Advanced Higher Computing Computer Networking Topic 5: Network Security

1. Advanced Higher ComputingComputer Networking Topic 5: Network Security

2. Symmetric Encryption • Data is encrypted using a secret key and an encryption algorithm Ciphertext • Data is decrypted using the same secret key and decryption algorithim

3. Asymmetric Encryption • Data is encrypted using the recipient’s public key and an encryption algorithm Ciphertext • Data is decrypted using the recipient’s private key and decryption algorithim

4. Digital Signature • A digital signature is a piece of code attached to a message which is calculated from the message and then encrypted using the sender’s private key • The signature can only be decrypted using their public key • This proves that the message came from them and that it has not been tampered with (so long as you know that the public key is genuine)

5. Digital Certificates • A digital certificate is issued by a certificate authority which authenticates a person’s public key

6. Network Architecture security • Client creates a random number and encrypts it with user’s secret key (password) • Server decrypts number, adds 1, re-encrypts it and sends it back to client • Client decrypts new number to confirm that it is authenticated • Server creates a session key which is used to encrypt any further messages

7. Password cracking • If the encryption algorithm known and the encrypted password file is available then passwords can be decrypted using the Brute Force method

8. Password cracking • Cracking program encrypts possible passwords • Program compares encrypted passwords with entries in the server’s password file • Program outputs any matched passwords

9. Encryption Classification • Encryption is classified according to how many bits are in the secret key used to encrypt the data • As computers increase in power, the time taken to crack a password decreases, so the bit size of the secret key has to be increased • The value of any information is time dependent