From: Adam Shostack <adam@lighthouse.homeport.org>
Date: Tue, 19 Dec 1995 13:41:40 +0800
To: cypherpunks@toad.com (Cypherpunks Mailing List)
Subject: PGP's randpool()
Message-ID: <199512190326.WAA20676@homeport.org>
MIME-Version: 1.0
Content-Type: text



	What does PGP do when it exhausts randpool?

	I've scanned the source, and found some useful tidbits, but
RANDPOOLBITS seems limited to ~408 bytes.  I can invoke commands that
should exhaust PGP's randpool, but don't seem to.  Doing "pgp
+makerandom=4000000 foo" repeatedly seemingly would cause PGP to
prompt me to type in some random stuff, but it doesn't.

	I'm trying to see how pgp reacts to me taking all its random
bytes because I'm writing some shell scripts that use pgp to generate
random passphrases.  (This is a case where I don't think bunches of
system data are enough.)

	(Note to reporters who might be listening: This is an fairly
unusual invocation of PGP where a user would not interact with the
program at all to supply new randomness.  Its not an attack on PGP's
security in any interesting or newsworthy sense.)

random.c:
 * - Every time you run PGP, especially when responding to one of PGP's
 *   prompts, PGP samples the keystrokes for use as random numbers.
 *   It is a shame to throw this entropy (randomness) away just because
 *   there is no need for it in the current invocation of PGP

[... Further down...]

/*
 * Performs an accumulation of random bits.  As long as there are fewer bits
 * in the buffer than are needed (the number passed, plus pending bits),
 * prompt for more.
[heavily cut]

void
trueRandAccum(unsigned count)	/* Get this many random bits ready */
{
LANG("\nWe need to generate %u random bits.  This is done by measuring the\
\ntime intervals between your keystrokes.  Please enter some random text\
\non your keyboard until you hear the beep:\n"), count-trueRandBits);


-- 
"It is seldom that liberty of any kind is lost all at once."
					               -Hume