Encryption and Decryption Using Blow Fish Algorithm

8/11/2019 Encryption and Decryption Using Blow Fish Algorithm

1/6

1. Encryption and decryption using Blow Fish algorithm

Abstract:

Blowfish, a new secret-key block cipher, is proposed. It is a Feistel network, iterating a

simple encryption function 16 times. The block size is 64 bits, and the key can be any

length up to 448 bits. Although there is a complex initialization phase required before any

encryption can take place, the actual encryption of data is very efficient on large

microprocessors.

The cryptographic community needs to provide the world with a new encryption standard.

DES [16], the workhorse encryption algorithm for the past fifteen years, is nearing the end

of its useful life. Its 56-bit key size is vulnerable to a brute-force attack [22], and recent

advances in differential cryptanalysis [1] and linear cryptanalysis [10] indicate that DES is

vulnerable to other attacks as well.

If the world is to have a secure, unpatented, and freely- available encryption algorithm by

the turn of the century, we need to develop several candidate encryption algorithms now.

These algorithms can then be subjected to years of public scrutiny and cryptanalysis. Then,

the hope is that one or more candidate algorithms will survive this process, and can

eventually become a new standard.

This paper discusses the requirements for a standard encryption algorithm. While it may notbe possible to satisfy all requirements with a single algorithm, it may be possible to satisfy

them with a family of algorithms based on the same cryptographic principles

Existing System:

Advanced Encryption Standard was proposed by National Institute of Standard and

technology (NIST) in order to replace DES. The only known attack to AES is the brute force

attack that allows an attacker to test combination of characters in order to break the

security. However, Brute Force is not an easy job even for a super computer if the number

of combination is arbitrarily high.


2/6

Proposed system:

Blowfish is the most commonly used algorithm around the world, developed by Bruce

Schneier, the president of Counterpane Systems, a firm that deals with cryptography and

security. Blowfish is known to be the secret-key cipher that uses a variable number of bits

ranging from 16 - 448 bits and encrypts the data 16 times to make it impossible for a

hacker to decrypt it. Until now, no attack has been discovered to break the blowfish

encryption.

Performance Comparison

As far as performance comparison is confirmed, AES and blowfish perform better in

comparison to others.

For a data of about 256 MB, following were the results.

The performance of each algorithm depends on the configuration of the system used. These

tests were conducted on P4 2.1 GHZ CPU running Windows XP SP1.

The above test clearly shows that Blowfishis the best of all, where the performance is very

high. Also, AES had a high performance rate in comparison to DES and 3DES, and the

throughput is almost 1/3rdof them.

Module Discription:

Encryption Algorithm:

Blowfish is a variable-length key block cipher. It is suitable for applications where thekey does not change often, like a communications link or an automatic file encryptor. It is

significantly faster than most encryption algorithms when implemented on 32-bit

microprocessors with large data caches.

Encryption

Blowfish has 16 rounds.The input is a 64-bit data element, x.

Divide x into two 32-bit halves: xL, xR.

Then, for i = 1 to 16:


3/6

xL = xL XOR Pi

xR = F(xL) XOR xR

Swap xL and xR

After the sixteenth round, swap xL and xR again to undo the last swap.Then, xR = xR XOR P17 and xL = xL XOR P18.

Finally, recombine xL and xR to get the ciphertext.

Decryption Algorithm;

The decryption algorithm of a block cipher should be identical to encryption algorithm step by

step in reverse order. But for Blowfish cipher, the encryption algorithm is so well designed, thatthe decryption algorithm is identical to the encryption algorithm step by step in the same order,only with the sub-keys applied in the reverse order.

To help us to approve the decryption algorithm, we have to write the encryption algorithm andthe decryption algorithm with temporary variables.

Encryption algorithm with temporary variables:

Input:

T: 64 bits of clear text

P1, P2, ..., P18: 18 sub-keys

F(): Round function

Output:

C: 64 bits of cipher text

Algorithm:

(L0, R0) = T, dividing T into two 32-bit parts

L1 = L0 XOR P1

R2 = R0 XOR F(L1) XOR P2

L3 = L1 XOR F(R2) XOR P3


L5 = L3 XOR F(R4) XOR P5R6 = R4 XOR F(L5) XOR P6






R12 = R10 XOR F(L11) XOR P12

L13 = L11 XOR F(R12) XOR P13

R14 = R12 XOR F(L13) XOR P14


4/6

L15 = L13 XOR F(R14) XOR P15

R16 = R14 XOR F(L15) XOR P16

L17 = L15 XOR F(R16) XOR P17

R18 = R16 XOR P18

C = (R18, L17)

Decryption algorithm with temporary variables:

Input:

CC: 64 bits of cipher text

P1, P2, ..., P18: 18 sub-keys

F(): Round function

Output:

TT: 64 bits of clear text

Algorithm:

(LL0, RR0) = CC, dividing CC into two 32-bit parts

LL1 = LL0 XOR P18

RR2 = RR0 XOR F(LL1) XOR P17

LL3 = LL1 XOR F(RR2) XOR P16













RR16 = RR14 XOR F(LL15) XOR P3LL17 = LL15 XOR F(RR16) XOR P2

RR18 = R16 XOR P1

TT = (RR18, LL17)

Here is how to approve the decryption algorithm:

Let:

T: 64 bits of clear text

C: 64 bits of cipher text encrypted from T

CC: 64 bits of cipher text

TT: 64 bits of clear text decrypted from CC

If:

CC = C

Then:

TT = T

Prove:

(LL0, RR0) = CC Initializing step in decryption

= C Assumption of CC = C


5/6

= (R18, L17) Finalizing step in encryption

LL1 = LL0 XOR P18 Applying P18 in decryption

= R18 XOR P18 Previous result

= R16 XOR P18 XOR P18 Applying P18 in encryption

= R16


Applying P17 in decryption

= L17 XOR F(R16) XOR P17

Previous result

= L15 XOR F(R16) XOR P17 XOR F(R16) XOR P17

Applying P17 in encryption

= L15

......


Applying P2 in decryption

= R2 XOR F(L1) XOR P2

Previous result= R0 XOR F(L1) XOR P2 XOR F(L1) XOR P2

Applying P2 in encryption

= R0

RR18 = RR16 XOR P1 Applying P1 in decryption

= L1 XOR P1 Previous result

= L0 XOR P1 XOR P1 Applying P1 in encryption

= L0

TT = (RR18, LL17) Finalizing step in decryption

= (L0, R0) Initializing step in encryption

= T

Software Requirements:

Operating System : Windows XP

Front End : Java Swing

Programming tool : net beans

Hardware Requirements:

Processor : Intel Pentium IV

Cache Memory : 1MB

HDD : 40 GB

RAM : 512 MB

Processor Speed : 600 MHz


6/6

Display Type : VGA

Mouse : Logitech

Monitor : 15 Samsung Color Monitor

Documents

Encryption and Decryption Using Blow Fish Algorithm