GNU Privacy Guard for Windows Home Page (GPG4Win) - The GPG4Win project recently released version 2.0.1 of their product, so I figured it was a good time to reexamine GPG4Win. There have been a few changes since version 1, most notable for me is that WinPT is no longer part of the GPG4Win distribution.

Installation

For getting started, I strongly recommend using the gpg4win-light package at first as you probably won't need Kleopatra or the german-only manuals). As for the optional modules, I'd recommend installing GPA and GPGEx at a minimum. Note that GPGOL is still only compatible with Outlook 2003 and Outlook 2007, so you may wish to not install that module if you use other versions of Microsoft Outlook. In addition, you probably won't need Claws Mail at first.

By default, GPG4Win puts your key files under (or wherever your HOMEPATH environment variable points to?):

C:\Documents and Settings\USERNAME\Application Data\gnupg

Make sure you include this location in any backup programs that you are using. Your public and secret keyrings are stored in this folder and need to be backed up regularly.

Public Key Pairs

Now we get into the theoretical realm, GPG now supports RSA signing and encryption keys (in addition to the older DSA for signing and Elgamal for encryption methods). DSA signing keys are limited to 1024 bit lengths, while RSA signing keys can be much longer (512 to 4096 bits are commonly used). The only restriction that you should keep in mind for RSA keys is that you should never sign with the same key that you use for encryption (and vice-versa). In GnuPG v2, the default is now to create (2) RSA keys for the account, one for encryption and one for signing.

Typically, you'll want signing keys to have a very long lifespan (at least 5 years, maybe as long as 20 or more). This allows you to build a much larger web of trust before your key can no longer be used to sign other keys. However, you should really expire your encryption key after a few years. Then, a bit before your encryption key expires, you should add a new encryption subkey to your key with a new expiration date.

Unfortunately, the default creation options in GnuPG will assign the same expiration to both the signing key and the encryption keys. But this can be fixed using the "gpg --edit-key" command.

Creating a GPG key

gpg --gen-key
gpg (GnuPG) 2.0.12; Copyright (C) 2009 Free Software Foundation, Inc.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Please select what kind of key you want:
(1) RSA and RSA (default)
(2) DSA and Elgamal
(3) DSA (sign only)
(4) RSA (sign only)
Your selection?

Unless you have a strong reason to use DSA/Elgamal, you may as well use the defaults in GPG v2 and pick "RSA and RSA".

RSA keys may be between 1024 and 4096 bits long.
What keysize do you want? (2048)

If you're creating a key that will expire in the next 5 years, I recommend 2048 bits. For longer durations, you may wish to use 3172 or 4096 bits.

Please specify how long the key should be valid.
0 = key does not expire
= key expires in n days
w = key expires in n weeks
m = key expires in n months
y = key expires in n years
Key is valid for? (0)

For an initial key where you're not protecting anything super critical, I suggest starting with a 25 year (entered as "25y") expiration date. You will be asked to confirm the expiration date (enter "y" to continue).

GnuPG needs to construct a user ID to identify your key.

Real name:

For personal use, I suggest just entering your name (i.e. "Thomas Harold"). But if you're creating a key for corporate/business use, I suggest adding a bit more information in this field to make things easier for others if they have more then one key with similar names. I recommend against using parenthesis in this field as it can be confusing later on. Square brackets "[]", curly braces "{}", or angle brackets "<>" are all good choices to set elements off from each other. Some examples:

Thomas Harold, Acme Inc.
Thomas Harold [Acme]
Thomas Harold
Thomas Harold {Example LTD}

Remember, that this and the next two fields are all public information that will be visible to everyone who uses your public key to send you things, or who uses your signing key to verify a signature.

EMail address:

This is very simple, you should enter the primary email address that you want associated with this key (i.e. "tgh@tgharold.com"). If you need to add additional email addresses, you can do that later using the "gpg --edit-key" command.

