Lecture Notes: Blowfish What is Blowfish? Blowfish is a symmetric-key block cipher that was designed by Bruce Schneier in 1993. It is known for its speed, simplicity, and security, making it a popular choice for encryption. Key Features of Blowfish ● Block Size: Blowfish operates on 64-bit blocks of data. ● Key Length: Blowfish supports variable key lengths ranging from 32 to 448 bits. ● Number of Rounds: The number of rounds in Blowfish is variable and depends on the key length. How Blowfish Works 1. Key Expansion: The input key is expanded into a series of subkeys that are used during the encryption process. 2. Initial Permutation: The plaintext block is subjected to an initial permutation. 3. Rounds: The plaintext block is processed through multiple rounds of encryption, each consisting of the following steps: ○ Substitution: Each byte of the block is replaced with a new byte using a substitution table. ○ Permutation: The bytes of the block are rearranged using a permutation table. ○ Key Addition: A round key is added to the block. 4. Final Permutation: The final round is followed by a final permutation. Advantages of Blowfish ● Speed: Blowfish is a relatively fast encryption algorithm, making it suitable for high-performance applications. ● Security: Blowfish is considered to be a secure algorithm, with no known practical attacks. ● Flexibility: Blowfish supports a wide range of key lengths, making it adaptable to different security requirements. Disadvantages of Blowfish ● Legacy Algorithm: Blowfish is an older algorithm and may not be considered as secure as more modern algorithms like AES. ● Limited Key Length: While Blowfish supports a wide range of key lengths, the maximum key length of 448 bits may be considered insufficient for some applications. Conclusion Blowfish remains a popular and efficient encryption algorithm, despite being somewhat older. It is still considered to be secure for many applications, especially when used with appropriate key lengths and security practices. However, for the highest level of security, more modern algorithms like AES may be preferred.