![]() The input to the algorithm is an 8-bit block of plaintext, which we first permute using the IP function: We then go back to the pair of 5-bit strings produced by the two LS-1 functions and perform a circular left shift of 2 bit positions on each string.įinally, P8 is applied again to produce K2. Next we apply P8, which picks out and permutes 8 of the 10 bits according to the following rule: From this key, two 8-bit subkeys are produced for use in particular stages of the encryption and decryption algorithm.įirst, permute the key in the following fashion. The output of P4 is the output of the function F.Ī 10-bit key shared between sender and receiver. Next, the 4 bits produced by S0 and S1 undergo a further permutation as follows: The entry in that row and column, in base 2, is the 2-bit output. ![]() The first and fourth input bits are treated as a 2-bit number that specify a row of the S-box, and the second and third input bits specify a column of the Sbox. The first 4 bits (first row of the preceding matrix) are fed into the S-box S0 to produce a 2- bit output, and the remaining 4 bits (second row) are fed into S1 to produce another 2-bit output. The first operation is an expansion/permutation operation: The input is a 4-bit number ( n1 n2 n3 n4). Selection of Function for Original and Modified S-Box It uses 10-bits of key for Encryption and Decryption. ![]() This Algo takes 8-bits of plaintext at a time and produces 8-bits of ciphertext. This is a program for Encryption and Decryption with Modifies & Simplified DES. We can concisely express the encryption algorithm as a composition1 of functions. The encryption algorithm 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 and finally a permutation function that is the inverse of the initial permutation (IP –1). 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. The S-DES encryption algorithm takes an 8-bit block of plaintext and a 10-bit key as input and produces an 8-bit block of ciphertext as output. ![]()
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