ccguess - Online in the Cloud

PROGRAM:

NAME

ccguess - search for ccrypt encryption keys

SYNOPSIS

ccguess [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. Therefore, 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 letter, 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 approximately 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
possibility 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 "gardenhouse", 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

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