Daniel Kahn Gillmor > Crypt-Nettle-0.3 > Crypt::Nettle::Cipher

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NAME ^

Crypt::Nettle::Cipher - Perl interface to symmetric encryption and decryption from libnettle

SYNOPSIS ^

  use Crypt::Nettle::Cipher;

  my $cleartext = '01234567';
  my $cipher = Crypt::Nettle::Cipher->new('encrypt', 'aes128', '02ds3m#soE2d^7dw', 'ecb');
  $ciphertext = $cipher->process($cleartext);
  printf("encrypted: %s\n", unpack('H*', $ciphertext));

ABSTRACT ^

Crypt::Nettle::Cipher provides an object interface to symmetric encryption and decryption from the nettle C library. Each Crypt::Nettle::Cipher object is initialized to do either encryption or decryption. If you need both encryption and decryption, make a separate object for each direction.

BASIC OPERATIONS ^

algos_available()

Get a list of strings that refer to the ciphers this perl module knows how to coax out of libnettle:

 my @algos = Crypt::Nettle::Cipher::algos_available();

modes_available()

Get a list of strings that refer to the cipher block modes this perl module knows how to coax out of libnettle:

 my @modes = Crypt::Nettle::Cipher::modes_available();

ENCRYPTION CONTEXT CREATION ^

new($is_encrypt, $algo, $key, $mode, $iv)

Create a new context for encryption:

  my $encrypt = Crypt::Nettle::Cipher->new('encrypt', 'aes128', '02ds3m#soE2d^7dw', 'ecb');

The parameter $algo must be the name of a symmetric encryption algorithm supported by libnettle.

Note that $key must match the key_size() for the selected algorithm.

If $is_encrypt is 'decrypt' or 0, the new object will do decryption; If $is_encrypt is 'encrypt' or 1, it will encrypt.

You can set the $mode of the cipher with 'ecb' (Electronic Code Book), 'cbc' (Cipher Block Chaining), or 'ctr' (Counter). ECB is the default because it is simpler to configure, but you probably want CBC or CTR for security.

If you use CBC or CTR, you'll need to supply an initialization vector (CBC) or initialization counter (CTR) in the $iv parameter. $iv should be the size of block_size().

On error, will return undefined.

Supported encryption algorithms are: aes128, aes192, aes256, arctwo40, arctwo64, arctwo128, arctwo_gutmann128, arcfour128, camellia128, camellia192, camellia256, cast128, serpent128, serpent192, serpent256, twofish128, twofish192, twofish256.

(you can retrieve these programmatically with algos_available()).

Every algorithm supports ECB, but some algorithms don't support some of the other modes. I recommend sticking to AES if you can.

copy()

Copy an existing Crypt::Nettle::Cipher object, including its internal state:

  my $new_cipher = $cipher->copy();

On error, will return undefined.

ENCRYPTION CONTEXT OPERATION ^

process($data)

Encrypt or decrypt $data with the cipher object:

  $cleartext = 'this is a secret';
  my $encrypt = Crypt::Nettle::Cipher->new('encrypt', 'aes128', '02ds3m#soE2d^7dw');
  $ciphertext = $encrypt->process($cleartext);

or:

  $ciphertext = 'adfasdfasdfasdf';
  my $encrypt = Crypt::Nettle::Cipher->new('decrypt', 'aes128', '02ds3m#soE2d^7dw');
  $cleartext = $encrypt->process($ciphertext);

Note that the length of $data must be an even multiple of $cipher->block_size().

process_in_place($data)

Process $data with the cipher object, overwriting $data with the result:

  $text = 'this is a secret';
  $encrypt->process_in_place($text);

Note that the length of $data must be an even multiple of $cipher->block_size().

ENCRYPTION DETAILS ^

is_encrypt()

Returns non-zero if the object is an encryption cipher, or zero if the object is set up for decryption.

  printf("Direction: %s\n", ($cipher->is_encrypt() ? 'encrypt' : 'decrypt'));

name()

Return the name of the encryption/decryption algorithm:

  printf("Symmetric Encryption Algorithm: %s\n", $cipher->name());

mode()

Returns a string representing the cipher block mode.

  printf("Cipher Block Mode: %s\n", $cipher->mode());

key_size()

Return the size (in bytes) of the key for a given algorithm. This can be called either on an encryption context, or just by passing the name of an algorithm to the module directly:

  printf("Key size: %d\n", $cipher->key_size());

or

  printf("Key size: %d\n", Crypt::Nettle::Cipher->key_size('aes128'));

block_size()

Return the block size (in bytes) of this encryption algorithm. This can be called either on an encryption context, or just by passing the name of an algorithm to the module directly:

  printf("Block size: %d\n", $cipher->block_size());

or

  printf("Block size: %d\n", Crypt::Nettle::Cipher->block_size('aes128'));

BUGS AND FEEDBACK ^

For algorithms with known weak keys (e.g. DES, ARCFOUR, and BLOWFISH) Crypt::Nettle::Cipher does not currently check for initialization with a weak key. It is recommended to use an algorithm like AES, which has no known weak keys at the time of this writing (March 2011).

It would be nice to buffer input for process() so that the user does not have to manage buffer sizes outside of Crypt::Nettle.

At the moment, $key and $iv probably need to be exactly the right size (key_size() and block_size(), respectively). Should we try to pad with zeros if the user passes the wrong size data?

It would be nice to be able to use a shorthand like 'aes' and have the module select the correct flavor of aes based on the length of the key argument.

Crypt::Nettle::Cipher has no other known bugs, mostly because no one has found them yet. Please write mail to the maintainer (dkg@fifthhorseman.net) with your contributions, comments, suggestions, bug reports or complaints.

AUTHORS AND CONTRIBUTORS ^

Daniel Kahn Gillmor <dkg@fifthhorseman.net>

COPYRIGHT AND LICENSE ^

Copyright © Daniel Kahn Gillmor

Crypt::Nettle is free software, you may redistribute it and/or modify it under the GPL version 2 or later (your choice). Please see the COPYING file for the full text of the GPL.

ACKNOWLEDGEMENTS ^

This module was initially inspired by the GCrypt.pm bindings made by Alessandro Ranellucci.

DISCLAIMER ^

This software is provided by the copyright holders and contributors "as is" and any express or implied warranties, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose are disclaimed. In no event shall the contributors be liable for any direct, indirect, incidental, special, exemplary, or consequential damages (including, but not limited to, procurement of substitute goods or services; loss of use, data, or profits; or business interruption) however caused and on any theory of liability, whether in contract, strict liability, or tort (including negligence or otherwise) arising in any way out of the use of this software, even if advised of the possibility of such damage.

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