Editing Microsoft Word (section)

=== Password protection ===
{{More citations needed section|date=December 2024}}{{Main|Microsoft Office password protection}}

Three password types can be set in Microsoft Word:

* Password to open a document<ref name="office.com-password-prot">{{cite web |title=Password protect documents, workbooks, and presentations |url=http://office.microsoft.com/en-us/word-help/password-protect-documents-workbooks-and-presentations-HA010148333.aspx |url-status=live |archive-url=https://web.archive.org/web/20140212134311/http://office.microsoft.com/en-us/word-help/password-protect-documents-workbooks-and-presentations-HA010148333.aspx |archive-date=February 12, 2014 |access-date=April 24, 2013 |work=[[Microsoft Office website]] |publisher=Microsoft}}</ref> 
* Password to modify a document<ref name="office.com-password-prot" />
* Password restricting formatting and editing<ref>{{cite web |date=June 22, 2010 |title=How to Restrict Editing in Word 2010/2007 |url=http://www.trickyways.com/2010/06/how-to-restrict-editing-in-word-2010-2007/ |url-status=live |archive-url=https://web.archive.org/web/20100626230112/http://www.trickyways.com/2010/06/how-to-restrict-editing-in-word-2010-2007/ |archive-date=June 26, 2010 |access-date=April 24, 2010 |work=Trickyways}}</ref>

The second and third password types were developed by Microsoft for convenient shared use of documents rather than for their protection. There is no [[encryption]] of documents that are protected by such passwords and the Microsoft Office protection system saves a [[hash sum]] of a password in a document's header where it can be easily accessed and removed by the specialized software. ''Password to open a document'' offers much tougher protection that had been steadily enhanced in the subsequent editions of Microsoft Office.

''Word 95'' and all the preceding editions had the weakest protection that utilized a conversion of a password to a 16-bit [[Encryption key|key]].

[[Key size|Key length]] in ''Word 97'' and ''2000'' was strengthened up to 40 bit. However, modern cracking software allows removing such a password very quickly – a persistent cracking process takes one week at most. Use of [[rainbow tables]] reduces password removal time to several seconds. Some [[password recovery]] software can not only remove a password but also find an actual password that was used by a user to encrypt the document using the [[brute-force attack]] approach. Statistically, the possibility of recovering the password depends on the [[password strength]].

Word's 2003/XP version default protection remained the same but an option that allowed advanced users to choose a [[Cryptographic Service Provider]] was added.<ref>{{cite web |title=How safe is Word encryption. Is it secure? |url=http://www.oraxcel.com/projects/encoffice/help/How_safe_is_Word_encryption.html |url-status=dead |archive-url=https://web.archive.org/web/20130417033732/http://www.oraxcel.com/projects/encoffice/help/How_safe_is_Word_encryption.html |archive-date=April 17, 2013 |access-date=April 24, 2013 |publisher=Oraxcel.com}}</ref> If a strong CSP is chosen, guaranteed document decryption becomes unavailable and, therefore, a password can't be removed from the document. Nonetheless, a password can be fairly quickly picked with a brute-force attack, because its speed is still high regardless of the CSP selected. Moreover, since the CSPs are not active by default, their use is limited to advanced users only.

Word 2007 offers significantly more secure document protection which utilizes the modern [[Advanced Encryption Standard]] (AES) that converts a password to a 128-bit key using a [[SHA-1]] hash function 50,000 times. It makes password removal impossible (as of today, no computer that can pick the key in a reasonable amount of time exists) and drastically slows the brute-force attack speed down to several hundreds of passwords per second.

Word's 2010 protection algorithm was not changed apart from the increasing number of SHA-1 conversions up to 100,000 times and consequently, the brute-force attack speed decreased two times more.