Internet Engineering Task Force (IETF)                          J. Touch
Request for Comments: 9235                        Independent Consultant
Category: Informational                                    J. Kuusisaari
ISSN: 2070-1721                                                 Infinera
                                                                May 2022


            TCP Authentication Option (TCP-AO) Test Vectors

Abstract

   This document provides test vectors to validate implementations of
   the two mandatory authentication algorithms specified for the TCP
   Authentication Option over both IPv4 and IPv6.  This includes
   validation of the key derivation function (KDF) based on a set of
   test connection parameters as well as validation of the message
   authentication code (MAC).  Vectors are provided for both currently
   required pairs of KDF and MAC algorithms: KDF_HMAC_SHA1 and HMAC-
   SHA-1-96, and KDF_AES_128_CMAC and AES-128-CMAC-96.  The vectors also
   validate both whole TCP segments as well as segments whose options
   are excluded for middlebox traversal.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are candidates for any level of Internet
   Standard; see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9235.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Revised BSD License text as described in Section 4.e of the
   Trust Legal Provisions and are provided without warranty as described
   in the Revised BSD License.

Table of Contents

   1.  Introduction
   2.  Conventions Used in This Document
   3.  Input Test Vectors
     3.1.  TCP Connection Parameters
       3.1.1.  TCP-AO Parameters
       3.1.2.  Active (Client) Side Parameters
       3.1.3.  Passive (Server) Side Parameters
       3.1.4.  Other IP Fields and Options
       3.1.5.  Other TCP Fields and Options
   4.  IPv4 SHA-1 Output Test Vectors
     4.1.  HMAC-SHA-1-96 (Default - Covers TCP Options)
       4.1.1.  Send (Client) SYN (Covers Options)
       4.1.2.  Receive (Server) SYN-ACK (Covers Options)
       4.1.3.  Send (Client) Non-SYN (Covers Options)
       4.1.4.  Receive (Server) Non-SYN (Covers Options)
     4.2.  HMAC-SHA-1-96 (Omits TCP Options)
       4.2.1.  Send (Client) SYN (Omits Options)
       4.2.2.  Receive (Server) SYN-ACK (Omits Options)
       4.2.3.  Send (Client) Non-SYN (Omits Options)
       4.2.4.  Receive (Server) Non-SYN (Omits Options)
   5.  IPv4 AES-128 Output Test Vectors
     5.1.  AES-128-CMAC-96 (Default - Covers TCP Options)
       5.1.1.  Send (Client) SYN (Covers Options)
       5.1.2.  Receive (Server) SYN-ACK (Covers Options)
       5.1.3.  Send (Client) Non-SYN (Covers Options)
       5.1.4.  Receive (Server) Non-SYN (Covers Options)
     5.2.  AES-128-CMAC-96 (Omits TCP Options)
       5.2.1.  Send (Client) SYN (Omits Options)
       5.2.2.  Receive (Server) SYN-ACK (Omits Options)
       5.2.3.  Send (Client) Non-SYN (Omits Options)
       5.2.4.  Receive (Server) Non-SYN (Omits Options)
   6.  IPv6 SHA-1 Output Test Vectors
     6.1.  HMAC-SHA-1-96 (Default - Covers TCP Options)
       6.1.1.  Send (Client) SYN (Covers Options)
       6.1.2.  Receive (Server) SYN-ACK (Covers Options)
       6.1.3.  Send (Client) Non-SYN (Covers Options)
       6.1.4.  Receive (Server) Non-SYN (Covers Options)
     6.2.  HMAC-SHA-1-96 (Omits TCP Options)
       6.2.1.  Send (Client) SYN (Omits Options)
       6.2.2.  Receive (Server) SYN-ACK (Omits Options)
       6.2.3.  Send (Client) Non-SYN (Omits Options)
       6.2.4.  Receive (Server) Non-SYN (Omits Options)
   7.  IPv6 AES-128 Output Test Vectors
     7.1.  AES-128-CMAC-96 (Default - Covers TCP Options)
       7.1.1.  Send (Client) SYN (Covers Options)
       7.1.2.  Receive (Server) SYN-ACK (Covers Options)
       7.1.3.  Send (Client) Non-SYN (Covers Options)
       7.1.4.  Receive (Server) Non-SYN (Covers Options)
     7.2.  AES-128-CMAC-96 (Omits TCP Options)
       7.2.1.  Send (Client) SYN (Omits Options)
       7.2.2.  Receive (Server) SYN-ACK (Omits Options)
       7.2.3.  Send (Client) Non-SYN (Omits Options)
       7.2.4.  Receive (Server) Non-SYN (Omits Options)
   8.  Observed Implementation Errors
     8.1.  Algorithm Issues
     8.2.  Algorithm Parameters
     8.3.  String Handling Issues
     8.4.  Header Coverage Issues
   9.  Security Considerations
   10. IANA Considerations
   11. References
     11.1.  Normative References
     11.2.  Informative References
   Acknowledgments
   Authors' Addresses

1.  Introduction

   This document provides test vectors to validate the correct
   implementation of the TCP Authentication Option (TCP-AO) [RFC5925]
   and its mandatory cryptographic algorithms defined in [RFC5926].  It
   includes the specification of all endpoint parameters to generate the
   variety of TCP segments covered by different keys and MAC coverage,
   i.e., both the default case and the variant where TCP options are
   ignored for middlebox traversal.  It also includes both default key
   derivation functions (KDFs) and MAC generation algorithms [RFC5926]
   and lists common pitfalls of implementing the algorithms correctly.

   The experimental extension to support NAT traversal [RFC6978] is not
   included in the provided test vectors.

   This document provides test vectors from multiple implementations
   that have been validated against each other for interoperability.

