Compression software companies PKWare and WinZip have agreed to make their rival approaches to encrypting zip files more compatible.

The latestbeta of WinZip's software is able to read files wrapped up and encrypted using PKWare's PKZip. Meanwhile PKZip, the free reader application, will be able to open up files compressed and encrypted in WinZip's programme.

The agreement eases fears that the ubiquitous Zip standard could become fragmented by incompatible methods of encryption. Both companies have agreed to support the other's password-based decryption.

This is positive for interoperability but shouldn't be confused as an agreement on a single standard for secure zip.

PKWare's PKZip uses an RSA-based encryption algorithm but was allegedly slow in revealing the specs of its technology to WinZip. Because of this alleged delay WinZip implemented a cryptographic approach based on AES, the next generation US –government backed encryption standard.

These rival approaches meant that, prior to this week's agreement, compressed files encrypted with one application couldn't be opened by the other - irrespective of whether or not you knew the correct password. Compatibility has never been a problem for unencrypted files.

CBRreports that co-operation on interoperability between secure zip files between the two firms was kick-started by PKWare's new licensing program. Thisprogram, announced last October, offers free Secure ZIP licenses to competitors.

Both firms continue to describe the others approach as proprietary, so an agreement for a single standard on secure Zip still looks some way away. ®