dispatch J. Rosenberg
Internet-Draft jdrosen.net
Intended status: Standards Track C. Jennings
Expires: October 3, 2011 Cisco
M. Petit-Huguenin
Stonyfish
April 1, 2011
A Usage of Resource Location and Discovery (RELOAD) for Public Switched
Telephone Network (PSTN) Verification
draft-petithuguenin-vipr-reload-usage-00
Abstract
Verification Involving PSTN Reachability (ViPR) is a technique for
inter-domain SIP federation. ViPR makes use of the RELOAD protocol
to store unverified mappings from phone numbers to RELOAD nodes, with
whom a validation process can be run. This document defines the
usage of RELOAD for this purpose.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. ViPR Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. PeerID Shim . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . . 6
6.2. Informative References . . . . . . . . . . . . . . . . . . 6
Appendix A. Release notes . . . . . . . . . . . . . . . . . . . . 6
A.1. Modifications between vipr-00 and dispatch-03 . . . . . . . 7
A.2. Modifications between dispatch-03 and dispatch-02 . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
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1. Introduction
This document relies heavily on the concepts and terminology defined
in [VIPR-OVERVIEW] and will not make sense if you have not read that
document first. As it defines a usage for RELOAD [P2PSIP-BASE], it
assumes the reader is also familiar with that specification. The
same DHT can also be used for a RELOAD SIP usage [P2PSIP-SIP].
2. ViPR Usage
The ViPR usage defines details for how the DHT is used for ViPR
operations.
The ViPR usage defines Kind-ID 0x00000001. This Kind-ID is a
dictionary entry. Its Resource-ID is defined through a
transformation which takes an E.164 based number, and computes a
Resource-ID as the least significant 128 bits of the SHA1 hash of the
following string: Cat(CHOICE(null, "COPY", "COPY2"), number) That
is, the Resource-ID is the hash of a string which is the
concatenation of the number, prefixed with nothing, or the words
"COPY1" or "COPY2".
For example, for number +14085555432:
Resource-ID = least128(SHA1("+14085555432"))
or
Resource-ID = least128(SHA1("COPY1+14085555432"))
or
Resource-ID = least128(SHA1("COPY2+14085555432"))
The object stored at this resource ID is a dictionary entry, which
has a key and a value:
Object = {key,value}
Here, the key is formed by taking the Node-ID of the storing node in
hex format, without the "0x", appending a "+", followed by the
VServiceID in hex format, without the "0x". For example, if a peer
with Node-ID
0x8f60f5eab753037e64ab6c53947fd532
receives a Publish with a VServiceID of
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0x7eeb6a7036478351
The resulting key is:
8f60f5eab753037e64ab6c53947fd532+7eeb6a7036478351
Both parts of this key are important. Using the Node-ID of the node
performing the store basically segments the keyspace of the
dictionary so that no two peers ever store using the same key.
Indeed, the responsible node will verify the signature over the
stored data and check the Node-ID against the value of the key, to
make sure that a conflict does not take place. The usage of the
VService allows for a single ViPR server to service multiple
clusters, and to ensure that numbers published by one cluster (using
one VServiceID) do not clobber or step on numbers published by
another cluster (using a different VServiceID). The responsible node
does not verify or check the VServiceID.
When a node receives a Store operation for this usage, the data
itself has a signature. The node responsible for storing the data
must verify this signature; the certificate will always be included
in the data and indicate which Node-ID is used. The responsible node
must check that this Node-ID is included in the cert. If the
signature verifies, the responsible node checks that the data model
is a dictionary entry. The key must meet the format above. The
responsible node must check that it is a 32 character sequence of
numbers and letters a-f, followed by a +, followed by a 16 character
sequence of numbers and letters a-f. If this checks, the key is
split in half along the plus. The first 32 characters are considered
a hex value and compared with the Node-ID used for the signature. If
they match, it is good. Otherwise the Store operation is rejected.
If they did match, next the responsible node checks the value. It
must be a TLV, with the same format used by VAP, and it must contain
a single Node-ID attribute. The Node-ID must match that used for the
signature. If they don't match, the Store operation is rejected. If
they do match, the next step is a quota check.
For each peer that the responsible node is storing data for, it must
maintain a count of the number of unique dictionary entries being
stored for that Node-ID. For each resourceID, each key constitutes a
unique dictionary entry. So if a peer is storing 5 resourceIDs, and
at each of those 5, there are two keys whose first 32 bits correspond
to a particular Node-ID, it means this node is currently storing 10
unique dictionary entries for that Node-ID.