Comment:

The comment field is a public field and will be seen by others. I recommend putting website information here, or the full company name, or a combination of the two. Keep in mind that the contents of this field are typically displayed as enclosed in parenthesis, so avoid using parenthesis or brackets/braces here. Some examples:

www.tgharold.com
Acme Corporation - www.acme.corp
Example LTD, www.example.com

You selected this USER-ID:
"Thomas Harold [Acme] (Acme Corporate Sales - www.acme.corp) "

Change (N)ame, (C)omment, (E)mail or (O)kay/(Q)uit?

After entering those three values, you will be presented with how it might look to another user. As you can see, the comment gets wrapped in parenthesis while the email address gets presented inside of angled brackets. Once you are satisfied with how it looks, enter "O" for "Okay" to continue.

GnuPG will then pop-up a window that prompts you for a passphrase. This is extremely important. The passphrase that protects your key from unauthorized use is the weakest link of the entire GnuPG encryption chain. Pick something lengthy, yet easy to type, that is extremely difficult for someone to guess or attack. Write it down if you want, but keep that slip of paper secure in a safe or safety deposit box.

You will eventually be presented with something that looks like:

gpg: checking the trustdb
gpg: 3 marginal(s) needed, 1 complete(s) needed, PGP trust model
gpg: depth: 0 valid: 2 signed: 0 trust: 0-, 0q, 0n, 0m, 0f, 2u
gpg: next trustdb check due at 2009-12-16
pub 3200R/AAFA2876 2009-11-21 [expires: 2009-12-16]
Key fingerprint = 0324 917E C27D 2FB0 DDEF ABFA 4DEE 71F0 AAFA 2876
uid Thomas Harold [Acme] (Acme Corporate Sales - www.acme.corp)
sub 3200R/1972B360 2009-11-21 [expires: 2009-12-16]

This means that GnuPG has finished generating your key and has saved it to your keyring. This sample key (both the encryption key and the signing key) will expire Dec 16, 2009.

The key fingerprint is an important piece of information that should be given to your contacts over a secure channel. It will allow them to verify that they have the correct key and that they are not subject to a man-in-the-middle (MitM) attack when they use the key. You can find out the fingerprints of keys in your keyring using the "gpg --fingerprint" command. Typically, you would send them your public encryption key via email or some other digital method while telling them the key's fingerprint over an entirely different medium such as a telephone call or a physical piece of paper (letter / package).

Editing your key

In order to edit your key using GnuPG, you must know the 8-digit key ID. In the above example it is listed on the line that starts with "pub". For example, the key that I just created has a key ID of "AAFA2876":

pub 3200R/AAFA2876 2009-11-21 [expires: 2009-12-16]

In order to edit the key, you will use the following command:

gpg --edit-key aaFa2876

As you can see, the key ID is not case sensitive as it is merely an 8-digit hexadecimal string.

gpg (GnuPG) 2.0.12; Copyright (C) 2009 Free Software Foundation, Inc.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Secret key is available.

pub 3200R/AAFA2876 created: 2009-11-21 expires: 2009-12-16 usage: SC
trust: ultimate validity: ultimate
sub 3200R/1972B360 created: 2009-11-21 expires: 2009-12-16 usage: E
[ultimate] (1). Thomas Harold [Acme] (Acme Corporate Sales - www.acme.corp)

Command>

This shows us a bunch of information. The line that starts with "pub" gives us the following information:

pub - indicates that this is the primary key (you will also see "sub"
3200R - this is a 3200 bit RSA key (R=RSA, D=DSA, g=Elgamal)
AAFA2876 - the key ID (or subkey ID)
created: / expire(d|s): - the creation and expiration dates
usage: - indicates how the key can be used (S=sign, E=encrypt)

Useful commands at this point are:

fpr - show key fingerprint
list - list key and user IDs
quit - exit without making changes

Changing the expiration date

By default, all operations will occur to the primary key (the "pub" line) in this keyset. So before you edit a subkey, you need to tell GnuPG to work with that key. These keys are simply numbered 1-N as they are shown in the list.

