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
|
KITTEN WG N. Williams
Internet-Draft Sun
Expires: April 19, 2006 October 16, 2005
Clarifications and Extensions to the GSS-API for the Use of Channel
Bindings
draft-ietf-kitten-gssapi-channel-bindings-01.txt
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on April 19, 2006.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document clarifies and generalizes the GSS-API "channel
bindings" facility. This document also specifies the format of the
various types of channel bindings.
Williams Expires April 19, 2006 [Page 1]
Internet-Draft GSS-API Channel Bindings October 2005
Table of Contents
1. Conventions used in this document . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Generic Structure for GSS-API Channel Bindings . . . . . . . . 5
3.1. Proper Mechanism Use of Channel Bindings . . . . . . . . . 5
4. Channel Bindings for SSHv2 . . . . . . . . . . . . . . . . . . 6
4.1. GSS_Make_sshv2_channel_bindings() . . . . . . . . . . . . 6
4.1.1. C-Bindings . . . . . . . . . . . . . . . . . . . . . . 7
5. Channel Bindings for TLS . . . . . . . . . . . . . . . . . . . 8
5.1. GSS_Make_tls_channel_bindings() . . . . . . . . . . . . . 8
5.1.1. C-Bindings . . . . . . . . . . . . . . . . . . . . . . 9
6. Channel Bindings for IPsec . . . . . . . . . . . . . . . . . . 10
6.1. GSS_Make_ipsec_channel_bindings() . . . . . . . . . . . . 10
6.1.1. C-Bindings . . . . . . . . . . . . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
8.1. Normative . . . . . . . . . . . . . . . . . . . . . . . . 13
8.2. Informative . . . . . . . . . . . . . . . . . . . . . . . 13
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . . . . 16
Williams Expires April 19, 2006 [Page 2]
Internet-Draft GSS-API Channel Bindings October 2005
1. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Williams Expires April 19, 2006 [Page 3]
Internet-Draft GSS-API Channel Bindings October 2005
2. Introduction
The concept of "channel bindings" and the abstract construction of
channel bindings for several types of channels are described in
[CHANNEL-BINDINGS]
To actually use channel bindings in GSS-API aplications additional
details are required that are given below.
First the structure given to channel bindings data in [RFC2744] is
generalized to all of the GSS-API, not just its C-Bindings.
Then the actual construction of channel bindings to SSHv2, TLS and
IPsec channels is given.
Williams Expires April 19, 2006 [Page 4]
Internet-Draft GSS-API Channel Bindings October 2005
3. Generic Structure for GSS-API Channel Bindings
The base GSS-API v2, update 1 specification [RFC2743]describes
channel bindings as an OCTET STRING and leaves it to the GSS-API v2,
update 1 C-Bindings specification to specify the structure of the
contents of the channel bindings OCTET STRINGs. The C-Bindings
specification [RFC2744]then defines, in terms of C, what should be
generic structure for channel bindings. The Kerberos V GSS mechanism
[RFC1964]then defines a method for encoding GSS channel bindings in a
way that is independent of the C-Bindings!
In other words, the structure of GSS channel bindings given in
[RFC2744] is actually generic, rather than specific to the C
programming language.
Here, then, is a generic re-statement of this structure, in pseudo-
ASN.1:
GSS-CHANNEL-BINDINGS := SEQUENCE {
initiator-address-type INTEGER,
initiator-address OCTET STRING,
acceptor-address-type INTEGER,
acceptor-address OCTET STRING,
application-data OCTET STRING,
}
The values for the address fields are described in [RFC2744].
Language-specific bindings of the GSS-API should specify a language-
specific formulation of this structure.
3.1. Proper Mechanism Use of Channel Bindings
As described in [CHANNEL-BINDINGS], GSS mechanisms should exchange
integrity protected proofs of channel bindings, where the proof is
obtained by running a strong hash of the channel bindings data
(encoded as per some mechanism-specific, such as in [RFC1964]) and a
binary value to represent the initiator->acceptor, and opposite,
direction.
