path: root/papers/draft-gsenger-secure-anycast-tunneling-protocol-02.txt

Network Working Group                                         O. Gsenger
Internet-Draft                                                  May 2008
Expires: November 2, 2008


                secure anycast tunneling protocol (SATP)
           draft-gsenger-secure-anycast-tunneling-protocol-02

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Abstract

   The secure anycast tunneling protocol (SATP) defines a protocol used
   for communication between any combination of unicast and anycast
   tunnel endpoints.  It allows tunneling of every ETHER TYPE protocol
   (ethernet, ip ...).  SATP directly includes cryptography and message
   authentication based on the methods used by the Secure Real-time
   Transport Protocol(SRTP) [RFC3711].  It can be used as an encrypted
   alternative to IP Encapsulation within IP [RFC2003] and Generic
   Routing Encapsulation (GRE) [RFC2784].  Both anycast receivers and
   senders are supported.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Notational Conventions . . . . . . . . . . . . . . . . . .  3
   2.  Motivation and usage scenarios . . . . . . . . . . . . . . . .  4
     2.1.  Usage scenarions . . . . . . . . . . . . . . . . . . . . .  4
       2.1.1.  Tunneling from unicast hosts over anycast routers
               to other unicast hosts . . . . . . . . . . . . . . . .  4
       2.1.2.  Tunneling from unicast hosts to anycast networks . . .  5
       2.1.3.  Redundant tunnel connection of 2 networks  . . . . . .  5
     2.2.  Encapsulation  . . . . . . . . . . . . . . . . . . . . . .  6
   3.  Using SATP on top of IP  . . . . . . . . . . . . . . . . . . .  8
     3.1.  Fragmentation  . . . . . . . . . . . . . . . . . . . . . .  8
     3.2.  ICMP messages  . . . . . . . . . . . . . . . . . . . . . .  8
   4.  Protocol specification . . . . . . . . . . . . . . . . . . . .  9
     4.1.  Header format  . . . . . . . . . . . . . . . . . . . . . .  9
     4.2.  sequence number  . . . . . . . . . . . . . . . . . . . . .  9
     4.3.  sender ID  . . . . . . . . . . . . . . . . . . . . . . . .  9
     4.4.  MUX  . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     4.5.  payload type . . . . . . . . . . . . . . . . . . . . . . . 10
     4.6.  payload  . . . . . . . . . . . . . . . . . . . . . . . . . 10
     4.7.  padding (OPTIONAL) . . . . . . . . . . . . . . . . . . . . 10
     4.8.  padding count (OPTIONAL) . . . . . . . . . . . . . . . . . 10
     4.9.  MKI (OPTIONAL) . . . . . . . . . . . . . . . . . . . . . . 10
     4.10. authentication tag (RECOMMENDED) . . . . . . . . . . . . . 10
     4.11. Encryption . . . . . . . . . . . . . . . . . . . . . . . . 11
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
     5.1.  Replay protection  . . . . . . . . . . . . . . . . . . . . 12
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     7.2.  Informational References . . . . . . . . . . . . . . . . . 14
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 16
   Intellectual Property and Copyright Statements . . . . . . . . . . 17




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1.  Introduction

   SATP is a mixture of a generic encapsulation protocol like GRE
   [RFC2784] and a secure tunneling protocol as IPsec [RFC2401] in
   tunnel mode.  It can be used to build redundant virtual private
   network (VPN) connections.  It supports peer-to-peer tunnels, where
   tunnel endpoints can be any combination of unicast, multicast or
   anycast hosts, so it defines a Host Anycast Service [RFC1546].
   Encryption is done per packet, so the protocol is robust against
   packet loss and routing changes.  To reduce header overhead,
   encryption techniques of SRTP [RFC3711] are being used.

1.1.  Notational Conventions

   The keywords "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 [RFC2119].


































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2.  Motivation and usage scenarios

   This section gives an overview of possible usage scenarios.  Please
   note that the protocols used in the figures are only examples and
   that SATP itself does not care about either transport protocols or
   encapsulated protocols.  Routing is not done by SATP and each
   implemetation MAY choose it's own way of doing this task (e.g. using
   functions provided by the operating system).  SATP is used only to
   encapsulate and encrypt data.

2.1.  Usage scenarions

2.1.1.  Tunneling from unicast hosts over anycast routers to other
        unicast hosts

   An example of SATP used to tunnel in a unicast client - anycast
   server model

                       --------- router -----------
                      /                            \
       unicast ------+---------- router ------------+------ unicast
       host           \                            /        host
                       --------- router -----------

     unicast  | encrypted     |  anycast  | encrypted     |  unicast
     tunnel   | communication |  tunnel   | communication |  tunnel
     endpoint | using SATP    |  endpoint | using SATP    |  endpoint

                                 Figure 1

   In this scenario the payload is encapsuleted into a SATP packet by a
   unicast host and gets transmitted to one of the anycast routers.
   After transmisson the packet gets decapsulated by the router.  This
   router makes a routing descision based on the underlying protocol and
   transmits a new SATP package to one or more unicast hosts depending
   on this decision.















