first XORing P17 and P18 to the ciphertext block, then using the P-entries in reverse order).īlowfish's key schedule starts by initializing the P-array and S-boxes with values derived from the hexadecimal digits of pi, which contain no obvious pattern (see nothing up my sleeve number). A common misconception is to use inverse order of encryption as decryption algorithm This is not so obvious because xor is commutative and associative. The final 32-bit output (see image in the upper right corner).Īfter the 16th round, undo the last swap, and XOR L with K18 and R with K17 (output whitening).ĭecryption is exactly the same as encryption, except that P1, P2.
The outputs are added modulo 2 32 and XORed to produce The S-boxes accept 8-bit input and produce 32-bit output. The F-function splits the 32-bit input into four eight-bit quarters, and uses the quarters as input to the S-boxes. XOR the F-function's output with the right half (R) of the data Use the XORed data as input for Blowfish's F-function XOR the left half (L) of the data with the r th P-array entry There are five subkey-arrays: one 18-entry P-array (denoted as K in the diagram, to avoid confusion with the Plaintext) and four 256-entry S-boxes (S0, S1, S2 andĮvery round r consists of 4 actions: Action 1 The adjacent diagram shows Blowfish's encryption routine. In structure it resembles CAST-128, which uses fixed S-boxes. Notable features of the design include key-dependent S-boxes and a highly complex key schedule.Blowfish has a 64-bit block size and a variable key length from 32 bits up to 448 bits. It is a 16-round FeistelĬipher and uses large key-dependent S-boxes.
The algorithm is hereby placed in the public domain, and can be freely used by anyone." Schneier has stated that, "Blowfish is unpatented, and will remain so in all countries. At the time Blowfish was released, many other designs were proprietary,Įncumbered by patents or were commercial or government secrets.
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Schneier designed Blowfish as a general-purpose algorithm, intended as an alternative to the aging DES and free of the problems and constraints associated with other algorithms. However, the Advanced Encryption Standard (AES) now receives more attention, and Schneier recommends Twofish for modern applications.
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Blowfish provides a good encryption rate in software and no effective cryptanalysis of
Blowfish is a symmetric-key block cipher, designed in 1993 by Bruce Schneier and included in many cipher suites and encryption products.