Internet DRAFT - draft-gsenger-secure-anycast-tunneling-protocol
draft-gsenger-secure-anycast-tunneling-protocol
Network Working Group O. Gsenger
Internet-Draft May 6, 2008
Expires: November 7, 2008
secure anycast tunneling protocol (SATP)
draft-gsenger-secure-anycast-tunneling-protocol-02
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Copyright (C) The IETF Trust (2008).
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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) [1]. It can be used as an encrypted
alternative to IP Encapsulation within IP [3] and Generic Routing
Encapsulation (GRE) [4]. 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 [4]
and a secure tunneling protocol as IPsec [5] 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 [6]. Encryption is done per packet, so the
protocol is robust against packet loss and routing changes. To
reduce header overhead ncryption techniques of SRTP [1] 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 [2].
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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 which lower layer protocol is used. 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 [3].
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 [7] .
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 [1] 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 [1]. This section
will only discuss some small changes that HAVE TO be made. Please
read SRTP RFC3711 section 3-9 [1] 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 [1], it shares
the same security issues. This section will only discuss some small
changes. Please read SRTP RFC3711 section 9 [1] 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
[1] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, March 2004.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[3] Perkins, C., "IP Encapsulation within IP", RFC 2003,
October 1996.
7.2. Informational References
[4] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina,
"Generic Routing Encapsulation (GRE)", RFC 2784, March 2000.
[5] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.
[6] Partridge, C., Mendez, T., and W. Milliken, "Host Anycasting
Service", RFC 1546, November 1993.
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URIs
[7] <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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