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I want a colleague of mine to send me a sensitive Microsoft Word document via e-mail. Since Word's encryption is questionable, I would like to encrypt the file using a passphrase.

Do you know of any encryption method that a novice user can easily use? I wouldn't like to prompt for keys or anything like this - just provide a simple interface for single file encryption.

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Udui: Try putting your solution into an answer and mark it as accepted. That way it is possible to earn rep from your answer, and it fits in with the model of SU better. –  David Pearce Jul 24 '09 at 3:55
    
I have added it, in details, below. –  Adam Matan Jul 24 '09 at 13:55

5 Answers 5

Although it might be a bit overkill, TrueCrypt allows you to encrypt files and folders and shows up as a removable device in My Computer. It is free and (in my opinion) user friendly.

Main Features:

  • Creates a virtual encrypted disk within a file and mounts it as a real disk.

  • Encrypts an entire partition or storage device such as USB flash drive or hard drive.

  • Encrypts a partition or drive where Windows is installed (pre-boot authentication).

  • Encryption is automatic, real-time (on-the-fly) and transparent.

  • Parallelization and pipelining allow data to be read and written as fast as if the drive was not encrypted.

  • Provides plausible deniability, in case an adversary forces you to reveal the password:

  • Hidden volume (steganography) and hidden operating system.

  • Encryption algorithms: AES-256, Serpent, and Twofish. Mode of operation: XTS.

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Does it support simple SINGLE-FILE encryption? From what I remember, it only supports volume encryption. –  Adam Matan Jul 23 '09 at 9:27
    
It doesn't support single-file encryption unfortunately. But it's a very strong encryption. –  KovBal Jul 23 '09 at 9:30

Check out AxCrypt. It's open source and made for encrypting individual files.

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+1: I used AxCrypt for years before I switched to TrueCrypt. It worked like a champ. –  Jon Tackabury Jul 23 '09 at 13:43
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+1 great for single file use - even using in conjunction with drop box to use on multiple computers –  Seth May 30 '10 at 11:54

There are two ways for this.

You can compress your file with some archiver like 7-Zip. They can encrypt the content. However, watch out because older versions of WinZIP for example doesn't use strong encryption. In contrast, 7-Zip uses strong AES encryption and can even encrypt file names.

Or you can use EFS. EFS works on NTFS. It doesn't ask you for a password because it uses your Windows credentials. It's important to know that this way you can't securely transfer your files. Your files are only encrypted on your HDD. If you use an USB flash drive or send a file in e-mail than it won't be encrypted.

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How strong is the new 7-zip encryption? –  Adam Matan Jul 23 '09 at 9:36
    
can't see how EFS will help with sending encrypted document in an email –  Joakim Elofsson Jul 23 '09 at 9:37
    
EFS won't help but it's great for single-file encryption though. –  KovBal Jul 23 '09 at 9:52
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+1 For 7-zip. You really have two answers here. –  Liam Nov 9 '11 at 15:09
up vote 3 down vote accepted

I have solved this using Putty Secure Copy, through a Linux box I have on the net. The user downloaded scp to the same directory where the file was, and I have send him the exact scp command by mail.

Kind of reversed the problem - using encrypted connection rather than encrypting the file. Of course, this solution might not fit everyone's needs - it works only if you have a trustworthy server.

But in second thought, one can always install a virtual machine, set the router to port-forward the ports and ask his novice friend to ssh to the virtual machine... But perhaps that's a rather long shot.

UPDATE

winscp works even better. It has simple and nice GUI that every novice user can handle.

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GPG (and the commercial PGP) have the option to encrypt something symmetrically as well as the more common (for these two applications) asymmetric option. i.e. It let you encrypt something using a passphase, and later decrypt it using that passphase. Either program can decrypt what the other one have encrypted (using the right passphase obviously).

To encrypt a file with symmetric encryption, the syntax is:

gpg --symmetric filename

To encrypt a file so that the encrypted output is in plain text, rather than as a binary file:

gpg --symmetric --armor filename

To decrypt the file:

gpg -d encrypted-filename

Since you probably want your original file back as a file, rather than coming back at you as lots of (binary) text, you'll want to redirect the output to a file:

gpg -d encrypted-filename > filename

Of course, you can use a GUI front end to do all that as well.

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It's great, but the user is used to "next->next->next", and will probably won't understand command line. Moreover, the file names are in Hebrew, which causes trouble to many apps. –  Adam Matan Jul 24 '09 at 21:08
    
Neither PGP nor GPG itself have a problem en/decrypting a file with non-ASCII name. They only care about the file content itself, not what you call it before/after. That said, Windows itself does have a problem dealing with non-ASCII text in the command prompt so one will struggle passing the file to the program which mean you would have to use a GUI frontend. PGP have GUI frontend as standard, GPG's will have to be installed separately. –  KTC Jul 24 '09 at 21:59
    
Correction - PGP itself is a GUI application, not just a frontend to something. –  grawity Jul 25 '09 at 12:53

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