Understanding Blowfish Encryption Algorithm | 2023

Key Features, Encryption Process, Python Implementation, Examples and Advantages of Blowfish Algorithm | Karthikeyan Nagaraj

Karthikeyan Nagaraj
3 min readFeb 25, 2023


Blowfish is a symmetric-key block cipher encryption algorithm designed by Bruce Schneier in 1993, and it has gained popularity for its efficient encryption and decryption process.

In this article, we will explore the key features, encryption process, python implementation, examples, and advantages of Blowfish.

Key Features of Blowfish

  • Block Cipher: Blowfish is a block cipher encryption algorithm that operates on 64-bit blocks of plaintext at a time.
  • Symmetric Key Encryption: Blowfish uses a symmetric key encryption system, meaning that the same key is used for both encryption and decryption.
  • Variable Key Size: Blowfish allows for variable key sizes of up to 448 bits, making it more secure compared to other encryption algorithms.
  • Feistel Cipher: Blowfish uses the Feistel Cipher structure, which splits the plaintext into two halves and then iteratively encrypts each half using a series of mathematical operations.

Encryption Process

The encryption process of Blowfish involves the following steps:

  1. Key Generation: The encryption key is generated by applying the key expansion algorithm to the original key, which generates a series of subkeys.
  2. Initial Permutation: The 64-bit plaintext is subjected to an initial permutation.
  3. Splitting: The 64-bit block is split into two halves, each with 32 bits.
  4. Rounds: Blowfish consists of 16 rounds, with each round involving a complex sequence of substitutions and permutations to both halves of the block.
  5. Final Permutation: After the 16 rounds, a final permutation is applied to the output to produce the ciphertext.

Python Implementation of Blowfish Algorithm (Encryption):

Blowfish can be implemented in Python using the PyCrypto library, which provides cryptographic functions for secure communication. Here is an example Python program that demonstrates the encryption and decryption process using Blowfish:

In this example, we generate a random 128-bit encryption key, create a Blowfish cipher object with the encryption key, encrypt the plaintext “Hello, World!”, decrypt the ciphertext and print the results.

Decryption Process for Blowfish

The decryption process for Blowfish is essentially the reverse of the encryption process.

The ciphertext is first divided into 64-bit blocks, just like in the encryption process. The subkeys are generated in the same way as in the encryption process, using the same key schedule.

  • To decrypt a block of ciphertext, the block is first passed through the F function a total of 16 times, using the 16 subkeys in reverse order.
  • The final output of the F function is then XORed with the previous 32 bits of the ciphertext block. This is repeated for each 64-bit block of the ciphertext until all blocks have been decrypted.

Python Implementation of Blowfish Algorithm (Decryption):

Below is an example of how to implement the Blowfish encryption algorithm in Python:


Blowfish is used in various applications to provide secure communication and data protection. Some examples are:

  • Password Storage: Blowfish is used to store and protect passwords for online accounts and systems.
  • Secure File Transfer: Blowfish is used to encrypt files during transfer to prevent unauthorized access.
  • Virtual Private Networks (VPNs): Blowfish is used to encrypt VPN traffic to provide secure communication between two devices.
  • Email Encryption: Blowfish is used to encrypt email messages to protect sensitive information from being intercepted.

Advantages of Blowfish

  • Blowfish is a widely used encryption algorithm that is fast, efficient, and secure.
  • The variable key size of Blowfish makes it more secure compared to other encryption algorithms.
  • Blowfish is easy to implement and is compatible with various programming languages and platforms.


  • Blowfish is a popular encryption algorithm that provides secure communication and data protection in various applications. With its variable key size, symmetric key encryption system, and Feistel Cipher structure, Blowfish offers strong security features that make it a preferred choice for many organizations.
  • In addition, its fast and efficient encryption and decryption process, and ease of implementation in various programming languages and platforms, make it a versatile encryption algorithm.

However, it is important to note that Blowfish has been around for almost three decades and is not considered as secure as some of the newer encryption algorithms available today.

For example, the Advanced Encryption Standard (AES) is considered to be more secure than Blowfish and is widely used for sensitive data protection.

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Author: Karthikeyan Nagaraj ~ Cyberw1ng



Karthikeyan Nagaraj

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