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Versions: 00                                                            
INTERNET-DRAFT                                         Graydon Hoare
draft-hoare-nics-00.txt                          <graydon@pobox.com>
expires July 15 1997                                     Jan 15 1997

                               NICS
           Network of Identifier and Credential Servers
                       (first public draft)

                       Status of this Memo

This document is an Internet-Draft. 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".

To learn the current status of any Internet-Draft, please check the
"1id-abstracts.txt" listing contained in the Internet-Drafts Shadow
Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe),
munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or
ftp.isi.edu (US West Coast).


Abstract

NICS is a proposed system which meets the requirements of large-
scale, unique principal identification, for use in conjunction with
an arbitrary set of security systems such as have been proposed by
members of the IETF.

This proposal outlines the motivation for the development of NICS,
and gives a general description of its internal workings and
interfaces with higher-level protocols.

It should be emphasized up front that NICS is not a complete
security system, nor does it aim to replace any existing components
of the internet which already work. The design draws off the fact
that many security systems already have flexible name schemes, and
are therefore considered components which are used in conjunction
with NICS to achieve an improved level of service, flexibility and
reliability, while introducing many desirable features such as
anonymous identifiers, self-optimization, and low-overhead
operation.

For the purpose of initial evaluation, the remainder of this paper
is short and to the point, and requires a little work on the
reader's side to understand the reasoning. Additional discussion is
welcome on the mailing list.



jan 15 1997            draft-nics-00.txt               graydon hoare


Rationale

The intent of the author is to produce a stable, self-maintaining
distributed database capable of identifying (naming) an extremely
large number of principals and providing their credentials to any
principals who ask. Such an intent initially appears to overshadow
pre-existing systems such as DNS, X.500, SDSI, etc. However this is
not the case: all currently existing naming schemes allow for, or
require at some point in their operation a unique, unchanging
reference name for a given principal. Currently existing standards
to refer to each other by default: SDSI imports global names out of
the DNS, X.500 imports names out of the MX map of the DNS, DNSSEC
imports names from X.500/509 names, or from IP numbers etc. None of
these exported names are static, or even acceptably detached from
real-world organizational structures. Most standards also allow for
additional naming schemes. NICS is an attempt to define such a
naming scheme on which all others may optionally be built, or on
which low-overhead security services may directly operate. NICS does
not guarantee anonymity in all cases, nor does it guarantee any sort
of directory service. The design does not specify a security
framework -- the issue is implementation specific. The only feature
NICS adds to the internet is strong universal naming, for purposes
of customization, accounting, authentication, authorization, and
other ``security'' procedures. It is beyond the scope of this
initial document to describe these procedures further; the reader is
assumed to be familliar with modern security systems.


Design

NICS is a system for serving the values of a single relating table
to anyone connected to the global internet. The table consists of
identifiers (which uniquely identify communicating principals) and
their associated credentials. This is called the NICS Database. It
is served by Identifier and Credential Servers (ICSs). The format
for NICS IDentifiers (NIDs) is specific and fixed: they are all 16-
bytenetwork order unsigned integers. The numeric space afforded by
16bytes is immense, as no NIDs go unused within NICS. In
comprehensible terms, a 128-bit length would allow each of 6 billion
people to allocate 1 billion new NIDs every milisecond of the day
for 1.8 million millennia before the range is exhausted. It is
therefore suggested that 16 bytes is sufficient even for the large
task of unique identification.

The format for credentials is variable, but each type of credential
must conform to the following criteria:

* it must be possible to encode, transmit and store the credentials
as a string of bytes (octets)



jan 15 1997            draft-nics-00.txt               graydon hoare


* the standard from which the credentials are derived must be
recognized and numbered by IANA.

Every principal within NICS is represented solely by its NID. A
principal uses its NID and its associated credentials to establish
any further relationships, but the basic NICS record is just a NID -
> Credential mapping called a Principal Record (PR).

An ICS will use credentials within its local database to evaluate
and authenticate transactions with other principals, including other
ICSs. It is therefore essential that at minimum an ICS maintains its
own PR in a safe, local store.

