Hash Generator

A cryptographic hash reduces input of any size to a fixed-length fingerprint. The same input always produces the same output, and changing a single bit changes the result completely. That makes hashes ideal for answering one question very cheaply: is this file byte-for-byte identical to the one I expected?

That is the everyday use, and it is a good one. When a project publishes a SHA-256 alongside a download, hashing your copy and comparing confirms the file arrived intact and was not swapped en route. Comparing a 64-character string is far easier than comparing gigabytes.

The security picture is where care is needed. MD5 has been broken since 2004 — attackers can construct two different files with the same MD5, cheaply, on a laptop. SHA-1 fell in 2017 when researchers demonstrated a practical collision. Neither should be used where an attacker could benefit from forging a match: signatures, certificates, integrity checks on untrusted input. Both remain perfectly adequate for their common non-adversarial job of detecting accidental corruption, which is why they are still here. SHA-256 and above have no known practical attacks and are the right default for anything security-relevant.

One misuse is worth calling out plainly: **none of these algorithms is suitable for storing passwords**. They are designed to be fast, which is exactly wrong for password storage — speed is what lets an attacker try billions of guesses per second against a stolen database. Password hashing needs a deliberately slow, salted algorithm such as bcrypt, scrypt or Argon2. Adding a salt to SHA-256 helps but does not fix the underlying speed problem.

SHA hashing here uses the Web Crypto API, your browser's native implementation, so even large files hash quickly. MD5 is implemented in JavaScript because Web Crypto deliberately omits it.