Cryptology ePrint Archive: Report 2004/078

Analysis of the WinZip encryption method

Tadayoshi Kohno

Abstract: WinZip is a popular compression utility for Microsoft Windows computers, the latest version of which is advertised as having "easy-to-use AES encryption to protect your sensitive data." We exhibit several attacks against WinZip's new encryption method, dubbed "AE-2" or "Advanced Encryption, version two." We then discuss secure alternatives. Since at a high level the underlying WinZip encryption method appears secure (the core is exactly Encrypt-then-Authenticate using AES-CTR and HMAC-SHA1), and since one of our attacks was made possible because of the way that WinZip Computing, Inc.~decided to fix a different security problem with its previous encryption method AE-1, our attacks further underscore the subtlety of designing cryptographically secure software.

Category / Keywords: applications / WinZip, Zip, compression, encryption, applied cryptography, attacks, security fixes.

Date: received 12 Mar 2004, last revised 9 May 2004

Contact author: tkohno at cs ucsd edu

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Version: 20040509:080710 (All versions of this report)

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