2.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Input Test Vectors

3.1.  TCP Connection Parameters

   The following parameters are used throughout this suite of test
   vectors.  The terms 'active' and 'passive' are used as defined for
   TCP [RFC0793].

3.1.1.  TCP-AO Parameters

   The following values are used for all exchanges.  This suite does not
   test key switchover.  The KeyIDs are as indicated for TCP-AO
   [RFC5925].  The Master_Key is used to derive the traffic keys
   [RFC5926].

      Active (client) side KeyID: 61 decimal (0x3d hexadecimal)

      Passive (server) side KeyID: 84 decimal (0x54 hexadecimal)

      Master_Key: "testvector" (length = 10 bytes)

3.1.2.  Active (Client) Side Parameters

   The following endpoint parameters are used on the active side of the
   TCP connection, i.e., the side that initiates the TCP SYN.

      For IPv4: 10.11.12.13 (dotted decimal)

      For IPv6: fd00::1 (IPv6 hexadecimal)

      TCP port: (varies)

3.1.3.  Passive (Server) Side Parameters

   The following endpoint parameters are used for the passive side of
   the TCP connection, i.e., the side that responds with a TCP SYN-ACK.

      For IPv4: 172.27.28.29 (dotted decimal)

      For IPv6: fd00::2 (IPv6 hexadecimal)

      TCP port = 179 decimal (BGP)

3.1.4.  Other IP Fields and Options

   No IP options are used in these test vectors.

   All IPv4 packets use the following other parameters [RFC0791]:
   Differentiated Services Code Point (DSCP) = 111000 binary (CS7) as is
   typical for BGP, Explicit Congestion Notification (ECN) = 00 binary,
   set the Don't Fragment (DF) bit, and clear the More Fragments (MF)
   bit.

   IPv4 uses a TTL of 255 decimal; IPv6 uses a hop limit of 255 decimal.

   All IPv6 packets use the following other parameters [RFC8200]:
   traffic class = 0xe0 hexadecimal (DSCP = 111000 binary CS7, as is
   typical for BGP, with ECN = 00 binary) and no Extension Headers
   (EHs).

3.1.5.  Other TCP Fields and Options

   The SYN and SYN-ACK segments include Maximum Segment Size (MSS)
   [RFC0793], No Operation (NOP), Window Scale [RFC7323], Selective
   Acknowledgment (SACK) permitted [RFC2018], Timestamp [RFC7323], and
   TCP-AO [RFC5925], in that order.

   All other example segments include NOP, NOP, Timestamp, and TCP-AO,
   in that order.

   All segment urgent (URG) pointers are zero [RFC0793].  All segments
   with data set the push (PSH) flag [RFC0793].

   Each TCP connection below uses the Initial Sequence Numbers (ISNs) as
   indicated at the front of each corresponding section.

4.  IPv4 SHA-1 Output Test Vectors

   The SHA-1 KDF and MAC algorithms, KDF_HMAC_SHA1 and HMAC-SHA-1-96,
   are computed as specified for TCP-AO [RFC5926].

   In the following sections, all values are indicated as 2-digit
   hexadecimal values with spacing per line representing the contents of
   16 consecutive bytes, as is typical for data dumps.  The IP/TCP data
   indicates the entire IP packet, including the TCP segment and its
   options (whether covered by TCP-AO or not, as indicated), including
   TCP-AO.

4.1.  HMAC-SHA-1-96 (Default - Covers TCP Options)

4.1.1.  Send (Client) SYN (Covers Options)

   Client ISN = 0xfbfbab5a

   Send_SYN_traffic_key:

     6d 63 ef 1b 02 fe 15 09 d4 b1 40 27 07 fd 7b 04
     16 ab b7 4f

   IPv4/TCP:

     45 e0 00 4c dd 0f 40 00 ff 06 bf 6b 0a 0b 0c 0d
     ac 1b 1c 1d e9 d7 00 b3 fb fb ab 5a 00 00 00 00
     e0 02 ff ff ca c4 00 00 02 04 05 b4 01 03 03 08
     04 02 08 0a 00 15 5a b7 00 00 00 00 1d 10 3d 54
     2e e4 37 c6 f8 ed e6 d7 c4 d6 02 e7

   MAC:

     2e e4 37 c6 f8 ed e6 d7 c4 d6 02 e7

4.1.2.  Receive (Server) SYN-ACK (Covers Options)

   Server ISN = 0x11c14261

   Receive_SYN_traffic_key:

     d9 e2 17 e4 83 4a 80 ca 2f 3f d8 de 2e 41 b8 e6
     79 7f ea 96

   IPv4/TCP:

     45 e0 00 4c 65 06 40 00 ff 06 37 75 ac 1b 1c 1d
     0a 0b 0c 0d 00 b3 e9 d7 11 c1 42 61 fb fb ab 5b
     e0 12 ff ff 37 76 00 00 02 04 05 b4 01 03 03 08
     04 02 08 0a 84 a5 0b eb 00 15 5a b7 1d 10 54 3d
     ee ab 0f e2 4c 30 10 81 51 16 b3 be

   MAC:

     ee ab 0f e2 4c 30 10 81 51 16 b3 be

4.1.3.  Send (Client) Non-SYN (Covers Options)

   Send_other_traffic_key:

     d2 e5 9c 65 ff c7 b1 a3 93 47 65 64 63 b7 0e dc
     24 a1 3d 71

   IPv4/TCP:

     45 e0 00 87 36 a1 40 00 ff 06 65 9f 0a 0b 0c 0d
     ac 1b 1c 1d e9 d7 00 b3 fb fb ab 5b 11 c1 42 62
     c0 18 01 04 a1 62 00 00 01 01 08 0a 00 15 5a c1
     84 a5 0b eb 1d 10 3d 54 70 64 cf 99 8c c6 c3 15
     c2 c2 e2 bf ff ff ff ff ff ff ff ff ff ff ff ff
     ff ff ff ff 00 43 01 04 da bf 00 b4 0a 0b 0c 0d
     26 02 06 01 04 00 01 00 01 02 02 80 00 02 02 02
     00 02 02 42 00 02 06 41 04 00 00 da bf 02 08 40
     06 00 64 00 01 01 00

