Computer Science for IGCSE & O level - Data Transmission (Section 9 - No. 6)

What is the main purpose of a 'key' in cryptography?

To detect errors in data transmission.

To ensure data availability.

To encrypt and decrypt data.

To compress the data size.

Keys are essential for the encryption and decryption of data, enabling both the conversion of plaintext into ciphertext, and vice versa.