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# Note for Cryptography And Network Security - CNS by Lingaraj Panigahy

• Cryptography And Network Security - CNS
• Note
• Biju Patnaik University of Technology BPUT - BPUT
• Computer Science Engineering
• B.Tech
• 1062 Views
Lingaraj Panigrahy
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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

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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

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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

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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.