   MAC:

     70 64 cf 99 8c c6 c3 15 c2 c2 e2 bf

4.1.4.  Receive (Server) Non-SYN (Covers Options)

   Receive_other_traffic_key:

     d9 e2 17 e4 83 4a 80 ca 2f 3f d8 de 2e 41 b8 e6
     79 7f ea 96

   IPv4/TCP:

     45 e0 00 87 1f a9 40 00 ff 06 7c 97 ac 1b 1c 1d
     0a 0b 0c 0d 00 b3 e9 d7 11 c1 42 62 fb fb ab 9e
     c0 18 01 00 40 0c 00 00 01 01 08 0a 84 a5 0b f5
     00 15 5a c1 1d 10 54 3d a6 3f 0e cb bb 2e 63 5c
     95 4d ea c7 ff ff ff ff ff ff ff ff ff ff ff ff
     ff ff ff ff 00 43 01 04 da c0 00 b4 ac 1b 1c 1d
     26 02 06 01 04 00 01 00 01 02 02 80 00 02 02 02
     00 02 02 42 00 02 06 41 04 00 00 da c0 02 08 40
     06 00 64 00 01 01 00

   MAC:

     a6 3f 0e cb bb 2e 63 5c 95 4d ea c7

4.2.  HMAC-SHA-1-96 (Omits TCP Options)

4.2.1.  Send (Client) SYN (Omits Options)

   Client ISN = 0xcb0efbee

   Send_SYN_traffic_key:

     30 ea a1 56 0c f0 be 57 da b5 c0 45 22 9f b1 0a
     42 3c d7 ea

   IPv4/TCP:

     45 e0 00 4c 53 99 40 00 ff 06 48 e2 0a 0b 0c 0d
     ac 1b 1c 1d ff 12 00 b3 cb 0e fb ee 00 00 00 00
     e0 02 ff ff 54 1f 00 00 02 04 05 b4 01 03 03 08
     04 02 08 0a 00 02 4c ce 00 00 00 00 1d 10 3d 54
     80 af 3c fe b8 53 68 93 7b 8f 9e c2

   MAC:

     80 af 3c fe b8 53 68 93 7b 8f 9e c2

4.2.2.  Receive (Server) SYN-ACK (Omits Options)

   Server ISN = 0xacd5b5e1

   Receive_SYN_traffic_key:

     b5 b2 89 6b b3 66 4e 81 76 b0 ed c6 e7 99 52 41a
     01 a8 30 7f

   IPv4/TCP:

     45 e0 00 4c 32 84 40 00 ff 06 69 f7 ac 1b 1c 1d
     0a 0b 0c 0d 00 b3 ff 12 ac d5 b5 e1 cb 0e fb ef
     e0 12 ff ff 38 8e 00 00 02 04 05 b4 01 03 03 08
     04 02 08 0a 57 67 72 f3 00 02 4c ce 1d 10 54 3d
     09 30 6f 9a ce a6 3a 8c 68 cb 9a 70

   MAC:

     09 30 6f 9a ce a6 3a 8c 68 cb 9a 70

4.2.3.  Send (Client) Non-SYN (Omits Options)

   Send_other_traffic_key:

     f3 db 17 93 d7 91 0e cd 80 6c 34 f1 55 ea 1f 00
     34 59 53 e3

   IPv4/TCP:

     45 e0 00 87 a8 f5 40 00 ff 06 f3 4a 0a 0b 0c 0d
     ac 1b 1c 1d ff 12 00 b3 cb 0e fb ef ac d5 b5 e2
     c0 18 01 04 6c 45 00 00 01 01 08 0a 00 02 4c ce
     57 67 72 f3 1d 10 3d 54 71 06 08 cc 69 6c 03 a2
     71 c9 3a a5 ff ff ff ff ff ff ff ff ff ff ff ff
     ff ff ff ff 00 43 01 04 da bf 00 b4 0a 0b 0c 0d
     26 02 06 01 04 00 01 00 01 02 02 80 00 02 02 02
     00 02 02 42 00 02 06 41 04 00 00 da bf 02 08 40
     06 00 64 00 01 01 00

   MAC:

     71 06 08 cc 69 6c 03 a2 71 c9 3a a5

4.2.4.  Receive (Server) Non-SYN (Omits Options)

   Receive_other_traffic_key:

     b5 b2 89 6b b3 66 4e 81 76 b0 ed c6 e7 99 52 41
     01 a8 30 7f

   IPv4/TCP:

     45 e0 00 87 54 37 40 00 ff 06 48 09 ac 1b 1c 1d
     0a 0b 0c 0d 00 b3 ff 12 ac d5 b5 e2 cb 0e fc 32
     c0 18 01 00 46 b6 00 00 01 01 08 0a 57 67 72 f3
     00 02 4c ce 1d 10 54 3d 97 76 6e 48 ac 26 2d e9
     ae 61 b4 f9 ff ff ff ff ff ff ff ff ff ff ff ff
     ff ff ff ff 00 43 01 04 da c0 00 b4 ac 1b 1c 1d
     26 02 06 01 04 00 01 00 01 02 02 80 00 02 02 02
     00 02 02 42 00 02 06 41 04 00 00 da c0 02 08 40
     06 00 64 00 01 01 00

   MAC:

     97 76 6e 48 ac 26 2d e9 ae 61 b4 f9

5.  IPv4 AES-128 Output Test Vectors

   The AES-128 KDF and MAC algorithms, KDF_AES_128_CMAC and AES-128-
   CMAC-96, are computed as specified for TCP-AO [RFC5926].

