SHA-256 Hash Generator

What is SHA-256?

SHA-256 is the most widely used member of the SHA-2 family of hash functions, designed by the U.S. National Security Agency and published by NIST in 2001 (today in FIPS 180-4). It splits the input into 512-bit blocks, mixes each one through 64 rounds of 32-bit additions, rotations and logical functions, and outputs a 256-bit digest, written as 64 hex characters or 44 Base64 characters. No practical attack is known against the full algorithm: finding two inputs with the same SHA-256 hash, or an input matching a given hash, remains far beyond reach.

How to use the SHA-256 generator

1. Type or paste text in the Text tab; the hash updates instantly. Switch the input to hex or Base64 if you are hashing raw bytes.
2. For a file, use the File tab. The file is streamed in 4 MB chunks on your device, so large disk images work without filling memory.
3. Choose lowercase hex (Linux, macOS), uppercase hex (Windows) or Base64 (web and API formats).
4. Enter an HMAC key to get an HMAC-SHA256 instead of a plain hash.
5. Paste a published checksum into the compare box to verify a download. For several algorithms at once, open the full hash generator.

Where SHA-256 is used

Bitcoin and blockchains

Bitcoin’s proof of work is built on SHA-256: miners repeatedly hash a block header twice with SHA-256 (“double SHA-256”) until the result falls below a target value, and block and transaction IDs are double-SHA-256 hashes. Bitcoin addresses use SHA-256 followed by RIPEMD-160. The same property that makes mining hard, that the only way to find a hash with certain properties is to try inputs one by one, is what makes SHA-256 useful everywhere else.

TLS certificates and HTTPS

Almost every HTTPS certificate is signed with a SHA-256-based signature such as sha256WithRSAEncryption or ECDSA with SHA-256; browsers stopped trusting SHA-1 certificates in 2017. Inside the connection, TLS 1.3 cipher suites such as TLS_AES_128_GCM_SHA256 use SHA-256 for key derivation (HKDF) and handshake integrity.

Code signing and software supply chains

Windows Authenticode, Apple code signing, Android APK signatures, Linux package repositories and Docker image digests (sha256:…) all rely on SHA-256 to prove that the code you run is the code the publisher signed. Git also supports a SHA-256 object format as an alternative to its original SHA-1 hashes.

Web and API security

Subresource Integrity attributes (integrity="sha256-…") contain a Base64 SHA-256 of a script or stylesheet, which you can produce here by choosing Base64 output. Webhooks from payment and developer platforms are commonly signed with HMAC-SHA256, and JSON Web Tokens signed with HS256 use the same construction.

Verify a file’s SHA-256 checksum

Compare every character, or paste both values here and let the compare box do it. Hex is case-insensitive, so Windows’ uppercase output matches Linux’s lowercase output.

SHA-256, HMAC and length extension

SHA-256 is a Merkle–Damgård hash, which means that anyone who knows SHA-256(secret + message) and the secret’s length can compute the hash of the message with extra data appended, without knowing the secret. This “length-extension attack” has broken real API signature schemes. The fix is to use HMAC-SHA256, which this page computes when you enter a key, or a hash that is not vulnerable, such as SHA-512/256 or SHA3-256, both available in the hash generator.

SHA-256 compared with other hashes

For almost every new checksum or integrity job, SHA-256 is still the right default because every operating system, language and library supports it.

SHA-256 is not a password hash

SHA-256 is designed to be fast, so an attacker with a graphics card can try billions of password guesses per second against it. Passwords should be stored with a slow, salted algorithm such as Argon2id, bcrypt or scrypt. Try the bcrypt generator if you need one.

Frequently asked questions