Hash Generator

How to use Hash Generator

1. Type or paste text, or drop a file onto the panel to hash its contents.
2. All algorithms compute at once and display as lowercase hexadecimal.
3. Paste a known checksum into the compare field to verify a match.

Which hash algorithm should I use?

MD5 and SHA-1 are broken in a specific sense: practical collision attacks exist. Two different files can be constructed with the same MD5 — this was demonstrated in 2004 and can now be done in seconds. SHA-1 fell to the SHAttered attack in 2017. Both remain fine for detecting accidental corruption, where nobody is deliberately constructing a collision, and both are unsuitable for anything where an adversary chooses the input.

How do I verify a downloaded file?

Drop the file here, read the SHA-256, and compare it to the checksum published by the source. If they match character for character, the file is byte-identical to what was published.

This catches two distinct problems. Accidental corruption — a truncated download or a bad disk sector — changes the hash and is caught immediately. Deliberate tampering, where someone substitutes a modified installer on a mirror, is also caught, provided the checksum itself came from a trustworthy channel.

That proviso is the whole game. A checksum published on the same page as the download, over the same connection, protects against corruption but not against an attacker who controls that page. This is why signed releases and GPG signatures exist, and why Linux distributions publish checksums signed with a key you can verify independently.

Can a hash be reversed?

Not by computation. Hash functions are one-way by design — SHA-256 compresses arbitrary input into 256 bits, so information is necessarily destroyed and the original cannot be reconstructed.

What can be done is guessing. A "hash cracker" hashes billions of candidate inputs and looks for a match. Against a short password from a predictable distribution, this succeeds quickly: a rainbow table or a GPU rig covers the entire space of eight-character passwords in hours.

This is exactly why passwords must never be stored as a plain SHA-256. Password storage needs a slow, salted, memory-hard function — Argon2id, scrypt, or bcrypt — which are deliberately expensive to evaluate and defeat precomputation. A general-purpose hash is designed to be fast, which is precisely the wrong property.

What is the avalanche effect?

A one-bit change in the input flips roughly half the output bits, unpredictably. Hash "hello" and "hellp" and the two SHA-256 values share no visible relationship.

This is what makes hashes useful for integrity checking. There is no partial similarity to exploit and no way to tell from two hashes whether their inputs were nearly identical or completely different.

It also explains why you cannot use a cryptographic hash for fuzzy matching or deduplication of similar files. Perceptual hashes and locality-sensitive hashes exist for that, and they are built on deliberately opposite properties.

Frequently asked questions