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2.1.2.  Tunneling from unicast hosts to anycast networks

   An example of SATP used to encrypt data between a unicast host and
   anycast networks

                          -------Router -+---- DNS Server
                         /                \
                        /                  --- 6to4 Router
                       /
       unicast -------+----------Router --+--- DNS Server
       host            \                   \
                        \                   --- 6to4 Router
                         \
                          -------Router -+---- DNS Server
                                          \
                                           --- 6to4 Router

     unicast  | encrypted     |  anycast  | plaintext
     tunnel   | communication |  tunnel   | anycast
     endpoint | using SATP    |  endpoint | services


                                 Figure 2

   When the unicast hosts wants to transmit data to one of the anycast
   DNS servers, it encapsulates the data and sends a SATP packet to the
   anycast address of the routers.  The packet arrives at one of the
   routers, gets decapsulated and is then forwarded to the DNS server.
   This method can be used to tunnel between clients and networks
   providing anycast services.  It can also be used the other way to
   virtually locate a unicast service within anycasted networks.

2.1.3.  Redundant tunnel connection of 2 networks

   An example of SATP used to connect 2 networks

                 Router -----------   ---------------Router
               /                   \ /                     \
       Network - Router ------------x                       Network
          A    \                   / \                     /   B
                 Router -----------   ---------------Router

               | packets       |  packets  |  packets      |
    plaintext  | get           |  take a   |  get          | plaintext
    packets    | de/encrypted  |  random   |  de/encrypted | packets
               |de/encapsulated|   path    |de/encapsulated|





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                                 Figure 3

   Network A has multiple routers which act as gateway/tunnel endpoints
   to another network B. This way a redundant encrypted tunnel
   connection between the two networks is built up.  All tunnel
   endpoints of network A share the same anycast address and all tunnel
   endpoints of network B share another anycast address.  When a packet
   from network A is transmitted to network B, it first arrives on one
   of network A's border routers.  Which router is used is determined by
   network A's internal routing.  This router encapsulates the package
   and sends it to the anycast address of network B's routers.  After
   arrival the SATP packet gets decapsulated and routed to its
   destination within network B.

2.2.  Encapsulation

   SATP does not depend on the lower layer protocol.  This section only
   gives an example of how packets could look like.

































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   Examples of SATP used with different lower layer and payload
   protocols

       +------+-----+-------------------------------+
       |      |     |      +----------------+-----+ |
       | IPv6 | UDP | SATP | Ethernet 802.3 | ... | |
       |      |     |      +----------------+-----+ |
       +------+-----+-------------------------------+

   Tunneling of Ethernet over UDP/IPv6

       +------+-----+---------------------------+
       |      |     |      +------+-----+-----+ |
       | IPv4 | UDP | SATP | IPv6 | UDP | RTP | |
       |      |     |      +------+-----+-----+ |
       +------+-----+---------------------------+

   Tunneling of IPv6 over UDP/IPv4 with RTP payload

       +------+-------------------------------+
       |      |      +----------------+-----+ |
       | IPv6 | SATP | Ethernet 802.3 | ... | |
       |      |      +----------------+-----+ |
       +------+-------------------------------+

   Tunneling of Ethernet over IPv6

       +------+---------------------------+
       |      |      +------+-----+-----+ |
       | IPv4 | SATP | IPv6 | UDP | RTP | |
       |      |      +------+-----+-----+ |
       +------+---------------------------+

   Tunneling of IPv6 over IPv4 with RTP payload

                                 Figure 4















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3.  Using SATP on top of IP

3.1.  Fragmentation

   The only way of fully supporting fragmentation would be to
   synchronise fragments between all anycast servers.  This is
   considered to be too much overhead, so there are two non-perfect
   solutions for these problems.  Either fragmentation HAS TO be
   disabled or if not all fragments arrive at the same server the IP
   datagramm HAS TO be discarded.  As routing changes are not expected
   to occur very frequently, the encapsulated protocol can do a
   retransmission and all fragments will arrive at the new server.

   If the payload type is IP and the IP headers' Don't Fragment (DF) bit
   is set, then the DF bit of the outer IP header HAS TO be set as well.

3.2.  ICMP messages

   ICMP messages MUST be relayed according to rfc2003 section 4
   [RFC2003].  This is needed for path MTU detection.































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4.  Protocol specification

4.1.  Header format

   Protocol Format

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         sequence number                       | |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
     |           sender ID           |              MUX              | |
   +#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+ |
   | |         payload type          |                               | |
   | +-------------------------------+                               | |
   | |              ....        payload        ...                   | |
   | |                               +-------------------------------+ |
   | |                               | padding (OPT) | pad count(OPT)| |
   +#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+-+
   | ~                          MKI (OPTIONAL)                       ~ |
   | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
   | :                 authentication tag (RECOMMENDED)              : |
   | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
   |                                                                   |
   +- Encrypted Portion                       Authenticated Portion ---+

                                 Figure 5

4.2.  sequence number

   The sequence number is a 32 bit unsigned integer in network byte
   order.  It starts with a random value and is increased by 1 for every
   sent packet.  After the maximum value it starts over from 0.  This
   overrun causes the ROC to be increased.

