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    Microsoft Excel documents can utilize three passwords:

    • Password to open
    • Password to modify
    • Protect sheet or Protect workbook

    Password to Open

    The Password to open requires a user to enter a password to view the document.

    When the user sets a Password to open, the entire Microsoft Excel document is encrypted with the RC4 stream cipher.

    Password to Modify

    The Password to modify requires a user to enter a password to make changes to the document.

    When a user sets a Password to modify, the password is stored inside the Microsoft Excel document. The password can be viewed or changed with a hex editor.

    Protect Sheet or Protect workbook

    The Protect sheet or Protect workbook password requires the user to enter a password to no longer protect the worksheet or the workbook.

    When a user sets a Protect sheet or Protect workbook password, the 32-bit password hash is stored in the document. The password hash can be viewed or changed with a hex editor.

    Applying Passwords in Microsoft Excel

    To apply a Password to open or modify to a Microsoft Excel document, click click <File>, <Save As>, <Tools>, <General Options>. Then, select the desired encryption algorithm and the key length to use with that algorithm.

    The supported algorithms are:

    • Weak Encryption (XOR)
    • Office 97/2000 Compatible
    • RC4, Microsoft Base Cryptographic Provider v1.0
    • RC4, Microsoft Base DSS and Diffie-Hellman Cryptographic Provider
    • RC4, Microsoft DH SChannel Cryptographic Provider
    • RC4, Microsoft Enhanced Cryptographic Provider v1.0
    • RC4, Microsoft Enhanced DSS and Diffie-Hellman Cryptographic Provider
    • RC4, Microsoft Enhanced RSA and AES Cryptographic Provider (Prototype)
    • RC4, Microsoft RSA SChannel Cryptographic Provider
    • RC4, Microsoft Strong Cryptographic Provider

    The default is “Office 97/2000 Compatible.” However, even Microsoft states that this is not recommended!

    To apply a Protect sheet or Protect workbook password to a Microsoft Excel document, click <Tools>, <Protection>.

    Microsoft Excel Password Recovery

    It is possible simply to edit the Password to modify with a hex editor. It is also possible to edit the hash of the Protect sheet or Protect workbook password.

    The Password to open can be attacked with a dictionary attack or a brute force attack.

    Several programs, with widely varying capabilities, are available to help recover a lost Microsoft Excel password:

    Additional Reading on Excel Password Recovery

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    One comment
    1. Denis Gladysh

      18 December, 2014 at 11:07 am

      Here are a few important remarks about Password to Open.

      1. It’s not required to search for the password set for Excel 97-2003 (with 40-bit encryption key). The password complexity does not matter because the document can be decrypted online
      using Rainbow Tables and it will take a few minutes.

      2. Choose programs
      supporting video cards to increase the speed of searching passwords set
      for Excel 2007-2013. Searching for passwords on GPU can differ greatly.

      Reply
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