In Office XP and 2003 an opportunity to use a custom protection algorithm was added. The protection presents no difficulties to hacking software. The Office-algorithm contains multiple vulnerabilities rendering it insecure. Office 97, 2000, XP and 2003 use RC4 with 40 bits. They can be cracked instantly with the help of precomputation tables. Because it's only like a Vigenere Cipher. Hacking software is now readily available to find a 16-byte key and decrypt the password-protected document. In Excel and Word 95 and prior editions a weak protection algorithm is used that converts a password to a 16-bit verifier and a 16-byte XOR obfuscation array key. History of Office Encryption Weak encryptions In Excel passwords restrict modification of the workbook, a worksheet within it, or individual elements in the worksheet.
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