What is the difference between a cryptographic hash function and a regular hash function?

A cryptographic hash function and a regular hash function differ primarily in their intended purposes and properties.

A regular hash function is designed to efficiently map data of arbitrary size to a fixed-size output, typically a hash value or hash code. It is commonly used in various applications such as data retrieval, data indexing, and checksum verification. Regular hash functions prioritize speed and efficiency, aiming to minimize collisions (i.e., different inputs producing the same hash value) while providing a reasonably distributed output.

On the other hand, a cryptographic hash function is specifically designed for security purposes. It not only maps data to a fixed-size output but also possesses certain cryptographic properties that make it suitable for various security applications. These properties include:

1. Deterministic: Given the same input, a cryptographic hash function will always produce the same output.
2. Pre-image resistance: It is computationally infeasible to determine the original input from its hash value.
3. Second pre-image resistance: Given an input, it is computationally infeasible to find another input that produces the same hash value.
4. Collision resistance: It is computationally infeasible to find two different inputs that produce the same hash value.

Cryptographic hash functions are widely used in digital signatures, password storage, message integrity verification, and other security protocols. They provide a high level of data integrity, ensuring that even a small change in the input data will result in a significantly different hash value.

In summary, while both regular hash functions and cryptographic hash functions perform the task of mapping data to a fixed-size output, cryptographic hash functions possess additional security properties that make them suitable for secure applications.