summaryrefslogtreecommitdiffstats
path: root/nts_ke_server.c
blob: ece1b4c01b21f208c54f37f458d4425511394085 (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
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
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
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
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
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
/*
  chronyd/chronyc - Programs for keeping computer clocks accurate.

 **********************************************************************
 * Copyright (C) Miroslav Lichvar  2020
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
 * published by the Free Software Foundation.
 * 
 * This program 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 this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 * 
 **********************************************************************

  =======================================================================

  NTS-KE server
  */

#include "config.h"

#include "sysincl.h"

#include "nts_ke_server.h"

#include "array.h"
#include "conf.h"
#include "clientlog.h"
#include "local.h"
#include "logging.h"
#include "memory.h"
#include "ntp_core.h"
#include "nts_ke_session.h"
#include "privops.h"
#include "siv.h"
#include "socket.h"
#include "sched.h"
#include "sys.h"
#include "util.h"

#define SERVER_TIMEOUT 2.0

#define SERVER_COOKIE_SIV AEAD_AES_SIV_CMAC_256
#define SERVER_COOKIE_NONCE_LENGTH 16

#define KEY_ID_INDEX_BITS 2
#define MAX_SERVER_KEYS (1U << KEY_ID_INDEX_BITS)
#define FUTURE_KEYS 1

#define DUMP_FILENAME "ntskeys"
#define DUMP_IDENTIFIER "NKS0\n"

#define INVALID_SOCK_FD (-7)

typedef struct {
  uint32_t key_id;
  unsigned char nonce[SERVER_COOKIE_NONCE_LENGTH];
} ServerCookieHeader;

typedef struct {
  uint32_t id;
  unsigned char key[SIV_MAX_KEY_LENGTH];
  SIV_Instance siv;
} ServerKey;

typedef struct {
  uint32_t key_id;
  unsigned char key[SIV_MAX_KEY_LENGTH];
  IPAddr client_addr;
  uint16_t client_port;
  uint16_t _pad;
} HelperRequest;

/* ================================================== */

static ServerKey server_keys[MAX_SERVER_KEYS];
static int current_server_key;
static double last_server_key_ts;
static int key_rotation_interval;

static int server_sock_fd4;
static int server_sock_fd6;

static int helper_sock_fd;
static int is_helper;

static int initialised = 0;

/* Array of NKSN instances */
static ARR_Instance sessions;
static NKSN_Credentials server_credentials;

/* ================================================== */

static int handle_message(void *arg);

/* ================================================== */

static int
handle_client(int sock_fd, IPSockAddr *addr)
{
  NKSN_Instance inst, *instp;
  int i;

  /* Leave at least half of the descriptors which can handled by select()
     to other use */
  if (sock_fd > FD_SETSIZE / 2) {
    DEBUG_LOG("Rejected connection from %s (%s)",
              UTI_IPSockAddrToString(addr), "too many descriptors");
    return 0;
  }

  /* Find an unused server slot or one with an already stopped session */
  for (i = 0, inst = NULL; i < ARR_GetSize(sessions); i++) {
    instp = ARR_GetElement(sessions, i);
    if (!*instp) {
      /* NULL handler arg will be replaced with the session instance */
      inst = NKSN_CreateInstance(1, NULL, handle_message, NULL);
      *instp = inst;
      break;
    } else if (NKSN_IsStopped(*instp)) {
      inst = *instp;
      break;
    }
  }

  if (!inst) {
    DEBUG_LOG("Rejected connection from %s (%s)",
              UTI_IPSockAddrToString(addr), "too many connections");
    return 0;
  }

  assert(server_credentials);

  if (!NKSN_StartSession(inst, sock_fd, UTI_IPSockAddrToString(addr),
                         server_credentials, SERVER_TIMEOUT))
    return 0;

  return 1;
}

/* ================================================== */

static void
handle_helper_request(int fd, int event, void *arg)
{
  SCK_Message *message;
  HelperRequest *req;
  IPSockAddr client_addr;
  int sock_fd;

