CCGUESS(1) Encryption CCGUESS(1)NAMEccguess - search for ccrypt encryption keys
SYNOPSISccguess [options] file...
DESCRIPTION
The ccguess program attempts to guess ccrypt(1) encryption keys by
searching the relevant part of the key space. This is done by prompting
the user for an approximate key and then trying many variations of this
key. This is intended to assist ccrypt users in recovering mistyped or
forgotten keys, provided that they remember at least part of the key.
Note that ccrypt provides strong cryptographic security: there are no
special back doors or shortcuts to recovering forgotten keys. There‐
fore, the ccguess program does not have any special powers. It simply
works by trying different keys until a possible match is found.
A search of the entire key space is not usually a practical option.
ccguess therefore works by prompting the user for an approximate key.
It then tries all variations that can be obtained by applying a small
number of changes. Here, each change is either a deletion of one let‐
ter, an insertion of one letter, a replacement of one letter by
another, or a transposition of two adjacent letters. By default,
ccguess searches all keys that differ from the approximate key by up to
5 changes. The number of changes searched can be adjusted with the
--depth option.
The mechanism by which ccguess determines whether a key is a "possible
match" is the same as that used by ccrypt to reject non-matching
decryption keys. There is a small chance of a false match, i.e.,
ccguess may find a key that turns out not to be the true encryption key
and does not decrypt the file correctly. A false match happens approxi‐
mately once for every 4.3 billion keywords tried, so the longer your
search goes on, the higher the likelihood that a false match is found.
Normally, ccguess stops after the first possible match is found, but
the -c option can be used to search for additional keys. The possibil‐
ity of a false match can be further reduced by supplying multiple files
that have been encrypted with the same key. In this case, ccguess will
search for keys that match any of the files, but will print a warning
for keys that do not match all of the files.
OPTIONS
The following options are supported:
-h, --help
Help. Print usage information and exit.
-L, --license
Print license info and exit.
-V, --version
Print version info and exit.
-K key, --key key
Specify the approximate key on the command line, rather than
prompting the user for it.
-d n, --depth n
Search keys that contain up to n changes. The default is 5.
-c, --continue
Keep trying more keys even after the first match is found. By
default, ccguess will stop after the first key is found that
matches all input files.
-t chars, --chartable chars
Specify the list of characters to try for replacements and
insertions. By default, ccguess will try all printable ASCII
characters. If you know, for example, that your key only used
lowercase letters and numbers, you can speed up the search by
specifying a list of characters explicitly. This option is
mutually exclusive with -n.
-n, --non-printable
Allow non-printable characters in keys. By default, ccguess
will only try printable ASCII characters. Note that the use
of this option slows down the search significantly. This
option is mutually exclusive with -t.
ARGUMENTS
file The name of a file that has been encrypted with the unknown
key. This file is only read from, not written to. The special
filename "-" is used to denote standard input.
If multiple files are specified, ccguess will search for keys
that match any of the files, but will print a warning for
keys that do not match all of the files.
EXAMPLE
Suppose the file myfile.cpt has been encrypted with the key "garden‐
house", but the user remembers "gardenhose". The command
ccguess-K gardenhose myfile.cpt
will find the correct key after 2318 guesses.
EXIT STATUS
The exit status is 0 if at least one possible match is found, 1 if no
matches are found, and >=2 if an error occurred.
VERSION
1.10
AUTHOR
Peter Selinger <selinger at users.sourceforge.net>
COPYRIGHT
Copyright (C) 2000-2012 Peter Selinger
This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2 of the License, or (at your
option) any later version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MER‐
CHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
Public License for more details.
You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation, Inc.,
59 Temple Place, Suite 330, Boston, MA 02111-1307, USA. See also
http://www.gnu.org/.
Version 1.10 October 2012 CCGUESS(1)
