Blowfish is a symmetric encryption method designed in 1993 by Bruce Schneier. It uses a 64-bit block size, which means it takes chunks of 64 bits of data to encrypt. The goal was to create a fast, free alternative to older encryption methods like DES and IDEA. It’s unpatented and open to anyone, but while it outpaces both DES and IDEA in speed, its limited 64-bit block size leaves it vulnerable to specific attacks like birthday attacks and timing attacks.
To tackle these issues, Schneier introduced Twofish, which utilizes a sturdier 128-bit block size. He suggests that users migrate from Blowfish to Twofish due to the latter’s improved security. Despite the concerns, Blowfish hasn’t been completely cracked through standard cryptanalysis, and it remains in use today in various encryption products, including virtual private networks and password managers.
At its core, Blowfish is symmetric encryption, meaning the same key encrypts and decrypts data. It processes 64 bits of plaintext at a time using a key that can range from 32 to 448 bits. Longer keys mean better security. The encryption involves 16 rounds of what’s called a Feistel structure. It splits the 64-bit block into two 32-bit sections, manipulating each half with a series of operations. Once the 16 rounds finish, the two halves combine to form the ciphertext. Decryption simply reverses the process using the same key.
The encryption process begins with generating 18 subkeys from a key expansion phase. The algorithm uses a fixed string of pi to initialize these subkeys and generate four S-boxes—essential tables for the process. Each round of encryption takes one of the subkeys from the P-array, continuously modifying the data through a mix of substitution and permutation operations.
For instance, if you take the phrase “Hi world,” it gets split into 64 bits, broken down further into two 32-bit halves. Each half goes through the encryption process with the subkeys, winding through the 16 rounds until a final ciphertext is produced.
Blowfish packs a punch in terms of speed and efficiency. It’s faster than its predecessors and allows for variable key sizes, offering flexibility for users. It’s free to use and, after the initial setup phase, is efficient in processing data. However, if you need to change keys frequently, its speed can take a hit. The small block size can also expose it to certain vulnerabilities. Plus, without built-in authentication or integrity checks, there’s a heightened risk of data leaks.
Blowfish still finds a place in many applications today, including bulk encryption, password management, and mobile processing. Some well-known software products like PasswordWallet and PeaZip utilize it for secure password storage and file management. Though many platforms have shifted to newer encryption methods, Blowfish remains part of the encryption landscape, ensuring data remains clandestine in its encrypted form.