The Zip file format itself is open source (available to the public). Compression and encryption formats used in WinZip are available as listed below.
WinZip incorporates compression code by the Info-Zip group, used with their permission. The original
Info-Zip sources are freely available by anonymous ftp. Info-Zip provides information and downloads on their web page.
Portions of the gzip source by Jean-loup Gailly is used by permission. The original sources to gzip are available here.
WinZip uses AES encryption and decryption routines written by Dr. Brian Gladman. The source code for these routines is available to any interested party under an open source BSD or GPL license from the AES project page on Dr. Gladman's web site. This is the same AES code that is incorporated into WinZip.
WinZip also makes use of Decoding subroutines based on the UUDeview package copyrighted by Frank Pilhofer, the PPM algorithm of Dmitry Shkarin, the "carryless rangecoder" placed into the public domain by Dmitry Subbotin, the open source bzip2 compression tool by Julian Seward, and the open source WavPack compression technology of David Bryant. WinZip decompresses 7z archives using the 7zxa.dll library. 7zxa.dll is a part of the 7-zip archiver available on www.7-zip.org and distributed under the LGPL license.
Questions about these various formats should be directed to the persons or companies mentioned.