   In the following sections, all values are indicated as 2-digit
   hexadecimal values with spacing per line representing the contents of
   16 consecutive bytes, as is typical for data dumps.  The IP/TCP data
   indicates the entire IP packet, including the TCP segment and its
   options (whether covered by TCP-AO or not, as indicated), including
   TCP-AO.

5.1.  AES-128-CMAC-96 (Default - Covers TCP Options)

5.1.1.  Send (Client) SYN (Covers Options)

   Client ISN = 0x787a1ddf

   Send_SYN_traffic_key:

     f5 b8 b3 d5 f3 4f db b6 eb 8d 4a b9 66 0e 60 e3

   IP/TCP:

     45 e0 00 4c 7b 9f 40 00 ff 06 20 dc 0a 0b 0c 0d
     ac 1b 1c 1d c4 fa 00 b3 78 7a 1d df 00 00 00 00
     e0 02 ff ff 5a 0f 00 00 02 04 05 b4 01 03 03 08
     04 02 08 0a 00 01 7e d0 00 00 00 00 1d 10 3d 54
     e4 77 e9 9c 80 40 76 54 98 e5 50 91

   MAC:

     e4 77 e9 9c 80 40 76 54 98 e5 50 91

5.1.2.  Receive (Server) SYN-ACK (Covers Options)

   Server ISN = 0xfadd6de9

   Receive_SYN_traffic_key:

     4b c7 57 1a 48 6f 32 64 bb d8 88 47 40 66 b4 b1

   IPv4/TCP:

     45 e0 00 4c 4b ad 40 00 ff 06 50 ce ac 1b 1c 1d
     0a 0b 0c 0d 00 b3 c4 fa fa dd 6d e9 78 7a 1d e0
     e0 12 ff ff f3 f2 00 00 02 04 05 b4 01 03 03 08
     04 02 08 0a 93 f4 e9 e8 00 01 7e d0 1d 10 54 3d
     d6 ad a7 bc 4c dd 53 6d 17 69 db 5f

   MAC:

     d6 ad a7 bc 4c dd 53 6d 17 69 db 5f

5.1.3.  Send (Client) Non-SYN (Covers Options)

   Send_other_traffic_key:

     8c 8a e0 e8 37 1e c5 cb b9 7e a7 9d 90 41 83 91

   IPv4/TCP:

     45 e0 00 87 fb 4f 40 00 ff 06 a0 f0 0a 0b 0c 0d
     ac 1b 1c 1d c4 fa 00 b3 78 7a 1d e0 fa dd 6d ea
     c0 18 01 04 95 05 00 00 01 01 08 0a 00 01 7e d0
     93 f4 e9 e8 1d 10 3d 54 77 41 27 42 fa 4d c4 33
     ef f0 97 3e ff ff ff ff ff ff ff ff ff ff ff ff
     ff ff ff ff 00 43 01 04 da bf 00 b4 0a 0b 0c 0d
     26 02 06 01 04 00 01 00 01 02 02 80 00 02 02 02
     00 02 02 42 00 02 06 41 04 00 00 da bf 02 08 40
     06 00 64 00 01 01 00

   MAC:

     77 41 27 42 fa 4d c4 33 ef f0 97 3e

5.1.4.  Receive (Server) Non-SYN (Covers Options)

   Receive_other_traffic_key:

     4b c7 57 1a 48 6f 32 64 bb d8 88 47 40 66 b4 b1

   IPv4/TCP:

     45 e0 00 87 b9 14 40 00 ff 06 e3 2b ac 1b 1c 1d
     0a 0b 0c 0d 00 b3 c4 fa fa dd 6d ea 78 7a 1e 23
     c0 18 01 00 e7 db 00 00 01 01 08 0a 93 f4 e9 e8
     00 01 7e d0 1d 10 54 3d f6 d9 65 a7 83 82 a7 48
     45 f7 2d ac ff ff ff ff ff ff ff ff ff ff ff ff
     ff ff ff ff 00 43 01 04 da c0 00 b4 ac 1b 1c 1d
     26 02 06 01 04 00 01 00 01 02 02 80 00 02 02 02
     00 02 02 42 00 02 06 41 04 00 00 da c0 02 08 40
     06 00 64 00 01 01 00

   MAC:

     f6 d9 65 a7 83 82 a7 48 45 f7 2d ac

5.2.  AES-128-CMAC-96 (Omits TCP Options)

5.2.1.  Send (Client) SYN (Omits Options)

   Client ISN = 0x389bed71

   Send_SYN_traffic_key:

     2c db ae 13 92 c4 94 49 fa 92 c4 50 97 35 d5 0e

   IPv4/TCP:

     45 e0 00 4c f2 2e 40 00 ff 06 aa 4c 0a 0b 0c 0d
     ac 1b 1c 1d da 1c 00 b3 38 9b ed 71 00 00 00 00
     e0 02 ff ff 70 bf 00 00 02 04 05 b4 01 03 03 08
     04 02 08 0a 00 01 85 e1 00 00 00 00 1d 10 3d 54
     c4 4e 60 cb 31 f7 c0 b1 de 3d 27 49

   MAC:

     c4 4e 60 cb 31 f7 c0 b1 de 3d 27 49

5.2.2.  Receive (Server) SYN-ACK (Omits Options)

   Server ISN = 0xd3844a6f

   Receive_SYN_traffic_key:

     3c e6 7a 55 18 69 50 6b 63 47 b6 33 c5 0a 62 4a

   IPv4/TCP:

     45 e0 00 4c 6c c0 40 00 ff 06 2f bb ac 1b 1c 1d
     0a 0b 0c 0d 00 b3 da 1c d3 84 4a 6f 38 9b ed 72
     e0 12 ff ff e4 45 00 00 02 04 05 b4 01 03 03 08
     04 02 08 0a ce 45 98 38 00 01 85 e1 1d 10 54 3d
     3a 6a bb 20 7e 49 b1 be 71 36 db 90