  /* Receive the helper request with the NTS-KE session socket.
     With multiple helpers EAGAIN errors are expected here. */
  message = SCK_ReceiveMessage(fd, SCK_FLAG_MSG_DESCRIPTOR);
  if (!message)
    return;

  sock_fd = message->descriptor;
  if (sock_fd < 0) {
    /* Message with no descriptor is a shutdown command */
    SCH_QuitProgram();
    return;
  }

  if (!initialised) {
    DEBUG_LOG("Uninitialised helper");
    SCK_CloseSocket(sock_fd);
    return;
  }

  if (message->length != sizeof (HelperRequest))
    LOG_FATAL("Invalid helper request");

  req = message->data;

  /* Extract the current server key and client address from the request */
  server_keys[current_server_key].id = ntohl(req->key_id);
  assert(sizeof (server_keys[current_server_key].key) == sizeof (req->key));
  memcpy(server_keys[current_server_key].key, req->key,
         sizeof (server_keys[current_server_key].key));
  UTI_IPNetworkToHost(&req->client_addr, &client_addr.ip_addr);
  client_addr.port = ntohs(req->client_port);

  if (!SIV_SetKey(server_keys[current_server_key].siv, server_keys[current_server_key].key,
                  SIV_GetKeyLength(SERVER_COOKIE_SIV)))
    LOG_FATAL("Could not set SIV key");

  if (!handle_client(sock_fd, &client_addr)) {
    SCK_CloseSocket(sock_fd);
    return;
  }

  DEBUG_LOG("Accepted helper request fd=%d", sock_fd);
}

/* ================================================== */

static void
accept_connection(int listening_fd, int event, void *arg)
{
  SCK_Message message;
  IPSockAddr addr;
  int log_index, sock_fd;
  struct timespec now;

  sock_fd = SCK_AcceptConnection(listening_fd, &addr);
  if (sock_fd < 0)
    return;

  if (!NCR_CheckAccessRestriction(&addr.ip_addr)) {
    DEBUG_LOG("Rejected connection from %s (%s)",
              UTI_IPSockAddrToString(&addr), "access denied");
    SCK_CloseSocket(sock_fd);
    return;
  }

  SCH_GetLastEventTime(&now, NULL, NULL);

  log_index = CLG_LogServiceAccess(CLG_NTSKE, &addr.ip_addr, &now);
  if (log_index >= 0 && CLG_LimitServiceRate(CLG_NTSKE, log_index)) {
    DEBUG_LOG("Rejected connection from %s (%s)",
              UTI_IPSockAddrToString(&addr), "rate limit");
    SCK_CloseSocket(sock_fd);
    return;
  }

  /* Pass the socket to a helper process if enabled.  Otherwise, handle the
     client in the main process. */
  if (helper_sock_fd != INVALID_SOCK_FD) {
    HelperRequest req;

    memset(&req, 0, sizeof (req));

    /* Include the current server key and client address in the request */
    req.key_id = htonl(server_keys[current_server_key].id);
    assert(sizeof (req.key) == sizeof (server_keys[current_server_key].key));
    memcpy(req.key, server_keys[current_server_key].key, sizeof (req.key));
    UTI_IPHostToNetwork(&addr.ip_addr, &req.client_addr);
    req.client_port = htons(addr.port);

    SCK_InitMessage(&message, SCK_ADDR_UNSPEC);
    message.data = &req;
    message.length = sizeof (req);
    message.descriptor = sock_fd;

    errno = 0;
    if (!SCK_SendMessage(helper_sock_fd, &message, SCK_FLAG_MSG_DESCRIPTOR)) {
      /* If sending failed with EPIPE, it means all helpers closed their end of
         the socket (e.g. due to a fatal error) */
      if (errno == EPIPE)
        LOG_FATAL("NTS-KE helpers failed");
      SCK_CloseSocket(sock_fd);
      return;
    }

