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Re: why we are arguing for more resistant variants
On Sun, Oct 19, 1997 at 07:15:00PM +0100, Adam Back wrote:
>
> Kent Crispin <[email protected]> writes:
> > On Sun, Oct 19, 1997 at 10:25:08AM +0100, Adam Back wrote:
> > > Also I must raise the point that it is not a lone stand. Other people
> > > are arguing against PGP Inc's CMR proposal, and are arguing for more
> > > GAK resistant variants, and alternatives.
> >
> > Apparently for some internal reason you must raise the point, but it
> > is irrelevant. I said your *proposals* were vaporware, not your
> > motivations. It is, as I have said, a waste of time (and yes, mental
> > masturbation) to argue about motivations.
>
> Motivation is irrelevant.
Good. We agree, and can therefore move on.
> You made one contribution in this area in your last post. Keep up the
> technical contributions, and scenario likelihood evaluations.
>
> > > However the biggest point of all is that: communications keys are more
> > > valuable to any attacker (government, unscrupulous little brother, or
> > > industrial spy) than storage keys.
> > >
> > > I would be interested to see any one willing to burn their
> > > reputational capital refuting that simple point.
> >
> > *Long term* communication keys. Nobody is going to burn reputation
> > capital on that point because it's obvious, and really doesn't need to
> > be argued.
>
> If it doesn't need to be argued, why does pgp2.x and pgp5.x use long
> term communication keys?
History. Backward compatibility. Time pressures. And a design for
short term communication keys for email does not yet exist -- not from
you, not from anyone. [Your CDR proposal uses *long term*
communication keys.]
These seem pretty compelling reasons to me.
Just because something is desirable doesn't mean it is practical, or
even possible.
[...]
>
> Surely the most straight forward way to provide recovery for email
> archives is to archive the emails encrypted to a storage-only key,
> with this key escrowed in some way? You then don't need to recover
> email in transit -- you don't even have a copy of it.
>
> This is clearly more resistant to government abuse. Do you disagree?
>
> (The above paragraph is basically all my CDR proposal is .. it seems
> straight forward, intuitive, more secure; I went through and countered
> your previous objections to worked example #1, you did not reply to
> those counter-points).
I did not because you presented it as a throwaway, with statements to
the effect that you already knew it was defective but you were
presenting it anyway. Besides, in all honesty I did not find your
counterarguments very compelling, and I was content to wait until I
saw a "real" proposal. If I have a chance, though, I will go back
and address that...
BTW, perhaps you remember a fairly long thread sometime back where I
discussed the pros and cons of a "keysafe" model for data recovery
keys?
> > Furthermore the point applies just as well to current PGP keys. The
> > *only* additional vulnerabilities of CMR come from 1) the volume of
> > data makes it a more interesting target and 2) the management of the
> > CMR key(s) may be problematic.
>
> You missed a couple:
>
> 3) the goverment will love to get come ask for your CMR key because it
> protects all past emailed ciphertext
>
> 4) some governments (eg France) will probably ask for one of the CMR
> keys to be theirs
I include both of those under my number 1.
> > However, in a large organization the management of *user* keys is
> > problematic, as well, and management of the CMR key(s), on balance,
> > will probably be better. So the additional vulnerability of CMR comes
> > from the fact that it makes a lot of data accessible from one key.
> > This vulnerability could be reduced by having multiple CMR keys -- the
> > accounting dept has one, the CEO has one, and it is the same as his
> > private key that is not escrowed anywhere, etc etc etc.
>
> Yes. Several people have suggested this. Also secret sharing is
> being considered by PGP Inc for the next version I think.
>
> > [Is it true that the private key associated with a CMR public key
> > could simply be discarded, rather than escrowed, and everything would
> > still work? -- except that you couldn't recover anything, of course...]
>
> I would think so. This would argue for updating the CMR
> communications key as frequency as is practicable to minimise danger.
^^^^^^^^^frequently?
?I don't see the connection. My point was that you can generate a key
pair, throw away the private key, and use the public key as the CMR
key. Perhaps you could just use random bits in the correct format for
the public key, and never generate a key pair at all. This would meet
external requirement of having a CMR key, but it would be meaningless,
since the missing private key could never be used to decrypt anything.
Thus, though externally an organization (say an ISP) would be
complying with a regulation, in fact it would be impossible to
recover any email anyway...
In any case, I presume the "danger" you refer to is the danger that
someone will snarf the CMR key. Changing it frequently will reduce
the number of compromised messages if any given key is compromised.
(Of course, the CMR keys will have to be preserved forever in a
little database of some sort -- if you change them often, that
database will be large...)
> (Same argument as update requirements for user communications keys).
> Hal Finney discussed this requirement of matching expiry frequency on
> comms keys & corresponding CMR keys a few messages back.
>
> > A more interesting argument is as follows: what is the real level of
> > security needed for the business communications that will be covered
> > by CMR? It seems obvious that the level of security required, on
> > average, is really quite low. Note that businesses send all kinds of
> > important documents through regular mail, only protected *gasp* by
> > PAPER ENVELOPES.
>
> This suggests that Tim May is right, and the simplest solution is to
> store the decrypted received emails in clear on the disk. Most of the
> companies are in fact storing on disk.
It is the MUA that uses PGP (Eudora, Mutt, whatever) that decides how
to store the decrypted files, not PGP. PGP decrypts the files and
gives them to the MUA, which displays them to the user. The MUA has
the option of storing it encrypted or not, as delivered, or with
another key. PGP isn't in control, it's the MUA, isn't it?
> > Anyway, Adam, I anxiously await the paper you are working on that
> > gives the real details of your proposals. I'm sure it's readability
> > will be vastly improved if you religiously avoid the use of the word
> > GAK :-)
>
> Could you provide a less emotive suitable alternative word which I can
> use as a replacement to describe government communications key
> grabbing attempts? GACK is what Carl Ellison proposed as a more
> accurate way to express "Goverment Access to Communications Keys" than
> terms such as "key escrow", "key recovery", which are government
> coined terms. PGP Inc themselves being mostly cypherpunks and
> pro-privacy people use the term GACK also.
>
> GACK seems a pretty good acronym to me, accurate, descriptive. Are we
> getting goverment-correct now as well (as politically-correct)? So
> that we must not use terms which are offensive to governments?
>
> (I will attempt to avoid negative political comments about PGP Inc's
> implementation, and phrase in terms of constructive criticisms though,
> and perhaps this was your point given my earlier outbursts in this
> regard; perhaps you can help proof read for this).
Whatever. It does strike me that you seem to have difficulty in
maintaining composure whenever the term comes up, your prose gets
hasty, with missing words and odd syntax, and I suspect that your
usually razor-sharp edge suffers as well.... :-)
--
Kent Crispin "No reason to get excited",
[email protected] the thief he kindly spoke...
PGP fingerprint: B1 8B 72 ED 55 21 5E 44 61 F4 58 0F 72 10 65 55
http://songbird.com/kent/pgp_key.html