Lab 18th August 2009

Mr. Zaki was covered 2 labs on 18^th August which were Lab 4, Cryptography Extended and Lab 5, Web Application Security. In Lab 4 has describes about the Symmetric and Asymmetric cryptography. The basic principle in Symmetric Key Cryptography is the both the parties involved in the communication must agree on the encryption key in advance. This means that both parties use the same key. One of the simplest forms is sometimes known as the Caesar cipher which is used by Julius Caesar to conceal messages. The process is simply one of shifting the alphabet so many places in one direction or another. However, the cipher text encrypted using Caesar cipher method is easily broken by using a brute force attack. In order to improve the deciphering process, we can use the Vigeneré Cipher method. This is a method of encrypting the alphabet text by using a series of different Caesar ciphers based on the letters of a keyword. It is a simple form of polyalphabetic substitution. So, we are going to use simple substitution cipher text method to encrypt or decrypt in task 1 and encrypt and decrypt using Vigeneré Cipher method in the task 2.

The term Asymmetric Cryptography essentially means public key cryptography. The usual way public key cryptography works is that one person has the private key and keeps it safe not letting anyone else to know. Then everyone is told the public key which will enable them to unlock the private key and read the data. RSA algorithm is an asymmetric algorithm and plays a key role in public key cryptography. It is widely used in electronic commerce protocols. The algorithm was described in 1977 by Ron Rivest, Adi Shamir and Len Adleman who were all at MIT at the time. The letters of RSA are the initials of their surnames. In this part, Mr. Zaki has showed us how to calculate the RAS algorithm in order to generate a public key and a private key. I was confused because the calculation is quite complicated. Thus, we need to know the formula to calculate RSA algorithm when doing the task 3.