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Date: Sat, 17 Jun 2006 04:56:38 +0400
From: Solar Designer <>
Subject: Re: JtR -show output

On Fri, Jun 16, 2006 at 05:56:57PM -0500, Randy B wrote:
> >        john --show passwd | fgrep : > cracked
> Random question, and has to do more with coding style than anything -
> I'm sure you had a reason for not printing those to STDERR; would you
> mind sharing it?

Well, those last two lines are not an error message, so it is not
obviously right to print them to stderr.

Here's what I might change John to do:

1. Send the primary output of --show (the cracked passwords) to stdout.

2. Flush stdio buffers for stdout.

3. Send the "Cracked ... left ..." line to stderr.  (And not print an
empty line before it at all.)

With no output redirection, the above change would affect the console
output slightly (the empty line would not be printed).

One disadvantage of this approach is that it would cause people to
redirect stderr from John to /dev/null in some of their scripts.  Then
they would not get a chance to see real error messages, if any are
printed.  This is probably a good enough reason for not applying the
above change.

Another reason is that the distinction between stdout and stderr is
non-obvious and hard to take advantage of for many non-Unix users.

Instead, the --show option might be enhanced to accept an optional
parameter list, which is needed for other reasons as well.  For example:

	john --show=no-partial,no-summary passwd

(in a future version of John) might print only fully-cracked passwords
and not print the "Cracked ... left ..." line.

Alexander Peslyak <solar at>
GPG key ID: B35D3598  fp: 6429 0D7E F130 C13E C929  6447 73C3 A290 B35D 3598 - bringing security into open computing environments

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