From owner-cypherpunks () toad com Sun Sep 17 21:38:21 1995
From: Ian Goldberg <iang () CS Berkeley EDU>
Message-Id: <199509180441.VAA16683 () lagos CS Berkeley EDU>
Subject: Netscape SSL implementation cracked!
To: cypherpunks () toad com
Date: Sun, 17 Sep 1995 21:41:01 -0700 (PDT)
X-Mailer: ELM [version 2.4 PL23]
Content-Type: text/plain; charset=US-ASCII
Sender: owner-cypherpunks () toad com
As some of you may recall, a few weeks ago I posted a
reverse-compilation of the random number generation routine used by
netscape to choose challenge data and encryption keys.
Recently, one of my officemates (David Wagner <daw () cs berkeley edu>)
and I (Ian Goldberg <iang () cs berkeley edu>) finished the job
of seeing exactly how the encryption keys are picked.
What we discovered is that, at least on the systems we checked (Solaris
and HP-UX), the seed value for the RNG was fairly trivial to guess by
someone with an account on the machine running netscape (so much so
that in this situation, it usually takes less than 1 minute to find
the key), and not too hard for people without accounts, either.
See below for details.
I've included the header to a program we wrote to do this key-cracking
below. I would like to get some information, though:
o Where should I put the full source (1 file, ~12k) so that ITAR lovers
don't get mad at me?
o Where can I find a version of netscape that does RC4-128? It is
likely that it suffers from the same problem, and even a brute-force
search of the entire seed space is _much_ less than 128 bits.
- Ian "who just saw _Hackers_ today with some other Bay Area cypherpunks,
and it put me in the mood"
/* unssl.c - Last update: 950917
Break netscape's shoddy implementation of SSL on some platforms
(tested for netscape running RC4-40 on Solaris and HP-UX; other
Unices are probably similar; other crypt methods are unknown, but
it is likely that RC4-128 will have the same problems).
The idea is this: netscape seeds the random number generator it uses
to produce challenge-data and master keys with a combination of the
time in seconds and microseconds, the pid and the ppid. Of these,
only the microseconds is hard to determine by someone who
(a) can watch your packets on the network and
(b) has access to any account on the system running netscape.
Even if (b) is not satisfied, the time can often be obtained from
the time or daytime network daemons; an approximation to the pid can
sometimes be obtained from a mail daemon (the pid is part of most
Message-ID's); the ppid will usually be not much smaller than the pid,
and has an higher than average chance of being 1. Clever guessing
of these values will in all likelihood cut the expected search space
down to less than brute-forcing a 40-bit key, and certainly is less
than brute-forcing a 128-bit key.
Subsequent https: connections after the first (even to different hosts)
seem to _not_ reseed the RNG. This makes things much easier, once
you've broken the first message. Just keep generating 16 bytes of
random numbers until you get the challenge-data for the next message.
The next key will then be the 16 random bytes after that.
main() and bits of MD5Transform1 by Ian Goldberg <iang () cs berkeley edu>
and David Wagner <daw () cs berkeley edu>. The rest is taken from the
standard MD5 code; see below.
This code seems to want to run on a big-endian machine. There may be
other problems as well. This code is provided as-is; if it causes you
to lose your data, sleep, civil liberties, or SO, that's your problem.
On the command line, give the time in seconds, the pid, the ppid and
the SSL challenge data (each byte in hex, separated by some non-hex
character like a colon) of the _first_ SSL message generated by
the instance of netscape. This program will search through the
microsecond values. You may need to run it again with a slightly
different value for the seconds, depending on how accurately you know
the time on the system running netscape. The output will be the
master key (all 16 bytes; note you never even told the program the
11 bytes you knew) and the value for the microseconds that produced it.
As a benchmark, this code runs in just under 25 seconds real time
(for an unsuccessful search through 1<<20 values for the microseconds)
on an unloaded HP 712/80.