Crypt::Mode::CFB(3) User Contributed Perl Documentation Crypt::Mode::CFB(3)
NAME
Crypt::Mode::CFB - Block cipher mode CFB [Cipher feedback]
SYNOPSIS
use Crypt::Mode::CFB;
my $m = Crypt::Mode::CFB->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 CFB 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::CFB->new('AES');
new
my $m = Crypt::Mode::CFB->new($name);
#or
my $m = Crypt::Mode::CFB->new($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
CFB 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(3), Crypt::Cipher(3)
o Crypt::Cipher::AES(3), Crypt::Cipher::Blowfish(3), ...
o <https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Cipher_feedback_.28CFB.29>
perl v5.34.3 2026-05-11 Crypt::Mode::CFB(3)
cryptx 0.89.0 - Generated Tue May 12 07:47:12 CDT 2026