PGP Comment feature weakens remailer security

[anonymous-remailer at shell.portal.com]

On Wed, 8 Nov 1995, Raph Levien wrote:

>    On an unrelated topic... cypherpunks like to count bits, right?

Mmmm, sometimes we do ... <g>

Sometimes we even think, if I were a lil wa'bbit, where would I go hide
... especially when we do a bad Elmer Fudd impression of Bugs Bunny. <p>

> What is the correct number of pseudorandom bits to use in a MIME
> multipart separator? If the data has a line which matches the
> separator, the message is corrupted.  Of course, if you can take
> multiple passes through the data, you can simply verify that it does
> not contain a line which matches the separator. But if you're
> restricted to a single pass, then the only way to do it is to use a
> randomly generated separator.

An interesting problem.  

If you are going to take multiple passes, and do top-down and bottom up
analysis, then you can't really parse on the fly. It pretty much has to be
a batch job, I think.  You have to get your data, and then check it.  You
can't simply *trust* that there is not any corruption, and pass all of
your data through. 

And if you're going to parse in a single pass, then we're back to the 
problem of monkeys sitting at typewriters and Shakespeare's sonnets.

>    I figure that 128 bits should _definitely_ be enough (that's what
> is in the new premail code now). Even 64 bits should ensure that it is
> unlikely that anyone will ever experience message corruption over the
> expected lifetime of premail. However, it makes me nervous. What do
> people think?

Unfortunately, it's not quite that simple.  

The likelyhood of corruption is not based on each past run.  It's just 
like rolling dice.  The odds of rolling boxcars is 1 in 36 (I think) no 
matter how many prior times, you've rolled boxcars.

Twenty passes doesn't influence whether you crap out or not on a single
roll.  Nothing *remembers* past performance to ensure that something
doesn't happen (or happens) many, many times in a row.  I guess, this is
why Atlantic City, Baden Baden, and Las Vegas generally do as well as they
do. 



Alice de 'nonymous ...

                                  ...just another one of those...


P.S.  This post is in the public domain.
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