Info-ZIP is a set of open source software for working with ZIP archives, developed by the group of programmers known by the same name.
Internal ZIP unpacker, used in Total Commander by default to unpack ZIP files, is based on code of UnZip from Info-ZIP. The source of early build 1.0 beta of original info-unz.dll used by Total Commander is available on the Internet inofficially . The official way to get it by making a request by email.
What is Info-ZIP? page in Total Commander online Help