A company allows employees to connect to its file server from home. The company uses a virtual private network (VPN). Before sending a confidential document...
Question 1 Report
A company allows employees to connect to its file server from home. The company uses a virtual private network (VPN). Before sending a confidential document, an employee’s device encrypts it using the company server’s public key. Only the server holds the matching private key. The administrator also stores a hash of each file so that later changes can be detected.
| Stage | Description |
|---|---|
| 1 | Employee creates plaintext document P. |
| 2 | Device encrypts P using the server public key. |
| 3 | Encrypted data travels through the internet VPN connection. |
| 4 | Server decrypts the data and compares file hashes. |
(a) State what is meant by plaintext. [1]
(b) Identify the encryption method described: symmetric or asymmetric. [1]
(c) Complete the sentence: the server uses its ________ key to decrypt the document. [1]
(d) Complete the term for an algorithm that produces a fixed-length value from data: a ________ function. [1]
(e) Give two characteristics of a secure password policy. [2]
(f) Explain how comparing hashes can indicate that a downloaded file has been altered. [3]
(g) State one advantage of using a VPN when an employee is connected through public Wi-Fi. [2]
(h) Identify the security property mainly provided by encryption: confidentiality, integrity or availability. [1]
(i) Give one reason why a public key may be shared openly but a private key must be kept secret. [2]
Answer Details
(a) Plaintext is data in its original readable, unencrypted form. Here, the employee’s document is plaintext before encryption takes place. [1 mark]
(b) The method is asymmetric encryption. It uses a matched pair of different keys: a public key and a private key. [1 mark]
(c) The server uses its private key to decrypt the document. The document was encrypted with the corresponding public key, so only the holder of the matching private key can decrypt it. [1 mark]
(d) The required term is a hash function. It produces a fixed-length hash value from input data. [1 mark]
(e) Two characteristics of a secure password policy are:
- requiring a minimum password length, making passwords harder to guess or brute-force;
- requiring a mixture of upper- and lower-case letters, numbers and/or symbols, increasing the range of possible passwords.
Other valid characteristics include preventing password reuse, blocking common passwords, or using multi-factor authentication. [2 marks]
(f) First, the original file’s hash is stored. After the file is downloaded, a hash is calculated again from the downloaded file. The new hash is compared with the stored original hash. If the two hash values differ, the file data must have changed, indicating possible corruption or tampering. Hash comparison therefore checks integrity, rather than keeping the file secret. [3 marks]
(g) A VPN encrypts traffic travelling across the public Wi-Fi network and the internet. This reduces the risk that another user on the public network can intercept and read the confidential document. [2 marks]
(h) Encryption mainly provides confidentiality, because it prevents people without the correct decryption key from reading the data. Integrity is mainly checked here by hashes; availability concerns whether systems and data remain accessible. [1 mark]
(i) A public key can be shared because it is used to encrypt data intended for the key owner or to verify signatures; knowing it does not allow an attacker to decrypt messages encrypted with it. The private key must remain secret because it can decrypt data intended for its owner. If it were disclosed, an unauthorised person could gain access to confidential data. [2 marks]
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