DES and SDES cryptosystems PDF

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practice materials on DES and SDES cyptosystems....

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Tutorial 05 and 06 1 Answer: The general characteristics of the SDES algorithm are; 1. This algorithm has similar properties and structure to DES. 2. It is used in examination and instructive purpose. 3. Input and Output Block, Key, Number of Rounds, Encryption and Decryption are its working order. 4. Number of rounds: 2 5. Key (as an input): 10bit 6. Plaintext(input): 8-bit block 7. Cipher-text (output after encryption): 8-bit block 8. No. of keys used in entire process: 2 9. No. of substitution boxes: 2 10.Different kind of permutation table are used like; initial permutation, expansion permutation, permutation 10,8,4 and inverse of initial permutation. 2 Answer: The round key generation algorithm for the SDES algorithm are as follows; 1.Apply P10 to the key K (10-bit).

2.Apply LS-1 to the output of P10 from Step 01. 3.Apply P8 to the output of LS-1 from Step 02 and this gives us the first key K1 (8-bit). 4. Apply LS-2 to the LS-1 from Step 02. 5.Apply P8 to the output of LS-2 from Step 04 and this gives us the second key K2 (8-bit).

3 Answer: The encryption steps for the SDES algorithm are; 1.An Initial Permutation IP.

2.A complex function fk containing S-P operations and depends on key K. 3.A simple permutation function that switches (SW) the two halves of data. 4. The complex function fk again. 5.A permutation function IP-1.

4 Answer: It is important to utilize E/P on the 4-bit parts of the plain content amid the encryption procedure of the SDES calculation since we have plaintext of 8bit and key of 10 bit. After the round key age steps, we need to utilize two diverse keys for encryption which are of 8bit in size. At that point we partition the plaintext into two parts then we begin to figure the capacity for example FK(L,R)= (L XOR F(R.Sk),R) is the encryption procedure of Left half and Fk(R,L)= (R XOR F(L.Sk),L) OF Right 50% of plain content. We need to compute the estimation of F(R.Sk). Utilizing the correct portion of plaintext and first key (K1) where the span of plain content is 4bit and K1 is 8 bit. Here we can't encode 4bit plain content using8 bit key so we need to extend 4bit plain content into 8 bit by utilizing Expansion Permutation.

5 Answer: Decryption Steps in S-DES algorithm 1.Apply IP to cipher text

2.Calculate function using Key (K2) 3.Permutation function that switches the two halves of data 4. Calculate function using another Key (K1) 5. Apply inverse of IP at last to generate plain text

6 Answer: SDES crypto systems - Input Plaintext: 8bit - Size if key: 10bit - Key of encryption: 2 - No. of substitution boxes: 2 - Actual size of key used for encryption: 8bit

DES crypto systems - Input Plaintext: 64bit block - Size of key: 56bit - Key for encryption: 16 - No. of substitution boxes: 16 - Actual size of key used for encryption: 48bit...