    SCK_CloseSocket(sock_fd);
  } else {
    if (!handle_client(sock_fd, &addr)) {
      SCK_CloseSocket(sock_fd);
      return;
    }
  }

  DEBUG_LOG("Accepted connection from %s fd=%d", UTI_IPSockAddrToString(&addr), sock_fd);
}

/* ================================================== */

static int
open_socket(int family)
{
  IPSockAddr local_addr;
  int backlog, sock_fd;
  char *iface;

  if (!SCK_IsIpFamilyEnabled(family))
    return INVALID_SOCK_FD;

  CNF_GetBindAddress(family, &local_addr.ip_addr);
  local_addr.port = CNF_GetNtsServerPort();
  iface = CNF_GetBindNtpInterface();

  sock_fd = SCK_OpenTcpSocket(NULL, &local_addr, iface, 0);
  if (sock_fd < 0) {
    LOG(LOGS_ERR, "Could not open NTS-KE socket on %s", UTI_IPSockAddrToString(&local_addr));
    return INVALID_SOCK_FD;
  }

  /* Set the maximum number of waiting connections on the socket to the maximum
     number of concurrent sessions */
  backlog = MAX(CNF_GetNtsServerProcesses(), 1) * CNF_GetNtsServerConnections();

  if (!SCK_ListenOnSocket(sock_fd, backlog)) {
    SCK_CloseSocket(sock_fd);
    return INVALID_SOCK_FD;
  }

  SCH_AddFileHandler(sock_fd, SCH_FILE_INPUT, accept_connection, NULL);

  return sock_fd;
}

/* ================================================== */

static void
helper_signal(int x)
{
  SCH_QuitProgram();
}

/* ================================================== */

static int
prepare_response(NKSN_Instance session, int error, int next_protocol, int aead_algorithm)
{
  NKE_Context context;
  NKE_Cookie cookie;
  char *ntp_server;
  uint16_t datum;
  int i;

  DEBUG_LOG("NTS KE response: error=%d next=%d aead=%d", error, next_protocol, aead_algorithm);

  NKSN_BeginMessage(session);

  if (error >= 0) {
    datum = htons(error);
    if (!NKSN_AddRecord(session, 1, NKE_RECORD_ERROR, &datum, sizeof (datum)))
      return 0;
  } else if (next_protocol < 0) {
    if (!NKSN_AddRecord(session, 1, NKE_RECORD_NEXT_PROTOCOL, NULL, 0))
      return 0;
  } else if (aead_algorithm < 0) {
    datum = htons(next_protocol);
    if (!NKSN_AddRecord(session, 1, NKE_RECORD_NEXT_PROTOCOL, &datum, sizeof (datum)))
      return 0;
    if (!NKSN_AddRecord(session, 1, NKE_RECORD_AEAD_ALGORITHM, NULL, 0))
      return 0;
  } else {
    datum = htons(next_protocol);
    if (!NKSN_AddRecord(session, 1, NKE_RECORD_NEXT_PROTOCOL, &datum, sizeof (datum)))
      return 0;

    datum = htons(aead_algorithm);
    if (!NKSN_AddRecord(session, 1, NKE_RECORD_AEAD_ALGORITHM, &datum, sizeof (datum)))
      return 0;

    if (CNF_GetNTPPort() != NTP_PORT) {
      datum = htons(CNF_GetNTPPort());
      if (!NKSN_AddRecord(session, 1, NKE_RECORD_NTPV4_PORT_NEGOTIATION, &datum, sizeof (datum)))
        return 0;
    }

    ntp_server = CNF_GetNtsNtpServer();
    if (ntp_server) {
      if (!NKSN_AddRecord(session, 1, NKE_RECORD_NTPV4_SERVER_NEGOTIATION,
                          ntp_server, strlen(ntp_server)))
        return 0;
    }