   MAC:

     3a 6a bb 20 7e 49 b1 be 71 36 db 90

5.2.3.  Send (Client) Non-SYN (Omits Options)

   Send_other_traffic_key:

     03 5b c4 00 a3 41 ff e5 95 f5 9f 58 00 50 06 ca

   IPv4/TCP:

     45 e0 00 87 ee 91 40 00 ff 06 ad ae 0a 0b 0c 0d
     ac 1b 1c 1d da 1c 00 b3 38 9b ed 72 d3 84 4a 70
     c0 18 01 04 88 51 00 00 01 01 08 0a 00 01 85 e1
     ce 45 98 38 1d 10 3d 54 75 85 e9 e9 d5 c3 ec 85
     7b 96 f8 37 ff ff ff ff ff ff ff ff ff ff ff ff
     ff ff ff ff 00 43 01 04 da bf 00 b4 0a 0b 0c 0d
     26 02 06 01 04 00 01 00 01 02 02 80 00 02 02 02
     00 02 02 42 00 02 06 41 04 00 00 da bf 02 08 40
     06 00 64 00 01 01 00

   MAC:

     75 85 e9 e9 d5 c3 ec 85 7b 96 f8 37

5.2.4.  Receive (Server) Non-SYN (Omits Options)

   Receive_other_traffic_key:

     3c e6 7a 55 18 69 50 6b 63 47 b6 33 c5 0a 62 4a

   IPv4/TCP:

     45 e0 00 87 6a 21 40 00 ff 06 32 1f ac 1b 1c 1d
     0a 0b 0c 0d 00 b3 da 1c d3 84 4a 70 38 9b ed 72
     c0 18 01 00 04 49 00 00 01 01 08 0a ce 45 98 38
     00 01 85 e1 1d 10 54 3d 5c 04 0f d9 23 33 04 76
     5c 09 82 f4 ff ff ff ff ff ff ff ff ff ff ff ff
     ff ff ff ff 00 43 01 04 da c0 00 b4 ac 1b 1c 1d
     26 02 06 01 04 00 01 00 01 02 02 80 00 02 02 02
     00 02 02 42 00 02 06 41 04 00 00 da c0 02 08 40
     06 00 64 00 01 01 00

   MAC:

     5c 04 0f d9 23 33 04 76 5c 09 82 f4

6.  IPv6 SHA-1 Output Test Vectors

   The SHA-1 KDF and MAC algorithms, KDF_HMAC_SHA1 and HMAC-SHA-1-96,
   are computed as specified for TCP-AO [RFC5926].

6.1.  HMAC-SHA-1-96 (Default - Covers TCP Options)

6.1.1.  Send (Client) SYN (Covers Options)

   Client ISN = 0x176a833f

   Send_SYN_traffic_key:

     62 5e c0 9d 57 58 36 ed c9 b6 42 84 18 bb f0 69
     89 a3 61 bb

   IPv6/TCP:

     6e 08 91 dc 00 38 06 40 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 01 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 02 f7 e4 00 b3 17 6a 83 3f
     00 00 00 00 e0 02 ff ff 47 21 00 00 02 04 05 a0
     01 03 03 08 04 02 08 0a 00 41 d0 87 00 00 00 00
     1d 10 3d 54 90 33 ec 3d 73 34 b6 4c 5e dd 03 9f

   MAC:

     90 33 ec 3d 73 34 b6 4c 5e dd 03 9f

6.1.2.  Receive (Server) SYN-ACK (Covers Options)

   Server ISN = 0x3f51994b

   Receive_SYN_traffic_key:

     e4 a3 7a da 2a 0a fc a8 71 14 34 91 3f e1 38 c7
     71 eb cb 4a

   IPv6/TCP:

     6e 01 00 9e 00 38 06 40 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 02 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 01 00 b3 f7 e4 3f 51 99 4b
     17 6a 83 40 e0 12 ff ff bf ec 00 00 02 04 05 a0
     01 03 03 08 04 02 08 0a bd 33 12 9b 00 41 d0 87
     1d 10 54 3d f1 cb a3 46 c3 52 61 63 f7 1f 1f 55

   MAC:

     f1 cb a3 46 c3 52 61 63 f7 1f 1f 55

6.1.3.  Send (Client) Non-SYN (Covers Options)

   Send_other_traffic_key:

     1e d8 29 75 f4 ea 44 4c 61 58 0c 5b d9 0d bd 61
     bb c9 1b 7e

   IPv6/TCP:

     6e 08 91 dc 00 73 06 40 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 01 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 02 f7 e4 00 b3 17 6a 83 40
     3f 51 99 4c c0 18 01 00 32 9c 00 00 01 01 08 0a
     00 41 d0 91 bd 33 12 9b 1d 10 3d 54 bf 08 05 fe
     b4 ac 7b 16 3d 6f cd f2 ff ff ff ff ff ff ff ff
     ff ff ff ff ff ff ff ff 00 43 01 04 fd e8 00 b4
     01 01 01 79 26 02 06 01 04 00 01 00 01 02 02 80
     00 02 02 02 00 02 02 42 00 02 06 41 04 00 00 fd
     e8 02 08 40 06 00 64 00 01 01 00

   MAC:

     bf 08 05 fe b4 ac 7b 16 3d 6f cd f2

6.1.4.  Receive (Server) Non-SYN (Covers Options)

   Receive_other_traffic_key:

     e4 a3 7a da 2a 0a fc a8 71 14 34 91 3f e1 38 c7
     71 eb cb 4a

   IPv6/TCP:

