6. Symmetric Block Cipher BLOWFISH Performance. Memory space. 3. Simplicity The length of the key. The length of the data block is 64.

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1 belongs to the same class of conventional symmetric ciphers. The basic principles of have been published in 1994 by Bruce Schneier, as an alternative to the Data encryption standard (DES) to satisfy the next requirements. 1. Performance. The ciphering and deciphering procedures require minimal CPU time. ciphers 64 bit data block based on the bit microprocessor during the 18 cycle per byte. 2. Memory space. requires computer memory space less than 5 Kbytes. 3. Simplicity. The structure of very simple for implementation, as well as for cryptographic strength evaluation. 4. The length of the key. The length of the key should be enough to eliminate so called direct attack by trying to apply all possible values of keys. At the same time should allow to high rate of enciphering and deciphering procedure. That is why offers variable key length. It takes value in between and 448 bits. 5. The length of the data block is 64. operates with 64 plaintext blocks and corresponding 64 ciphertext blocks. At nowadays have been implemented within the numerous product and have got excellent estimates. 1

2 Sub keys and S-matrixes calculation Key. allows to use the key with the length from one bit word K 1 up to the fourteen bit words K 1,K 2,,K j, 1 j 14. Sub Keys. Sub keys store in the P-array as P 1,P 2,,P 18. words S-matrixes. There are four S-matrixes. Each matrix consists of 256 -bit S 1,0,S 1,1,,S 1,255 S 2,0,S 2,1,,S 2,255 S 3,0,S 3,1,,S 3,255 S 4,0,S 4,1,,S 4,255 2

3 Sub keys and S-matrixes calculation Algorithm 1. or P-array and S-matrixes initialization the number π is used. Such a way that the P 1 equals to the first bits of π the next bits assigns to P 2 and so on. irst of all initialization concerns the P-array, then four S-matrixes. or the hexadecimal notation there are P 1 =2436A88, P 2 =85A308D3,, S 4,254 =57DE3, S 4,255 =3AC372E6. 2. Bit wise XOR operation is perform between P-array and K-array, repeating the value of key words if necessary. or example, for the maximal length key P 1 =P 1 K 1, P 2 =P 2 K 2,,P 14 =P 14 K 14,P 15 =P 15 K 1,,P 18 =P 18 K Based on the current value of P- and K-arrays 64 bits all zero data block is enciphering, then the 64 for ciphertext is used as a new values for P 1 and P 2, as well as plaintext data block for the next iteration. New value of P- and K-arrays is used for following enciphering iteration to get new values for P 3 and P 4. This procedure can be presented as P 1,P 2 [0], P 3,P 4 [P 1 P 2 ], P 5,P 6 [P 3 P 4 ], P 17,P 18 [P 15 P 16 ], S 1,0,S 1,1 [P 17 P 18 ], S 1,2,S 1,3 [S 1,0 S 1,1 ],,S 4,254,S 4,255 [S 4,252 S 4,253 ]. 3

4 P 1 64 bit LE 0 bit bit RE 0 LE 1 RE 1 P 16 LE 15 RE 15 Enciphering or i=1 to 16 do LE 17 =RE 16 P 18 RE 17 =LE 16 P 17 RE i =LE i-1 P i LE i =[RE i ]RE i-1 LE 16 RE 16 P 18 P 17 LE 17 RE 17 4

5 P bit LD 0 bit bit RD 0 LD 1 RD 1 P 3 LD 15 RD 15 Deciphering or i=1 to 16 do LD 17 =RD 16 P 1 RD 17 =LD 16 P 2 RD i =LD i-1 P 19-i LD i =[RD i ]RD i-1 LD 16 RD 16 P 1 P 2 LD 17 RD 17 5

6 L i-1 R i-1 P i S-matrix S-matrix #1 S-matrix #2 S-matrix #3 S-matrix #4 + + L i 6 R i

7 There are two basic operation for implementation: + addition by modulo 2 16 bit wise Exclusive Or operation. All iteration during ciphering and deciphering includes complex function, as well as substitutions defined by S-matrixes. irst of all bits input value is divided into four pieces a, b, c, d, 8 bits each. According to the 8 bits code and S-matrix, new value is generated as the output code. our S-matrixes are generated operands for function. General expression for this function is: (a, b, c, d)=(s 1,a +S 2,b )S 3,c +S 4,d 7

8 has next advantages: 6. Symmetric Block Cipher 1. Compare with DES algorithm S-matrixes for are depending on the key. 2. During each iteration there are data transformation for both part of the data block left and right. 3. The enciphering and deciphering rate for is the highest compare with classical symmetric algorithms. Algorithm Number of cycles for iteration Number of iteration Number of cycles for data block enciphering DES IDEA Triple DES