Hash generator: SHA-256, SHA-512 and MD5 online.

A cryptographic hash function turns any input, from one letter to a multi-gigabyte file, into a short fixed-length fingerprint called a digest. The same input always gives the same digest, and changing a single bit changes about half of the output bits, the avalanche effect. SHA-256 always produces 256 bits, written as 64 hexadecimal characters; MD5 gives 32 characters, SHA-1 40, SHA-384 96 and SHA-512 128.

A secure hash has three properties. Preimage resistance: given a digest, you cannot find an input that produces it. Second-preimage resistance: given one input, you cannot find another with the same digest. Collision resistance: you cannot find any two inputs with the same digest. When the last property breaks, the hash is no longer safe for signatures or certificates.

MD5 (RFC 1321, 1992) has been broken since 2004, when practical collisions were published; chosen-prefix collisions followed and were used to forge a code-signing certificate in the Flame malware. SHA-1 fell in 2017, when the first public collision was demonstrated, and NIST has scheduled it for retirement. Both remain fine for spotting accidental corruption or as cache keys, but never for anything an attacker could tamper with.

SHA-256, SHA-384 and SHA-512 belong to the SHA-2 family (FIPS 180-4) and have no practical attacks. SHA-256 is the everyday default for checksums, Git's newer object format, software supply chains and digital signatures. SHA-384 and SHA-512 offer longer digests and appear in TLS cipher suites and Subresource Integrity attributes. SHA-3 (FIPS 202) is a different design kept as an alternative; it is not offered here because the browser's Web Crypto API does not provide it.

One subtle point: MD5, SHA-1, SHA-256 and SHA-512 are all vulnerable to length-extension, so hash(secret + message) is not a safe way to sign a message. Use HMAC, for example HMAC-SHA256, which is built for message authentication and is what signs JWTs with HS256 and most webhook payloads.

Software publishers list a SHA-256 checksum next to a download so you can confirm the file you received is byte-for-byte the file they released. Switch to File, drop the download in, and paste the published checksum into the compare box. A green match tells you the file is complete and unmodified; no match means a corrupted or different file, so download it again from the official source.

A checksum proves integrity, not authenticity. If an attacker controls the website, they can replace both the file and its checksum. For that, publishers sign releases with GPG or Sigstore, and app stores and package managers verify signatures automatically. On the command line, sha256sum on Linux, shasum -a 256 on macOS and Get-FileHash or certutil on Windows give the same values as this page.

General-purpose hashes are designed to be fast, and fast is exactly wrong for passwords. A modern GPU can compute billions of SHA-256 or MD5 hashes per second, so when a database of unsalted fast hashes leaks, most human-chosen passwords are recovered quickly with wordlists and rules. Identical passwords also produce identical hashes, revealing which users share a password.

Store passwords with a password-hashing function that is salted and deliberately slow and memory-hard: Argon2id is the current recommendation from OWASP, with scrypt, bcrypt or PBKDF2 where Argon2id is unavailable or FIPS validation is required. Libraries for every major language handle the salt and parameters for you. Our web app authentication guide covers sessions, tokens and passkeys, and the OWASP Top 10 lists cryptographic failures among the most common web vulnerabilities.

Hashing is one-way: there is no key and no way to turn a digest back into the input, except by guessing inputs until one matches. Encryption is two-way: data is scrambled with a key and anyone with the right key can recover it. Encoding, such as Base64 or URL encoding, is not protection at all, just a reversible change of format.

Choose by purpose. To check that data has not changed, hash it. To keep data secret and read it later, encrypt it. To move binary data through a text-only channel, encode it with a tool such as the Base64 encoder.

Almost always the input differs by an invisible character. echo "hello" | sha256sum hashes 'hello' plus a newline, which gives a completely different digest; use printf 'hello' or echo -n. Windows line endings (CRLF), a byte-order mark at the start of a file, trailing spaces, or a different text encoding such as UTF-16 all change the result. This page hashes text exactly as typed, encoded as UTF-8, and hashes files byte for byte.

Format matters too. Hex is case-insensitive, so the Uppercase hex option changes only how the digest looks, and the compare box ignores case. Some systems show digests in Base64 rather than hex, such as Subresource Integrity values like sha384-…, so the same hash can look entirely different.

SHA-1, SHA-256, SHA-384 and SHA-512 are computed with your browser's Web Crypto API, the same native code browsers use for TLS. Browsers do not provide MD5, so this page computes it with our own implementation of RFC 1321, tested against the standard test vectors. Files are read into memory in this tab and never uploaded, which is why there is a 200 MB limit and why the page is safe for confidential documents and builds.

Beyond download checksums, hashes identify content everywhere in modern software: Git commits, container image digests written as sha256:…, cache-busting file names such as app.3f9a1c.js, ETags for HTTP caching and file deduplication. For any of these, SHA-256 is the safe default. It is fast enough for almost every workload and is hardware-accelerated on many current processors, so there is rarely a reason to reach for MD5 or SHA-1 in new code.