Integrity vs Non-repudiation

Fundamentals

Making sure information stays correct and complete, and is not changed by accident or without permission.

Formal

The property that information is accurate and complete, and that any change to it is made only by those allowed to, in a way that can be noticed. Hashing and digital signatures are common ways to show that nothing has been altered.

In plain English

Like a recipe card - if someone quietly changes “one teaspoon of salt” to “one cup”, everyone who follows it ruins the dish without knowing why.

In practice

An attacker inside a supplier's mailbox changes the account number on an invoice sent to a municipality, and a finance clerk pays a large sum to the wrong account.

Why it matters

Decisions, payments and even medical treatment rely on data being right; wrong data can do more harm than missing data because nobody questions it.

Non-repudiation

Fundamentals

Proof of who did something that is strong enough that they cannot later deny having done it.

Formal

The assurance that the sender of a message gets proof of delivery and the receiver gets proof of who sent it, so neither can later deny their part. It usually rests on digital signatures, which only the holder of a private key could have made.

In plain English

Like signing for a parcel in front of a witness - you cannot later claim it never came, and the courier cannot claim to have left it with you if they did not.

In practice

A supplier signs a contract with a Danish region using a digital signature; when it later disputes the agreed price, the region can show that only the supplier's own key could have produced that signature.

Why it matters

Contracts, payments and audit records are only worth something if people cannot simply say “that was not me” afterwards.

Shared connections

Digital signature