Data integrity refers to the accuracy, legitimacy, and consistency of information in a system. When a message is sent, particularly using an untrusted medium, data integrity provides us confidence that the message wasn’t tampered with.

What Are Potential Causes of Illegitimate Data?

Data integrity provides protection from a wide range of problems which involve data being mutated against the purposes of the system. Some potential problems include:

Physical Accident – Bits of data sent over an imperfect medium can become corrupted. For example, a wireless signal could be lost temporarily, or a wire could experience a noisy electrical signal.

Digital Accident – The software responsible for communicating the message could have bugs that unintentionally mutate a subset of messages.

Malicious Actor – A man-in-the-middle could be altering messages in order to confuse correspondents or learn valuable information.

Solution – Checksum

A checksum solves all three of the potential data integrity problems listed above. A checksum is a deterministic value derived from the message data and can be transmitted separately. This means checksum for a given message will always be the same.

The receiver of a message can generate a checksum from the message, and if the generated checksum matches the one that was sent then the message couldn’t have been tampered with.

It is important to note that if the medium over which the checksum was obtained is untrusted then a malicious actor could alter the message and the checksum. It is common good practice to sign the checksum using a digital signature. The digital signature provides proof that the sender of the checksum is who they say they are.

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