Looking for Elgamal sign+encrypt key information

Newton Hammet newton at hammet.net
Tue Mar 16 16:16:54 CET 2004

The below argument is why I simply have two 4096-bit RSA
keys 1 for signing and 1 for encryption.  Don't know how
safe 4096 bit keys are but I suspect they are pretty safe
for now, even from a TWIRL or TWINKLE machine.  I believe
in erroring on the side of caution.  4096 bit keys are
no longer a hurdle to either create or use for signing or
encryption with today's speedy chips.

I have also downloaded the source code for gnupg-1.2.4 and
made one modification:  doubling the arbitrary limit of
4096 bits for RSA to a new arbitrary limit of 8192 bits,
which for the moment may be overkill -- Thanks to the
developers of gnupg who even thought they claim that keys larger
than 4096 bits are not nesc. did not limit the capability of
gnupg to produce larger keys.


>>If Mallory can break a 1024-bit encryption key through brute
>>force (as opposed to an algorithm-specific weakness), we can
>>assume that she can also forge signatures from 1024-bit keys.
>>This is the case that you are worried about.  BUT, if she does
>>so even once, she introduces into the public record an example
>>of a forged 1024-bit signature, and when the actual owner of
>>that key is confronted with the fake signature (which would
>>likely happen quickly if the signed document was of any importance),
>>that owner will know that 1024-bit encryption can be broken and
>>would be able to document that fact in public.
> Yes, I've seen this argument before.  However, in my opinion, it makes
> two errant assumptions: 1) It assumes that the "forgery" will be
> discovered soon after it is created.  The whole point of a paper trail
> is to leave a documentational record of actions.  Many paper trails,
> however, are not fastidiously checked until and unless there are
> problems.  The other problem (which is more important in my opinion): 2)
> It assumes that the owner of the key will be believed when he or she
> announces that it was broken.  Forgers aren't going to wear a sign
> saying "I'm a key forger".  They are going to deny forging it, so that
> the document appears real.  The whole point of digital signatures is to
> add authenticity.  Forged documents are not going to be created on a
> whim, they are going to be created when there is a dispute in order to
> validate the oposing side's position.  In any dispute, there will be
> people who believe both sides.  An example:
> John is an employee at a cigarette manufacture; middle management in
> advertising.  For a time, he is involved in a scheme perpetuated by
> upper management to promote cigarettes in advertisements targetted to
> teens and pre-teens.  After a certain length of time, his concience
> causes him to go to government and civil anti-smoking groups.  A huge
> lawsuit forms from this.  Part of the evidence is a 1024-bit-key signed
> and dated document trail organizing the campaign, and these documents
> cite upper-management as the source of authority and show that they were
> CCed to upper management.  This, as you might guess, is a potentially
> multi-billion-dollar type lawsuit.  These type of lawsuits are also
> often many years in the making before they actually go to trial.
> The cigarette manufacturer has the financial incentive to crack that
> key.  During the ensuing court battle, John produces these documents
> that are dated back to the time when he was an employee, and uses them
> to show that upper management knew and directed the campaign.  The
> defending cigarette manufacturer produces a different set of documents -
> a paper trail that is identical to that shown by John, but that omits
> any reference to upper-management's authority and omits references to
> them being CCed to upper management.  The defense makes the argument
> that he did the initiative on his own in order to increase sales and
> obtain larger personal comissions, and when it was discovered by
> upper-management, he was fired and then made up the story that the whole
> affair was ordered by, and done with the knowledge of upper-management.
> We now have two conflicting sets of documents.  Both apparently signed
> by the same key.  Part of a large court battle.  Is the world in general
> going to believe that the cigarette manufacturer cracked John's 1024-bit
> key?  Or is the world going to believe that John is trying to cash in on
> the anti-cigarette-manufacturer sentiment after having been caught in an
> ilicit campaign to increase his own fortunes.
> What I know, is that business and government has a large mass.  And a
> controversy where there is a very plausible explanation just might not
> have the inertia necessary to cause a global awakening and make people
> use larger keys.  Especially if the public in general is convinced by
> the cigarette manufacturer's spin doctors.  Oh, 1024-bit keys are
> secure.  This was just a guy who got caught with his hands in the cookie
> jar.  No need to panic.
> The point is, if 1024-bit keys are not strong enough to trust with your
> important encryption, they are not strong enough for your important
> signatures.  For any signatures.  Who knows when and where a false
> document will pop up, and who knows who will believe it is false.
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