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This seems like a simple question to find an answer for on Google but I'm having no luck, and when sites do mention anything about it, I fear that they are using "password protect" and "encrypt" interchangeably. If I compress a file using the built-in Windows XP compression capabilities, then go to File, Set Password, and set a password on that file, is that file actually being encrypted using ANY cipher (regardless of how strong), or is the password just some Windows XP function that can be easily bypassed by opening it with a different program or something?

Also, if it is being encrypted, any idea what the cipher is?

I know I could use better tools like 7-zip or something, but for the sake of argument I'm just wondering what the built-in tool is doing.

UPDATE: For anyone that needs this, the answer to my question specifically is here: http://security.stackexchange.com/a/20937

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Your answer can be found here: security.stackexchange.com/questions/5447/… –  Shiki Nov 1 '12 at 17:21
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Which built-in Windows XP compression capability are you using? File compression (EFS) or archive compression (zip)? The answer to this question is completely different depending on exactly what you're doing. –  David Schwartz Nov 1 '12 at 17:22
    
@Shiki thanks. I saw that post while googling, but the responses with the most votes were not very useful since the question asked "how secure" instead of asking for specifics. But after looking again, someone did provide useful info security.stackexchange.com/a/20937 Thanks! –  electronsrock Nov 1 '12 at 17:31

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In the documentation for Encrypting File System:

  • Files or folders that are compressed cannot also be encrypted. If the user marks a file or folder for encryption, that file or folder will be uncompressed.

In other words, if you use Windows XP's native tools to compress your files, then they cannot be encrypted.

This document provides a very good overview on the Encrypting File System. Some important details: - Encryption happens at the file-system level, therefore there is no impact to applications - File encryption uses a symmetric key, which is then encrypted with the public key of an encryption key pair, and is bound to user identity. In short, your windows username / password, as well as 2 further layer of security is applied. - Your Windows logon password is the weakest link - The ciper (algorithm / implementation) used is FIPS-140

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