Modern Cryptography – Part 1

Venue : BK7, Building FTMK.
Date : 12-8-2009
Time : 9.00 a.m. – 10.50 a.m.

After understanding the concept of basic cryptography through the two lectures previously, we have learnt something much deeper about the cryptography for today’s lecture. Yeah, the title of the slides today is “Modern Cryptography”. It was taught in the same place, and was being taught by the same lecturer, Mr Zaki. Topics to be covered in this chapter are:

• Modern Cryptography Algorithm


• Block and Stream


• DES


• AES


• MAC


• Digital Signature, RSA

However, Mr Zaki managed to cover until the topic AES only because everyone in the class felt dizzy and scared to continue after listening the algorithms used in DES and AES (p/s: that was really though and I do not think that I am able to remember them in a day, oh my god!). The lecture began with a brief explanation about Modern Cryptography Algorithm given by Mr Zaki. In modern cryptography, the ciphers use a sequence of binary digits such as ASCII most of the time. Basically, Exclusive OR (XOR or Å) is the method used to combine two bits since modern ciphers applying binary digits on their algorithm. The four results of XOR are:

• 0 Å 0 = 0


• 0 Å 1 = 1


• 1 Å 0 = 1


• 1 Å 1 = 0

After that, Mr Zaki explained about the differences between Stream Ciphers and Block Ciphers. Stream Ciphers is the process to convert one symbol of plaintext immediately into a symbol of ciphertext; whereas Clock Ciphers is the process to encrypt a group of plaintext symbols as one block. The next topic after this was Data Encryption Standards (DES). The algorithm for DES is very complicated, so how it works? First, divide the plaintext 64 bit blocks with a key of 56 bits(with 8 bit parity). Then, process through 16 round of Expansion, substitution, key mixing and permutation process. The diagram below depicts how it actually works:


The last topic for today is Advance Encryption Standard (AES). It is used to replace DES. Instead of using 64 bits, AES uses 128 bit data and 128 or 192 or 256 bit keys. Mr Zaki taught this topic by using a flash clip, so it was quite interesting although the algorithm is much complicated than DES. We need time to digest the two algorithms, so everyone asked Mr Zaki to stop there and continue next week. Hope that next week won’t have this kind of algorithms to learn any more before i can understand algorithms just now… ^^