Lecture 3: Block Ciphers and the Data Encryption Standard ...

Lecture 3: Block Ciphers and the Data EncryptionStandardLecture Notes on Computer and Network Security by Avi Kak 26, 20213:43pm 2021 Avinash Kak, Purdue UniversityGoals: To introduce the notion of a Block cipher in the modern context. To talk about the infeasibility ofideal Block Ciphers To introduce the notion of theFeistel Cipher Structure To go overDES, the Data Encryption Standard To illustrate important DES steps with Python and Perl codeCONTENTSS ection Block of the Encryption Key for the Ideal Block Feistel Structure for Block Description of Each Round in the10 Feistel in Ciphers Based on the Feistel : The Data Encryption Round of Processing in S-Box for the Substitution Step in Each Substitution P-Box Permutation in the Feistel DES Key Schedule.

depends on R and the encryption key. The operation carried out on the left half L is referred to as the Feistel Function. The permutation step at the end of each round consists of swapping the modified L and R. Therefore, the L for the next round would be R of the current round. And R for the next round be the output L of the current round.

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