The encoding of channel bindings used in [RFC1964], with the addition
of a binary value as described above, and the substitution of SHA-1
for MD5 is a reasonable, generic encoding of GSS-CHANNEL-BINDINGS
that any future GSS mechanisms can use.
Williams Expires April 19, 2006 [Page 5]
Internet-Draft GSS-API Channel Bindings October 2005
4. Channel Bindings for SSHv2
The SSHv2 channel bindings are constructed as an octet string for the
'application-data' field of the channel bindings by concatenating the
following values and in this order:
1. The ASCII string "GSS SSHv2 CB:"
2. The SSHv2 session ID
3. Any additional application-provided data, encoded as the DER
encoding of an ASN.1 OCTET STRING
4.1. GSS_Make_sshv2_channel_bindings()
Inputs:
o session_id OCTET STRING,
o additional_app_data OCTET STRING
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o channel_bindings_app_data OCTET STRING
Return major_status codes:
o GSS_S_COMPLETE indicates no error.
o GSS_S_FAILURE indicates failure to construct the channel bindings
as a result, perhaps, of a memory management, or similar failure.
This function constructs an OCTET STRING for use as the value of the
application-data field of the GSS-CHANNEL-BINDINGS structure
described above.
Williams Expires April 19, 2006 [Page 6]
Internet-Draft GSS-API Channel Bindings October 2005
4.1.1. C-Bindings
OM_uint32 gss_make_sshv2_channel_bindings(
OM_uint32 *minor_status,
const gss_buffer_t session_id,
const gss_buffer_t additional_app_data,
gss_buffer_t channel_bindings_app_data
);
Williams Expires April 19, 2006 [Page 7]
Internet-Draft GSS-API Channel Bindings October 2005
5. Channel Bindings for TLS
The TLS channel bindings are constructed as an octet string for the
'application-data' field of the channel bindings by concatenating the
following values and in this order:
1. The ASCII string "GSS TLSv1.0 CB:"
2. The TLS finished message sent by the client
3. The TLS finished message sent by the server
4. Any additional application-provided data, encoded as the DER
encoding of an ASN.1 OCTET STRING
5.1. GSS_Make_tls_channel_bindings()
Inputs:
o client_finished_msg OCTET STRING,
o server_finished_msg OCTET STRING,
o additional_app_data OCTET STRING
Outputs:
o major_status INTEGER,
o minor_status INTEGER,
o channel_bindings_app_data OCTET STRING
Return major_status codes:
o GSS_S_COMPLETE indicates no error.
o GSS_S_FAILURE indicates failure to construct the channel bindings
as a result, perhaps, of a memory management, or similar failure.
This function constructs an OCTET STRING for use as the value of the
application-data field of the GSS-CHANNEL-BINDINGS structure
described above.
Williams Expires April 19, 2006 [Page 8]
Internet-Draft GSS-API Channel Bindings October 2005
5.1.1. C-Bindings
OM_uint32 gss_make_tls_channel_bindings(
OM_uint32 *minor_status,
const gss_buffer_t client_finished_msg,
const gss_buffer_t server_finished_msg,
const gss_buffer_t additional_app_data,
gss_buffer_t channel_bindings_app_data
);
Williams Expires April 19, 2006 [Page 9]
Internet-Draft GSS-API Channel Bindings October 2005
6. Channel Bindings for IPsec
The IPsec channel bindings are constructed as an octet string for the
'application-data' field of the channel bindings by concatenating the
following values and in this order:
1. The ASCII string "GSS IPsec CB:"
2. The transform ID for encryption, as a 16-bit big-endian word
3. The transform ID for integrity protection, as 16-bit in big-
endian word
4. NOTE: The following needs to be updated to take into account
progress of BTNS.
