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- Cryptography And Network Security - CNS
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**Biju Patnaik University of Technology BPUT - BPUT**- Computer Science Engineering
- B.Tech
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This structure is a particular form of the substitution-permutation network (SPN) Feistel network depends on the choice of the following parameters and design features Block size, Key size, Number of rounds, Subkey generation algorithm, Round function, Fast software encryption/decryption, Ease of analysis Feistel Encryption and Decryption

Simplified DES educational rather than a secure encryption algorithm. It has similar properties and structure to DES with much smaller parameters Simplified DES Scheme The S-DES encryption algorithm takes an 8-bit block of plaintext (example: 10111101) and a 10-bit key as input and produces an 8-bit block of ciphertext as output. The S-DES decryption algorithm takes an 8-bit block of ciphertext and the same 10-bit key used to produce that ciphertext as input and produces the original 8-bit block of plaintext. Involves five functions: an initial permutation (IP); a complex function labeled fK, which involves both permutation and substitution operations and depends on a key input; a simple permutation function that switches (SW) the two halves of the data; the function fK again; finally a permutation function that is the inverse of the initial permutation (IP–1). Algorithm rename these 8 bits

Key Generation for Simplified DES Plain Text Key P10 LS-1 P8 (K1) 3 5 2 7 4 10 1 9 8 6 6 3 7 4 8 5 10 9 Simplified DES Encryption Detail 1 0 1 0 0 1 2 0 1 0 1 1 3 1 0 1 1 1 4 0 0 1 0 0 5 1 0 0 0 1 6 0 1 0 1 0 7 0 1 1 1 0 8 0 1 1 1 1 9 10 10 11 1 0

LS-2 P8 (K2) IP (PT) R (IP) EP K1 XOR S0 (10 11) P4 P4 XOR L SWITCH 2 6 3 1 4 8 5 7 4 1 2 3 2 3 4 1 EP(SW(R)) XOR K2 S0 & S1 P4 XOR L IP-1 CT 1 0 0 0 1 1 0 1 0 0 0 0 1 0 0 0 0 1 0 0 0 0 1 1 1 1 0 1 1 1 1 S0 = 10 0 0 0 1 0 0 1 1 0 0 1 1 0 0 1 0 1 0 0 1 1 0 1 0 0 0 1 1 1 0 0 0 1 1 0 0 1 0 0 0 0 1 0 0 0 1 1 0 0 0 1 1 0 1 1 1 11 0 10 0 1 0 0 1 00 1 1 10 1 S1 = 0 0 0 0 0 0 0 1 0 0 1 1 0 0 1 1 1 1 0 0 1 0 1 1 0 0 1 1 1 01 0 The Data Encryption Standard (DES) Overview DES Encryption o General Depiction of DES Encryption Algorithm o Initial Permutation o Permutation Tables for DES o Details of Single Round o Calculation of F(R, K) o Definition of DES S-Boxes o Key Generation DES Decryption The Avalanche Effect Overview data are encrypted in 64-bit blocks using a 56-bit key. The algorithm transforms 64-bit input in a series of steps into a 64-bit output. The same steps, with the same key, are used to reverse the encryption DES Encryption there are two inputs to the encryption function: the plaintext to be encrypted and the key. In this case, the plaintext must be 64 bits in length and the key is 56 bits in length General Depiction of DES Encryption Algorithm processing of the plaintext proceeds in three phases. First, the 64-bit plaintext passes through an initial permutation (IP) that rearranges the bits to produce the permuted input. This is followed by a phase consisting of 16 rounds of the same function, which involves both permutation and substitution functions. o The output of the sixteenth round consists of 64 bits that are a function of the input plaintext and the key o The left and right halves of the output are swapped to produce the preoutput.

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