Blowfish Cipher Tutorials - Herong's Tutorial Examples - Version 1.21, by Dr. Herong Yang
"bf-cfb" Cipher with Literal Key
A tutorial example is provided to show you how to use the 'bf-cfb' (Blowfish in CFB mode) cipher with Literal Key to encrypt and decrypt binary data files.
So far we have learned both "enc -bf-ecb" and "enc -bf-cbc" commands to perform Blowfish encryption in ECB (Electronic CodeBook) and CBC (Cipher Block Chaining) operation modes. Let's move on to the "enc -bf-cfb" command for Blowfish encryption in CFB (Cipher FeedBack) operation mode.
In case you forgot how CFB (Cipher FeedBack) works, here a shortest version of the CFB algorithm:
Input: P: The plaintext in multiple blocks K: The secret key IV: The Initialization Vector E(K,B): The block encryption function Output: C: The ciphertext in multiple blocks Algorithm - CFB (Cipher FeedBack) Operation Mode: (P[1], P[2], P[3},...) = P : Split plaintext into blocks C[1] = P[1] XOR E(K, IV) Loop i over 2,3,... C[i] = P[i] XOR E(K, C[i-1]) End Loop C = (C[1], C[2], C[3},...) : Concatenate ciphertext blocks
The CFB algorithm can also be illustrated by this simple diagram:
Algorithm - CFB (Cipher FeedBack) Operation Mode: IV ---->| ---->| ---->| E(K) / E(K) / E(K) | / | / | | / | / | P[1]--XOR / P[2]--XOR / P[3]--XOR | / | / | | / | / | C[1] C[2] C[3] ...
Comparing with the ECB mode we have discussed earlier, the CFB mode does use the IV (Initialization Vector). So we need to pay attention to how to control the IV with the OpenSSL "enc -bf-cfb" command.
Similar to ECB mode tutorials, let's follow the "Literal Key" way first by running the OpenSSL "enc -bf-cfb" command with "-K" and "-iv" options. In the example below, I am trying to perform encryption on a full block of 0x00:
C:\herong> perl -e "binmode(STDOUT); print pack('H*', '0000000000000000')" > 0000000000000000.txt C:\herong>\local\gnuwin32\bin\openssl enc -bf-cfb -e -K 00000000000000000000000000000000 -iv 0000000000000000 -in 0000000000000000.txt -out cipher.txt -nopad -p salt=0200000028264901 key=00000000000000000000000000000000 iv =0000000000000000 C:\herong>perl -e "while (read(STDIN,$_,1)){print unpack('H*',$_);}" < cipher.txt 4ef997456198dd78 C:\herong>\local\gnuwin32\bin\openssl enc -bf-cfb -d -K 00000000000000000000000000000000 -iv 0000000000000000 -in cipher.txt -out decrypted.txt -nopad -p salt=0200000000265C01 key=00000000000000000000000000000000 iv =0000000000000000 C:\herong>perl -e "while (read(STDIN,$_,1)){print unpack('H*',$_);}" < decrypted.txt 0000000000000000
Pretty cool, I have successfully encrypted a block of binary zeros with "bf-cfb" cipher, and decrypted it back.
The ciphertext, 0x4ef997456198dd78, is correct, because it matches the test vector published at https://www.schneier.com/code/vectors.txt. Not that for a single plaintext block, CFB operation mode will just run Blowfish encryption on the IV, then XOR with the plaintext.
key bytes clear bytes cipher bytes 0000000000000000 0000000000000000 4EF997456198DD78
Last update: 2015.
Table of Contents
OpenSSL "enc -bf-ecb" for Blowfish/ECB Encryption
OpenSSL "enc -bf-cbc" for Blowfish/CBC Encryption
►OpenSSL "enc -bf-cfb" for Blowfish/CFB Encryption
►"bf-cfb" Cipher with Literal Key
"bf-cfb" Cipher on Multiple Blocks
"bf-cfb" Encryption Verification
"bf-cfb" Cipher with Salted Key
"bf-cfb" Cipher with Random Salt