Crypt::CBC Padding Option Tests

Blowfish Cipher Tutorials - Herong's Tutorial Examples

∟Crypt::CBC Padding Option Tests

A tutorial example is provided to how different Crypt::CBC padding options behave. The 'standard' (PKCS#5) padding option seems to be the best.

In the previous tutorial, we saw that Crypt::CBC offers 6 padding options. In this tutorial, we will see some examples of how different padding options behave.

The following Perl script will be used generate those examples:

#- Crypt-CBC-Blowfish-Padding-Test.pl
#- Copyright (c) 2015 HerongYang.com, All Rights Reserved.
#-
   use Crypt::CBC;
   $algorithm = "Blowfish";
   my ($passHex, $plainHex, $padding) = @ARGV;

   print("Crypt::CBC Padding Test - output in Hex:\n");
   $passHex = "1122334455667788" unless $passHex;
   $plainHex = "" unless $plainHex;
   $padding = "standard" unless $padding;
   
   $passStr = pack("H*", $passHex);
   $plainStr = pack("H*", $plainHex);
   print("   Passphrase       ($passHex)\n");
   print("   Plaintext        ($plainHex)\n");
   print("   Padding          ($padding)\n");

   print("Creating Crypt::CBC with Passphrase...\n");
   $cipher = Crypt::CBC->new( 
      -cipher => $algorithm,
      -key => $passStr,
      -salt => '1',
      -header => 'salt',
      -padding => $padding,
      );0123456789abcdef

   print("Encrypting plaintext...\n");
   $cipherStr = $cipher->encrypt($plainStr);
   $cipherHex = unpack("H*", $cipherStr);
   print("   Cipher Output    ($cipherHex)\n");

   $headerNameHex = substr($cipherHex,0,16);
   $headerValueHex = substr($cipherHex,16,16);
   $realCipherHex = substr($cipherHex,32);
   print("   Header Name      ($headerNameHex)\n");
   print("   Header Value     ($headerValueHex)\n");
   print("   Ciphertext       ($realCipherHex)\n");

   $passStr = $cipher->passphrase();
   $passHex = unpack("H*", $passStr);
   print("   Pass Phrase      ($passHex)\n");

   $saltStr = $cipher->salt();
   $saltHex = unpack("H*", $saltStr);
   print("   Salt             ($saltHex)\n");

   $ivStr = $cipher->iv();
   $ivHex = unpack("H*", $ivStr);
   print("   IV               ($ivHex)\n");
      
   print("Decrypting ciphertext...\n");
   $decryptStr = $cipher->decrypt($cipherStr);
   $decryptHex = unpack("H*", $decryptStr);
   print("   Decrypted text   ($decryptHex)\n");

   print("Getting Padded Plaintext...\n");
   $cipher = Crypt::CBC->new( 
      -cipher => $algorithm,
      -key => $passStr,
      -salt => '1',
      -header => 'salt',
      -padding => 'none',
      );
   $decryptStrPadded = $cipher->decrypt($cipherStr);
   $decryptHexPadded = unpack("H*", $decryptStrPadded);
   print("   Padded Plaintext ($decryptHexPadded)\n");

Example 1 - 'standard' (PKCS#5) padding on a full block:

C:\herong>perl Crypt-CBC-Blowfish-Padding-Test.pl \
   1122334455667788 0123456789abcdef standard
   
Crypt::CBC Padding Test - output in Hex:
   Passphrase       (1122334455667788)
   Plaintext        (0123456789abcdef)
   Padding          (standard)
Creating Crypt::CBC with Passphrase...
Encrypting plaintext...
   Cipher Output    (53616c7465645f5f80bd5c7cab632670
                     05880f479ada3d75c496ec8b92f67788)
   Header Name      (53616c7465645f5f)
   Header Value     (80bd5c7cab632670)
   Ciphertext       (05880f479ada3d75c496ec8b92f67788)
   Pass Phrase      (1122334455667788)
   Salt             (80bd5c7cab632670)
   IV               (74fa2dc14decd610)
Decrypting ciphertext...
   Decrypted text   (0123456789abcdef)
Getting Padded Plaintext...
   Padded Plaintext (0123456789abcdef0808080808080808)
                                     ----------------
                                     padding

Example 2 - 'standard' (PKCS#5) padding on a half block:

C:\herong>perl Crypt-CBC-Blowfish-Padding-Test.pl \
   1122334455667788 01234567 standard
   
Crypt::CBC Padding Test - output in Hex:
   Passphrase       (1122334455667788)
   Plaintext        (01234567)
   Padding          (standard)
Creating Crypt::CBC with Passphrase...
Encrypting plaintext...
   Cipher Output    (53616c7465645f5fbd05365dbf81b68dc993d497767c6ed9)
   Header Name      (53616c7465645f5f)
   Header Value     (bd05365dbf81b68d)
   Ciphertext       (c993d497767c6ed9)
   Pass Phrase      (1122334455667788)
   Salt             (bd05365dbf81b68d)
   IV               (d387a235a1185750)
Decrypting ciphertext...
   Decrypted text   (01234567)
Getting Padded Plaintext...
   Padded Plaintext (0123456704040404)
                             --------
                             padding

Example 3 - 'oneandzeroes' padding on a full block:

C:\herong>perl Crypt-CBC-Blowfish-Padding-Test.pl \
   1122334455667788 0123456789abcdef oneandzeroes
   
Crypt::CBC Padding Test - output in Hex:
   Passphrase       (1122334455667788)
   Plaintext        (0123456789abcdef)
   Padding          (oneandzeroes)
Creating Crypt::CBC with Passphrase...
Encrypting plaintext...
   Cipher Output    (53616c7465645f5f27a2d3069672a6e9
                     f0656434f0047185dea87f8efb582fa7)
   Header Name      (53616c7465645f5f)
   Header Value     (27a2d3069672a6e9)
   Ciphertext       (f0656434f0047185dea87f8efb582fa7)
   Pass Phrase      (1122334455667788)
   Salt             (27a2d3069672a6e9)
   IV               (466af4f00d3194c7)
Decrypting ciphertext...
   Decrypted text   (0123456789abcdef)
Getting Padded Plaintext...
   Padded Plaintext (0123456789abcdef8000000000000000)
                                     ----------------
                                     padding

Example 4 - 'oneandzeroes' padding on a half block:

C:\herong>perl Crypt-CBC-Blowfish-Padding-Test.pl \
   1122334455667788 01234567 oneandzeroes
   
Crypt::CBC Padding Test - output in Hex:
   Passphrase       (1122334455667788)
   Plaintext        (01234567)
   Padding          (oneandzeroes)
Creating Crypt::CBC with Passphrase...
Encrypting plaintext...
   Cipher Output    (53616c7465645f5f334ce16204763f979e98aa2fcb9b2321)
   Header Name      (53616c7465645f5f)
   Header Value     (334ce16204763f97)
   Ciphertext       (9e98aa2fcb9b2321)
   Pass Phrase      (1122334455667788)
   Salt             (334ce16204763f97)
   IV               (9781c7f912887fd5)
Decrypting ciphertext...
   Decrypted text   (01234567)
Getting Padded Plaintext...
   Padded Plaintext (0123456780000000)
                             --------
                             padding