Cryptology ePrint Archive: Report 2005/007

The Misuse of RC4 in Microsoft Word and Excel

Hongjun Wu

Abstract: In this report, we point out a serious security flaw in Microsoft Word and Excel. The stream cipher RC4 with key length up to 128 bits is used in Microsoft Word and Excel to protect the documents. But when an encrypted document gets modified and saved, the initialization vector remains the same and thus the same keystream generated from RC4 is applied to encrypt the different versions of that document. The consequence is disastrous since a lot of information of the document could be recovered easily.

Category / Keywords: applications / Microsoft Word, Excel, Encryption, RC4, Initialization Vector

Date: received 10 Jan 2005

Contact author: hongjun at i2r a-star edu sg

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Version: 20050111:090215 (All versions of this report)

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