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2CCGUESS(1)                        Encryption                        CCGUESS(1)
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NAME

7       ccguess - search for ccrypt encryption keys
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SYNOPSIS

10       ccguess [options] file...
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DESCRIPTION

13       The  ccguess  program  attempts  to  guess ccrypt(1) encryption keys by
14       searching the relevant part of the key space. This is done by prompting
15       the user for an approximate key and then trying many variations of this
16       key. This is intended to assist ccrypt users in recovering mistyped  or
17       forgotten keys, provided that they remember at least part of the key.
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19       Note  that  ccrypt provides strong cryptographic security: there are no
20       special back doors or shortcuts to recovering  forgotten  keys.  There‐
21       fore,  the  ccguess program does not have any special powers. It simply
22       works by trying different keys until a possible match is found.
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24       A search of the entire key space is not  usually  a  practical  option.
25       ccguess  therefore  works by prompting the user for an approximate key.
26       It then tries all variations that can be obtained by applying  a  small
27       number  of  changes. Here, each change is either a deletion of one let‐
28       ter, an insertion of  one  letter,  a  replacement  of  one  letter  by
29       another,  or  a  transposition  of  two  adjacent  letters. By default,
30       ccguess searches all keys that differ from the approximate key by up to
31       5  changes.  The  number  of  changes searched can be adjusted with the
32       --depth option.
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34       The mechanism by which ccguess determines whether a key is a  "possible
35       match"  is  the  same  as  that  used  by ccrypt to reject non-matching
36       decryption keys. There is a  small  chance  of  a  false  match,  i.e.,
37       ccguess may find a key that turns out not to be the true encryption key
38       and does not decrypt the file correctly. A false match happens approxi‐
39       mately  once  for  every 4.3 billion keywords tried, so the longer your
40       search goes on, the higher the likelihood that a false match is  found.
41       Normally,  ccguess  stops  after the first possible match is found, but
42       the -c option can be used to search for additional keys. The  possibil‐
43       ity of a false match can be further reduced by supplying multiple files
44       that have been encrypted with the same key. In this case, ccguess  will
45       search  for  keys that match any of the files, but will print a warning
46       for keys that do not match all of the files.
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OPTIONS

49       The following options are supported:
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51       -h, --help
52                 Help. Print usage information and exit.
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54       -L, --license
55                 Print license info and exit.
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57       -V, --version
58                 Print version info and exit.
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60       -K key, --key key
61                 Specify the approximate key on the command line, rather  than
62                 prompting the user for it.
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64       -d n, --depth n
65                 Search keys that contain up to n changes. The default is 5.
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67       -c, --continue
68                 Keep trying more keys even after the first match is found. By
69                 default, ccguess will stop after the first key is found  that
70                 matches all input files.
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72       -t chars, --chartable chars
73                 Specify  the  list  of characters to try for replacements and
74                 insertions. By default, ccguess will try all printable  ASCII
75                 characters. If you know, for example, that your key only used
76                 lowercase letters and numbers, you can speed up the search by
77                 specifying  a  list  of characters explicitly. This option is
78                 mutually exclusive with -n.
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80       -n, --non-printable
81                 Allow non-printable characters in keys. By  default,  ccguess
82                 will  only  try printable ASCII characters. Note that the use
83                 of this option slows  down  the  search  significantly.  This
84                 option is mutually exclusive with -t.
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ARGUMENTS

87       file      The  name  of a file that has been encrypted with the unknown
88                 key. This file is only read from, not written to. The special
89                 filename "-" is used to denote standard input.
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91                 If multiple files are specified, ccguess will search for keys
92                 that match any of the files, but will  print  a  warning  for
93                 keys that do not match all of the files.
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EXAMPLE

96       Suppose  the  file  myfile.cpt has been encrypted with the key "garden‐
97       house", but the user remembers "gardenhose". The command
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99          ccguess -K gardenhose myfile.cpt
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101       will find the correct key after 2318 guesses.
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EXIT STATUS

104       The exit status is 0 if at least one possible match is found, 1  if  no
105       matches are found, and >=2 if an error occurred.
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VERSION

108       1.10
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AUTHOR

111       Peter Selinger <selinger at users.sourceforge.net>
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114       Copyright (C) 2000-2012 Peter Selinger
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116       This program is free software; you can redistribute it and/or modify it
117       under the terms of the GNU General Public License as published  by  the
118       Free  Software Foundation; either version 2 of the License, or (at your
119       option) any later version.
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121       This program is distributed in the hope that it  will  be  useful,  but
122       WITHOUT  ANY  WARRANTY;  without  even  the  implied  warranty  of MER‐
123       CHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU  General
124       Public License for more details.
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126       You should have received a copy of the GNU General Public License along
127       with this program; if not, write to the Free Software Foundation, Inc.,
128       59  Temple  Place,  Suite  330,  Boston,  MA  02111-1307, USA. See also
129       http://www.gnu.org/.
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133Version 1.10                     October 2012                       CCGUESS(1)
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