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Man Pages


Manual Reference Pages  -  CRYPT::GCRYPT (3)

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NAME

Crypt::GCrypt - Perl interface to the GNU Cryptographic library

CONTENTS

SYNOPSIS



  use Crypt::GCrypt;
 
  my $cipher = Crypt::GCrypt->new(
    type => cipher,
    algorithm => aes,
    mode => cbc
  );
  $cipher->start(encrypting);
 
  $cipher->setkey(my secret key);
  $cipher->setiv(my init vector);

  my $ciphertext  = $cipher->encrypt(plaintext);
  $ciphertext .= $cipher->finish;

  my $plaintext  = $cipher->decrypt($ciphertext);
  $plaintext .= $cipher->finish;



ABSTRACT

Crypt::GCrypt provides an object interface to the C libgcrypt library. It currently supports symmetric encryption/decryption and message digests, while asymmetric cryptography is being worked on.

BINDING INFO

gcrypt_version()

Returns a string indicating the running version of gcrypt.

built_against_version()

Returns a string indicating the version of gcrypt that this module was built against. This is likely only to be useful in a debugging situation.

SYMMETRIC CRYPTOGRAPHY

cipher_algo_available()

Determines whether a given cipher algorithm is available in the local gcrypt installation:



  if (Crypt::GCrypt::cipher_algo_available(aes)) {
    # do stuff with aes
  }



new()

In order to encrypt/decrypt your data using a symmetric cipher you first have to build a Crypt::GCrypt object:



  my $cipher = Crypt::GCrypt->new(
    type => cipher,
    algorithm => aes,
    mode => cbc
  );



The type argument must be cipher and algorithm is required too. See below for a description of available algorithms and other initialization parameters:
algorithm This may be one of the following:
<B>3desB> Triple-DES with 3 Keys as EDE. The key size of this algorithm is 168 but you have to pass 192 bits because the most significant bits of each byte are ignored.
<B>aesB> AES (Rijndael) with a 128 bit key.
<B>aes192B> AES (Rijndael) with a 192 bit key.
<B>aes256B> AES (Rijndael) with a 256 bit key.
<B>blowfishB> The blowfish algorithm. The current implementation allows only for a key size of 128 bits (and thus is not compatible with Crypt::Blowfish).
<B>cast5B> CAST128-5 block cipher algorithm. The key size is 128 bits.
<B>desB> Standard DES with a 56 bit key. You need to pass 64 bit but the high bits of each byte are ignored. Note, that this is a weak algorithm which can be broken in reasonable time using a brute force approach.
<B>twofishB> The Twofish algorithm with a 256 bit key.
<B>twofish128B> The Twofish algorithm with a 128 bit key.
<B>arcfourB> An algorithm which is 100% compatible with RSA Inc.’s RC4 algorithm. Note that this is a stream cipher and must be used very carefully to avoid a couple of weaknesses.
mode This is a string specifying one of the following encryption/decryption modes:
<B>streamB> only available for stream ciphers
<B>ecbB> doesn’t use an IV, encrypts each block independently
<B>cbcB> the current ciphertext block is encryption of current plaintext block xor-ed with last ciphertext block
<B>cfbB> the current ciphertext block is the current plaintext block xor-ed with the current keystream block, which is the encryption of the last ciphertext block
<B>ofbB> the current ciphertext block is the current plaintext block xor-ed with the current keystream block, which is the encryption of the last keystream block

If no mode is specified then <B>cbcB> is selected for block ciphers, and <B>streamB> for stream ciphers.

padding When the last block of plaintext is shorter than the block size, it must be padded before encryption. Padding should permit a safe unpadding after decryption. Crypt::GCrypt currently supports two methods:
<B>standardB> This is also known as PKCS#5 padding, as it’s binary safe. The string is padded with the number of bytes that should be truncated. It’s compatible with Crypt::CBC.
<B>nullB> Only for text strings. The block will be padded with null bytes (00). If the last block is a full block and blocksize is 8, a block of 0000000000000000 will be appended.
<B>noneB> By setting the padding method to none, Crypt::GCrypt will only accept a multiple of blklen as input for encrypt().
secure If this option is set to a true value, all data associated with this cipher will be put into non-swappable storage, if possible.
enable_sync Enable the CFB sync operation.
Once you’ve got your cipher object the following methods are available:

start()



   $cipher->start(encrypting);
   $cipher->start(decrypting);



This method must be called before any call to setkey() or setiv(). It prepares the cipher for encryption or decryption, resetting the internal state.

setkey()



   $cipher->setkey(my secret key);



Encryption and decryption operations will use this key until a different one is set. If your key is shorter than the cipher’s keylen (see the keylen method) it will be zero-padded, if it is longer it will be truncated.

setiv()



   $cipher->setiv(my iv);



Set the initialisation vector for the next encrypt/decrypt operation. If IV is missing a standard IV of all zero is used. The same IV is set in newly created cipher objects.

encrypt()



   $ciphertext = $cipher->encrypt($plaintext);



This method encrypts $plaintext with $cipher, returning the corresponding ciphertext. The output is buffered; this means that you’ll only get multiples of $cipher’s block size and that at the end you’ll have to call finish().

finish()



    $ciphertext .= $cipher->finish;
   
    $plaintext .= $cipher->finish;



The CBC algorithm must buffer data blocks internally until there are even multiples of the encryption algorithm’s blocksize (typically 8 or 16 bytes). After the last call to encrypt() or decrypt() you should call finish() to flush the internal buffer and return any leftover data. This method will also take care of padding/unpadding of data (see the padding option above).

decrypt()



   $plaintext = $cipher->decrypt($ciphertext);



The counterpart to encrypt, decrypt takes a $ciphertext and produces the original plaintext (given that the right key was used, of course). The output is buffered; this means that you’ll only get multiples of $cipher’s block size and that at the end you’ll have to call finish().

keylen()



   print "Key length is " . $cipher->keylen();



Returns the number of bytes of keying material this cipher needs.

blklen()



   print "Block size is " . $cipher->blklen();



As their name implies, block ciphers operate on blocks of data. This method returns the size of this blocks in bytes for this particular cipher. For stream ciphers 1 is returned, since this implementation does not feed less than a byte into the cipher.

sync()



   $cipher->sync();



Apply the CFB sync operation.

MESSAGE DIGESTS

digest_algo_available()

Determines whether a given digest algorithm is available in the local gcrypt installation:



   if (Crypt::GCrypt::digest_algo_available(sha256)) {
      # do stuff with sha256
   }



new()

In order to create a message digest, you first have to build a Crypt::GCrypt object:



  my $digest = Crypt::GCrypt->new(
    type => digest,
    algorithm => sha256,
  );



The type argument must be digest and algorithm is required too. See below for a description of available algorithms and other initialization parameters:
algorithm Depending on your available version of gcrypt, this can be one of the following hash algorithms. Note that some gcrypt installations do not implement certain algorithms (see digest_algo_available()).
<B>md4B>
<B>md5B>
<B>ripemd160B>
<B>sha1B>
<B>sha224B>
<B>sha256B>
<B>sha384B>
<B>sha512B>
<B>tiger192B>
<B>whirlpoolB>
secure If this option is set to a true value, all data associated with this digest will be put into non-swappable storage, if possible.
hmac If the digest is expected to be used as a keyed-Hash Message Authentication Code (HMAC), supply the key with this argument. It is good practice to ensure that the key is at least as long as the digest used.
Once you’ve got your digest object the following methods are available:

digest_length()



    my $len = $digest->digest_length();



Returns the length in bytes of the digest produced by this algorithm.

write()



    $digest->write($data);



Feeds data into the hash context. Once you have called read(), this method can’t be called anymore.

reset()

Re-initializes the digest with the same parameters it was initially created with. This allows write()ing again, after a call to read().

clone()

Creates a new digest object with the exact same internal state. This is useful if you want to retrieve intermediate digests (i.e. read() from the copy and continue write()ing to the original).

read()



    my $md = $digest->read();



Completes the digest and return the resultant string. You can call this multiple times, and it will return the same information. Once a digest object has been read(), it may not be written to.

THREAD SAFETY

libgcrypt is initialized with support for Pthread, so this module should be thread safe.

SEE ALSO

Crypt::GCrypt::MPI supports Multi-precision integers (bignum math) using libgcrypt as the backend implementation.

BUGS AND FEEDBACK

There are no known bugs. You are very welcome to write mail to the author (aar@cpan.org) with your contributions, comments, suggestions, bug reports or complaints.

AUTHORS AND CONTRIBUTORS

Alessandro Ranellucci <aar@cpan.org>

Daniel Kahn Gillmor (message digests) <dkg@fifthhorseman.net>

COPYRIGHT AND LICENSE

Copyright (c) Alessandro Ranellucci. Crypt::GCrypt is free software, you may redistribute it and/or modify it under the same terms as Perl itself.

ACKNOWLEDGEMENTS

This module was initially inspired by the GCrypt.pm bindings made by Robert Bihlmeyer in 2002. Thanks to users who give feedback and submit patches (see Changelog).

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 regents or 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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