Question

What are the weaknesses of DES? Why triple DES is better than Double DES?

What is Trusted Third Party (TTP)? What are the problems with TTP?

Using Caesar cipher algorithm and key value = 4, encrypt the plain text “Network Security”. Show your work

Using the following Polybius Square encrypt the plaintext “CRYPTOGRAPHY”. Show your work

Answer 1

1.Weakness of DES(Small amount of weakness)

• 1. Weak keys : the key that is selected on the rounds is considered as a problem . During splitting of keys to two half and exchanging  them might end up the same result if they have continuous 1’s and 0’s. which ends up in using the same key through out the 16-cycles

• There can be same output from the S-Boxes on different inputs on permutationand called Semi weak keys.
• If the message is encrypted with a particular key, and is taken 1’s compliment of that encryption will be same as that of the encryption of the compliment message and compliment key.

2.triple DES is better than double DES

• Triple DES is more secure than double DES
• if we take a few plain texts and encode it and if we take a few encrypted valuess and start to decrpypt we need to check for almost middle with same values .this will reveal the key.
• triple DES will avoid this becuase of middle step .ie we need to check for the middle value and we cant simple look for the 1st and last oprtn poduce same result

3.TTP

• A trusted third party (TTP) is an entity in a domain that is trusted to perform a specific service.

• it facilitates the interactions between two parties who both trust third party.

• third party checks for critical transaction communications btwn them based on creating fraudlent ditital content

4.problems with TTP

• costly and risky

5.

plain text:NETWORK SECURITY

KEY=4

ABCDEFGHIJKLMNOPQRSTUVWXYZ

when key is added

EFGHIJKLMNOPQRSTUVWXYZABCD

here N gets replaced with R

E gets replaced with I

T gets replaced with X

and so on

encrypted text= RIXASVO WIGYVMXC

6.