Command> key 1

pub 3200R/AAFA2876 created: 2009-11-21 expires: 2009-12-16 usage: SC
trust: ultimate validity: ultimate
sub* 3200R/1972B360 created: 2009-11-21 expires: 2009-12-16 usage: E

This puts an asterisk by the "sub*" line telling us that we're going to work on the subkey with ID "1972B360".

Command> expire
Changing expiration time for a subkey.
Please specify how long the key should be valid.
0 = key does not expire
= key expires in n days
w = key expires in n weeks
m = key expires in n months
y = key expires in n years
Key is valid for? (0) 6m
Key expires at 05/19/10 20:28:31 Eastern Daylight Time
Is this correct? (y/N) y

You need a passphrase to unlock the secret key for
user: "Thomas Harold [Acme] (Acme Corporate Sales - www.acme.corp) "
3200-bit RSA key, ID AAFA2876, created 2009-11-21

pub 3200R/AAFA2876 created: 2009-11-21 expires: 2009-12-16 usage: SC
trust: ultimate validity: ultimate
sub* 3200R/1972B360 created: 2009-11-21 expires: 2010-05-20 usage: E

As you can see, the subkey's expiration date changed from "2009-12-16" to "2010-05-20". If we had wanted to change the primary key's expiration date, we would've entered "key 0" then "expire" at the "Command>" prompt.

Once you are happy with the new expiration dates, enter "save" to save and quit the key editor.

Adding another User ID to the key

Let's say that you want to add a second email address to your key pairs. As before, you're going to use the "gpg --edit-key" command to do this.

gpg --edit-key AaFa2876

Then you'll issue the "adduid" command.

Command> adduid
Real name: Thomas Harold [Example]
Email address: tgh@example.com
Comment: www.example.com
You selected this USER-ID:
"Thomas Harold [Example] (www.example.com) "

Change (N)ame, (C)omment, (E)mail or (O)kay/(Q)uit? O

Your key will now look like:

pub 3200R/AAFA2876 created: 2009-11-21 expires: 2012-11-20 usage: SC
trust: ultimate validity: ultimate
sub 3200R/1972B360 created: 2009-11-21 expires: 2010-05-20 usage: E
[ultimate] (1) Thomas Harold [Acme] (Acme Corporate Sales - www.acme.corp)
[ unknown] (2). Thomas Harold [Example] (www.example.com)

Now that we have two User IDs associated with this key, we should flag one of them as the primary.

Command> uid 2
Command> primary
Command> uid 0

pub 3200R/AAFA2876 created: 2009-11-21 expires: 2012-11-20 usage: SC
trust: ultimate validity: ultimate
sub 3200R/1972B360 created: 2009-11-21 expires: 2010-05-20 usage: E
[ultimate] (1) Thomas Harold [Example] (www.example.com)
[ultimate] (2). Thomas Harold [Acme] (Acme Corporate Sales - www.acme.corp)

The asterisk by the number in parenthesis is the currently selected user ID. If you see a dot/period after the number in parenthesis, that indicates which user ID is the primary.

Backing up your key

The following command allows you to export your secret key to an ASCII armored text file.

gpg -a --export-secret-keys aafa2876 >> my-secret-key.asc

You should also export your currently usable public encryption key.

gpg -a --export aafa2876 >> my-public-key.asc

You should print these files out as well as keeping an electronic copy in a secure location such as a safe or safe-deposit box. Don't leave the secret key ASCII file laying around. A sealed security envelope with a phrase and the current date written across the sealed flap and then covered with transparent tape is a good countermeasure to detect tampering.

Labels: 2009, Encryption, GnuPG

posted by Thomas at 18:04 (0 comments)

Back when one of my users created their GPG keys, they put some bogus text in the Comment field because they didn't realize the public nature of the field. So their name looks like:

Joe Smith (bogus text) jsmith@example.com

Which isn't really what we wanted it to look like. So the question is how to adjust the key on the fly using WinPT and publish the changes. We could just revoke the key and create a new one, but that would require re-signing and re-doing trust information for the new key.

