1. Basics Of Symmetric Encryption
Network Security

2. Basics Of Symmetric Encryption
Objectives of the Topic
After completing this topic, a student will be able to
describe basics of symmetric encryption.

3. Basics Of Symmetric Encryption
Figures and material in this topic have been
adapted from “Network Security Essentials: Applications and Standards”, 2014, by William Stallings.

4. Basics Of Symmetric Encryption
Symmetric encryption, or single-key encryption, was the only type of encryption in use prior to the development of public key encryption in the 1970s.

5. Basics Of Symmetric Encryption
Some Basic Terminology
Plaintext - original message
Ciphertext - coded message
Cipher - algorithm for transforming plaintext to ciphertext .

6. Basics Of Symmetric Encryption
Key - info used in cipher known only to sender/receiver
Encipher (encrypt) - converting plaintext to ciphertext
Decipher (decrypt) - recovering ciphertext from plaintext

7. Basics Of Symmetric Encryption
Cryptography - study of encryption principles/methods
Cryptanalysis (code breaking) - study of principles/methods of deciphering ciphertext without knowing key
Cryptology - field of both cryptography and cryptanalysis

8. Basics Of Symmetric Encryption
Symmetric Encryption Principles
A symmetric encryption scheme has five ingredients

9. Basics Of Symmetric Encryption
Plaintext
This is the original intelligible message or data that is fed into the algorithm as input.
Encryption Algorithm
It performs various substitutions and transformations on the plaintext.

10. Basics Of Symmetric Encryption
Secret Key
It is also input to the encryption algorithm. The key is a value independent of the plaintext and of the algorithm.

11. Basics Of Symmetric Encryption
Secret Key …
The algorithm will produce a different output depending on the specific key being used at the time.
The exact substitutions and transformations performed depend on the key.

12. Basics Of Symmetric Encryption
Ciphertext
This is the scrambled message produced as output. It depends on the plaintext and the secret key. For a given message, two different keys will produce two different ciphertexts ( is unintelligible).

13. Basics Of Symmetric Encryption
Decryption algorithm
This is essentially the encryption algorithm run in reverse.
It takes the ciphertext and the secret key and produces the original plaintext.

14. Basics Of Symmetric Encryption
Model of Symmetric Encryption

15. Basics Of Symmetric Encryption
Requirements
Two requirements for secure use of symmetric encryption

16. Basics Of Symmetric Encryption
1. We need a strong encryption algorithm.
An opponent should be unable to decrypt ciphertext or discover the key even if he is in possession of a no. of ciphertexts together with the plaintext that produced each ciphertext.

17. Basics Of Symmetric Encryption
2. Sender and receiver must have obtained copies of the secret key in a secure fashion and must keep the key secure.
If someone discovers the key and knows the algorithm, all communication using this key is readable.

18. Basics Of Symmetric Encryption
The security of symmetric encryption depends on the secrecy of the key, not the secrecy of the algorithm

19. Basics Of Symmetric Encryption
It is impractical to decrypt a message on the basis of the ciphertext plus knowledge of the encryption/decryption algorithm.
This makes it feasible for widespread use.

20. Basics Of Symmetric Encryption
Manufacturers can and have developed low-cost chip implementations of data encryption algorithms.
These chips are widely available and incorporated into a number of products.
End