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How secure is Microsoft Word 2007 encryption

Microsoft word 2007 enables you to use password encryption. This is standard functionality; no additional data encryption software is needed. But how strong is Word 2007 encryption? The security of a password protected file depends on the strength of the encryption algorithm and the strength of the password. This article describes Microsoft Office 2007 password protection in depth. This includes Word 2007, Excel 2007 and PowerPoint 2007.

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How secure is Microsoft Word 2007 encryption

  1. In Office 2007 the security has improved dramatically compared to Office 2003
  2. Strong encryption is used by default. According to the National Security Agency (NSA) the encryption algorithm is allowed for TOP SECRET information
  3. Usage of strong passwords is very important
  4. To be on the safe side, we recommend a minimum password length of 10 characters
  5. Password cracker vendors declare that they do not have an easy solution for Word 2007 password protection and do not guarantee password recovery when using their tools
When should you use password protection? If your Microsoft Word 2007 document contains sensitive data, always make sure that you encrypt and password protect the file when you:
  • Store the file in a shared location or folder.
  • send the file by email (without using email encryption)
  • Store the file on a workstation that you share with other people.

History of password protection in MS-Word

In Word 95, 97 and 2000 the encryption method contains vulnerabilities. This means that the document can be decrypted within 10 seconds without knowing the password. There are password crackers that even offer online services to do this.

In Word 2002 and 2003, the default encryption method is "97/2000 compatible", which means that the same insecure encryption method is used. To achieve good encryption, one has to select a strong encryption method. See here for a description of the proper security settings in Word 2002/2003.

In Office 2007 the security has improved dramatically. Office 2007 uses strong encryption by default. This means that the only way to break the protection of a "password to open" is to guess the password. If a strong password is used, this could take years.

Strong encryption

Microsoft Office 2007 uses 128 bit AES for password encryption. In 2003, the US Government announced that the AES encryption algorithm may be used for classified information. This is specified in The National Policy on the use of the Advanced Encryption Standard (AES) to Protect National Security Systems and National Security Information (CNSSP-15).

"CNSSP-15 states that AES with either 128 or 256-bit keys are sufficient to protect classified information up to the SECRET level. Protecting TOP SECRET information would require the use of 256-bit AES keys as well as numerous other controls on manufacture, handling and keying. These same key sizes are suitable for protecting both national security and non-national security related information throughout the US Government." (, see also AES in wikipedia)

Word 2007 by default uses AES 128 bit strong encryption. Also, if you open a document created in the older versions of office (2002, 2003) in Office 2007 with the default encryption mode, the old encryption algorithm will be replaced with the strong 128-bit encryption. Itís even possible to use 256-bit encryption.

This means that Word 2007 encryption can be used for top secret information as far as the encryption algorithm is concerned. But the password strength is just as important.

Secure password

If the encryption method is strong, the only way for a cracker to break the document security is by trying to find the password. It's important to know the difference between weak and strong passwords.
  • A weak password is easy to guess or quick to crack.
  • A strong password is hard to guess but easy to remember. It has enough length and complexity.
Let's have a look on how specialized tools break password protection. This gives us an idea of what weak passwords are.

How password crackers work

Password crackers are automated tools dedicated to finding passwords. Usually the steps are:
  1. password guessing
    • Name of partner, child, pet animal, holiday destination, date of birth, etc. Someone who knows you is able to guess your password!
    • Simple words or given names combined with the numbers of the month are considered weak as well, e.g. "welcome01", "Alex11", etc.
  2. dictionary attack (trying all words from a dictionary list, e.g. list of names)
    • "qwerty", "letmein", "Aaron",
  3. optimized brute force attack (trying all character combinations that might be an existing word)
    • This dramatically boosts Brute-Force attack speed by skipping password checks of nonsense combinations of characters. Some suppliers claim 95% recovery rate for English words.
    • Usable for passwords up to 9 characters length
  4. brute force attack (if nothing else works: try every possible combination of characters) .
    • "a", "b", "c", .., "aa", "ab", "ac", .. , "a1", "a$", "a{", etc.
    • Short passwords (less than 5 characters) are weak because the number of possible combinations is limited. These short passwords can be cracked within seconds.
    • Usable for passwords up to 7 characters length
To be on the safe side, we recommend a minimum password length of 10 characters.

Password cracker vendors do not have an easy solution for Word 2007

Unless the password is very short, can be guessed or consists of a simple dictionary word, you have to try a brute-force attack. When brute-forcing, the time to crack the password depends on the amount of possible passwords that the cracker has to try. The amount of possible passwords increases with password length and with increasing diversity of characters being used (complexity).

On Word 2007 password protected documents it is possible to use the regular brute force method. However, the password encryption algorithm uses a technology that significantly slows down and complicates the brute force attack. The result is that a password cracker will need a great amount of time, ranging from several months to many years. Even the most optimized password breaker works very slowly.

Password cracker vendors do not have an easy solution for Word 2007 password protection and do not guarantee success. This is why they even started to provide their service on a no cure, no pay basis. Only if the password is found, the program informs you and prompts you to pay the Service Fee.

EncOffice: Easy and Safe Encryption of Word 2002\2003 documents
  • Adds a "Safe Encrypted" button to the Word toolbar
  • Helps to choose a strong password
  • Makes encrypted copy of the original document with extension ".enc.doc"
  • You can open the encrypted document with a standard Word version
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