4.3.  sender ID

   The sender ID is a 16 bit unsigned integer.  It HAS TO be unique for
   every sender sharing the same anycast address.

4.4.  MUX

   The MUX (multiplex) field is a 16 bit unsigned integer.  It is used
   to distinguish multiple tunnel connections.







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4.5.  payload type

   The payload type field defines the payload protocol.  ETHER TYPE
   protocol numbers are used.  See IANA assigned ethernet numbers [1] .
   The values 0000-05DC are reserverd and MUST NOT be used.

   Some examples for protocol numbers

   HEX
   0000 Reserved
   .... Reserved
   05DC Reserved
   0800 Internet IP (IPv4)
   6558 transparent ethernet bridging
   86DD IPv6

                                 Figure 6

4.6.  payload

   A packet of type payload type (e.g. an IP packet).

4.7.  padding (OPTIONAL)

   Padding of max 255 octets.  None of the pre-defined encryption
   transforms uses any padding; for these, the plaintext and encrypted
   payload sizes match exactly.  Transforms are based on transforms of
   the SRTP protocol and therefore might use the RTP padding format, so
   a RTP-like padding is supported.  If the padding count field is
   present, the padding count field MUST be set to the padding length.

4.8.  padding count (OPTIONAL)

   The number of octets of the padding field.  This field is optional.
   Its presence is signaled by the key management and not by this
   protocol.  If this field isn't present, the padding field MUST NOT be
   present as well.

4.9.  MKI (OPTIONAL)

   The MKI (Master Key Identifier) is OPTIONAL and of configurable
   length.  See SRTP Section 3.1 [RFC3711] for details.

4.10.  authentication tag (RECOMMENDED)

   The authentication tag is RECOMMENDED and of configurable length.  It
   contains a cryptographic checksum of the sender ID, sequence number
   and the encrypted portion, but not of the MKI.  On transmitter side



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   encryption HAS TO be done before calculating the authentication tag.
   A receiver HAS TO calculate the authentication tag before decrypting
   the encrypted portion.

4.11.  Encryption

   Encryption is done in the same way as for SRTP [RFC3711].  This
   section will only discuss some small changes that HAVE TO be made.
   Please read SRTP RFC3711 section 3-9 [RFC3711] for details.

   The least significant bits of SSRC are replaced by the sender ID and
   the most significant bits are replaced by the MUX.  For the SRTP SEQ
   the 16 least significant bits of the SATP sequence number are used
   and the 16 most significant bits of the sequence number replace the
   16 least significant bits of the SRTP ROC.

   Difference between SRTP and SATP

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     SATP    sequence number                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                       =
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  SRTP ROC least significant   |           SRTP SEQ            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           SATP  MUX           |       SATP sender ID          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                       =
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                           SRTP SSRC                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 7











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5.  Security Considerations

   As SATP uses the same encryption techniques as SRTP [RFC3711], it
   shares the same security issues.  This section will only discuss some
   small changes.  Please read SRTP RFC3711 section 9 [RFC3711] for
   details.

5.1.  Replay protection

   Replay protection is done by a replay list.  Every anycast receiver
   has its own replay list, which SHOULDN'T be syncronised because of
   massive overhead.  This leads to an additional possible attack.  An
   attacker is able to replay a captured packet once to every anycast
   receiver.  This attack is considered be very unlikely because
   multiple attack hosts in different locations are needed to reach
   seperate anycast receivers and the number of replays is limited to
   count of receivers - 1.  Such replays might also happen because of
   routing problems, so a payload protocol HAS TO be robust against a
   small number of duplicated packages.  The window size and position
   HAS TO be syncronised between multiple anycast receivers to limit
   this attack.






























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6.  IANA Considerations

   The protocol is intended to be used on top of IP or on top of UDP (to
   be compatible with NAT routers), so UDP and IP protocol numbers have
   to be assiged by IANA.














































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7.  References

7.1.  Normative References

   [RFC3711]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
              Norrman, "The Secure Real-time Transport Protocol (SRTP)",
              RFC 3711, March 2004.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2003]  Perkins, C., "IP Encapsulation within IP", RFC 2003,
              October 1996.

7.2.  Informational References

   [RFC2784]  Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
              Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
              March 2000.

   [RFC2401]  Kent, S. and R. Atkinson, "Security Architecture for the
              Internet Protocol", RFC 2401, November 1998.

   [RFC1546]  Partridge, C., Mendez, T., and W. Milliken, "Host
              Anycasting Service", RFC 1546, November 1993.


























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URIs

   [1]  <http://www.iana.org/assignments/ethernet-numbers>
















































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Author's Address

   Othmar Gsenger
   Puerstingerstr 32
   Saalfelden  5760
   AT

   Phone:
   Email: satp@gsenger.com
   URI:   http://www.gsenger.com/satp/









































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Full Copyright Statement

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