     6e 01 00 9e 00 73 06 40 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 02 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 01 00 b3 f7 e4 3f 51 99 4c
     17 6a 83 83 c0 18 01 00 ee 6e 00 00 01 01 08 0a
     bd 33 12 a5 00 41 d0 91 1d 10 54 3d 6c 48 12 5c
     11 33 5b ab 9a 07 a7 97 ff ff ff ff ff ff ff ff
     ff ff ff ff ff ff ff ff 00 43 01 04 fd e8 00 b4
     01 01 01 7a 26 02 06 01 04 00 01 00 01 02 02 80
     00 02 02 02 00 02 02 42 00 02 06 41 04 00 00 fd
     e8 02 08 40 06 00 64 00 01 01 00

   MAC:

     6c 48 12 5c 11 33 5b ab 9a 07 a7 97

6.2.  HMAC-SHA-1-96 (Omits TCP Options)

6.2.1.  Send (Client) SYN (Omits Options)

   Client ISN = 0x020c1e69

   Send_SYN_traffic_key:

     31 a3 fa f6 9e ff ae 52 93 1b 7f 84 54 67 31 5c
     27 0a 4e dc

   IPv6/TCP:

     6e 07 8f cd 00 38 06 40 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 01 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 02 c6 cd 00 b3 02 0c 1e 69
     00 00 00 00 e0 02 ff ff a4 1a 00 00 02 04 05 a0
     01 03 03 08 04 02 08 0a 00 9d b9 5b 00 00 00 00
     1d 10 3d 54 88 56 98 b0 53 0e d4 d5 a1 5f 83 46

   MAC:

     88 56 98 b0 53 0e d4 d5 a1 5f 83 46

6.2.2.  Receive (Server) SYN-ACK (Omits Options)

   Server ISN = 0xeba3734d

   Receive_SYN_traffic_key:

     40 51 08 94 7f 99 65 75 e7 bd bc 26 d4 02 16 a2
     c7 fa 91 bd

   IPv6/TCP:

     6e 0a 7e 1f 00 38 06 40 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 02 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 01 00 b3 c6 cd eb a3 73 4d
     02 0c 1e 6a e0 12 ff ff 77 4d 00 00 02 04 05 a0
     01 03 03 08 04 02 08 0a 5e c9 9b 70 00 9d b9 5b
     1d 10 54 3d 3c 54 6b ad 97 43 f1 2d f8 b8 01 0d

   MAC:

     3c 54 6b ad 97 43 f1 2d f8 b8 01 0d

6.2.3.  Send (Client) Non-SYN (Omits Options)

   Send_other_traffic_key:

     b3 4e ed 6a 93 96 a6 69 f1 c4 f4 f5 76 18 f3 65
     6f 52 c7 ab

   IPv6/TCP:

     6e 07 8f cd 00 73 06 40 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 01 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 02 c6 cd 00 b3 02 0c 1e 6a
     eb a3 73 4e c0 18 01 00 83 e6 00 00 01 01 08 0a
     00 9d b9 65 5e c9 9b 70 1d 10 3d 54 48 bd 09 3b
     19 24 e0 01 19 2f 5b f0 ff ff ff ff ff ff ff ff
     ff ff ff ff ff ff ff ff 00 43 01 04 fd e8 00 b4
     01 01 01 79 26 02 06 01 04 00 01 00 01 02 02 80
     00 02 02 02 00 02 02 42 00 02 06 41 04 00 00 fd
     e8 02 08 40 06 00 64 00 01 01 00

   MAC:

     48 bd 09 3b 19 24 e0 01 19 2f 5b f0

6.2.4.  Receive (Server) Non-SYN (Omits Options)

   Receive_other_traffic_key:

     40 51 08 94 7f 99 65 75 e7 bd bc 26 d4 02 16 a2
     c7 fa 91 bd

   IPv6/TCP:

     6e 0a 7e 1f 00 73 06 40 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 02 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 01 00 b3 c6 cd eb a3 73 4e
     02 0c 1e ad c0 18 01 00 71 6a 00 00 01 01 08 0a
     5e c9 9b 7a 00 9d b9 65 1d 10 54 3d 55 9a 81 94
     45 b4 fd e9 8d 9e 13 17 ff ff ff ff ff ff ff ff
     ff ff ff ff ff ff ff ff 00 43 01 04 fd e8 00 b4
     01 01 01 7a 26 02 06 01 04 00 01 00 01 02 02 80
     00 02 02 02 00 02 02 42 00 02 06 41 04 00 00 fd
     e8 02 08 40 06 00 64 00 01 01 00

   MAC:

     55 9a 81 94 45 b4 fd e9 8d 9e 13 17

7.  IPv6 AES-128 Output Test Vectors

   The AES-128 KDF and MAC algorithms, KDF_AES_128_CMAC and AES-128-
   CMAC-96, are computed as specified for TCP-AO [RFC5926].

7.1.  AES-128-CMAC-96 (Default - Covers TCP Options)

7.1.1.  Send (Client) SYN (Covers Options)

   Client ISN = 0x193cccec

   Send_SYN_traffic_key:

     fa 5a 21 08 88 2d 39 d0 c7 19 29 17 5a b1 b7 b8

   IP/TCP:

     6e 04 a7 06 00 38 06 40 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 01 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 02 f8 5a 00 b3 19 3c cc ec
     00 00 00 00 e0 02 ff ff de 5d 00 00 02 04 05 a0
     01 03 03 08 04 02 08 0a 13 e4 ab 99 00 00 00 00
     1d 10 3d 54 59 b5 88 10 74 81 ac 6d c3 92 70 40

   MAC:

     59 b5 88 10 74 81 ac 6d c3 92 70 40

7.1.2.  Receive (Server) SYN-ACK (Covers Options)

   Server ISN = 0xa6744ecb

   Receive_SYN_traffic_key:

     cf 1b 1e 22 5e 06 a6 36 16 76 4a 06 7b 46 f4 b1

   IPv6/TCP:

     6e 06 15 20 00 38 06 40 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 02 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 01 00 b3 f8 5a a6 74 4e cb
     19 3c cc ed e0 12 ff ff ea bb 00 00 02 04 05 a0
     01 03 03 08 04 02 08 0a 71 da ab c8 13 e4 ab 99
     1d 10 54 3d dc 28 43 a8 4e 78 a6 bc fd c5 ed 80

   MAC:

     dc 28 43 a8 4e 78 a6 bc fd c5 ed 80

7.1.3.  Send (Client) Non-SYN (Covers Options)

   Send_other_traffic_key:

     61 74 c3 55 7a be d2 75 74 db a3 71 85 f0 03 00

   IPv6/TCP:

     6e 04 a7 06 00 73 06 40 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 01 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 02 f8 5a 00 b3 19 3c cc ed
     a6 74 4e cc c0 18 01 00 32 80 00 00 01 01 08 0a
     13 e4 ab a3 71 da ab c8 1d 10 3d 54 7b 6a 45 5c
     0d 4f 5f 01 83 5b aa b3 ff ff ff ff ff ff ff ff
     ff ff ff ff ff ff ff ff 00 43 01 04 fd e8 00 b4
     01 01 01 79 26 02 06 01 04 00 01 00 01 02 02 80
     00 02 02 02 00 02 02 42 00 02 06 41 04 00 00 fd
     e8 02 08 40 06 00 64 00 01 01 00

   MAC:

     7b 6a 45 5c 0d 4f 5f 01 83 5b aa b3

7.1.4.  Receive (Server) Non-SYN (Covers Options)

   Receive_other_traffic_key:

     cf 1b 1e 22 5e 06 a6 36 16 76 4a 06 7b 46 f4 b1

   IPv6/TCP:

     6e 06 15 20 00 73 06 40 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 02 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 01 00 b3 f8 5a a6 74 4e cc
     19 3c cd 30 c0 18 01 00 52 f4 00 00 01 01 08 0a
     71 da ab d3 13 e4 ab a3 1d 10 54 3d c1 06 9b 7d
     fd 3d 69 3a 6d f3 f2 89 ff ff ff ff ff ff ff ff
     ff ff ff ff ff ff ff ff 00 43 01 04 fd e8 00 b4
     01 01 01 7a 26 02 06 01 04 00 01 00 01 02 02 80
     00 02 02 02 00 02 02 42 00 02 06 41 04 00 00 fd
     e8 02 08 40 06 00 64 00 01 01 00

   MAC:

     c1 06 9b 7d fd 3d 69 3a 6d f3 f2 89

7.2.  AES-128-CMAC-96 (Omits TCP Options)

7.2.1.  Send (Client) SYN (Omits Options)

   Client ISN = 0xb01da74a

   Send_SYN_traffic_key:

     a9 4f 51 12 63 e4 09 3d 35 dd 81 8c 13 bb bf 53

   IPv6/TCP:

     6e 09 3d 76 00 38 06 40 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 01 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 02 f2 88 00 b3 b0 1d a7 4a
     00 00 00 00 e0 02 ff ff 75 ff 00 00 02 04 05 a0
     01 03 03 08 04 02 08 0a 14 27 5b 3b 00 00 00 00
     1d 10 3d 54 3d 45 b4 34 2d e8 bb 15 30 84 78 98

   MAC:

     3d 45 b4 34 2d e8 bb 15 30 84 78 98

7.2.2.  Receive (Server) SYN-ACK (Omits Options)

   Server ISN = 0xa6246145

   Receive_SYN_traffic_key:

     92 de a5 bb c7 8b 1d 9f 5b 29 52 e9 cd 30 64 2a

   IPv6/TCP:

     6e 0c 60 0a 00 38 06 40 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 02 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 01 00 b3 f2 88 a6 24 61 45
     b0 1d a7 4b e0 12 ff ff a7 0c 00 00 02 04 05 a0
     01 03 03 08 04 02 08 0a 17 82 24 5b 14 27 5b 3b
     1d 10 54 3d 1d 01 f6 c8 7c 6f 93 ac ff a9 d4 b5

   MAC:

     1d 01 f6 c8 7c 6f 93 ac ff a9 d4 b5

7.2.3.  Send (Client) Non-SYN (Omits Options)

   Send_other_traffic_key:

     4f b2 08 6e 40 2c 67 90 79 ed 65 d4 bf 97 69 3d

   IPv6/TCP:

     6e 09 3d 76 00 73 06 40 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 01 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 02 f2 88 00 b3 b0 1d a7 4b
     a6 24 61 46 c0 18 01 00 c3 6d 00 00 01 01 08 0a
     14 27 5b 4f 17 82 24 5b 1d 10 3d 54 29 0c f4 14
     cc b4 7a 33 32 76 e7 f8 ff ff ff ff ff ff ff ff
     ff ff ff ff ff ff ff ff 00 43 01 04 fd e8 00 b4
     01 01 01 79 26 02 06 01 04 00 01 00 01 02 02 80
     00 02 02 02 00 02 02 42 00 02 06 41 04 00 00 fd
     e8 02 08 40 06 00 64 00 01 01 00

   MAC:

     29 0c f4 14 cc b4 7a 33 32 76 e7 f8

7.2.4.  Receive (Server) Non-SYN (Omits Options)

   Receive_other_traffic_key:

     92 de a5 bb c7 8b 1d 9f 5b 29 52 e9 cd 30 64 2a

   IPv6/TCP:

     6e 0c 60 0a 00 73 06 40 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 02 fd 00 00 00 00 00 00 00
     00 00 00 00 00 00 00 01 00 b3 f2 88 a6 24 61 46
     b0 1d a7 8e c0 18 01 00 34 51 00 00 01 01 08 0a
     17 82 24 65 14 27 5b 4f 1d 10 54 3d 99 51 5f fc
     d5 40 34 99 f6 19 fd 1b ff ff ff ff ff ff ff ff
     ff ff ff ff ff ff ff ff 00 43 01 04 fd e8 00 b4
     01 01 01 7a 26 02 06 01 04 00 01 00 01 02 02 80
     00 02 02 02 00 02 02 42 00 02 06 41 04 00 00 fd
     e8 02 08 40 06 00 64 00 01 01 00

   MAC:

     99 51 5f fc d5 40 34 99 f6 19 fd 1b

8.  Observed Implementation Errors

   The following is a partial list of implementation errors that this
   set of test vectors is intended to validate.