According to various sources, the proper way to do this is with the "REVUID" command (not the "DELUID" command). While you can never remove a UID associated with your keys from the public key servers, a revocation tells people that the old identity (UID) is no longer used.

Performing the key edit in WinPT:

1. Open up the WinPT key manager, find your key, right-click and choose "Key Edit"
   
2. The "Key Edit" window will display showing the keys associated with this key set (top pane) and the User IDs (UIDs) associated with the key set (lower pane).
   
3. Highlight the incorrect UID, pick "REVUID" from the Command list and click "Ok"
   
4. You will be prompted for your passphrase. Enter it.
   
5. You will be asked to confirm this operation.
   
6. The Validity column for this UID will now say "Revoked".
   
7. In the Command list, choose "ADDUID" and click "OK".
   
8. Enter the correct information for your new ID. Remember that all 3 fields are public information. Comment is typically either the name of your company or a website URL.
   
9. Backup your keys (especially the secret key).
   
10. Distribute your updated public key.
    

For information on backing up a key, see my previous post on GPG4Win.

Note #1: If you have multiple UIDs associated with a key, you can use the "PRIMARY" command to flag one of the UIDs as the default UID to display in the key list. Simply select "PRIMARY" from the Command list, highlight the UID you want as the primary and click "OK". However, this only works in WinPT... in most other implementations, the default UID is the last one added to the key.

Note #2: Prior to exporting the key or giving it to anyone else, you can use the DELUID to remove UIDs from the key. But once you have published a UID for a particular key, only the REVUID command will do what you want.

Labels: 2006, Encryption, GnuPG, Security

EMail-Security using GnuPG for Windows - GPG4Win offers better integration of GnuPG into Windows them past products (such as using WinPT with the command-line version of GnuPG). That means that the user experience is a lot nicer and it doesn't seem as clunky.

You can download GPG4Win here. The current version is: 1.0.2

Notes:

• GPGol (the MS Outlook plugin) only works with Microsoft Outlook 2003 (or later?), so if you are using older versions of MSOutlook be sure to *not* install this
  
• You probably won't need to install Sylpheed-Claws either, unless you are looking for a new e-mail program
  
• I prefer WinPT over GPA, but your tastes may be different
  

Installation:

1. Download and run the gpg4win-1.0.2.exe file
   
2. When you reach the "Choose Components" screen, you should deselect GPGol, GPA and Sypheed. And unless you speak German, you should deselect the Novice Manual and Advanced Manual components. So for most users you will only be installing: GnuPG, WinPT and GPGee.
   
3. Click "Next" and proceed.
   
4. At the "Install Options", I recommend only installing links to the "Start Menu" (and not the Desktop or Quick Launch bar).
   
5. Finally, proceed forward (using the "Next") button until you reach the "Install" button.
   
6. Clicking on "Install" will begin the installation.
   
7. After installation finishes, you can click on "Next" and "Finish" to exit the installation wizard.
   

Getting started

1. Go to "Start" --> "Programs" --> GnuPG for Windows --> WinPT
   
2. That will start the WinPT application.
   
3. If you have pre-existing GnuPG keyrings, you should probably select the import option (Copy GnuPG keyrings from another location). But you can also import existing keys at a later time.
   
4. For now, we will create a GnuPG key pair
   
5. Click on the "Expert" button
   
6. Key type: DSA and ELG (default)
   
7. Subkey size in bits: 2048 (you may wish to use 3072 or 4096)
   
8. Real name: (enter the name that you wish to associate with this key) This name will appear alongside your key on public keyservers.
   
9. Comment (optional): (typically a company name) Note that comments are public information and will appear alongside your key on the keyserver. Most people put their company name in this field, while others enter their website address (i.e. "www.tgharold.com").
   
