nonce[i - 1] + (uint_fast16_t) num_as_nonce[i - 1];
        nonce[i - 1] = (unsigned char) carry;
        carry >>= 8;
    }
}

/* Fill the given nonce with random bytes. */
void random_nonce(uint8_t *nonce)
{
    randombytes(nonce, crypto_box_NONCEBYTES);
}

/* Fill a key crypto_box_KEYBYTES big with random bytes */
void new_symmetric_key(uint8_t *key)
{
    randombytes(key, crypto_box_KEYBYTES);
}

/* Gives a nonce guaranteed to be different from previous ones.*/
void new_nonce(uint8_t *nonce)
{
    random_nonce(nonce);
}

/* Create a request to peer.
 * send_public_key and send_secret_key are the pub/secret keys of the sender.
 * recv_public_key is public key of receiver.
 * packet must be an array of MAX_CRYPTO_REQUEST_SIZE big.
 * Data represents the data we send with the request with length being the length of the data.
 * request_id is the id of the request (32 = friend request, 254 = ping request).
 *
 *  return -1 on failure.
 *  return the length of the created packet on success.
 */
int create_request(const uint8_t *send_public_key, const uint8_t *send_secret_key, uint8_t *packet,
                   const uint8_t *recv_public_key, const uint8_t *data, uint32_t length, uint8_t request_id)
{
    if (!send_public_key || !packet || !recv_public_key || !data) {
        return -1;
    }

    if (MAX_CRYPTO_REQUEST_SIZE < length + 1 + crypto_box_PUBLICKEYBYTES * 2 + crypto_box_NONCEBYTES + 1 +
            crypto_box_MACBYTES) {
        return -1;
    }

    uint8_t *nonce = packet + 1 + crypto_box_PUBLICKEYBYTES * 2;
    new_nonce(nonce);
    uint8_t temp[MAX_CRYPTO_REQUEST_SIZE]; // TODO(irungentoo): sodium_memzero before exit function
    memcpy(temp + 1, data, length);
    temp[0] = request_id;
    int len = encrypt_data(recv_public_key, send_secret_key, nonce, temp, length + 1,
                           1 + crypto_box_PUBLICKEYBYTES * 2 + crypto_box_NONCEBYTES + packet);

    if (len == -1) {
        return -1;
    }

    packet[0] = NET_PACKET_CRYPTO;
    memcpy(packet + 1, recv_public_key, crypto_box_PUBLICKEYBYTES);
    memcpy(packet + 1 + crypto_box_PUBLICKEYBYTES, send_public_key, crypto_box_PUBLICKEYBYTES);

    return len + 1 + crypto_box_PUBLICKEYBYTES * 2 + crypto_box_NONCEBYTES;
}

/* Puts the senders public key in the request in public_key, the data from the request
 * in data if a friend or ping request was sent to us and returns the length of the data.
 * packet is the request packet and length is its length.
 *
 *  return -1 if not valid request.
 */
int handle_request(const uint8_t *self_public_key, const uint8_t *self_secret_key, uint8_t *public_key, uint8_t *data,
                   uint8_t *request_id, const uint8_t *packet, uint16_t length)
{
    if (!self_public_key || !public_key || !data || !request_id || !packet) {
        return -1;
    }

    if (length <= crypto_box_PUBLICKEYBYTES * 2 + crypto_box_NONCEBYTES + 1 + crypto_box_MACBYTES ||
            length > MAX_CRYPTO_REQUEST_SIZE) {
        return -1;
    }

    if (public_key_cmp(packet + 1, self_public_key) != 0) {
        return -1;
    }

    memcpy(public_key, packet + 1 + crypto_box_PUBLICKEYBYTES, crypto_box_PUBLICKEYBYTES);
    const uint8_t *nonce = packet + 1 + crypto_box_PUBLICKEYBYTES * 2;
    uint8_t temp[MAX_CRYPTO_REQUEST_SIZE]; // TODO(irungentoo): sodium_memzero before exit function
    int len1 = decrypt_data(public_key, self_secret_key, nonce,
                            packet + 1 + crypto_box_PUBLICKEYBYTES * 2 + crypto_box_NONCEBYTES,
                            length - (crypto_box_PUBLICKEYBYTES * 2 + crypto_box_NONCEBYTES + 1), temp);

    if (len1 == -1 || len1 == 0) {
        return -1;
    }

    request_id[0] = temp[0];
    --len1;
    memcpy(data, temp + 1, len1);
    return len1;
}