Lecture 2 : Basic Cryptogrphy

::Cryptography Concept

Disguise the information in such a way that it meaning make a unintelligible to an authorized person. So we have many way to prevent others to read or manipulate our message content.

::Cryptography Terminology

There are many term in cryptography that i had learn such as plaintext, ciphertext, encrypt and decrypt.


::Cryptography Algorithm

Symmetric algorithms P = D (K,E (K,P))

qAsymmetric algorithms P=D(Kd, E(Ke, P))

Symmetric Cryptography Principles

Symmetric Cryptography Requirements

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1 ) two requirements for secure use of symmetric encryption:
* a strong encryption algorithm
* a secret key known only to sender / receiver

2) mathematically have: C = EK(P) P = DK(C)
3) assume encryption algorithm is known implies a secure channel to distribute key

Encryption using Asymmetric Cryptography

Methods use in Cryptography Algorithm

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Substitution
a) monoalphabetic substitution
- Formed by shifting the letters of the original alphabet
b) polyalphabetic substitution
- Extension of monoalphabetic substitution system
- Using Vigenere Tableau

Transposition
a) unkeyed transposition
- Rearrange letters by using matrix
b) keyed transposition
- Rearrange letters by using matrix where the size of matrix is determined by the length of the key used.