RE: Why are 1024 bit keys the limit right now?

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AaronH4321@aol.com writes:
> I am just starting at this. I know that part of RSA/PGP's strength
> comes from the size key you choose. What prevents someone from
> writting a 2048 bit key?  Is it because computers can't handle it? Is
> 1024 top of the prime number size right now? Am I way off track? 

In just about every way possible... :-)

The RSA algorithm can use keys of arbitrary length.

All current versions of PGP allow key sizes up to 2048* bits.  (When
asked for the size of the key to generate, it allows you to select 512,
768, 1024, OR TO *TYPE IN THE NUMBER OF BITS DESIRED*.) There are older,
partially incompatible versions that allow even larger keys, though
there is little reason to go higher. Beyond something like 3100 bits, it
is surmised that the 128-bit IDEA session key is easier to attack. 

As for prime numbers, no, 1024 bits isn't even close to the largest
found (there are of course an infinite number of primes).  The latest
discovery was of a Mersenne prime, the 35th such found. It was 1,398,269
bits long (all 1's, of course).

Tunny 
* OK, there is a minor bug in 2.6.2 that in some cases limits keys to
"only" 2047 bits -- the difference is utterly insignificant in terms of
security.  This message is signed by such a 2047-bit key. 
======================================================================
 James A. Tunnicliffe   | WWWeb: http://www.inference.com/~tunny
 Inference Corporation  | PGP Fingerprint:   CA 23 E2 F3 AC 2D 0C 77
 tunny@Inference.com    |                    36 07 D9 33 3D 32 53 9C
======================================================================

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Comment: which I won in the PGP raffle at Cypherpunks 12/96...

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On Wed, 8 Jan 1997, James A. Tunnicliffe wrote:

> All current versions of PGP allow key sizes up to 2048* bits.  (When
> asked for the size of the key to generate, it allows you to select 512,
> 768, 1024, OR TO *TYPE IN THE NUMBER OF BITS DESIRED*.) There are older,
> partially incompatible versions that allow even larger keys, though
> there is little reason to go higher. Beyond something like 3100 bits, it
> is surmised that the 128-bit IDEA session key is easier to attack.

RSAREF limits the size of the key being generated to 1024 bits.  RSADSI
permitted PGP to distribute a slightly altered version that supports keys up
to 2048 bits with the U.S. version.  2.6.3 does not have the altered RSAREF
code, so the U.S. version cannot use keys larger than 1024 bits (unless, of
course, one uses the rsaref library distributed with 2.6.2).


Mark
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There is no PGP 2.6.3; at least not that came from MIT... Someone
else may have made something claiming to be 2.6.3, but it did not
originate from MIT.

-derek

"Mark M." <markm@voicenet.com> writes:

> 
> -----BEGIN PGP SIGNED MESSAGE-----
> 
> On Wed, 8 Jan 1997, James A. Tunnicliffe wrote:
> 
> > All current versions of PGP allow key sizes up to 2048* bits.  (When
> > asked for the size of the key to generate, it allows you to select 512,
> > 768, 1024, OR TO *TYPE IN THE NUMBER OF BITS DESIRED*.) There are older,
> > partially incompatible versions that allow even larger keys, though
> > there is little reason to go higher. Beyond something like 3100 bits, it
> > is surmised that the 128-bit IDEA session key is easier to attack.
> 
> RSAREF limits the size of the key being generated to 1024 bits.  RSADSI
> permitted PGP to distribute a slightly altered version that supports keys up
> to 2048 bits with the U.S. version.  2.6.3 does not have the altered RSAREF
> code, so the U.S. version cannot use keys larger than 1024 bits (unless, of
> course, one uses the rsaref library distributed with 2.6.2).
> 
> 
> Mark
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> 

-- 
       Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
       Member, MIT Student Information Processing Board (SIPB)
    Home page: http://www.mit.edu:8001/people/warlord/home_page.html
       warlord@MIT.EDU    PP-ASEL     N1NWH    PGP key available

On 8 Jan 1997, Derek Atkins wrote:

> There is no PGP 2.6.3; at least not that came from MIT... Someone
> else may have made something claiming to be 2.6.3, but it did not
> originate from MIT.

There is a pgp 2.6.3i. Apparently, it's another "international" version. I
believe it's on one of the usual sites, but I don't know what's changed in
it.


--
Good government. Good government. Sit. Stay.