Shannon and 5 good criteria of a good cipher

Shannon and 5 Criteria of a good cipher

Sina Manavi [email protected]

03.11.2011

(April 30, 1916 – February 24, 2001)

American mathematician, electronic engineer, and cryptographer.

Graduated from MIT known as "the father of

information theory“.

Claude Elwood Shannon Shannon Biography

Plaintext: text to be protected

Cipher (or cypher): algorithm for performing encryption or decryption

Ciphertext: encrypted/decrypted plaintext.

Terminology

1. The amount of secrecy needed should determine the amount of labor appropriate for the encryption and decryption. Need of more security, needs more encryption

5 criteria of a good cipher:

2. The set of keys and the enciphering algorithm should be free from complexity.

5 criteria of a good cipher:

3. The implementation of the process should be as simple as possible.

5 criteria of a good cipher:

Undermining security

Complexity implementati

on

Message Transmission

4. Errors in ciphering should not propagate and cause corruption of further information in the message. one error should not throw off the entire process

5 criteria of a good cipher:

5. The size of the enciphered text should be no larger than the text of the original message.

5 criteria of a good cipher:

Longer ciphertext :

More space of storageEasier detection of pattern by Cryptanalysis

Longer time to communicate

Shannon developed these criteria before modern digital computers.

Some the concern he expressed, is not a limitation anymore.

We don’t need to implement a simple cipher with modern fast computers, whereas complexity of implementation has become easier

BUT

World is not safe, be careful of your information and privacy

Be secure