Lab 4 : Cryptography Extended

Caesar Cipher

A cipher or cryptosystem is a method for message concealment.
The key provides the means for efficient encipherment (encryption).

Plaintext – message in readable form
Ciphertext – encrypted message

example the plaintext encrypted to get the cipher text in

The term steganography is applied to the activity of hiding the existence of a
message.

Cryptanalysis gets extended to other contexts where the messages are hidden (or suspected to e hidden) in text, pictures, music, etc.

Symmetric (or classic secret-key) cryptology relies on the correspondents agreeing on key information over the key (secure) channel.

Asymmetric (public-key) requires two key steps
- one key for encipherment
- A second key for decipherment

Vigenere Cipher

Explanation
EACH column of this table forms a dictionary of symbols representing thealphabet: thus, in the A column, the symbol is the same as the letterrepresented; in the B column, A is represented by B, B by C, and so on.

To use the table, some word or sentence should be agreed on by twocorrespondents. This may be called the `key-word', or `key-sentence',and should be carried in the memory only.

In sending a message, write the key-word over it, letter for letter,repeating it as often as may be necessary: the letters of the key-wordwill indicate which column is to be used in translating each letter ofthe message, the symbols for which should be written underneath: thencopy out the symbols only, and destroy the first paper. It will now beimpossible for any one, ignorant of the key-word, to decipher the message,even with the help of the table.

RSA algorithm

The RSA algorithm is one of the earliest, yet most versatile public key algorithm

The original intent for this algorithm is for keyestablishment/transfer, signing/verification, data integrity, and encryption/decryption

To honour them, the method was referred to as the RSA Scheme. The system uses a private and a public key. To start two large prime numbers are selected and then multiplied together; n=p*q.

RSA takes advantage of the fact that prime numbers are easy to compute and factoring them is reasonably difficult