Decrypting Microsoft Excel / Word documents

Password-protected Microsoft Office 97-2000 documents are encrypted using a short encryption key, only 40 bits in length. That’s why it’s possible to direct the attack against the key, not against the password. As soon the key is found, the document can be decrypted instantly. The key search time and document decryption time do not depend on password length or complexity.

The time needed to find the encryption key depends on the search method used but is always less than the time needed to recover a complex password.

Passcovery Suite implements two encryption key search methods:

  1. Key search in the rainbow tables. To search for the key, the application uses an array of pre-computed values organized in tables, whose full size is about 13 GB. The average key search time is 20 to 30 seconds. This approach is recommended if it’s vital to get access to encrypted data as soon as possible. Rainbow tables are available only under the Ultimate License.
  2. Key search by direct enumeration. To search for a 40-bit key, you need to check 240 values. Depending on the computing power available, full enumeration of all possible values may take from a few hours to several days.

As soon as the encryption key is found, the document can be decrypted in a matter of seconds.


Please note: Key search and document decryption is available only for password-protected Adobe PDF and Microsoft Office documents that have been encrypted using a 40-bit key (Microsoft Excel/Word 97-2000 and newest versions in the mode of compatibility with Office 97-2003).

 
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