Cryptography, in plain terms

Cryptography is the technique of securing information and communication through codes, so that only the people the information is intended for can read it. The word combines the Greek for "hidden" and "writing" — which is a fair description of what it does: convert a readable message into something unreadable to anyone without the key.

Modern cryptography relies on mathematical algorithms — for key generation, digital signing, verification and encryption to support things like private data storage, secure browsing and confidential transactions such as card payments.

The four properties

• Confidentiality — only the intended recipient can access the information.
• Integrity — the information is not altered in storage or in transit.
• Non-repudiation — the sender cannot later deny having sent it.
• Authentication — the identity of sender and receiver, and the origin of the message, can be confirmed.

A system that only delivers confidentiality but not integrity, or authentication without non-repudiation, is incomplete each property covers a different failure mode, and dropping one reopens it. Encryption also underpins access control more broadly: a resource is only accessible to a party with both the right permissions and the correct key, which is what makes cryptography the basis for so much of practical information security rather than a niche within it.