Hash Function

A hash function is a cryptographic algorithm that converts an input message into a fixed-length hash value (digest).

They are widely used in cryptography for ensuring data integrity, authentication, and secure storage of sensitive information.

It is irreversible, meaning you cannot retrieve the original message from the hash.

Key Properties of Hash Functions:

For a hash function to be considered secure, it must satisfy the following properties:

1.) Deterministic Output:

The same input always produces the same output.
Example: If you hash the word “Hello”, it should always return the same digest, regardless of how many times you hash it.

2.) Fast Computation:

Hash functions should be efficient and able to compute the hash quickly, even for large inputs.
This is essential for real-time security applications like digital signatures and message authentication.

3.) Pre-Image Resistance (Irreversibility):

It should be computationally infeasible to reverse-engineer the original input from its hash value.
Example: Given a hash output like “5d41402abc4b2a76b9719d911017c592”, an attacker should not be able to determine the original input “hello”.

4.) Collision Resistance:

No two different inputs should produce the same hash value.
This prevents collision attacks, where an attacker finds two different inputs with the same hash.
Example: If “Alice” and “Bob” both produce the same hash, it can lead to serious security issues in digital signatures and authentication systems.

5.) Avalanche Effect:

A small change in the input should produce a completely different hash output.
Example:
- Input: “hello” → Hash: 5d41402abc4b2a76b9719d911017c592
- Input: “Hello” (capitalized ‘H’) → Hash: 8b1a9953c4611296a827abf8c47804d7
- This property ensures that even minor modifications to a message can be easily detected.

Applications of Hash Functions:

Common Hash Functions: