# Block cipher | Information Systems homework help

Block Cipher

Question:

1. Let temp_block denote a Sage variable that contains the output of the first application of function fK (f_K in the Sage example code) while encrypting with Simplified DES.  Using subroutines from the example sage Code, write sage code to recover the input block passed to Simplifed DES Decrypt.  Meaning reverse the first steps in Simplified DES Encrypt. You may assume that you have the first round key in a variable K1.
2. Using subroutines from the Sage example code for Simplified DES, write a function to compute Simplified DES Decrypt.

Online: If you do not have Sage installed on your computer and just want to try some commands, use it online at –

http://sagecell.sagemath.org

Sage Online Tutorial:

https://doc.sagemath.org/html/en/tutorial/index.html

GettingStartedSage.doc

Matrix Linear Algebra Examples.doc

Programming Sage.doc

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