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1995-11-09 - Small keysizes do make sense (was PGP Comment weakens…)

Header Data

From: Raph Levien <raph@CS.Berkeley.EDU>
To: perry@piermont.com
Message Hash: b932f229e4b7720ffa01ca002c3202e8a15304ce7729178d6a5dc5f87889b1c5
Message ID: <199511091725.JAA17620@kiwi.cs.berkeley.edu>
Reply To: <199511091413.JAA15288@jekyll.piermont.com>
UTC Datetime: 1995-11-09 18:20:49 UTC
Raw Date: Fri, 10 Nov 1995 02:20:49 +0800

Raw message

From: Raph Levien <raph@CS.Berkeley.EDU>
Date: Fri, 10 Nov 1995 02:20:49 +0800
To: perry@piermont.com
Subject: Small keysizes do make sense (was PGP Comment weakens...)
In-Reply-To: <199511091413.JAA15288@jekyll.piermont.com>
Message-ID: <199511091725.JAA17620@kiwi.cs.berkeley.edu>
MIME-Version: 1.0
Content-Type: text/plain


> > I agree entirely. That's why my PGP key at school is 382 bits. It's a
> > lot easier to compromise my machine than factor a 382 bit number.
> 
> On the other hand, it costs nothing by most people's standards to use
> a 1024 bit key, so why not use one? I find that there is only a point
> in using low security for anything in particular when there is a
> perceivable cost to it -- if the cost is typing a different number
> while doing key generation, I don't see why one should suffer the
> tradeoff.

Perhaps it costs you "nothing," Perry, but not all of us have the
massively parrallel 64-way interleaved banked memory nanosecond-latency
box you have on your desk.

Since RSA decryption is cubic in key size, it takes about twenty times
as long to sign or decrypt a message. Since latency-hiding (for example,
caching the decrypted session keys) is not widely implemented, the user
actually sees the difference.

For applications such as remailers, a 20-fold factor can make the
difference between smooth operation and totally hosing the machine.

Another reason to use small keys is to communicate the relative insecurity
of the machine to senders. A 382-bit key says, loud and clear, "don't send
sensitive or incriminating information using this key."

Raph

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