10. Email address: (enter the e-mail address associated with the key) Again, this is public information that will be on the keyservers to allow people to find your public key.
    
11. Expire Date: Uncheck "Never" and enter an expiration date of a few years (I'd recommend 2 or 3 years).
    
12. Click the "Start" button
    
13. Enter the passphrase that you wish to use when protecting this key. I would recommend a rather strong one made up of numerous randomly picked words, letters, numbers and symbols. I will talk about protecting this passphrase later on.
    
14. Repeat your passphrase in the new window. This is done to ensure that you didn't mistype it the first time.
    
15. The progress dialog will now appear as GnuPG creates the keys for you. This can take a while as GnuPG needs to obtain random data from the system. You can speed the process up by typing nonsense into a document and moving the mouse in an erratic manner.
    
16. When GnuPG finishes, it will pop up a window that says "Key Generation Completed"
    
17. You will be offered the chance to backup your keyring. Click "Yes" and choose a location. I would recommend a USB key or a floppy disk as a backup target.
    
18. The key has been created and is now listed in the WinPT Key Manager
    

Configuring WinPT Options

1. Right-click on the WinPT icon in the System Tray
   
2. Select Preferences --> WinPT
   
3. Any options that I do not mention are optional and can be set to anything you desire. (Meaning that I don't have a specific recommendation for that option.)
   
4. CHECK - Do not use any temporary files
   
5. CHECK - Use clipboard viewer to display the plaintext
   
6. Cache passphrase for N minutes should be set to a value that you are comfortable with. If you set your machine to automatically lock after 5 minutes, you could cache the passphrase for longer. But if you don't automatically lock your workstation whenever you are away from the machine you should choose a shorter timeout period.
   
7. CHECK - Automatic keyring backup
   
8. SELECT "Backup to" and choose a folder location that is on a drive other then C: (such as a USB key drive or a TrueCrypt volume)
   

Configuring GnuPG Options

1. Right-click on the WinPT icon in the System Tray
   
2. Select Preferences --> GPG
   
3. There's nothing in particular that I feel needs to be changed here, but it does let you add a comment line for ASCII armored files.
   

Importing old keys into WinPT

1. Right-click on the WinPT icon in the System Tray
   
2. Select "Key Manager"
   
3. Under the "Key" menu, select "Import"
   
4. Browse to your old secring.gpg file
   
5. Highlight the keys that you want to import and click "Import"
   
6. For each key that you've imported, you will need to set the "trust" level of the key. Note that you can only set "owner/trust" values for keys that have not expired (see the "Validity" column in the key manager).
   
7. Right-click the key and choose "Properties"
   
8. If you are able to change the trust level, the "Change" button next to the "Ownertrust" field will be enabled. Click on "Change" and set your trust level for a particular key.
   
9. Note: Trust values are important. Never set a trust level higher then you feel comfortable with. Verify that you have the right key and that you have validated the fingerprint of the key through a secure channel.
   
10. 2nd Note: WinPT does sometimes crash after importing large quantities of keys. And you sometimes have to exit the Key Manager before you can see newly imported keys.
    

Final notes:

• I would recommend not using the "encrypt current window" functionality of WinPT. It is not working properly for me at the moment. However, the encrypt/decrypt clipboard functionality works fine.
  
• Make sure that you backup your secret key files
  

Backing up your secret key and passphrase on paper

1. In the WinPT Key Manager, highlight your key
   
2. From the menu, choose "Key" then "Export Secret Key"
   
3. Export this key to a secure location (such as a USB key drive, a floppy disk, or a encrypted volume / folder)
   
4. Open the .ASC file in Notepad
   
5. Change the font size using "Format, Font...". I would suggest a font of "Courier New" in a 11 or 12 point font.
   
6. Print out a copy of your private key block. That way, in a worst-case scenario, you could hand-enter (or OCR) it back into a new machine.
   
7. Jot a note to yourself at the bottom of the page to remind yourself what the passphrase is for this secret key. You may wish to be explicit or simply leave yourself vague hints.
   
