Blowfish Cipher Tutorials - Herong's Tutorial Examples

∟PHP Mcrypt Extension for Blowfish

∟"ncfb/nofb" for Block Chaining Ciphers

This section provides a tutorial example on how to use 'ncfb' and 'nofb' mode codes to perform standard block chaining cipher operations using the PHP Mcrypt mcrypt_encrypt() function with Blowfish algorithm.

After reading again the PHP Mcrypt documentation at http://php.net/manual/en/intro.mcrypt.php, I noticed that this "CFB/OFB are 8bit by default." statement in the introduction paragraph.

This tells me that both "cfb" and "ofb" mode codes in the Mcrypt extension represent a byte (8-bit) chaining cipher operation, not the standard block chaining cipher operation.

If you want standard block chaining cipher operations in CFB and OFB modes, you need to use "ncfb" and "nofb" codes.

Test 1: Re-run a CFB 2-block test vector with "ncfb" mode code. The result should match the expected ciphertext: 

C:\herong>php Blowfish-Block-Chaining-Cipher.php \
   0000000000000000 E1C030E74C14D2614EF997456198DD78 ncfb \
   0000000000000000 af39a7a22d8c0f19ce94e96f7a22ac91
   
Secret Key: 0000000000000000 + IV: 0000000000000000
Plaintext: e1c030e74c14d2614ef997456198dd78
Oper. Mode: ncfb
Ciphertext: af39a7a22d8c0f19ce94e96f7a22ac91
PHP Result: af39a7a22d8c0f19ce94e96f7a22ac91
Validation: 1

Test 2: Re-run an OFB 2-block test vector with "ncfb" mode code. The result should match the expected ciphertext: 

C:\herong>php Blowfish-Block-Chaining-Cipher.php \
   0000000000000000 E1C030E74C14D2614EF997456198DD78 nofb \
   0000000000000000 af39a7a22d8c0f19af39a7a22d8c0f19

Secret Key: 0000000000000000 + IV: 0000000000000000
Plaintext: e1c030e74c14d2614ef997456198dd78
Oper. Mode: nofb
Ciphertext: af39a7a22d8c0f19af39a7a22d8c0f19
PHP Result: af39a7a22d8c0f19af39a7a22d8c0f19
Validation: 1

Conclusion: the PHP Mcrypt extension uses "cfb" and "ofb" mode codes for byte chaining cipher operations, and "ncfb" and "nofb" mode codes for block chaining cipher operations. PHP Mcrypt Web page does a poor job to explain these differences.

Table of Contents

 About This Book

 Blowfish Cipher Algorithm

 Perl Crypt::Blowfish Module

 Perl Crypt::ECB Perl Module

 Perl Crypt::CBC Module

 Perl Crypt::CFB Perl Module

 OpenSSL "enc -bf-ecb" for Blowfish/ECB Encryption

 OpenSSL "enc -bf-cbc" for Blowfish/CBC Encryption

 OpenSSL "enc -bf-cfb" for Blowfish/CFB Encryption

 OpenSSL "enc -bf-ofb" for Blowfish/OFB Encryption

►PHP Mcrypt Extension for Blowfish

 What is PHP Mcrypt Extension

 PHP Mcrypt Blowfish Block Cipher

 Mycrypt Blowfish Block Chaining Cipher

►"ncfb/nofb" for Block Chaining Ciphers

 Performing CFB Operation Manually

 php_blowfish.php - PHP Blowfish Demo

 Blowfish 8-Bit Cipher in PHP

 References

 Full Version in PDF/EPUB