    context.algorithm = aead_algorithm;

    if (!NKSN_GetKeys(session, aead_algorithm, &context.c2s, &context.s2c))
      return 0;

    for (i = 0; i < NKE_MAX_COOKIES; i++) {
      if (!NKS_GenerateCookie(&context, &cookie))
        return 0;
      if (!NKSN_AddRecord(session, 0, NKE_RECORD_COOKIE, cookie.cookie, cookie.length))
        return 0;
    }
  }

  if (!NKSN_EndMessage(session))
    return 0;

  return 1;
}

/* ================================================== */

static int
process_request(NKSN_Instance session)
{
  int next_protocol_records = 0, aead_algorithm_records = 0;
  int next_protocol_values = 0, aead_algorithm_values = 0;
  int next_protocol = -1, aead_algorithm = -1, error = -1;
  int i, critical, type, length;
  uint16_t data[NKE_MAX_RECORD_BODY_LENGTH / sizeof (uint16_t)];

  assert(NKE_MAX_RECORD_BODY_LENGTH % sizeof (uint16_t) == 0);
  assert(sizeof (uint16_t) == 2);

  while (error < 0) {
    if (!NKSN_GetRecord(session, &critical, &type, &length, &data, sizeof (data)))
      break;

    switch (type) {
      case NKE_RECORD_NEXT_PROTOCOL:
        if (!critical || length < 2 || length % 2 != 0) {
          error = NKE_ERROR_BAD_REQUEST;
          break;
        }

        next_protocol_records++;

        for (i = 0; i < MIN(length, sizeof (data)) / 2; i++) {
          next_protocol_values++;
          if (ntohs(data[i]) == NKE_NEXT_PROTOCOL_NTPV4)
            next_protocol = NKE_NEXT_PROTOCOL_NTPV4;
        }
        break;
      case NKE_RECORD_AEAD_ALGORITHM:
        if (length < 2 || length % 2 != 0) {
          error = NKE_ERROR_BAD_REQUEST;
          break;
        }

        aead_algorithm_records++;

        for (i = 0; i < MIN(length, sizeof (data)) / 2; i++) {
          aead_algorithm_values++;
          if (ntohs(data[i]) == AEAD_AES_SIV_CMAC_256)
            aead_algorithm = AEAD_AES_SIV_CMAC_256;
        }
        break;
      case NKE_RECORD_ERROR:
      case NKE_RECORD_WARNING:
      case NKE_RECORD_COOKIE:
        error = NKE_ERROR_BAD_REQUEST;
        break;
      default:
        if (critical)
          error = NKE_ERROR_UNRECOGNIZED_CRITICAL_RECORD;
    }
  }

  if (error < 0) {
    if (next_protocol_records != 1 || next_protocol_values < 1 ||
        (next_protocol == NKE_NEXT_PROTOCOL_NTPV4 &&
         (aead_algorithm_records != 1 || aead_algorithm_values < 1)))
      error = NKE_ERROR_BAD_REQUEST;
  }

  if (!prepare_response(session, error, next_protocol, aead_algorithm))
    return 0;

  return 1;
}

/* ================================================== */

static int
handle_message(void *arg)
{
  NKSN_Instance session = arg;

  return process_request(session);
}

/* ================================================== */

static void
generate_key(int index)
{
  int key_length;

  if (index < 0 || index >= MAX_SERVER_KEYS)
    assert(0);

  key_length = SIV_GetKeyLength(SERVER_COOKIE_SIV);
  if (key_length > sizeof (server_keys[index].key))
    assert(0);

  UTI_GetRandomBytesUrandom(server_keys[index].key, key_length);

  if (!server_keys[index].siv ||
      !SIV_SetKey(server_keys[index].siv, server_keys[index].key, key_length))
    LOG_FATAL("Could not set SIV key");

