Hashing

Hashing is the process of transforming an input (or "message") into a fixed-size string of bytes, typically a digest that represents the original data. It is commonly used in data structures, security, and authentication.

Cryptographic hash functions are designed to be irreversible, meaning the original data cannot be retrieved from the hash. They should be resistant to collisions and pre-image attacks.

Examples: SHA-256, MD5 (now considered weak), SHA-3

A hash collision occurs when two different inputs produce the same hash value. Good hash functions minimize the likelihood of collisions.

Methods for Handling Collisions:

• Chaining - storing multiple values in a linked list at the same hash index
• Open Addressing - finding the next available slot

Hash tables use hashing to store key-value pairs efficiently, allowing for quick lookups, insertions, and deletions.

They are widely used in databases, caching, and indexing.

Hashing is used in a variety of fields, including:

• Password storage (storing hashed passwords rather than plaintext)
• Digital signatures and integrity checks
• Data indexing in databases
• Cryptographic security measures