Encrypting stored data

Encryption is the process of scrambling data so that it cannot be understood by anyone who does not have the key to unlock it. It uses an encryption algorithm (a set of mathematical steps) together with an encryption key to turn readable plaintext into unreadable ciphertext.

To turn the ciphertext back into plaintext you decrypt it, which needs a decryption key, password or code. Without the correct key the ciphertext is meaningless rubbish, even to someone holding the file. The correct term is decrypt, not decode.

What encryption can and cannot do

Encryption does not stop data being intercepted or stolen: a thief can still copy a file or walk off with a laptop. What it does is make the stolen data unreadable, so the thief gains nothing useful.

It is also not the same as putting a password on a file. A password prompt can be bypassed by someone who knows how to get around the software, but properly encrypted ciphertext stays unreadable until it is decrypted with the key.

Encrypting stored data

Encrypting stored data means files, databases or a whole drive are held in encrypted form, so a decryption key is needed to read them. This protects the contents if a device or storage medium is lost or stolen, because whoever finds it cannot read anything on it.

For example, Priya keeps her coursework and a list of part-time job customers on a tablet. Because she encrypts the whole drive, the person who finds the tablet she left on a bus cannot open a single file. Had she encrypted only the coursework folder, her customer list would still be readable.

Following the data through

Plaintext is encrypted with the encryption key to produce ciphertext, which is stored. Later, the ciphertext is decrypted with the decryption key, giving the decrypted text, which is the plaintext again. The key features are the encryption key, the ciphertext, the decryption key and the decrypted text.