  UTI_GetRandomBytes(&server_keys[index].id, sizeof (server_keys[index].id));

  /* Encode the index in the lowest bits of the ID */
  server_keys[index].id &= -1U << KEY_ID_INDEX_BITS;
  server_keys[index].id |= index;

  DEBUG_LOG("Generated server key %"PRIX32, server_keys[index].id);

  last_server_key_ts = SCH_GetLastEventMonoTime();
}

/* ================================================== */

static void
save_keys(void)
{
  char buf[SIV_MAX_KEY_LENGTH * 2 + 1], *dump_dir;
  int i, index, key_length;
  double last_key_age;
  FILE *f;

  /* Don't save the keys if rotation is disabled to enable an external
     management of the keys (e.g. share them with another server) */
  if (key_rotation_interval == 0)
    return;

  dump_dir = CNF_GetNtsDumpDir();
  if (!dump_dir)
    return;

  f = UTI_OpenFile(dump_dir, DUMP_FILENAME, ".tmp", 'w', 0600);
  if (!f)
    return;

  key_length = SIV_GetKeyLength(SERVER_COOKIE_SIV);
  last_key_age = SCH_GetLastEventMonoTime() - last_server_key_ts;

  if (fprintf(f, "%s%d %.1f\n", DUMP_IDENTIFIER, SERVER_COOKIE_SIV, last_key_age) < 0)
    goto error;

  for (i = 0; i < MAX_SERVER_KEYS; i++) {
    index = (current_server_key + i + 1 + FUTURE_KEYS) % MAX_SERVER_KEYS;

    if (key_length > sizeof (server_keys[index].key) ||
        !UTI_BytesToHex(server_keys[index].key, key_length, buf, sizeof (buf)) ||
        fprintf(f, "%08"PRIX32" %s\n", server_keys[index].id, buf) < 0)
      goto error;
  }

  fclose(f);

  /* Rename the temporary file, or remove it if that fails */
  if (!UTI_RenameTempFile(dump_dir, DUMP_FILENAME, ".tmp", NULL)) {
    if (!UTI_RemoveFile(dump_dir, DUMP_FILENAME, ".tmp"))
      ;
  }

  return;

error:
  DEBUG_LOG("Could not %s server keys", "save");
  fclose(f);

  if (!UTI_RemoveFile(dump_dir, DUMP_FILENAME, NULL))
    ;
}

/* ================================================== */

#define MAX_WORDS 2

static int
load_keys(void)
{
  char *dump_dir, line[1024], *words[MAX_WORDS];
  unsigned char key[SIV_MAX_KEY_LENGTH];
  int i, index, key_length, algorithm;
  double key_age;
  FILE *f;
  uint32_t id;

  dump_dir = CNF_GetNtsDumpDir();
  if (!dump_dir)
    return 0;

  f = UTI_OpenFile(dump_dir, DUMP_FILENAME, NULL, 'r', 0);
  if (!f)
    return 0;

  if (!fgets(line, sizeof (line), f) || strcmp(line, DUMP_IDENTIFIER) != 0 ||
      !fgets(line, sizeof (line), f) || UTI_SplitString(line, words, MAX_WORDS) != 2 ||
        sscanf(words[0], "%d", &algorithm) != 1 || algorithm != SERVER_COOKIE_SIV ||
        sscanf(words[1], "%lf", &key_age) != 1)
    goto error;

  key_length = SIV_GetKeyLength(SERVER_COOKIE_SIV);
  last_server_key_ts = SCH_GetLastEventMonoTime() - MAX(key_age, 0.0);

  for (i = 0; i < MAX_SERVER_KEYS && fgets(line, sizeof (line), f); i++) {
    if (UTI_SplitString(line, words, MAX_WORDS) != 2 ||
        sscanf(words[0], "%"PRIX32, &id) != 1)
      goto error;

    if (UTI_HexToBytes(words[1], key, sizeof (key)) != key_length)
      goto error;

    index = id % MAX_SERVER_KEYS;

    server_keys[index].id = id;
    assert(sizeof (server_keys[index].key) == sizeof (key));
    memcpy(server_keys[index].key, key, key_length);

    if (!SIV_SetKey(server_keys[index].siv, server_keys[index].key, key_length))
      LOG_FATAL("Could not set SIV key");