8.1.  Algorithm Issues

   *  The underlying implementation of HMAC-SHA-1-96 or AES-128-CMAC-96
      does not pass their corresponding test vectors [RFC2202]
      [RFC4493].

   *  The SNE algorithm does not consider corner cases, possibly because
      the pseudocode in [RFC5925] was not intended as complete, as
      discussed in [RFC9187], the latter of which includes its own
      validation sequence.

8.2.  Algorithm Parameters

   *  KDF context length is incorrect, e.g., it does not include TCP
      header length + payload length (it should, per Section 5.2 of
      TCP-AO [RFC5925]).

   *  KDF calculation does not start from counter i = 1 (it should, per
      Section 3.1.1 of TCP-AO crypto algorithms [RFC5926]).

   *  KDF calculation does not include output length in bits, contained
      in two bytes in network byte order (it should, per Section 3.1.1
      of the TCP-AO crypto algorithms [RFC5926]).

   *  KDF uses keys generated from current TCP segment sequence numbers
      (KDF should use only local and remote ISNs or zero, as indicated
      in Section 5.2 of TCP-AO [RFC5925]).

8.3.  String Handling Issues

   The strings indicated in TCP-AO and its algorithms are indicated as a
   sequence of bytes of known length.  In some implementations, string
   lengths are indicated by a terminal value (e.g., zero in C).  This
   terminal value is not included as part of the string for
   calculations.

   *  The password includes the last zero-byte (it should not).

   *  The label "TCP-AO" includes the last zero byte (it should not).

8.4.  Header Coverage Issues

   *  TCP checksum and/or MAC is not zeroed properly before calculation
      (both should be).

   *  TCP header is not included in the MAC calculation (it should be).

   *  TCP options are not included in the MAC calculation by default.

   There is a separate parameter in the Master Key Tuple (MKT) [RFC5925]
   to ignore options; this document provides test vectors for both
   options-included and options-excluded cases.

9.  Security Considerations

   This document is intended to assist in the validation of
   implementations of TCP-AO to further enable its more widespread use
   as a security mechanism to authenticate not only TCP payload contents
   but the TCP headers and protocol.

   The Master_Key of "testvector" used here for test vector generation
   SHOULD NOT be used operationally.

10.  IANA Considerations

   This document has no IANA actions.

11.  References

11.1.  Normative References

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              DOI 10.17487/RFC0791, September 1981,
              <https://www.rfc-editor.org/info/rfc791>.

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, DOI 10.17487/RFC0793, September 1981,
              <https://www.rfc-editor.org/info/rfc793>.

   [RFC2018]  Mathis, M., Mahdavi, J., Floyd, S., and A. Romanow, "TCP
              Selective Acknowledgment Options", RFC 2018,
              DOI 10.17487/RFC2018, October 1996,
              <https://www.rfc-editor.org/info/rfc2018>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
              June 2010, <https://www.rfc-editor.org/info/rfc5925>.

   [RFC5926]  Lebovitz, G. and E. Rescorla, "Cryptographic Algorithms
              for the TCP Authentication Option (TCP-AO)", RFC 5926,
              DOI 10.17487/RFC5926, June 2010,
              <https://www.rfc-editor.org/info/rfc5926>.

   [RFC6978]  Touch, J., "A TCP Authentication Option Extension for NAT
              Traversal", RFC 6978, DOI 10.17487/RFC6978, July 2013,
              <https://www.rfc-editor.org/info/rfc6978>.

   [RFC7323]  Borman, D., Braden, B., Jacobson, V., and R.
              Scheffenegger, Ed., "TCP Extensions for High Performance",
              RFC 7323, DOI 10.17487/RFC7323, September 2014,
              <https://www.rfc-editor.org/info/rfc7323>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

11.2.  Informative References

   [RFC2202]  Cheng, P. and R. Glenn, "Test Cases for HMAC-MD5 and HMAC-
              SHA-1", RFC 2202, DOI 10.17487/RFC2202, September 1997,
              <https://www.rfc-editor.org/info/rfc2202>.

   [RFC4493]  Song, JH., Poovendran, R., Lee, J., and T. Iwata, "The
              AES-CMAC Algorithm", RFC 4493, DOI 10.17487/RFC4493, June
              2006, <https://www.rfc-editor.org/info/rfc4493>.

   [RFC9187]  Touch, J., "Sequence Number Extension for Windowed
              Protocols", RFC 9187, DOI 10.17487/RFC9187, January 2022,
              <https://www.rfc-editor.org/info/rfc9187>.

Acknowledgments

   This work benefited from feedback from Russ Housley and Michael
   Scharf as well as discussions on the IETF TCPM email list and with
   the IESG.

   This document was initially prepared using 2-Word-v2.0.template.dot.

Authors' Addresses

   Joe Touch
   Manhattan Beach, CA 90266
   United States of America
   Phone: +1 (310) 560-0334
   Email: touch@strayalpha.com


   Juhamatti Kuusisaari
   Infinera Corporation
   Sinimaentie 6c
   FI-02630 Espoo
   Finland
   Email: jkuusisaari@infinera.com