Encryption

Encryption is a prevention method that scrambles data using an algorithm and a key, so anyone who captures it sees meaningless characters instead of readable information.

How encryption works

The algorithm is the set of steps that rearranges the data. The key is the secret value that controls exactly how the rearrangement happens, so the same algorithm with a different key produces completely different scrambled data. Without the correct key, the scrambled data cannot be turned back into anything readable.

The receiver carries out decryption: the same process in reverse, using the key to turn the scrambled data back into its original form. For example, a school sends a pupil's report across the internet to a parent's email account. The report is encrypted with a key before it leaves the school, and the parent's email app decrypts it with the matching key so the report can be read. Anyone who captured the message on the way would hold only a jumble of characters.

What encryption does and does not do

• It protects data in transit, such as data travelling across a network, because an attacker who intercepts it cannot read it.
• It protects data at rest, such as the files stored on a tablet that is stolen, because the thief cannot open them without the key.
• It does not stop the interception or the theft from happening. The data can still be captured and the device can still be taken; encryption only makes what is taken unreadable.
• It does not stop a denial-of-service attack, where a service is flooded with traffic until it fails. Encryption does not reduce how much traffic reaches a server, so a firewall is the method used to block that traffic instead.

Encryption therefore limits the damage caused by data interception and theft rather than preventing those events, and it is used alongside other methods such as firewalls and user access levels.