    DEBUG_LOG("Loaded key %"PRIX32, id);

    current_server_key = (index + MAX_SERVER_KEYS - FUTURE_KEYS) % MAX_SERVER_KEYS;
  }

  fclose(f);

  return 1;

error:
  DEBUG_LOG("Could not %s server keys", "load");
  fclose(f);

  return 0;
}

/* ================================================== */

static void
key_timeout(void *arg)
{
  current_server_key = (current_server_key + 1) % MAX_SERVER_KEYS;
  generate_key((current_server_key + FUTURE_KEYS) % MAX_SERVER_KEYS);
  save_keys();

  SCH_AddTimeoutByDelay(key_rotation_interval, key_timeout, NULL);
}

/* ================================================== */

static void
run_helper(uid_t uid, gid_t gid, int scfilter_level)
{
  LOG_Severity log_severity;

  /* Finish minimal initialisation and run using the scheduler loop
     similarly to the main process */

  DEBUG_LOG("Helper started");

  /* Suppress a log message about disabled clock control */
  log_severity = LOG_GetMinSeverity();
  LOG_SetMinSeverity(LOGS_ERR);

  SYS_Initialise(0);
  LOG_SetMinSeverity(log_severity);

  if (!geteuid() && (uid || gid))
    SYS_DropRoot(uid, gid, SYS_NTSKE_HELPER);

  NKS_Initialise();

  UTI_SetQuitSignalsHandler(helper_signal, 1);
  if (scfilter_level != 0)
    SYS_EnableSystemCallFilter(scfilter_level, SYS_NTSKE_HELPER);

  SCH_MainLoop();

  DEBUG_LOG("Helper exiting");

  NKS_Finalise();
  SCK_Finalise();
  SYS_Finalise();
  SCH_Finalise();
  LCL_Finalise();
  PRV_Finalise();
  CNF_Finalise();
  LOG_Finalise();

  UTI_ResetGetRandomFunctions();

  exit(0);
}

/* ================================================== */

void
NKS_PreInitialise(uid_t uid, gid_t gid, int scfilter_level)
{
  int i, processes, sock_fd1, sock_fd2;
  const char **certs, **keys;
  char prefix[16];
  pid_t pid;

  helper_sock_fd = INVALID_SOCK_FD;
  is_helper = 0;

  if (CNF_GetNtsServerCertAndKeyFiles(&certs, &keys) <= 0)
    return;

  processes = CNF_GetNtsServerProcesses();
  if (processes <= 0)
    return;

  /* Start helper processes to perform (computationally expensive) NTS-KE
     sessions with clients on sockets forwarded from the main process */

  sock_fd1 = SCK_OpenUnixSocketPair(0, &sock_fd2);
  if (sock_fd1 < 0)
    LOG_FATAL("Could not open socket pair");

  for (i = 0; i < processes; i++) {
    pid = fork();

    if (pid < 0)
      LOG_FATAL("fork() failed : %s", strerror(errno));

    if (pid > 0)
      continue;

    is_helper = 1;

    UTI_ResetGetRandomFunctions();

    snprintf(prefix, sizeof (prefix), "nks#%d:", i + 1);
    LOG_SetDebugPrefix(prefix);
    LOG_CloseParentFd();

