System Security Principles for Beginners

Written by Nizar M.Ahmed
Sorchy Akre Technical Institute, Iraq

1. Security LECTURE

2. Cryptography Plaintext: is a clear message needs to be sent secretly. Ciphertext: is an encrypted message hided form intruders. Encryption: converting a plaintext to a ciphertext using a key. Decryption: the process of retrieving the plaintext from the ciphertext using a key.

3. Cryptography Cryptography is the science of keeping messages secret. Cryptography = Encryption + Decryption Cryptanalysis is the art of retrieving the plaintext without knowing the proper key

4. Cryptography Cryptography is the science of keeping messages secret. Cryptography = Encryption + Decryption Cryptanalysis is the art of retrieving the plaintext without knowing the proper key

5. Symmetric & asymmetric ciphers Symmetric Cipher

6. Symmetric & asymmetric ciphers Symmetric Cipher Symmetric algorithms can be divided into stream ciphers and block ciphers. Stream ciphers can encrypt a single bit of plaintext at a time, whereas block ciphers take a number of bits (typically 64 bits in modern ciphers), and encrypt them as a single unit.

7. Symmetric & asymmetric ciphers Assymmetric Cipher

8. Symmetric & asymmetric ciphers Asymmetric Cipher Asymmetric ciphers permit the encryption key to be public, allowing anyone to encrypt with the key, whereas only the proper recipient (who knows the decryption key) can decrypt the message. The encryption key is also called the public key and the decryption key the private key.

9. Cryptanalysis and Attacks on Cryptosystems Cryptanalysis is the art of deciphering encrypted communications without knowing the proper keys. Some of the cryptanalytic techniques: Ciphertext-only attack ( Only know algorithm / ciphertext, statistical): This is the situation where the attacker does not know anything about the contents of the message, and must work from ciphertext only.

10. Cryptanalysis and Attacks on Cryptosystems

11. Cryptanalysis and Attacks on Cryptosystems Known-plaintext attack (know/suspect plaintext & ciphertext to attack cipher): The attacker knows or can guess the plaintext for some parts of the ciphertext. The task is to decrypt the rest of the ciphertext blocks using this information.

12. Cryptanalysis and Attacks on Cryptosystems

13. Cryptanalysis and Attacks on Cryptosystems Chosen-plaintext attack (selects plaintext and obtain ciphertext to attack cipher): The attacker is able to have any text he likes encrypted with the unknown key. The task is to determine the key used for encryption. Some encryption methods, particularly RSA , are extremely vulnerable to chosen- plaintext attacks.

14. Cryptanalysis and Attacks on Cryptosystems

15. Cryptanalysis and Attacks on Cryptosystems Chosen Ciphertext Attacks ( select ciphertext and obtain plaintext to attack cipher ): Attacker obtains the decryption of any ciphertext of its choice (under the key being attacked)

16. Cryptanalysis and Attacks on Cryptosystems