What is the function of key stretching in encryption?

Key stretching is a technique used in cryptography to enhance the security of weak keys by applying a computationally intensive algorithm that increases the amount of time and resources needed to derive the key. This is particularly useful for passwords or keys that are not sufficiently complex or long enough to withstand brute-force attacks.

The process involves repeatedly hashing the original key or password, which effectively creates a longer and more robust encryption key. By requiring more computational effort to generate the final, usable key from a weaker source, key stretching mitigates the risks associated with using simple or easily guessable keys. This approach helps protect sensitive data against potential attacks aimed at compromising encryption through the use of weak keys.

While other options might highlight different aspects of cryptography, they do not align with the specific purpose of key stretching. Generating keys more rapidly, shortening key lengths, or combining keys does not address the fundamental goal of making weak keys stronger, which is the essence of key stretching.