    SCK_CloseSocket(sock_fd1);
    SCH_AddFileHandler(sock_fd2, SCH_FILE_INPUT, handle_helper_request, NULL);

    run_helper(uid, gid, scfilter_level);
  }

  SCK_CloseSocket(sock_fd2);
  helper_sock_fd = sock_fd1;
}

/* ================================================== */

void
NKS_Initialise(void)
{
  const char **certs, **keys;
  int i, n_certs_keys;
  double key_delay;

  server_sock_fd4 = INVALID_SOCK_FD;
  server_sock_fd6 = INVALID_SOCK_FD;

  n_certs_keys = CNF_GetNtsServerCertAndKeyFiles(&certs, &keys);
  if (n_certs_keys <= 0)
    return;

  if (helper_sock_fd == INVALID_SOCK_FD) {
    server_credentials = NKSN_CreateServerCertCredentials(certs, keys, n_certs_keys);
    if (!server_credentials)
      return;
  } else {
    server_credentials = NULL;
  }

  sessions = ARR_CreateInstance(sizeof (NKSN_Instance));
  for (i = 0; i < CNF_GetNtsServerConnections(); i++)
    *(NKSN_Instance *)ARR_GetNewElement(sessions) = NULL;

  /* Generate random keys, even if they will be replaced by reloaded keys,
     or unused (in the helper) */
  for (i = 0; i < MAX_SERVER_KEYS; i++) {
    server_keys[i].siv = SIV_CreateInstance(SERVER_COOKIE_SIV);
    generate_key(i);
  }

  current_server_key = MAX_SERVER_KEYS - 1;

  if (!is_helper) {
    server_sock_fd4 = open_socket(IPADDR_INET4);
    server_sock_fd6 = open_socket(IPADDR_INET6);

    key_rotation_interval = MAX(CNF_GetNtsRotate(), 0);

    /* Reload saved keys, or save the new keys */
    if (!load_keys())
      save_keys();

    if (key_rotation_interval > 0) {
      key_delay = key_rotation_interval - (SCH_GetLastEventMonoTime() - last_server_key_ts);
      SCH_AddTimeoutByDelay(MAX(key_delay, 0.0), key_timeout, NULL);
    }
  }

  initialised = 1;
}

/* ================================================== */

void
NKS_Finalise(void)
{
  int i;

  if (!initialised)
    return;

  if (helper_sock_fd != INVALID_SOCK_FD) {
    /* Send the helpers a request to exit */
    for (i = 0; i < CNF_GetNtsServerProcesses(); i++) {
      if (!SCK_Send(helper_sock_fd, "", 1, 0))
        ;
    }
    SCK_CloseSocket(helper_sock_fd);
  }
  if (server_sock_fd4 != INVALID_SOCK_FD)
    SCK_CloseSocket(server_sock_fd4);
  if (server_sock_fd6 != INVALID_SOCK_FD)
    SCK_CloseSocket(server_sock_fd6);

  if (!is_helper)
    save_keys();

  for (i = 0; i < MAX_SERVER_KEYS; i++)
    SIV_DestroyInstance(server_keys[i].siv);

  for (i = 0; i < ARR_GetSize(sessions); i++) {
    NKSN_Instance session = *(NKSN_Instance *)ARR_GetElement(sessions, i);
    if (session)
      NKSN_DestroyInstance(session);
  }
  ARR_DestroyInstance(sessions);

  if (server_credentials)
    NKSN_DestroyCertCredentials(server_credentials);
}

/* ================================================== */

void
NKS_DumpKeys(void)
{
  save_keys();
}

/* ================================================== */

void
NKS_ReloadKeys(void)
{
  /* Don't load the keys if they are expected to be generated by this server
     instance (i.e. they are already loaded) to not delay the next rotation */
  if (key_rotation_interval > 0)
    return;

  load_keys();
}

/* ================================================== */

/* A server cookie consists of key ID, nonce, and encrypted C2S+S2C keys */

int
NKS_GenerateCookie(NKE_Context *context, NKE_Cookie *cookie)
{
  unsigned char plaintext[2 * NKE_MAX_KEY_LENGTH], *ciphertext;
  int plaintext_length, tag_length;
  ServerCookieHeader *header;
  ServerKey *key;

