Multiple choiceQuestion 1 · Apply
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By the end you can describe how encryption protects data, explain what each access right allows, and combine the two to protect a set of records in a realistic organisation.
Lesson 2 drew a line between protecting the system (the machine, software and network) and protecting the data (the files themselves). This lesson is about the data side, and there are two main tools: encryption and access rights.
They cover different failures:
Used together, a copied file is unreadable and a logged-in user cannot open what their job does not require.
Encryption
Encryption is the process of converting readable data (plaintext) into an unreadable form (ciphertext) using an algorithm and a key. Converting it back is decryption, and it requires the correct key.
Encrypted data can be stored, copied or transmitted safely in the sense that an eavesdropper who lacks the key learns nothing from it.
| Symmetric encryption | Asymmetric encryption | |
|---|---|---|
| Keys used | One shared key encrypts and decrypts | A pair: a public key encrypts, the matching private key decrypts |
| Strength | Fast, good for large files | Slower, used for small amounts of data and for key exchange |
| Main problem | Both sides must share the key safely | Needs a trusted way to publish public keys (certificates) |
In practice the two are combined: a website uses asymmetric encryption to agree a temporary shared key, then uses fast symmetric encryption for the actual traffic (this is what HTTPS does).
Careful: digital signatures (lesson 3) use the same key pair the other way round. There the sender encrypts the hash with their private key and the receiver decrypts it with the sender's public key, because the aim is proving who sent it, not hiding it.
Where encryption is used to protect data:
Access rights
Access rights (also called permissions) are rules that state what a named user or group may do with a particular file, folder or record:
Rights are usually granted to groups rather than individuals, so that adding a new employee means adding them to a group instead of editing dozens of files.
On a file system, each file has an owner, and the owner or an administrator sets read, write, execute and delete rights for the owner, a group and everyone else. A folder's rights can be inherited by the files inside it, which is why a whole shared drive can be locked down in one step.
In a database, rights are set on tables or views: a receptionist's account may read a view showing only appointment times, while the underlying table with clinical notes is unavailable. Some systems go further and restrict rows, so a patient can read only their own record.
In an application, the program itself enforces the rule: a student's page shows only their own marks even though the database holds everyone's.
Two rules of thumb:
Access rights should be reviewed when someone changes role and removed when they leave. Rights that were granted "temporarily" years ago are one of the commonest real-world weaknesses.