the CIA triad

When you send a sealed letter you usually want three different promises at once. First, that only the right person can read it (it's sealed). Second, that nobody tampered with the words inside (the seal is unbroken). Third, that the letter actually gets delivered and isn't lost or held up. Those three wishes map exactly onto the CIA triad — Confidentiality, Integrity, and Availability — the standard checklist of what we mean by a message or system being secure.

Each leg is a separate, independent goal achieved by different tools. Confidentiality means only authorized parties can read the data — achieved with encryption, so an eavesdropper sees only scrambled bytes. Integrity means the data hasn't been altered, and you can detect it if it has — achieved with cryptographic hashes and message authentication codes, which act like a tamper-evident seal. Availability means the service is actually reachable and responsive when needed — defended by capacity, redundancy, and protection against denial-of-service attacks. Two further goals are usually bolted on: authentication (proving who someone is) and non-repudiation (a sender can't later deny having sent a message), typically provided by digital signatures.

Why it matters: the triad is useful precisely because the three properties are independent — you can have one without the others, and that's a common mistake. Encryption gives you confidentiality but, by itself, not integrity (an attacker can still flip bits in ciphertext); a backup gives availability but not confidentiality; a digital signature gives integrity and authentication but does nothing to hide the content. Naming the three goals separately forces you to ask, for any system, which ones you actually need and which tool delivers each — rather than assuming one measure covers everything.