  if (!initialised) {
    DEBUG_LOG("NTS server disabled");
    return 0;
  }

  /* The algorithm is hardcoded for now */
  if (context->algorithm != AEAD_AES_SIV_CMAC_256) {
    DEBUG_LOG("Unexpected SIV algorithm");
    return 0;
  }

  if (context->c2s.length < 0 || context->c2s.length > NKE_MAX_KEY_LENGTH ||
      context->s2c.length < 0 || context->s2c.length > NKE_MAX_KEY_LENGTH) {
    DEBUG_LOG("Invalid key length");
    return 0;
  }

  key = &server_keys[current_server_key];

  header = (ServerCookieHeader *)cookie->cookie;

  header->key_id = htonl(key->id);
  UTI_GetRandomBytes(header->nonce, sizeof (header->nonce));

  plaintext_length = context->c2s.length + context->s2c.length;
  assert(plaintext_length <= sizeof (plaintext));
  memcpy(plaintext, context->c2s.key, context->c2s.length);
  memcpy(plaintext + context->c2s.length, context->s2c.key, context->s2c.length);

  tag_length = SIV_GetTagLength(key->siv);
  cookie->length = sizeof (*header) + plaintext_length + tag_length;
  assert(cookie->length <= sizeof (cookie->cookie));
  ciphertext = cookie->cookie + sizeof (*header);

  if (!SIV_Encrypt(key->siv, header->nonce, sizeof (header->nonce),
                   "", 0,
                   plaintext, plaintext_length,
                   ciphertext, plaintext_length + tag_length)) {
    DEBUG_LOG("Could not encrypt cookie");
    return 0;
  }

  return 1;
}

/* ================================================== */

int
NKS_DecodeCookie(NKE_Cookie *cookie, NKE_Context *context)
{
  unsigned char plaintext[2 * NKE_MAX_KEY_LENGTH], *ciphertext;
  int ciphertext_length, plaintext_length, tag_length;
  ServerCookieHeader *header;
  ServerKey *key;
  uint32_t key_id;

  if (!initialised) {
    DEBUG_LOG("NTS server disabled");
    return 0;
  }

  if (cookie->length <= (int)sizeof (*header)) {
    DEBUG_LOG("Invalid cookie length");
    return 0;
  }

  header = (ServerCookieHeader *)cookie->cookie;
  ciphertext = cookie->cookie + sizeof (*header);
  ciphertext_length = cookie->length - sizeof (*header);

  key_id = ntohl(header->key_id);
  key = &server_keys[key_id % MAX_SERVER_KEYS];
  if (key_id != key->id) {
    DEBUG_LOG("Unknown key %"PRIX32, key_id);
    return 0;
  }

  tag_length = SIV_GetTagLength(key->siv);
  if (tag_length >= ciphertext_length) {
    DEBUG_LOG("Invalid cookie length");
    return 0;
  }

  plaintext_length = ciphertext_length - tag_length;
  if (plaintext_length > sizeof (plaintext) || plaintext_length % 2 != 0) {
    DEBUG_LOG("Invalid cookie length");
    return 0;
  }

  if (!SIV_Decrypt(key->siv, header->nonce, sizeof (header->nonce),
                   "", 0,
                   ciphertext, ciphertext_length,
                   plaintext, plaintext_length)) {
    DEBUG_LOG("Could not decrypt cookie");
    return 0;
  }

  context->algorithm = AEAD_AES_SIV_CMAC_256;

  context->c2s.length = plaintext_length / 2;
  context->s2c.length = plaintext_length / 2;
  assert(context->c2s.length <= sizeof (context->c2s.key));

  memcpy(context->c2s.key, plaintext, context->c2s.length);
  memcpy(context->s2c.key, plaintext + context->c2s.length, context->s2c.length);

  return 1;
}