# NAME

Crypt::Affine - Interface to the Affine cipher.

# VERSION

Version 0.08

# DESCRIPTION

The affine cipher is a type of mono alphabetic substitution cipher, wherein each letter in an alphabet is mapped to its numeric equivalent & then encrypted using a simple mathematical function. It inherits the weaknesses of all substitution ciphers. In the affine cipher the letters of an alphabet of size m are first mapped to the integers in the range 0..m-1. It then uses modular arithmetic to transform the integer that each plaintext letter corresponds to into another integer that correspond to a ciphertext letter.The function for encryption of a single letter can be defined as below:

E(x) = (mx + r) % l

where 'l' is the size of the alphabet and 'm' & 'r' are the key of cipher. The value 'm' must be choosen such that 'm' and 'l' are coprime.

Similarly the function for decryption of a single letter can be defined as below:

D(x) = (m ^ -1) (x - r) % l

where (m ^ -1) is the modular multiplicative inverse of 'm' modulo 'l' and it satisfies the equation below:

m (m ^ -1) % l = 1

# CONSTRUCTOR

The constructor expects the following parameters as described below in the table:

```
+----------+----------+-------------------------------------------------+
| Key | Required | Description |
+----------+----------+-------------------------------------------------+
| m | Yes | Any positive number. |
| r | Yes | Any positive number. |
| reverse | No | 0 or 1, depending whether to use reverse set of |
| | | alphabets. Default is 0. |
| source | No | Filename with complete path containing comma |
| | | separated list of alphabets. By default it uses |
| | | A-Z, a-z. |
+----------+----------+-------------------------------------------------+
use strict; use warnings;
use Crypt::Affine;
my $affine = Crypt::Affine->new({ m => 5, r => 8 });
```

# METHODS

## encrypt()

Encrypts the given string of alphabets ignoring any non-alphabets.

```
use strict; use warnings;
use Crypt::Affine;
my $affine = Crypt::Affine->new({ m => 5, r => 8 });
my $original = 'affine cipher';
my $encrypted = $affine->encrypt($original);
print "Original : [$original]\n";
print "Encrypted: [$encrypted]\n";
```

## decrypt()

Decrypts the given string of alphabets ignoring any non-alphabets.

```
use strict; use warnings;
use Crypt::Affine;
my $affine = Crypt::Affine->new({ m => 5, r => 8 });
my $original = 'affine cipher';
my $encrypted = $affine->encrypt('affine cipher');
my $decrypted = $affine->decrypt($encrypted);
print "Original : [$original]\n";
print "Encrypted: [$encrypted]\n";
print "Decrypted: [$decrypted]\n";
```

# AUTHOR

Mohammad S Anwar, `<mohammad.anwar at yahoo.com>`

# REPOSITORY

https://github.com/manwar/Crypt-Affine

# BUGS

Please report any bugs/feature requests to `bug-crypt-affine at rt.cpan.org`

or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Crypt-Affine. I will be notified & then you'll automatically be notified of progress on your bug as I make changes.

# SUPPORT

You can find documentation for this module with the perldoc command.

` perldoc Crypt::Affine`

You can also look for information at:

RT: CPAN's request tracker

AnnoCPAN: Annotated CPAN documentation

CPAN Ratings

Search CPAN

# LICENSE AND COPYRIGHT

Copyright (C) 2011 - 2015 Mohammad S Anwar.

This program is free software; you can redistribute it and/or modify it under the terms of the the Artistic License (2.0). You may obtain a copy of the full license at:

http://www.perlfoundation.org/artistic_license_2_0

Any use, modification, and distribution of the Standard or Modified Versions is governed by this Artistic License.By using, modifying or distributing the Package, you accept this license. Do not use, modify, or distribute the Package, if you do not accept this license.

If your Modified Version has been derived from a Modified Version made by someone other than you,you are nevertheless required to ensure that your Modified Version complies with the requirements of this license.

This license does not grant you the right to use any trademark, service mark, tradename, or logo of the Copyright Holder.

This license includes the non-exclusive, worldwide, free-of-charge patent license to make, have made, use, offer to sell, sell, import and otherwise transfer the Package with respect to any patent claims licensable by the Copyright Holder that are necessarily infringed by the Package. If you institute patent litigation (including a cross-claim or counterclaim) against any party alleging that the Package constitutes direct or contributory patent infringement,then this Artistic License to you shall terminate on the date that such litigation is filed.

Disclaimer of Warranty: THE PACKAGE IS PROVIDED BY THE COPYRIGHT HOLDER AND CONTRIBUTORS "AS IS' AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES. THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT ARE DISCLAIMED TO THE EXTENT PERMITTED BY YOUR LOCAL LAW. UNLESS REQUIRED BY LAW, NO COPYRIGHT HOLDER OR CONTRIBUTOR WILL BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING IN ANY WAY OUT OF THE USE OF THE PACKAGE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.