Is Zip coming undone?

Incompatible new versions of the popular file-compression format could put the squeeze on users and as a result unravel support for Zip.

David Becker Staff Writer, CNET News.com
David Becker
covers games and gadgets.
David Becker
5 min read
New versions of software based on a popular file-compression technology could create headaches for users through their use of incompatible formats.

For more than a decade, Zip has been the most common format for shrinking files in order to more easily store them or transmit them over the Internet. Dozen of software programs, including tools built into recent versions of Microsoft's Windows operating system, can read and decompress any file bearing the .zip extension.

But that accessibility has changed since the release, earlier this year, of a new version of the PKZip application for creating and reading Zip files from PKWare, the small, Wisconsin-based software maker that created and published the Zip standard. The new version and a subsequent update include advanced security features that--for now--are exclusive to PKWare.

Connecticut-based WinZip, creator of the most popular competing Zip utility, responded last month with a new version of its software. The WinZip update includes similar security extensions, but they're based on different encryption keys that are incompatible with PKWare's format.

Both programs use the basic .zip file extension to designate both secure and standard files. The upshot? People who receive a file with .zip now won't know until they try to open it whether it's one of three types: a secure file accessible only through PKWare's software; a secure file accessible only through WinZip; or a standard Zip file that can be accessed by any compression utility.

"The last thing you want to do is send someone an important file in a format they can't read," said Amy Wohl, an independent technology analyst.

PKWare and WinZip have pointed to each other as the source of the potential confusion. WinZip needed to add security enhancement to its software to stay competitive, company executives have said--and without access to PKWare's encryption scheme, it had no choice but to come up with its own.

The rival companies both sell data-compression utilities with tools for creating and managing compressed files, and these both compete with basic decompression programs available free from other software makers.

Finding a place for Zip
The need for file-compression utilities--once a staple of PC use--has diminished in recent years, as broadband Internet connections and huge hard drives have lessened the need for squeezing files to save space. In addition, support for basic reading and extraction of Zip files has been built into recent versions of Windows.

The security additions in both WinZip and PKZip are intended to attract enterprise customers, by emphasizing Zip as a secure way to exchange files rather than simply as a way to save space on a hard disk.

WinZip is the leader in the market, according to rankings on CNET Download.com, a sister site of CNET News.com. The site tallied more than 100 million downloads in nine months for the last version of WinZip, compared with 1.6 million in five months for PKZip.

WinZip said in a statement that its encryption methods are published and available to other software developers.

"It is the desire of WinZip Computing to avoid the potential splintering of the Zip file format...and the resulting incompatible Zip file utility programs...that would result from various vendors' introduction of proprietary and undocumented stronger encryption formats," read the statement, which accompanied the publication of its security methods and is posted on WinZip's Web site.

"We believe that use of the free encryption code and of this specification will make it easy for all developers to add compatible advanced encryption to their Zip file utilities," the statement read.

PKWare has said it plans to license its security technology as a standard for other software developers to add encryption to their Zip products. It will do this while it waits to see if it will be granted patents for the security-related extensions, applied for recently. Meanwhile, Zip users concerned about compatibility can stick to the standard Zip format.

"It is important to note that the integrity of the Zip standard has been preserved, and PKWare will make every attempt to support the open standard for the Zip file format as it relates to compression, which is part of the company's important heritage for the past 15 years," a PKWare representative said.

Caught in the middle
The format incompatibility affects dozens of software makers that include some level of Zip support in their products. Aladdin Systems, based in Watsonville, Calif., makes the popular line of StuffIt applications that read and create files compressed with the company's own format and with Zip.

Darryl Lovato, president and chief technology officer, said he hasn't figured out yet how to address the security extensions. He expects the resulting incompatibility will erode support for the aged Zip format.

"They've broken the only thing Zip still had going for it, which was ultimate compatibility," he said. "The Zip format has always been a sure thing--you knew a .zip file was a .zip file. Now, all of the sudden, people are going to get a .zip file they won't be able to open, and they'll assume it's corrupted."

Lovato said one interim solution would be for PKWare and WinZip to come up with a new file name other than the familiar .zip extension. "Then at least people would know it's not a regular .zip file," he said.

The PKWare representative said use of the .zip extension is still appropriate because the secure files are based on the standard Zip format, which includes "versioning" support that tells users if the file is secured. Secure files can be read using the free version of the company's PKZip Reader, the representative added.

The debate could also raise interest in other file-compression formats and programs, Lovato said.

Besides Aladdin's proprietary SIT format, open standards such as RAR and CAB are supported by most third-party compression utilities. "Once people have a choice of creating an incompatible Zip file, they may just decide to use something else," Lovato said.

Analysts said that may be inevitable, no matter what the outcome of the standards debate. Wohl said that much of the value of the Zip format had rested on the ability to shrink files so they could fit on a floppy disk. With recordable CD disks and USB (universal serial bus) drives close to rendering floppies obsolete, "a lot of the reason for using .zip...has sort of evaporated," she said.

Still, recasting Zip as a way to transmit files securely could add life to the format, Wohl said, especially as growing use of wireless networks raises new concerns about data security. But a secure Zip format won't be too attractive without reasonable assurance that the recipient can access the document.

"Until you get a single standard that everyone agrees on, then you've got a problem," Wohl said.