Cambridge AS & A Level9608

Security, privacy and data integrity

Computer Science 9608 Chapter Notes

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Security, privacy and data integrity
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In this chapter

  1. 1Security, Privacy, and Integrity Defined
  2. 2System Security: Firewalls & Authentication
  3. 3Data Security: Backups and Encryption
  4. 4Data Integrity: Validation and Verification
  5. 5Data Integrity in Transit: Parity & Checksums

1. Security, Privacy, and Integrity Defined

Understanding the difference between data security, privacy, and integrity is fundamental. Think of them as three different promises about your data. Data Security is the promise that your data won't be lost or corrupted and will be available when you need it. Data Privacy is the promise that your data will only be seen by authorised people. Data Integrity is the promise that your data is accurate and reliable. A system can be secure but not private (e.g., data is safe from loss, but everyone can see it), so all three are needed for a trustworthy system.

Key term

Data Integrity: A requirement for data to be accurate, complete, and up-to-date throughout its lifecycle.

Examiner insight

Examiners award marks for clear, distinct definitions. Use a simple analogy or example for each term to demonstrate full understanding.

Common pitfall

Confusing data security with data privacy. Security is about protecting data from loss and ensuring its availability, while privacy is about controlling who can see it.

Worked example 13 marks

A customer's bank balance is accidentally changed from £1500 to £150. A hacker then steals a list of customer names and addresses, but no financial data. Finally, a server crash makes all online banking unavailable for a day. For each incident, state whether it is a failure of security, privacy, or integrity.

  1. 1
    1. The bank balance changing from £1500 to £150 is a failure of data integrity. The data is no longer accurate.
  2. 2
    1. The hacker stealing a list of names and addresses is a failure of data privacy. Unauthorised individuals have gained access to personal data.
  3. 3
    1. The server crash making online banking unavailable is a failure of data security. The data is not available to authorised users when needed.

Recap

  • Data Security ensures data is available and protected from loss or corruption.
  • Data Privacy ensures data is only accessible to authorised individuals.
  • Data Integrity ensures data is accurate, complete, and up-to-date.
  • These three concepts are distinct but interconnected.
  • A failure in one area can often lead to failures in the others.

Quick check

  1. If a company's confidential financial report is leaked online, which principle has been breached?1 mark

2. System Security: Firewalls & Authentication

Protecting a computer system is the first line of defence. This involves preventing unauthorised access and malicious attacks. A firewall acts as a barrier between your computer or network and the internet. It inspects incoming and outgoing traffic (data packets) and decides whether to allow or block them based on a set of security rules. Authentication is the process of proving your identity. This is commonly done with something you know (a password), something you have (a security token or phone), or something you are (biometrics like a fingerprint or face scan). Strong systems often combine methods, known as multi-factor authentication (MFA), for greater security. Finally, user accounts with different permission levels (e.g., administrator vs. standard user) ensure that even authorised users can only access the parts of the system they need for their role.

Key term

Authentication: The process of verifying the identity of a user, process, or device, often as a prerequisite to allowing access to resources in an information system.

Examiner insight

When discussing authentication, provide specific examples for each method (e.g., fingerprint for biometrics, SMS code for 2FA) to earn full marks.

Common pitfall

Stating that a firewall 'stops viruses'. While it can block malicious traffic, its primary role is to control network access based on rules, not to scan for viruses like dedicated antivirus software does.

Fun fact

The term 'firewall' is taken from a building construction technique where a physical wall is built to stop a fire from spreading from one part of a building to another.

Worked example 14 marks

A school wants to improve the security of its computer network which is connected to the internet. Describe two measures that could be taken to ensure the security of the system.

  1. 1
    1. Install and configure a firewall: This will act as a barrier between the school's internal network and the external internet. It can be set up to block traffic from unknown sources or on specific ports, preventing unauthorised access attempts and blocking some types of malicious traffic.
  2. 2
    1. Implement strong authentication: Instead of simple passwords, the school could enforce a policy of strong passwords (long, complex) and implement two-factor authentication (2FA). For example, after entering a password, a teacher might need to approve the login via an app on their phone. This makes it much harder for an attacker to gain access even if they steal a password.

