Hashing

Security+ 🏆 • Cryptography 🔒 • Difficulty: free

Definition

Hashing is a one-way process that turns data of any size into a fixed-length value called a hash or digest. Hashing is used to verify integrity, store password verifiers safely, and support digital signatures, because small input changes produce very different outputs and the original input cannot be practically recovered from the hash.

Examples

  • A user downloads software and compares its published SHA-256 hash to confirm the file was not altered in transit.
  • A website stores passwords using a slow password hashing function so stolen hashes are harder to crack.

Discover 🔎

Hashing is one of the most common concepts in security, but it is also one of the most misunderstood. People sometimes treat hashes like encryption, as if you can reverse them. In reality, hashing is designed to be one-way. Its purpose is not to hide information, but to create a compact fingerprint of data that changes dramatically if the data changes.

Remember: Hashing is one-way. If you can “decrypt” it, it was not a hash, it was something else.
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