Crypt::Mode::OFB(3)   User Contributed Perl Documentation  Crypt::Mode::OFB(3)


NAME
       Crypt::Mode::OFB - Block cipher mode OFB [Output feedback]

SYNOPSIS
          use Crypt::Mode::OFB;
          my $m = Crypt::Mode::OFB->new('AES');
          my $key = '1234567890123456';
          my $iv = '1234567890123456';
          my $plaintext = 'example plaintext';
          my $chunk1 = 'example ';
          my $chunk2 = 'plaintext';

          # encrypt or decrypt in one call
          my $single_ciphertext = $m->encrypt($plaintext, $key, $iv);
          my $single_plaintext = $m->decrypt($single_ciphertext, $key, $iv);

          # encrypt more chunks
          $m->start_encrypt($key, $iv);
          my $chunked_ciphertext = '';
          $chunked_ciphertext .= $m->add($chunk1);
          $chunked_ciphertext .= $m->add($chunk2);

          # decrypt more chunks
          $m->start_decrypt($key, $iv);
          my $chunked_plaintext = '';
          $chunked_plaintext .= $m->add($chunked_ciphertext);

DESCRIPTION
       This module implements OFB cipher mode. Note: It works only with
       ciphers from CryptX (Crypt::Cipher::NNNN).

METHODS
       Unless noted otherwise, assume $m is an existing mode object created
       via "new", for example:

        my $m = Crypt::Mode::OFB->new('AES');

   new
        my $m = Crypt::Mode::OFB->new($name);
        #or
        my $m = Crypt::Mode::OFB->new($name, $cipher_rounds);

        # $name ............ [string] one of 'AES', 'Anubis', 'Blowfish', 'CAST5', 'Camellia', 'DES', 'DES_EDE',
        #                    'KASUMI', 'Khazad', 'MULTI2', 'Noekeon', 'RC2', 'RC5', 'RC6',
        #                    'SAFERP', 'SAFER_K128', 'SAFER_K64', 'SAFER_SK128', 'SAFER_SK64',
        #                    'SEED', 'Skipjack', 'Twofish', 'XTEA', 'IDEA', 'Serpent'
        #                    or any <NAME> for which there is a Crypt::Cipher::<NAME> module
        # $cipher_rounds ... [integer] optional, number of rounds for given cipher

   encrypt
       Encrypts the plaintext in a single call. Returns the ciphertext as a
       binary string.  The plaintext scalar is converted to bytes using Perl's
       usual scalar stringification. Defined scalars, including numbers and
       string-overloaded objects, are accepted. "undef" is treated as an empty
       string and may emit Perl's usual "uninitialized value" warning.

          my $ciphertext = $m->encrypt($plaintext, $key, $iv);

   decrypt
       Decrypts the ciphertext in a single call. Returns the plaintext as a
       binary string.  The ciphertext scalar is converted to bytes using
       Perl's usual scalar stringification. Defined scalars, including numbers
       and string-overloaded objects, are accepted. "undef" is treated as an
       empty string and may emit Perl's usual "uninitialized value" warning.

          my $plaintext = $m->decrypt($ciphertext, $key, $iv);

   start_encrypt
       Initializes encryption mode. Returns the object itself.

          $m->start_encrypt($key, $iv);

   start_decrypt
       Initializes decryption mode. Returns the object itself.

          $m->start_decrypt($key, $iv);

   add
       Feeds data to the encryption or decryption stream. Returns a binary
       string.

       Each argument is converted to bytes using Perl's usual scalar
       stringification.  Defined scalars, including numbers and
       string-overloaded objects, are accepted. "undef" is treated as an empty
       string and may emit Perl's usual "uninitialized value" warning.

          # in encrypt mode
          my $ciphertext = $m->add($plaintext);

          # in decrypt mode
          my $plaintext = $m->add($ciphertext);

   finish
       OFB is a streaming mode and does not use padding, so "finish" returns
       an empty string. It exists for API consistency with Crypt::Mode::CBC
       and Crypt::Mode::ECB and may be safely called or omitted.

          $m->start_encrypt($key, $iv);
          my $ciphertext = '';
          $ciphertext .= $m->add($chunk1);
          $ciphertext .= $m->add($chunk2);
          $ciphertext .= $m->finish;   # returns ''

SEE ALSO
       o   CryptX, Crypt::Cipher

       o   Crypt::Cipher::AES, Crypt::Cipher::Blowfish, ...

       o   <https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Output_feedback_.28OFB.29>

perl v5.42.2                      2026-05-12               Crypt::Mode::OFB(3)