The database is distributed amongst all known ICSs in a non-
hierarchical maner. It is devided amongst hosts by using Scopes. A
scope is stored as a tuple of 1 low NID and 1 high NID, which
together represent an inclusive numeric range. A scope is associated
with the NIDs of one or more ICSs acting as replication-peers for
that scope in a structure called a Service Record (SR). Every ICS in
an SR's peer table is responsible for storing a copy of every
allocated PR within the Scope. A change to a PR within a scope can
be initiated by any SR-peer, and inter-peer synchronization is
achieved through flooding of timestamped advisory locks and a simple
commit/rollback scheme. Any peer in an SR is responsible for
maintaining an accurate map of the SR, as well as an accurate map of
the 2 SRs with ranges immediately ``above'' and ``below'' the SR. If
a peer is a member of more than one SR (as will often be the case)
it must maintain these records for each SR independently. For every
change to a PR or SR, every peer in the SR-peer list needs to
acknowledge the change. SR updates should additionally flood into
the neighbouring SRs, although acknowledges from neighbours may be
delayed or ignored.

Each SR has an implicit ``desired distribution'' which is calculated
based on its breadth of scope, among other things. The desired
distribution is the ideal number of hosts on which the scope should
be replicated in order to be considered reliable and fast --
obviously the calculation will need to take into account a few
factors. Every peer within an SR communicates the size of its
remaining allocated local storage to every other peer. Expansion of
an SR towards its desired distribution takes place using the
standard ICS flooding transaction method. An ICS will introduce a
new ICS into an SR that it is a member of, if and only if

* the desired distribution for the SR has not yet been met

* the new ICS has more free space available than any other willing
neighbours




jan 15 1997            draft-nics-00.txt               graydon hoare


The first ICS within an SR to reach its highwater mark in allocated
storage (which should be well beneath its real limit, as extra space
is needed in panic situations) signals its peers that it is running
out of space, and it is time for a ``split'' transaction. The SR
then splits at a NID specified by the initiating peer, and a new SR
is created beginning at the split NID + 1. The new SR excludes the
initiating peer. This split takes place on all peers in the SR. The
appropriate ``above'' and ``below'' SRs are adjusted, and the newly
split scope goes about its top priority which is always to reach the
desired distribution.

A peer may, at any time, ``resign'' from an SR provided the SR has
other active peers. In the unlikely event that all peers in an SR
resign or are disconnected in rapid succession, the neighbours of
the SR will be made aware of the fact, and are obliged to offer
assistance in transferring the portion of the database off the
crashing servers.

Aggregation may take place using an as-of-yet undecided strategy.
Since all peers within an SR are always aware of the NIDs of all
neighbouring peers, it is not difficult to imagine a strategy of SR-
boundary re-alignment in order to aggregate SRs. It should be
stressed however that stability through replication takes priority
over optimizing aggregations.

Any query which enters an ICS is answered by taking the following
steps (assuming principal authentication)

* If the PR is stored locally, return the credentials of the query

* Otherwise, forward the query to a random member of the SR with the
closest known range.

In these cases, forwarding can mean either returning the SR to the
client or actually performing a recursive query, much like DNS.
Usually a recursive query will yield better results. Anyone is
allowed to cache SRs, so locating an appropriate server should not
take too long. PRs are not intended to be cached unless they are
flagged with a special loose-security bit, which enables cached PRs
to use TTLs for cache-consistency. Any PR without the loose-security
bit set may be cached, but must have at minimum its hash-value
reloaded from an authoritative peer every time it is required by
another layer of the system. It will be hard to enforce this rule,
but adherance is recommended in order to close any possible windows
for attackers. In order to remain reasonably efficient in spite of
the heavy consistency requirements, the communication protocol must
be lightweight, and the cache of SRs much be as large as possible in
clients.




jan 15 1997            draft-nics-00.txt               graydon hoare


For update messages, the query is processed in a timestamped,
flooded two-phase commit, in which a transaction only proceeds after
a signed cookie is received from all peers in the SR. If an SR peer
is ever ``unreachable'', it is flagged as down and all commits are
assumed to be approved by it. If the peer ever comes back up, in
order to clear its down flag it must take whatever measures
necessary in requested transfers to provide to all members of the SR
with a signed digest of the most recent version of the SR. In the
interim, the SR may have abandonned the peer altogether and expanded
to the desired distribution using other peers. In such a case the
host is informed of its exclusion upon resuming contact with its old
SR. A peer is expected to abide by such a decision.

