Encryption, Encryption Protocols & Digital Certificates (Cambridge (CIE) A Level Computer Science): Exam Questions

Sheila has a customer called Fred. Fred wants to send Sheila a confidential document as part of a transaction.

Explain how Fred uses asymmetric encryption to send his document securely.

Quantum cryptography can be used to exchange encryption keys securely. However, few organisations use it at present.

State two drawbacks of quantum cryptography.

A bank exchanges encryption keys between its computers. At present, the security of this key exchange depends on mathematical algorithms. The bank is considering using quantum cryptography for the key exchange instead.

Explain why quantum cryptography can make the key exchange more secure.

A company uses a digital certificate on its website.

State two items of information that the digital certificate contains.

An engineering company is considering using quantum cryptography to exchange encryption keys on two different links.

• Link A connects the company's two offices, which are in the same city. The offices are joined by a dedicated fibre optic cable that only the company uses. Secret designs for new machines are sent over this link every day.

• Link B connects the company's website to thousands of customers in many different countries. The customers use their own computers and connect to the website over the internet.

Explain why quantum cryptography is suitable for Link A but is not suitable for Link B.

An online shop sells products to customers in many countries. The shop needs a digital certificate for its website.

Describe how the online shop acquires its digital certificate.

A software company sends an update for one of its programs to customers over the internet.

The company attaches a digital signature to the update. The customer's computer also receives the company's digital certificate.

Explain how the customer's computer uses the digital certificate and the digital signature to check that the update came from the company and has not been altered.

Data sent between a client and a server across the internet can be protected using SSL/TLS.

State two purposes of SSL/TLS.

A hospital allows patients to book appointments on its website. A patient uses a web browser to log in with a username and password. The patient then enters their date of birth and a description of their symptoms.

The hospital's web server uses SSL/TLS.

Explain why the use of SSL/TLS is appropriate in this situation.

A company encrypts a message before it sends the message over the internet.

State what is meant by plain text and cipher text.

A customer uses a web browser to connect to an online bank. The browser is the client and the bank's computer is the web server. The connection uses SSL/TLS.

Describe how SSL/TLS is used to set up secure communication between the browser and the web server.

Asymmetric cryptography uses a public key and a private key.

Describe the relationship between the public key and the private key.

A national weather agency publishes storm warnings to the public over the internet. Members of the public need to be sure that a warning really came from the agency, and not from someone pretending to be the agency.

The agency uses asymmetric cryptography.

Explain how the agency's keys are used so that members of the public can verify that a warning came from the agency.

Data can be encrypted using symmetric cryptography or asymmetric cryptography.

Tick (✓) one box in each row to show whether the statement applies to symmetric cryptography or asymmetric cryptography.

Two offices of a company send files to each other over the internet. The files are protected using symmetric cryptography.

Describe how a file is encrypted and decrypted using symmetric cryptography.

An online shop has thousands of customers. Each customer sends their payment details to the shop over the internet. No customer must be able to read the payment details of another customer.

Explain why the shop uses asymmetric cryptography rather than symmetric cryptography for these messages.