Recap

  • A firewall filters network traffic based on a set of security rules.
  • Authentication verifies a user's identity before granting access.
  • The three main types of authentication are based on knowledge, possession, and biometrics.
  • Multi-factor authentication (MFA) combines two or more authentication types for enhanced security.
  • User accounts with different privilege levels limit potential damage from a compromised account.

Quick check

  1. What is the primary function of a firewall?1 mark
  2. Give one example of biometric authentication.1 mark

3. Data Security: Backups and Encryption

While system security protects the computer, data security measures protect the actual information. The two most important measures are backups and encryption. Encryption is the process of scrambling data (plaintext) into an unreadable format (ciphertext) using a secret key and an algorithm. Only someone with the correct key can decrypt it back into plaintext. This protects data from being read if it is stolen or intercepted. Backups are copies of data stored separately from the original. They are essential for disaster recovery, allowing you to restore data if the original is lost, corrupted, or hit by a ransomware attack. A good backup strategy involves regular, automated backups, with at least one copy stored off-site.

Key term

Encryption: The process of converting data from a readable format (plaintext) into an encoded format (ciphertext) to prevent unauthorised access.

Examiner insight

For encryption questions, clearly distinguish between symmetric and asymmetric methods, paying close attention to how keys (secret, public, private) are used in each.

Common pitfall

Confusing backups with archives. Backups are for disaster recovery of current data, while archives are for long-term storage of data that is no longer in active use.

Worked example 14 marks

A small photography business stores all its client photos and invoices on a single computer. Describe a suitable backup policy to ensure data security.

  1. 1
    1. Implement the 3-2-1 rule: The business should have at least three copies of its data.
  2. 2
    1. Use two different media: For example, one backup could be to an external hard drive kept in the office (for fast recovery). The second backup should be on a different medium, such as a cloud backup service.
  3. 3
    1. Keep one copy off-site: The cloud backup service satisfies this requirement. This protects the data against local disasters like fire, flood, or theft of the office equipment.
  4. 4
    1. Automate and schedule: Backups should be performed automatically every night (e.g., an incremental backup of new files) with a full backup once a week, to ensure they are not forgotten and are always up-to-date.

Recap

  • Encryption scrambles data to make it unreadable without the correct key.
  • Backups are copies of data used for recovery in case of data loss.
  • A good backup strategy includes regular backups, multiple copies, and off-site storage.
  • Symmetric encryption uses a single secret key for both encryption and decryption.
  • Asymmetric encryption uses a public key to encrypt and a private key to decrypt.

Quick check

  1. Why is it important to keep a backup copy off-site?1 mark

4. Data Integrity: Validation and Verification

To ensure data has integrity, we must check it is correct upon entry. This involves two techniques: validation and verification. Validation is an automatic check performed by the computer to ensure that data is sensible, reasonable, and in the correct format. For example, it can check if a date is in DD/MM/YYYY format or if a number is within a certain range. However, validation cannot know if the data is factually correct. Verification is a check to ensure that data has been entered correctly by comparing it to the original source. This can be done by a human (e.g., proofreading) or by the computer (e.g., asking the user to type their new password twice - this is called double data entry).

Key term

Data Validation: An automated check performed by a computer to ensure that entered data is reasonable, sensible, and in an acceptable format.

Examiner insight

To get full marks, you must explain that validation cannot check if the data is *correct*, only if it is *plausible*. For example, a range check on age might accept '35' when the person is actually '53'.

Common pitfall

Mixing up validation and verification. Remember: Validation is an automated check for 'sense', Verification is a check for 'sameness' against a source.

Worked example 14 marks

A website registration form requires users to enter their email address, a password, and their age. Describe the difference between validation and verification in this context, giving an example of each.

  1. 1
    1. Difference: Validation is an automated check to see if the data is reasonable, while verification is a check to confirm the data was transcribed correctly.
  2. 2
    1. Validation Example: A format check could be used on the email address field to ensure it contains an '@' symbol and a '.' (e.g., 'user@domain.com'). A range check could be used on the age field to ensure the user is, for example, over 18.
  3. 3
    1. Verification Example: The form could ask the user to enter their password twice. The system then compares the two entries. If they match, the data is verified. This is an example of double data entry.

Recap

  • Validation is an automated check to see if data is sensible and in the right format.
  • Examples of validation checks include range, format, presence, and length checks.
  • Validation cannot check if data is factually correct.
  • Verification is a check to ensure data has been copied accurately.
  • Double data entry and proofreading are common verification methods.

Quick check

  1. A form field must not be left empty. What type of validation check is this?1 mark
  2. Is asking a user to enter their password twice an example of validation or verification?1 mark

5. Data Integrity in Transit: Parity & Checksums

When data is sent over a network cable or through the air, interference can cause bits to 'flip' (a 0 becomes a 1 or vice-versa), corrupting the data. We need methods to detect these errors. Parity Check is a simple method. For each byte of data, an extra bit (the parity bit) is added. In even parity, the parity bit is set to 1 or 0 to make the total number of 1s in the byte (including the parity bit) an even number. The receiver counts the 1s in each byte it gets. If a byte has an odd number of 1s, it knows an error occurred and can request the data be sent again. The weakness is that it can't detect an even number of bit errors. A Checksum is a more robust method. A mathematical algorithm is applied to a block of data to generate a number (the checksum). This checksum is sent along with the data. The receiver performs the exact same calculation on the data it receives and compares its result to the checksum it was sent. If they don't match, the data has been corrupted.

Key term

Parity Bit: An extra bit added to a string of binary code to ensure that the total number of 1-bits in the string is either even or odd, used for error detection.

Examiner insight

When describing parity checks or checksums, be sure to explain the process at both the sender's and the receiver's end to demonstrate a complete understanding.

Common pitfall

Thinking that a parity check can correct errors. Its basic form can only detect an odd number of bit errors in a byte; it cannot identify which bit is wrong or fix it.

Worked example 13 marks

A system uses even parity, with the parity bit added as the most significant bit (left-most bit) to a 7-bit ASCII code. What byte would be transmitted for the 7-bit code 1001011?

  1. 1
    1. Identify the parity type: The system uses even parity.
  2. 2
    1. Count the number of '1's in the original data: The code is 1001011. There are four '1's.
  3. 3
    1. Determine the parity bit: Since four is already an even number, the parity bit must be 0 to keep the total count of '1's even (4 + 0 = 4).
  4. 4
    1. Construct the transmitted byte: The parity bit (0) is added as the most significant bit to the 7-bit code. The transmitted byte is 01001011.

Recap

  • Parity checks and checksums are used to detect errors in data during transmission.
  • A parity bit is added to each byte to make the total number of 1s either even or odd.
  • Simple parity checking can only detect an odd number of bit errors in a byte.
  • A checksum is a value calculated from a block of data.
  • The receiver recalculates the checksum and compares it to the received checksum to detect errors.

Quick check

  1. Using odd parity, what would the parity bit be for the 7-bit data 1110001?1 mark
  2. What is the main limitation of a simple parity check?1 mark

End-of-chapter exercise

Test yourself on the whole chapter. Work through these before moving on.

  1. Define data privacy and give an example of a privacy breach.2 marks
  2. Name two distinct types of authentication and provide an example for each.4 marks
  3. Explain the difference between data validation and data verification, using the context of a user setting a new password on a website.4 marks
  4. A small business wants to protect its customer database from loss or unauthorised access. Describe two different data security measures it should implement.4 marks
  5. Describe how a firewall helps to protect a computer connected to the internet.3 marks
  6. A 7-bit byte of data, 1101001, is to be transmitted using even parity. The parity bit is added as the most significant bit (MSB). State the transmitted 8-bit byte. Explain what happens at the receiving end if this byte is received as 11101001.4 marks
  7. Compare and contrast symmetric and asymmetric encryption. Your answer must refer to the types of keys used and how they are managed.6 marks
  8. A new student registration form asks for a student's 'Forename', 'Date of Birth' (to be entered as DD/MM/YYYY), and a 6-character 'Postcode'. Describe three different validation checks that could be applied to this form, specifying which field each check applies to.6 marks
  9. Explain how a checksum is used to verify the integrity of a block of data after it has been transmitted over a network.3 marks
  10. A hospital's patient record system has been encrypted by a ransomware attack, making it inaccessible. Referring to the concepts of data security, privacy, and integrity, explain the issues caused by this attack.6 marks

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