- Block cipher: 64-bit block
- Variable key length: 32 bits to 448 bits
- Designed by Bruce Schneier
- Much faster than DES and IDEA
- Unpatented and royalty-free
- No license required
Blowfish is a symmetric block cipher that can be used as a drop-in replacement for DES or IDEA. It takes a variable-length key, from 32 bits to 448 bits, making it ideal for both domestic and exportable use. Blowfish was designed in 1993 by Bruce Schneier as a fast, free alternative to existing encryption algorithms. Since then it has been analyzed considerably, and it is slowly gaining acceptance as a strong encryption algorithm. Blowfish is unpatented and license-free, and is available free for all uses.
A graphical representation of the Blowfish algorithm appears in Figure 1. In this description, a 64-bit plaintext message is first divided into 32 bits. The “left” 32 bits are XORed with the first element of a P-array to create a value I'll call P', run through a transformation function called F, then XORed with the “right” 32 bits of the message to produce a new value I'll call F'. F' then replaces the “left” half of the message and P' replaces the “right” half, and the process is repeated 15 more times with successive members of the P-array. The resulting P' and F' are then XORed with the last two entries in the P-array (entries 17 and 18), and recombined to produce the 64-bit ciphertext.
Figure 2: Graphic representation of F
