What is Hashing?

by Paul Davies

Hashing

Hashing is a cryptographic process that transforms input data, such as a file or a password, into a fixed-length string of characters, known as a hash value or hash code.

This hash value is typically unique to the data, meaning that even small changes to the input will produce a significantly different hash. Hashing is widely used in data integrity checks, password storage, and digital signatures because it provides a fast and efficient way to verify data without needing to store the original data.

Some key aspects of hashing include:

  1. One-way Function: Hashing is designed to be irreversible, meaning you cannot easily derive the original data from the hash value. This makes it ideal for securely storing sensitive information, such as passwords.
  2. Deterministic: Given the same input, a hash function will always produce the same output. This consistency makes it useful for verifying the integrity of data, such as ensuring a file has not been altered during transmission.
  3. Collision Resistance: A good hashing algorithm minimises the chance of two different inputs producing the same hash value (known as a collision). Strong hashing algorithms, like SHA-256 and SHA-3, are designed to be collision-resistant.
  4. Efficiency: Hashing is computationally efficient, allowing it to process large amounts of data quickly.

Common uses of hashing include:

  • Password Storage: When users create accounts, their passwords are hashed and stored in the system rather than saving them as plain text. When they log in, their entered password is hashed and compared to the stored hash value to verify correctness.
  • Digital Signatures: Hashing is used in digital signatures to ensure the integrity and authenticity of documents or messages. The hash of the message is signed with the sender’s private key and can be verified by the receiver using the public key.
  • Data Integrity: Hashing is used to verify that files or messages haven't been altered. By comparing the hash of the original file with the hash of the received file, you can confirm whether it has been tampered with.

In summary, hashing is a crucial security mechanism used to verify the integrity of data, securely store information, and enable encryption processes across many applications in cybersecurity.