Windows has had built in zip file support with encryption since Windows XP, unfortunately the quality of this encryption is poor as evidenced by the number of commercial programmes available to crack it. Winzip, WinRAR are trialware commercial programs that offer secure AES encryption to your compressed files but cost between 23 and 30 Euros per user. 7-Zip is an open-source, free utility that offers AES-256bit encryption. In this how-to I will show you how to install and produce 256-bit encryption of your compressed files.
A short introduction to Encryption
Encryption is a way of scrambling the data within your files to prevent a third party eavesdropping. Encryption can be symmetric, where the same password is used for encrypting and decrypting the data. Asymmetric encryption is the method using the concept of public and private keys eliminating the need to transfer a password between the 2 parties.
Encryption within Windows
Windows supports the use of ZIP or compressed folders, however it is hampered by the use of weak encryption, that can be brute-forced using a myriad of programs in minutes to hours with a modern PC. Winzip, WinRAR, 7-Zip and others offer the more secure AES standard. AES, like any encryption scheme, can be broken given time, but this is likely to run into hundreds if not thousands of years.
Installing 7-Zip
1. Download the most modern non-beta version from here.
2. Install using default options.
Using Z-Zip
As default 7-Zip installs itself to with “explorer extensions” that allow you to right click on items on the desktop or in windows explorer to compress files. Z-Zip has its own file format 7z which is more efficient at compressing files than the standard zip extension, but this will mean the person you are sending the file to will also have to use 7zip. Using the zip format will enable people using other programs to de-compress the file.
1. Right click on the files or folder you wish to compress and encrypt.
2.Firstly change the Archive format to Zip (or use 7z if both you and your intended recipient use 7zip), then change the encryption method to the robust AES-256, thirdly enter your password. Then click OK. The rest of the options can be left as default.
Decryption
Simply right-click on the file, select extract then enter the password when requested.
Important Notes
Your data will still be vulnerable to a “dictionary attack” where an attacker cycles through common passwords such as “Love”, “Password” etc. To protect from this simply make your password a mixture of numbers and letters rather than simply a single English word. One way to protect from this would be to use a random generated password or use asymmetric encryption.
For a comparison of software for compressing files see here.
11 responses so far ↓
1 jonise // Nov 7, 2008 at 12:53 pm
I am trying to Decrypt a password comppresion files, i lost the password and i cannot remember the password.
please advice, if you have a software that can help me
jonise
2 James // Nov 7, 2008 at 8:17 pm
If you have used AES256 encryption then I suggest you just try all your usual passwords…otherwise err…no.
3 nick // Jan 1, 2009 at 11:48 pm
i encrypted my drive with TrueCrypt an encryption software. i now want to compress my drive to free up space. Is this possible?
4 James // Jan 2, 2009 at 8:07 pm
You can compress files that reside in an encrypted volume, which if anything will make the scheme more secure. You can’t compress an encrypted file or volume…if you could it would mean the encrpyption method is flawed.
Suggest you just 7-zip the files that are contained on the encrypted volume.
5 Jim // Jan 28, 2009 at 7:24 pm
Is it possible to build a programmitc interface to 7Zip that would allow me to extract data from a database into a CSV file and feed that CSV to 7Zip to produce an encrypted file?
6 James // Jan 28, 2009 at 7:33 pm
Yes
7 Andrew // Aug 3, 2009 at 6:46 pm
Is it possible to set the defaults format to zip instead of 7z and default AES 256 encryption when adding to archive or indeed opening the application?
If possible how would this be done? I suspect in the registry but don’t have a clue which entries!
Even more complex… can it be set so the user has to use a minimum number of characters in the password before encryption can be completed?
Thanks
8 Hi! // Aug 11, 2009 at 12:40 pm
Were part 2 of 10 killer free apps for the Medical Research Student (Windows) ;)?
(I can not post coment in that topic)
You do cool thing… gathering academic soft together
And try PDF-XChange Reader (FREE version for personal http://www.docu-track.com/home/prod_user/PDF-XChange_Tools/pdfx_viewer) that can add notes, highlite, adding text and more to your pdf-papers (with saving what you do).
For bibliography you may try Mendeley - it’s like Papers (Mac apps). It have a module to adding reference to MS Word or OO.org (OpenOffice). Or You can try Zotero with same features but it is FireFox extantion.
For translating try StarDict
p.s. sorry for my spelling.
9 Daniel // Aug 26, 2009 at 11:38 pm
Passwords are far easier to crack if file names are not encrypted.
To make your password-protected file secure you need to select the 7z file format and check the “Encrypt file names” option.
10 Euan // Aug 27, 2009 at 10:22 am
what characters are not supported with 7zip password?
I have created a password generator in SQL Server which covers all letters, numbers & characters but had issues with passwords including the ‘>’ character; do others exist which I can remove from the generator?
11 Joe // Jul 19, 2010 at 1:36 pm
Does 7 zip allow for data at rest encryption? In other words encryption “before” I compress and transmit?
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