A hash function such as SHA-1 was not designed for use as a MACand cannot be used directly for that purpose because it does not rely on a secret key.

Question

Quizplus · Accepted Answer

A hash function like SHA-1 is designed to produce a fixed-size output from any input data in a way that is hard to reverse or find collisions, but it does not incorporate a secret key in its process. For a function to be used as a MAC (Message Authentication Code), it needs to involve a secret key so that the output (the MAC) can be verified only by parties that know the key, ensuring the authenticity and integrity of the message.

A Hash Function Such as SHA-1 Was Not Designed for Use