Lookup File by Hash
SHA-1, SHA-256, MD5
SHA-1 and SHA-256 are popular cryptographic message digests. They can be used to detect accidental corruption, intentional modification, and can be used as unique identifiers for a file. The chance of there existing multiple files with the same hash is effectively zero due to random chance; the chance of somebody having intentionally created files with the same hash depends on the strength of the hash function.
SHA-256 is considered "strong" today and used in new software.Lower-case hexideximal, 64 characters
SHA-1 has shown weaknesses, but is used widely in data archiving software.Lower-case hexideximal, 40 characters
MD5 is an older but still commonly used checksum. It was originally designed in 1992 to be cryptographically secure, but is no longer considered secure in that context. It is still perfectly adequate for detecting accidental file corruption.Lower-case hexideximal, 32 characters