128-bit checksum — fast, but unfit for security
MD5 is a hash function that condenses arbitrary data into a 128-bit (32 hex-char) value. Designed in 1991, it was long used widely for file checksums and integrity checks.
However, collisions — where different inputs produce the same hash — can be created deliberately, so it must no longer be used for security-critical purposes like signatures, certificates, or passwords. Use it only for simple integrity checks.