It takes the StorageQuota configuration parameter for this DHT, which
measures the amount of numbers a particular node can store. That
value is multiplied by nine (a 3x factor to account for the
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application-layer copies (COPY1 and COPY2), and another 3x factor for
replicas). Then, an addition 3x factor is added for rounding to make
sure that the probability is low that a rejection occurs due to
imperfect distribution of resourceIDs across the ring. (Open Issue:
need to adjust this multiplier - basically birthday problem!) and
then divided by the fraction of the hashspace owned by this ViPR
server. If the result is less than one, it is rounded up to two.
This is the max number of unique entries that can be stored for this
storing peer ID. If the ViPR server is not yet storing this many
entries for that peer ID, the store is allowed.
The method for merging data after a partition follows the normal
RELOAD rules around temporal ordering.
3. PeerID Shim
Because the ViPR implementation of RELOAD protocol makes use of the
concept of multiple Node-ID on the same physical box, utilizing a
single cert, the TLS handshakes alone are not sufficient to determine
the entity on both sides of the TLS connection. As such, we will
have a small "shim" type of protocol, which runs after TLS, but is
not formally part of RELOAD.
When a node initiates a TLS connection towards another node, after
the TLS completes, it sends this message. The message contains the
Node-ID associated with this connection. The recipient gets this,
and sends back a similar message, containing its Node-ID. Both sides
will verify that, the Node-ID sent by the other side, are amongst the
Node-IDs listed in the certificate. The connections are then stored
in the connection tables, indexed by this Node-ID.
Furthermore, if, after this exchange, a node determines that it
already has a connection in its connection table with that Node-ID on
the far side, the older connection is closed. This is actually a
critical security function! Without this, a user could clone ViPR
servers utilizing the same certs, and each one can join the network.
Finally, once the exchange has taken place, the node compares the
Node-ID from its peer with the current set of blacklisted Node-ID
from the ACL that is distributed through the DHT. If the remote
Node-ID appears on the list, the node closes the TCP/TLS connection
immediately.
The reason we are using a non-reload message for this, is that we
need to be 100% sure that this never propagates. It is strictly over
a single connection and should never be routed. Indeed, had we not
had this idea of multiple Node-ID in a single cert, this would have
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effectively been accomplished through TLS. Alternatively, there is a
TLS command for telling the other side who I expect them to be;
however this is not implemented in older versions of OpenSSL, and so
our shim forms an alternative to that which can be run on top of
OpenSSL.
4. Security Considerations
TBD
5. IANA Considerations
TBD. Need to register items in IANA registries created by RELOAD.
6. References
6.1. Normative References
[P2PSIP-BASE]
Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and
H. Schulzrinne, "REsource LOcation And Discovery (RELOAD)
Base Protocol", draft-ietf-p2psip-base-13 (work in
progress), March 2011.
[VIPR-OVERVIEW]
Rosenberg, J., Jennings, C., and M. Petit-Huguenin,
"Verification Involving PSTN Reachability: Requirements
and Architecture Overview",
draft-jennings-vipr-overview-00 (work in progress),
April 2011.
6.2. Informative References
[P2PSIP-SIP]
Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and
H. Schulzrinne, "A SIP Usage for RELOAD",
draft-ietf-p2psip-sip-05 (work in progress), July 2010.
Appendix A. Release notes
This section must be removed before publication as an RFC.
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A.1. Modifications between vipr-00 and dispatch-03
o Moved to new Working Group.
A.2. Modifications between dispatch-03 and dispatch-02
o Nits.
o Shorter I-Ds references.
o Fixed the peerID and VServiceID to be hexadecimal.
o Fixed the description of the dictionary entry
o Fixed the description of the TLV.
o Used +1 408 555 prefix for phone numbers in examples.
o Replaced peerId by Node-ID
o Replaced resourceID by Resource-ID
Authors' Addresses
Jonathan Rosenberg
jdrosen.net
Monmouth, NJ
US
Email: jdrosen@jdrosen.net
URI: http://www.jdrosen.net
Cullen Jennings
Cisco
170 West Tasman Drive
San Jose, CA 95134
USA
Phone: +1 408 421-9990
Email: fluffy@cisco.com
Marc Petit-Huguenin
Stonyfish
Email: marc@stonyfish.com
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