"bf-cbc" Cipher on Multiple Blocks

Blowfish Cipher Tutorials - Herong's Tutorial Examples

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

∟"bf-cbc" Cipher on Multiple Blocks

A tutorial example is provided to show you how multiple plaintext blocks are encrypted in CBC operation mode. The encryption of each plaintext block is impacted by the encryption of the previous block.

Since CBC operation mode supports multiple plaintext blocks, let's run the "enc -bf-CBC" command with longer plaintext:

C:\herong> \
   perl -e "binmode(STDOUT); print pack('H*', '0000000000000000')" \
   > 2-block.txt

C:\herong> \
   perl -e "binmode(STDOUT); print pack('H*', '0000000000000000')" \
   >> 2-block.txt

C:\herong>\local\gnuwin32\bin\openssl enc -bf-cbc -e \
   -K 00000000000000000000000000000000 -iv 0000000000000000 \
   -in 2-block.txt -out cipher.txt -nopad -p
   
salt=0200000000265301
key=00000000000000000000000000000000
iv =0000000000000000

C:\herong>perl -e "while (read(STDIN,$_,1)){print unpack('H*',$_);}" \
   < cipher.txt
   
4ef997456198dd78 e1c030e74c14d261
---------------- ----------------
    block 1           block 2
    

C:\herong> \
   perl -e "binmode(STDOUT); print pack('H*', '0000000000000000')" \
   > 3-block.txt

C:\herong> \
   perl -e "binmode(STDOUT); print pack('H*', '0000000000000000')" \
   >> 3-block.txt

C:\herong> \
   perl -e "binmode(STDOUT); print pack('H*', '0000000000000000')" \
   >> 3-block.txt

C:\herong>\local\gnuwin32\bin\openssl enc -bf-cbc -e \
   -K 00000000000000000000000000000000 -iv 0000000000000000 \
   -in 3-block.txt -out cipher.txt -nopad -p
   
salt=0200000000265E01
key=00000000000000000000000000000000
iv =0000000000000000

C:\herong>perl -e "while (read(STDIN,$_,1)){print unpack('H*',$_);}" \
   < cipher.txt
   
4ef997456198dd78 e1c030e74c14d261 53e3b2a5a3bc297f
---------------- ---------------- ----------------
    block 1           block 2          block 3

The output matches my expectation. In CBC operation mode, the encryption of each plaintext block is impacted by the encryption of the previous block. This behavior definitely improves the strength of the encryption of the entire plaintext stream.