There is no defined means (yet) for dealing with multiple sets of
peers who consider one another mutually exclusive. One SR must yield
control of the given range to the other. Otherwise a ``shadow NICS''
emerges, much like the ``alternative'' domain name servers, except
that no integration is possible because there is supposedly only one
NID range. Such activity would therefore only be destructive to both
sets of peers, as they would no longer be able to distinguish which
NID was which. While such activity could be used as a means of
attack, sufficient CA data communicated out of band makes this
easily defended against.

Finally, announcement of an ICS proceeds exactly as does
announcement of any other principal: the principal sends a broadcast
challenge for valid authentication over its local link. The
challenge uses either its own previously-established PR or an out of
band PR. Any valid response it receives has proven itself to be
attached to the wider NICS, and it therefore added to the client's
list of local ICSs. If no response is received, a larger broadcast
may be necessary, or the use of some service-location protocol. If
an out of band PR is chosen, the next request will probably be a
query to set a new NID for the principal. Such a query is forwarded
a random number of times to random peers within the NICS and
eventually serviced (perhaps after a TTL expires) by assigning the
next consecutive NID in a scope with free space. NIDs are assigned
consecutively within scopes starting from a randomly chosen position
and overflowing onto the low end of the scope if necessary (in order
to better permit aggregation) but since scopes shift from one server
to another the actual value of a NID does not reveal any practical
information about the principal posessing it.

In fact, this is the primary motivation for NICS: principals may
have as many unassociated and (to varying degrees) anonymous NIDs as
they feel they need to maintain privacy. If a NID ever outlives its
usefulness, its PR may be set to NULL at which point no further
modifications are authorized to take place. It is ``dead''. It is
the responsibility of the principal to keep joinable data out of



jan 15 1997            draft-nics-00.txt               graydon hoare


their PR, and out of the hands of anyone they do not wish to trace
them, but under NICS it actually is an option to have anonymous
identities.


Implementation

At this time, no implementation is available. The author has begun
work on a portable ANSI C version of an ICS, but it will most likely
need to be rewritten several times in order to conform to emerging
GSSAPI & IPSEC standards. Most of the code required for such a
server has already been written -- there are libraries to handle
most authentication schemes, simple database management, caching,
and network communication. It should be stressed that NICS is
intended to be capable of operating in an extremely low-overhead
system, such as a consumer electronics device or embedded
controller. Several scenarios do not even include mutual
authentication -- systems relying on smart-cards or even magnetic
strip cards may benefit from a uniform identifier scheme.

In order to make NIDs easier to remember, certain transformations
are suggested such as mapping 16-bit chunks into a dictionary of
standard english words. A 2^16 entry dictionary was prepared as a
demonstration.

The random NIDs (in 2^16 decimal chunks)

* 56184.10819.11346.28658.8732.65087.5944.14558
* 38012.49371.6317.16111.20713.58321.55011.48691
* 6887.1175.33979.52356.53123.62765.14518.24799

map to

* sucks.claw.coefficient.incredible.capioma.yountsville.bmw.dedeaux
* misery.rillton.bootstraps.dome.flandry.tick.squeaky.renshaw
* breathes.aliquid.liveware.shackleton.sides.ways.declez.gulph

which, while not exactly easy to remember, are better than their
decimal counterparts. Such identifiers can be stored within any
other security system easily as extended name types, revealing as
little as is desired (or knowable) about the principal.



Further comments on NICS can be directed to the IPSEC mailing list
or to the author at graydon@pobox.com.