1. Unit 3 Section 6.4: Internet Security

2. Types of issues
Viruses
Spam
Worms
Phishing/Pharming
Spyware

3. Viruses
A small program that attacks computers and replicates itself by attaching itself to other programs or files.
List of computer viruses
How Computer Viruses Work
Computer viruses: description, prevention, and recovery

4. Spam Unsolicited junk emails What is spam?
Blind and partially sighted people are the inadvertent victims in a war being fought against the software robots used by spammers.
SPAMfighter wins big spam filter test in Germany’s largest computer magazine

5. Worms
A small program that attacks computers by exploiting network security weaknesses and replicates itself through computer networks.
Worm strikes down Windows 2000 systems
A computer worm is a self-replicating computer program.
The International Computer Science Institute is a non-profit institute in Berkeley, California. They pursue research on internet architecture and related networking issues.

6. Phishing and Pharming
Phishing is when someone tries to get you to give them your personal information.
Pharming is when a phisher changes DNS server information so that customers are directed to another site.
Bank turmoil fuels phishing boom
Committed to wiping out internet scams and fraud
Recognize phishing scams and fraudulent
Is a hacker’s attack aiming to redirect a website’s traffic to another, bogus website

7. Spyware
A computer program that tracks and records a user’s actions e.g. websites visited.
Can redirect a user’s browser to unwanted websites
Can change computer settings

8. Firewalls A hardware device or program
Controls traffic between Internet and computer system
Can be customised by setting rules on data packets allowed through
Traffic can be blocked from specific IP addresses, domain names and port numbers
Packet filtering
Proxy server

10. Encryption Encryption algorithm Plain text encrypted into cipher text
Decryption algorithm and decryption key
Cipher text decrypted to plain text
Cryptography
Cryptanalysis
THE NUM8ER MY5TERIES: the case of the uncrackable code

11. Symmetric Encryption
Cipher text can be decrypted using encryption algorithm and the encryption key
Enigma machine used during WW II
Code breakers at Bletchley Park
Difficult to distribute symmetric key without being intercepted
Easy to decrypt the message with key

12. Asymmetric encryption
Also called public key encryption e.g. RSA
Pair of keys – public and private
Private key is kept secret
Encryption algorithm and public keys are freely available
A message encrypted with A’s private key can only be decrypted with A’s public key
A message encrypted with A’s public key can only be decrypted by A with it’s private key
It’s slow

13. Digital Signatures and Certificates
To prove that an electronic message is genuine, a sender can digitally sign the message.
This means it can be detected if the message has been tampered with and the signature is proof that it has been sent by the correct person. Digital signatures use asymmetric encryption.
The process to send a message is as follows:

14. A digest (also known as a hash) is produced from the message using a hash function. The digest is a much reduced version of the original message (it is not possible to change a message digest back into the original message from which it was created).
Message
Digest
Hash Function

15. The digest is then encrypted using the sender’s private key
The digest is then encrypted using the sender’s private key. The sender’s private key must be used instead of the receiver’s public key to prove it has been encrypted by the sender. The encrypted digest result is the digital signature.
Encrypted Digest (Digital Signature)
Encrypt using sender’s private key
Digest

16. The encrypted digest (digital signature) is then appended to the original message.
Digital Signature
Appended with

17. Encrypt using receiver’s public key
The message and digital signature are then encrypted using the receiver’s public key. The receiver’s public key must be used here so that only the receiver can decrypt the message with the private key.
Message
Encrypted Message
Encrypt using receiver’s public key

18. The encrypted message is then sent by electronic mail.
Encrypted Message
Send by

19. Digital Signatures and Certificates The process to verify that a message is genuine is as follows:

20. Decrypt using receiver’s private key
The message and signature are decrypted using the receiver’s private key.
Message
Encrypted Message
Decrypt using receiver’s private key

21. Separate Digital Signature
The decrypted message is then separated into the original message and digital signature.
Message
Digital Signature
Separate Digital Signature

22. The digital signature (encrypted digest) is then decrypted using the sender’s public key. This proves it has been sent by the person who owns the private key.
Digital Signature (Encrypted Digest)
Decrypt using sender’s public key
Decrypted Digest

23. A new digest is produced from the original message using the same hash function as the original digest.
Message
Hash Function
New Digest

24. The decrypted digest is then compared to the new digest
The decrypted digest is then compared to the new digest. If the decrypted digest is the same as the new digest then the message has not been tampered with.
Decrypted Digest
New Digest

25. Digital Signatures and Certificates Although this process sounds complicated it is all handled by the signing software so the messages can be signed and received using a simple click.

26. Digital Signatures and Certificates A digital certificate is issued by a certification authority. It contains your name, a serial number, expiration dates, a copy of the certificate holder's public key (used for encrypting messages and digital signatures), and the digital signature of the certificate-issuing authority so that a recipient can verify that the certificate is real. Digital certificates can be kept in registries so that authenticating users can look up other users' public keys.

27. Virus detection Antivirus scanner software
Checks files against a dictionary of known viruses
Users must regularly update the dictionary
If infected file found then antivirus scanner will delete the virus from the file
If unable to delete virus then file quarantined where file can be deleted

28. Computer Security Procedures
Authentication used to verify user is legitimate
e.g. passwords, biometric data, security tokens, digital certificates
Digitally signed is used to authenticate the sender thus reducing phishing attacks
Authorisation by user ID and password
Users authorised to use certain resources
System administrator grants permissions to users
Passwords and encryption used to keep data secret from unauthorised persons
Accounting – systems generate activity logs e.g. website IP addresses logged

29. Past Paper Questions
The following past papers have questions on Internet
security. They are in the ‘6.4 Internet Security’ folder in
Learning resources.
January 2007 CPT5 Q5
January 2006 CPT5 Q7
January 2003 CPT5 Q5

30. Class work and Homework
Using the hyperlinks in this presentation research
Viruses
Spam
Worms
Phishing
Pharming
Spyware
Firewalls
Encryption
Complete the past paper questions