5. The initiator ID payload as used in the key exchange protocol
used for setting up the channel's SAs
6. The responder ID payload as used in the key exchange protocol
used for setting up the channel's SAs
7. Any additional application-provided data, encoded as the DER
encoding of an ASN.1 OCTET STRING
Note that traffic selectors are not included. Inclusion of
confidentiality/integrity algorithms protects against MITMs that can
compromise weaker algorithms that policy might permit, for the same
peers, for other traffic.
6.1. GSS_Make_ipsec_channel_bindings()
Inputs:
o encr_alg INTEGER,
o integ_alg INTEGER,
o initiator_id OCTET_STRING,
o acceptor_id OCTET_STRING,
o additional_app_data OCTET STRING
Outputs:
Williams Expires April 19, 2006 [Page 10]
Internet-Draft GSS-API Channel Bindings October 2005
o major_status INTEGER,
o minor_status INTEGER,
o channel_bindings_app_data OCTET STRING
Return major_status codes:
o GSS_S_COMPLETE indicates no error.
o GSS_S_FAILURE indicates failure to construct the channel bindings
as a result, perhaps, of a memory management, or similar failure.
This function constructs an OCTET STRING for use as the value of the
application-data field of the GSS-CHANNEL-BINDINGS structure
described above.
6.1.1. C-Bindings
OM_uint32 gss_make_ipsec_channel_bindings(
OM_uint32 *minor_status,
OM_uint32 encr_alg,
OM_uint32 integ_alg,
const gss_buffer_t initiator_id,
const gss_buffer_t acceptor_id,
const gss_buffer_t additional_app_data,
gss_buffer_t channel_bindings_app_data
);
Williams Expires April 19, 2006 [Page 11]
Internet-Draft GSS-API Channel Bindings October 2005
7. Security Considerations
For general security considerations relating to channel bindings see
[CHANNEL-BINDINGS]
Williams Expires April 19, 2006 [Page 12]
Internet-Draft GSS-API Channel Bindings October 2005
8. References
8.1. Normative
[RFC1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism",
RFC 1964, June 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2743] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000.
[RFC2744] Wray, J., "Generic Security Service API Version 2 :
C-bindings", RFC 2744, January 2000.
8.2. Informative
[RFC0854] Postel, J. and J. Reynolds, "Telnet Protocol
Specification", STD 8, RFC 854, May 1983.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2025] Adams, C., "The Simple Public-Key GSS-API Mechanism
(SPKM)", RFC 2025, October 1996.
[RFC2203] Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol
Specification", RFC 2203, September 1997.
[RFC2478] Baize, E. and D. Pinkas, "The Simple and Protected GSS-API
Negotiation Mechanism", RFC 2478, December 1998.
[RFC2623] Eisler, M., "NFS Version 2 and Version 3 Security Issues
and the NFS Protocol's Use of RPCSEC_GSS and Kerberos V5",
RFC 2623, June 1999.
[RFC3530] Shepler, S., Callaghan, B., Robinson, D., Thurlow, R.,
Beame, C., Eisler, M., and D. Noveck, "Network File System
(NFS) version 4 Protocol", RFC 3530, April 2003.
Williams Expires April 19, 2006 [Page 13]
Internet-Draft GSS-API Channel Bindings October 2005
Appendix A. Acknowledgments
The author would like to thank Mike Eisler for his work on the
Channel Conjunction Mechanism I-D and for bringing the problem to a
head, Sam Hartman for pointing out that channel bindings provide a
general solution to the channel binding problem, Jeff Altman for his
suggestion of using the TLS finished messages as the TLS channel
bindings, Bill Sommerfeld, for his help in developing channel
bindings for IPsec, and Radia Perlman for her most helpful comments.
Williams Expires April 19, 2006 [Page 14]
Internet-Draft GSS-API Channel Bindings October 2005
Author's Address
Nicolas Williams
Sun Microsystems
5300 Riata Trace Ct
Austin, TX 78727
US
Email: Nicolas.Williams@sun.com
Williams Expires April 19, 2006 [Page 15]
Internet-Draft GSS-API Channel Bindings October 2005
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Williams Expires April 19, 2006 [Page 16]
|