From: ygoland@edison.seas.ucla.edu (The Jester)
Newsgroups: sci.crypt,alt.security.pgp
Subject: What public key is REALLY good for
Date: 29 Sep 92 08:21:09 GMT
Followup-To: sci.crypt
Organization: PGP VER2 Key Available Upon Request

The question I pose in this post is:What is the proper role of
Public Key Encryption in an environment where absolute key
verification on a wide scale is not feasable.

Before I address this question I would like to point out a
particular case that I will NOT deal with. This case involves two
entities who wish to securely communicate and have extensive
previous contact. This situation affords several secure means of key
transmission. This situation is actually particularly well suited to
the use of public key encryption if an intial 'secure' key
transmission can be reasonable guaranted. However this issue has
been delt with in many other papers, posts, and so on, and need not
again be addressed here.

With that particular case out of the way, I shall first define why I
believe that the internet environment is not suitable for any form
of key verification on a 'grand' scale:

The most important aspect of key verification is the trust factor,
person A trusts Person B who trusts &  verifys person C's key. Thus person A
is supposed to accept C's key with B's validation. This chain can be
extended infinitely. Unfortunatly if the chain should break at any
point, the entire security of the system will collapse. Though it is
theoretically possible to produce redundancies in the system to
lessen the likelyhood of such a collapse. In practice it is
impossible to implement. The average use may know many people on the
net, but they do not know them personally and in almost all cases
most certainly don't know them well enough to 'trust' them. In
addition the very concept of 'trust' is faulty as it relies upon the
judgement of many individuals, any one of whom may be either
untrustworthy themselves or may have accepted as trustworthy
an untrustworthy individual. In addition the concept of 'levels' of trust
introduced in PGP does not aid the situation any as the 'level of
trust' of a system will always be that of the lowest part of that
system. Thus it is fair to assume that in the general circumstance
it is impossible for any real verification of key authenticity to
occur.

This having been said, the inevitable question is:What then is the
purpose of public key encryption in such an environment? The answer
is one of deterance. The main reason given for the use of public key
is to prevent nosy sysops and the NSA (and other related federal,
state, and local agencies) from having ready access to
communications. Even assuming a situation such as the one that
currently exists on the net where key authorization is not used.
This still prevents a strong deterant against invasion of privacy by
various agencies, IF encryption is used on a large scale. Assuming
that many keys have been violated, the NSA or related organization
would be required to keep records on what keys belonged to who, it
would have to update it's own records as keys are changed, it would
have to actively decrypt ALL mail, and so on and so forth. As long
as the process of changing keys once they have been distributed does
not become too mechanized (i.e. your software will not automatically
mail all your friends telling them that after two years your
changing to a different key, and then have your friend's software
automatically update their files (if you can do it, so can the NSA))
the organizational and computational challenges would quickly prove
to be a nightmare. In addition those individuals with a more
definite reason to fear surveilance can take stronger measures to
protect their privacy. However the general case is what is most
important here. Wide spread use of public key encryption, even if
key security is relatively weak, will prove to make wide spread
surveilance infeasable.

				Yaron (The Jester) Goland
-- 
 			The Jester
"Freedom isn't Free"-The U.S. Army
"Nothing is too wonderful to be true"-Faraday
"If I knew it all, what would I be doing HERE?"-The Jester
Newsgroups: sci.crypt