Blowfish is a new secret-key block cipher designed as a Feistel network with 16 rounds. It uses a 64-bit block size and supports variable-length keys up to 448 bits. The algorithm is efficient on large microprocessors and requires an initialization phase before encryption. The paper discusses the need for a new encryption standard due to the vulnerabilities of DES and other existing algorithms. It outlines requirements for a secure, unpatented, and freely available encryption algorithm, emphasizing efficiency, simplicity, and adaptability. Blowfish must be implementable on various platforms, including special hardware, large processors, medium processors, and small processors. It should be simple to code, have a flat keyspace, no weak keys, and support easy key management. It should also be modifiable for different security levels and manipulate data in byte-sized blocks. Design decisions include using large blocks (preferably 32 bits), a scalable key size, simple operations, and precomputable subkeys. Blowfish uses a variable number of iterations and avoids linear structures. It employs key-dependent S-boxes and combines operations from different algebraic groups. Blowfish consists of a key-expansion part and a data-encryption part. The key expansion converts the key into subkeys, and the encryption uses a 16-round Feistel network. The algorithm uses XOR, addition, and array lookups. Subkeys are precomputed and stored in cache for efficiency. Blowfish is described as a variable-length key, 64-bit block cipher. It is faster than DES on 32-bit processors with large caches. The encryption process involves dividing the data into halves, applying a key-dependent permutation and substitution, and swapping the halves. Decryption is similar but uses subkeys in reverse order. The subkeys are generated using a process that involves initializing the P-array and S-boxes with a fixed string, XORing with the key, and encrypting the all-zero string. The subkeys are then used to generate the final key. Blowfish is unpatented and placed in the public domain. It is recommended for use in applications where the key does not change often. The paper also discusses possible simplifications and acknowledges the contributions of various researchers.Blowfish is a new secret-key block cipher designed as a Feistel network with 16 rounds. It uses a 64-bit block size and supports variable-length keys up to 448 bits. The algorithm is efficient on large microprocessors and requires an initialization phase before encryption. The paper discusses the need for a new encryption standard due to the vulnerabilities of DES and other existing algorithms. It outlines requirements for a secure, unpatented, and freely available encryption algorithm, emphasizing efficiency, simplicity, and adaptability. Blowfish must be implementable on various platforms, including special hardware, large processors, medium processors, and small processors. It should be simple to code, have a flat keyspace, no weak keys, and support easy key management. It should also be modifiable for different security levels and manipulate data in byte-sized blocks. Design decisions include using large blocks (preferably 32 bits), a scalable key size, simple operations, and precomputable subkeys. Blowfish uses a variable number of iterations and avoids linear structures. It employs key-dependent S-boxes and combines operations from different algebraic groups. Blowfish consists of a key-expansion part and a data-encryption part. The key expansion converts the key into subkeys, and the encryption uses a 16-round Feistel network. The algorithm uses XOR, addition, and array lookups. Subkeys are precomputed and stored in cache for efficiency. Blowfish is described as a variable-length key, 64-bit block cipher. It is faster than DES on 32-bit processors with large caches. The encryption process involves dividing the data into halves, applying a key-dependent permutation and substitution, and swapping the halves. Decryption is similar but uses subkeys in reverse order. The subkeys are generated using a process that involves initializing the P-array and S-boxes with a fixed string, XORing with the key, and encrypting the all-zero string. The subkeys are then used to generate the final key. Blowfish is unpatented and placed in the public domain. It is recommended for use in applications where the key does not change often. The paper also discusses possible simplifications and acknowledges the contributions of various researchers.