Subject: Re: Huge CRLs

From: [email-masked]
Date: Wed, 15 Sep 1999 08:16:36 -0700

some of the issues in financial infrastructure

certificate binds some set of information which tends to relatively stable
state, certificates don't handle time series aggregation and/or realtime ... the
certificate bound information tends to be a subset of the information found in
accounts records ... which are the mainstay of current financial
infrastructures. the purpose of these certificates is to allow a move away from
centralized, account-record processing to independent, distributed processing.
emerging issue in the consumer world (including consumer financial world) is the
concern about abstracting privacy information for widely distributed processing
(i.e. the inclusion of any information in a certificate that might possibly
identify the consumer).

CRLs is an attempt to address some subset of the problem represented by
certificate information staleness. From a scaling standpoint, CRLs have
shortcoming that they tend to be proportional to the population size ... not
proportional to the work/transactions performed.

From a financial infrastructure standpoint ... it might be possible to veiw
certificates as a means of distributing relatively stable information from
account records into offline environments ... possibly involving the ability to
perform low-value operations not requiring the timeliness and/or aggregation
information dependent on account record implemenations (especially if no
identity information and/or anything related to a consumer is involved in the
certificate).

However, for financial operations that do have to touch account records (because
of possibly something like transaction aggregation, i.e. the current account
balance or privacy issues) ... then it follows that not only aren't CRLs
approprait but the certificates themselves are superfulous (i.e. we can alwas
show that for any combination of information that can be bound in certificate
...a superset of that can be "bound" in an account record).

This sort of abstraction then can be used to characterize evern Certification
Authority implemenation ... as the Certificate Authority contains "master"
account record copies of the information bound into certificates. Certificates
can propogate this information into a distributed environment involving an
arbritrary large (and possibly unknown) number of locations. CRLs is then an
attempt to contact all of this arbritary large number of locations regarding the
validity &/or staleness of certificate based information. Therefor, CRL
implemenation scaling can be an issue of both proportional to the population
size and also proportional to the possible number of locations (i.e. not actual
number of relying party locations where actually certificate exists but all
possible relying party locations where it might exist).

For arbritrary large certificate population (N) with arbritrary large number of
possible relying parties (M) than CRL processing becomes proporational the NxMxI
product (certificate population size times relying population size times
propability of information becoming stale/invalid).

By comparison a RADIUS and/or centrlized authentication mechanism has processing
overhead proportional to the number of transactions. So for an online
environment, the efficiency issues becomes whether the
     P(NxMxI) > P(trans)

i.e. is the CRL overhead (proportional to size of certificate population times
size of relying party population times probability information changes) greater
than contacting an authentication server on every transaction.

So one at one extreme is online requiring timely, aggregated and/or privacy
information access to the account record ... making use of a certificate (with
replicated, stale, subset  information) superfulous (as well as unnecessary
expense and infrastructure especially when information binding & authentication
infrastructure already exists).

At the other exterme is offline infrastructure with no existing information
binding & authentication infrastructure (aka 1980s offline email) where even
replicated, stale, information (bound in a certificate) may better than no
information.

In between are online environments needing authentication infrastructure with
distributed operation (with possibility of distributed information bound into
certificates) vis-a-vis online direct access with higher degrees of information
timelyness. The trade-offs come down on the side of certificates with low
propability of information staleness, small certificate populations, small
number of relying parties, no privacy issues and very large number of
transactions. The trade-offs would be away from certificates as the probability
of information staleness increases, there are privacy issues, the size of the
certificate population increases, the number of relying parties increases and/or
the number of transactions decrease.

Systems that have overheads/processing proportional to size of population & not
amount of work performed (or number of transactions) tend to run into scaling
problems ... if nothing else funding & processing capability tends to be size
based on amount of work being done  ... as opposed to size of pupulation.

As an aside, one characteristic contrasting the certificate-based processing as
fully distributed (potentially even down to both physical and logical
point-of-sale) and account-based "centralized" processing ... the current
account-based consumer electronic financial processing is hardly centralized.
All transactions against a specific account are routed to the processing unit
responsible for that account ... but there is a large (somewhat mesh) network
interconnecting millions of point-of-sale with possibly tens of thousands of
account-record processing locations.