8. Fold the paper up and place it into a "security" envelope. Security envelopes have printing on the inside of the envelope which is designed to prevent the contents of the letter from being read without opening the envelope. For additional security, you may wish to wrap a 2nd sheet of paper around your original sheet.
   
9. You may also include the floppy diskette containing the secret key inside of the envelope.
   
10. Seal the envelope
    
11. Write something memorable (signature, today's date, a song that is playing on the radio) along the sealed flap. That will give you a chance to detect tampering if the attacker does not reseal the envelope in a way that the markings still line up.
    
12. For additional security, place clear tape over the flap edge (and over your writing). That makes it more difficult to open without destroying your writing.
    
13. Jot a note to yourself on the outside of the envelope (today's date, the e-mail address of the key)
    
14. Place the envelope in a secure location (such as a bank vault, document safe), preferably at a location that is physically distant from your computer. You should keep this envelope as secure as you would your will or other important financial papers.
    

Labels: 2006, Encryption, GnuPG, Security

infoAnarchy Wiki

Eraser - File Wipe Tool (Note: I would recommend not using the new 5.8 beta until all the bugs are worked out.)

Wikipedia - File Wiping

Also, the GnuPG folks have upgraded their tools to be a little more integrated with Windows. See GPG4Win which includes WinPT, GPG and a few other tools collected into an easy to use and easy to install package. It's a lot nicer then the old system where WinPT called the commandline version of GnuPG.

...

Encryption 101

TrueCrypt - allows you to create "virtual" hard drives where the contents are fully encrypted. The simplest method is to create a virtual drive as a file on a hard drive. This file is then mounted and assigned to a drive letter. Once mounted, applications can use it just like any other drive with no compatibility issues. These drives are typically protected by pass phrases that you type in to mount the drive. Virtual drives can be configured to automatically dismount after a period if inactivity.

GPG4Win - e-mail / clipboard / file encryption. Requires the creation of a public/private keypair. The public key can be published and does not need to be kept secret at all (in fact, it's most useful when public). The private key needs to be kept secure and protected with a strong passphrase. Items encrypted with the public key can only be decrypted with the private key. For e-mail, someone would encrypt the contents of the e-mail with your private key, send it to you with the assurances that only you can decrypt the contents of the message (using your private key). In addition, messages can be encrypted with multiple public keys allowing them to be decrypted by any of the matching private keys (one message, multiple recipients). Individual files can also be encrypted by GPG/PGP, but must be decrypted before use.

Windows EFS (Encrypting File System) - A component of Windows 2000 / Windows XP. It allows you to flag individual folders or files on a hard drive for encryption on-the-fly. This allows you to work with encrypted files without having to manually decrypt/re-encrypt them. The downside is that it's difficult to backup the EFS keys, the keys can be compromised easily, and if the host O/S dies or is reinstalled you will lose access to the files. Mostly useful as a slight speedbump or in cases where you are concerned about data being left on a dead hard drive after it fails. Data kept safe using EFS must be backed up regularly (such as copying it to a TrueCrypt volume) in order to avoid data loss.

...

Practical uses:

A) Encrypted USB backup drive. I have a USB hard drive hooked up to my laptop. This drive contains a single TrueCrypt volume that I mount at login and use as a backup target every few hours. So if the laptop dies, I just install TrueCrypt on the new laptop/hard drive, mount the backup drive, and I can restore my data. But I don't have to worry about anyone else getting at the data and restoring it.

B) Encrypted volume on my laptop's hard drive. I have financial data stored on my laptop (since it's my primary machine). Needless to say, if someone were to steal my laptop, I worry greatly about their access to that information. So I have a TrueCrypt volume file in the root of my C: (C:\Personal.tc) that I mount to a drive letter whenever I need to access my financial records. In order to keep this data safe, I periodically copy the TC file to another drive or to CD-R.

Labels: 2006, Encryption, GnuPG, Security, TrueCrypt, WindowsEFS