What is a hash?
A cryptographic hash function takes an input of any size and produces a fixed-length output called a digest or hash. The same input always produces the same hash, but even a tiny change in the input produces a completely different hash. Hash functions are one-way — you cannot reverse a hash back to the original input.
Hash algorithms explained
MD5 produces a 128-bit (32 hex characters) digest. It is fast but considered cryptographically broken for security-sensitive uses due to collision vulnerabilities. Still widely used for checksums and non-security purposes. SHA-1 produces a 160-bit (40 hex characters) digest. Also deprecated for cryptographic use but still common in legacy systems. SHA-256 and SHA-512 are part of the SHA-2 family and remain secure for modern use. SHA-256 outputs 64 hex characters; SHA-512 outputs 128.
Use cases
Hash functions are used everywhere: verifying file integrity (checksums), storing passwords securely (with salting), digital signatures, message authentication codes (HMAC), and blockchain. When you download a file and check its SHA-256 checksum, you are using a hash to confirm the file was not corrupted or tampered with.
Security note
Never store plain passwords — always hash them with a slow, salted algorithm like bcrypt, Argon2, or PBKDF2. Fast hashes like MD5 and SHA-256 are not suitable for password storage on their own because they can be brute-forced quickly with modern hardware. This tool is intended for checksums, data verification, and learning.