[IP] more on FBI plans new Net-tapping push

Jon Callas jon at pgp.com
Sun Jul 9 05:56:15 PDT 2006

Brian Randell said:

>Just because the government *claims* it can't break a given
>code ... :-)

I realize that there was a smiley face at the end of this, and I
might be showing humorlessness about this, but this concerns my
profession in general, and my software in particular. Consequently, I
have no choice but to comment on this remark.

Modern cryptographic systems are essentially unbreakable,
particularly if an adversary is restricted to intercepts. We have
argued for, designed, and built systems with 128 bits of security
precisely because they are essentially unbreakable. It is very easy
to underestimate the power of exponentials. 2^128 is a very big
number. Burt Kaliski first came up with this characterization, and if
he had a nickel for every time I tell it, he could buy a latte or three.

Imagine a computer that is the size of a grain of sand that can test
keys against some encrypted data. Also imagine that it can test a key
in the amount of time it takes light to cross it. Then consider a
cluster of these computers, so many that if you covered the earth
with them, they would cover the whole planet to the height of 1
meter. The cluster of computers would crack a 128-bit key on average
in 1,000 years.

If you want to brute-force a key, it literally takes a planet-ful of
computers. And of course, there are always 256-bit keys, if you worry
about the possibility that government has a spare planet that they
want to devote to key-cracking.

Now of course, there are other ways to break the system.

They could know something we don't. They could know some fundamental
truth about mathematics (like how to factor really fast), some
effective form of symmetric cryptanalysis, or something else. They
could know about quantum computers, DNA computers, systems based upon
non-Einsteinian physics, and so on. Yes, it's possible. But this
quickly gets into true paranoid thought. There isn't a lot of
difference between the *presumption* that they have such things and
the presumption that they have aliens in a vault in Nevada. It isn't
falsifiable. It gets irrational quickly. The evidence that we have
about this suggests quite the opposite, but more on that later.

They could have something we don't. For example, they could know
about software flaws in my or other people's computer systems. Yes,
that's possible, too. At PGP Corporation, we guard against this by
making our software available to people for their examination.
Approximately 2,000 people per month do that. If you want to be one
of them, go to <http://www.pgp.com/downloads/> and look at it
yourself. While you're at it, take a look at our quality assurance
letter at <http://www.pgp.com/company/pgpassurance.html>.

They could be hacking people's systems. This is a much more
reasonable worry. If I were going to be doing this, it's what I would
do. The state of computer operational security is such that it makes
much more sense to invest time, money, and effort into rootkits than
into cryptanalysis.

However, there are things that we know that they *are* doing. One of
them is relevant to this particular case. That is work on cracking
the passphrases that people use to protect their keys. The
cryptography we're using is itself uncrackable, but about 2/3 of the
people in the world use a password (not even a passphrase) that
directly relates to a pet or loved one. The order of frequency seems
to be pets (living or dead), then children, then ex-loves. We know
that at least one government has a password cracker that is based
upon building a psychometric model of person who owns the key and
constructing passphrases on that model. If you're a Hollywood private
eye and they seize your computer and find on it that you're a
basketball fan from your browser cache, then "Lak3rz 4 Teh w1n!" is
actually a very bad passphrase. Don't blame me when they find it in
about two minutes.

It isn't just government that does this, either. Companies such as
Access Data and Elcomsoft have distributed password crackers. These
things aren't hacking the crypto, they're hacking the mind using the
crypto. My old friend and colleague, Drew Gross, who is a forensics
expert, has said, "I love crypto; it tells me what part of the system
not to bother attacking."

The last bit of evidence we have that suggests that they can't break
the crypto is that they are apparently devoting a lot of effort to
traffic analysis. Look at what we've learned in the last few months.
Listening for keywords is so twentieth century. They're looking at
call patterns, message flow, and so on. I could go on about this for
a long time, but it's a tangent from this. If you're interested in
more, I am going to be leading a panel at Defcon this August on
traffic analysis. Come liven up the discussion.


Jon Callas
PGP Corporation         Tel: +1 (650) 319-9016
3460 West Bayshore      Fax: +1 (650) 319-9001
Palo Alto, CA 94303     PGP: ed15 5bdf cd41 adfc 00f3
USA                          28b6 52bf 5a46 bc98 e63d

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