a brief introduction of Shannon his 5 good criteria of a cipher

1. Shannon and 5 Criteria of a
good cipher
Sina Manavi
Manavi.sina@gmail.com
03.11.2011

2. Claude Elwood Shannon Shannon Biography
(April 30, 1916 – February 24, 2001)
American mathematician, electronic
engineer, and cryptographer.
Graduated from MIT
known as "the father of information
theory“.

3. Terminology
Plaintext: text to be protected
Cipher (or cypher): algorithm for performing
encryption or decryption
Ciphertext: encrypted/decrypted plaintext.

4. 5 criteria of a good cipher:
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. 5 criteria of a good cipher:
2. The set of keys and the enciphering algorithm should
be free from complexity.

6. 5 criteria of a good cipher:
3. The implementation of the process should be as
simple as possible.
Undermining
security
Complexity
implementation

7. 5 criteria of a good cipher:
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

8. 5 criteria of a good cipher:
5. The size of the enciphered text should be no larger
than the text of the original message.
Longer ciphertext :
Easier detection of pattern More space of storage Longer time to communicate
by Cryptanalysis

9. BUT
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

10. Be secure
World is not safe, be careful of your information and privacy