Blowfish Cipher Tutorials - Herong's Tutorial Examples - Version 1.21, by Dr. Herong Yang
Crypt::CFB Not Requiring Padding
A tutorial example is provided to demonstrate that Crypt::CFB encryption does not require any padding to plaintext. The last XOR operation can be performed on a partial block.
In the previous tutorial, we figured out what is the default IV value used by the Crypt::CFB module. In this tutorial, we will try to see how it does the padding.
To do this, I wrote the follow example script that allows us to run Crypt::CFB encryption with any given secret key, IV and ciphertext:
#- Crypt-CFB-Blowfish-Encryption.pl
#- Copyright (c) 2015, HerongYang.com, All Rights Reserved.
use Crypt::CFB;
my ($keyHex, $ivHex, $plainHex) = @ARGV;
print("Crypt::CFB Encryption Test - output in Hex:\n");
$keyHex = "1122334455667788" unless $keyHex;
$ivHex = "1111111111111111" unless $ivHex;
$plainHex = "0123456789abcdef" unless $plainHex;
$keyStr = pack("H*", $keyHex);
$ivStr = pack("H*", $ivHex);
$plainStr = pack("H*", $plainHex);
print(" Secret Key ($keyHex)\n");
print(" IV ($ivHex)\n");
print(" Plaintext ($plainHex)\n");
print("Creating Crypt::CFB with secret key ...\n");
$cipher = Crypt::CFB->new($keyStr, 'Crypt::Blowfish', $ivStr);
print("Encrypting plaintext...\n");
$cipherStr = $cipher->encrypt($plainStr);
$cipherHex = unpack("H*", $cipherStr);
print(" Ciphertext ($cipherHex)\n");
print("Decrypting ciphertext...\n");
$cipher->reset();
$decryptStr = $cipher->decrypt($cipherStr);
$decryptHex = unpack("H*", $decryptStr);
print(" Decrypted text ($decryptHex)\n");
When running Crypt-CFB-Blowfish-Encryption.pl with a full block of plaintext, I got a full block of ciphertext as shown below. So no padding was added by Crypt::CFB.
C:\herong>perl Crypt-CFB-Blowfish-Encryption.pl 1122334455667788 0000000000000000 0123456789abcdef Crypt::CFB Encryption Test - output in Hex: Secret Key (1122334455667788) IV (0000000000000000) Plaintext (0123456789abcdef) Creating Crypt::CFB with secret key ... Encrypting plaintext... Ciphertext (c7de2d3fe72ea7ab) Decrypting ciphertext... Decrypted text (0123456789abcdef)
When running Crypt-CFB-Blowfish-Encryption.pl with a half block of plaintext, I got a half block of ciphertext as shown below. So no padding was added by Crypt::CFB.
C:\herong>perl Crypt-CFB-Blowfish-Encryption.pl 1122334455667788 0000000000000000 01234567 Crypt::CFB Encryption Test - output in Hex: Secret Key (1122334455667788) IV (0000000000000000) Plaintext (01234567) Creating Crypt::CFB with secret key ... Encrypting plaintext... Ciphertext (c7de2d3f) Decrypting ciphertext... Decrypted text (01234567)
Conclusion: Crypt::CFB implements CFB operation mode without padding. This is doable, because the last operation of the CFB algorithm is an XOR operation, which can be performed in a partial block of plaintext. So no need to pad the plaintext to a full block.
Last update: 2015.
Table of Contents
Installing Crypt::CFB 0.02 with ActivePerl
►Crypt::CFB Not Requiring Padding
Crypt::CFB Operation Simulation
OpenSSL "enc -bf-ecb" for Blowfish/ECB Encryption
OpenSSL "enc -bf-cbc" for Blowfish/CBC Encryption
OpenSSL "enc -bf-cfb" for Blowfish/CFB Encryption