Generate MD5, SHA-1, SHA-256, and SHA-512 hashes from any text. Uses the Web Crypto API for SHA hashes -- everything runs in your browser, nothing leaves your machine.
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Get Started FreeA hash function is a mathematical algorithm that takes an input (or "message") of arbitrary length and produces a fixed-size output called a hash value, digest, or checksum. The key properties of cryptographic hash functions are determinism (the same input always produces the same output), efficiency (the hash is computed quickly), pre-image resistance (given a hash, it is computationally infeasible to find the original input), and collision resistance (it is extremely difficult to find two different inputs that produce the same hash). These properties make hash functions fundamental building blocks in computer security, data integrity verification, and software engineering.
A collision occurs when two different inputs produce the same hash output. While collisions are theoretically inevitable for any hash function (since the output space is finite), a secure hash function makes finding collisions computationally infeasible. MD5 (128-bit output) was broken in 2004 when researchers demonstrated practical collision attacks, and it should no longer be used for security purposes. SHA-1 (160-bit) was theoretically broken in 2005 and practically demonstrated in 2017 with Google's SHAttered attack. The SHA-2 family (SHA-256 and SHA-512) remains secure with no known practical attacks. For new applications requiring cryptographic security, SHA-256 or SHA-512 are the recommended choices. MD5 and SHA-1 are still acceptable for non-security uses like checksums and hash tables.
Hash functions serve many purposes across software development and security. Password storage uses hashing (with salting and specialized algorithms like bcrypt or Argon2) to store password digests instead of plaintext passwords. File integrity verification compares hash checksums to detect file corruption or tampering during downloads. Digital signatures hash the message first, then encrypt the hash with a private key for authentication. Data deduplication uses hashes to identify identical blocks of data in storage systems. Git version control uses SHA-1 hashes to identify every commit, tree, and blob object in the repository. Blockchain technology chains blocks together using SHA-256 hashes, with each block containing the hash of the previous block.