Rarely does anything of significance arise out of the blue.  PGP (Pretty Good Privacy) is the culmination of a long history of cryptographic discoveries.  Cryptography is the science of writing messages in secret codes.  It is nothing new.  Since the human race became a species of its own, we have pondered the challenge of concealing our communications from others.  Secrecy--stealth--is not a preserve of the human species.  It is a matter of survival for all our brothers, sisters and cousins in the animal world from which we have evolved.  Whether in times of peace or in times of war, we all harbor secret thoughts, feelings, desires, objectives, and so forth that we want to share only with those we absolutely trust, and that we want to carefully conceal from those who would take advantage of us if they knew what we had in mind.

Encryption makes this possible, and one of the strongest encryption tools available to us today is PGP.

Phil Zimmermann invented PGP because he recognized that cryptography "is about the right to privacy, freedom of speech, freedom of political association, freedom of the press, freedom from unreasonable search and seizure, freedom to be left alone."  You can read Phil Zimmermann's fuller explanation as to why you need PGP.  In the development of PGP, Zimmermann was greatly assisted by his knowledge of the long history of cryptography.  Like Sir Isaac Newton, Zimmermann was able to achieve what he achieved because he "stood on the shoulders of giants" who went before him.

How does PGP work?

OK, here goes; put your thinking cap on...  If this gets overly technical for you, and your eyes start to glaze over, don't worry about it.  It's nice if you can understand what's going on with Public and Private Key encryption, but it's not necessary right away.  You'll understand it better as you start to use it and as you interact with others who use it and can explain what's going on.  For now, it's sufficient to just follow the sets of numbered steps carefully in order to learn the skills required to use PGP.  But read over what follows and understand it as best you can.

When you have successfully completed Step 3 of this tutorial, you'll have created two keys to lock and unlock the secrets of your encoded information.  A key is a block or string of alphanumeric text (letters and numbers and other characters such as !, ?, or %) that is generated by PGP at your request using special encryption algorithms.

The first of the two keys you'll create is your Public Key, which you'll share with anyone you wish (the tutorial also will show you how you can put your Public Key on an international server so that even strangers could send you encrypted data if they wanted).  Your Public Key is used to encrypt--put into secret code--a message so that its meaning is concealed to everyone except you

Then there is your Private Key, which you'll jealously guard by not sharing with anyone.  The Private Key is used to decrypt--decode--the data (messages and so forth) that have been encrypted using your Public Key.  This means that  the message encrypted (encoded) using your Public Key can only be decrypted (decoded) by you, the owner of the corresponding Private Key.

The designation of one of the two keys (Key1, say) as Public and the other (Key2) as Private is purely arbitrary since there is no functional difference between the two.  PGP chooses one to act as the Public Key and designates the other as the Private Key.  If it chooses to designate them in the other order (Public=Key2 and Private=Key1), it would make no difference. This is because when either key is used to encrypt something, the other will act as the corresponding decrypting key to convert the encrypted data back into its original form. This capability is at the heart of the "Signing" process mentioned in Steps 8 through 10 below.

Public and Private Key encryption solves one of two major problems with older methods of encryption, namely that you had to somehow share the key with anyone you wanted to be able to read (decrypt) your secret message.  The very act of sharing the key meant that some untrustworthy so-and-so could intercept it--and frequently did.  Which meant your code was practically useless.

The second major problem with older methods of encryption was the relative ease with which the code could be broken.  Codes have to be incredibly complex if they're to foil the attempts of astute humans to crack them.  This is all the more the case today when we have increasingly powerful computers to do the dirty, "brute force," work of trying every conceivable combination of  key possibilities for us.  PGP, and other similar encryption systems, use a key that is really--well--astronomically large, meaning that the number of binary bits (1s and 0s) used to create it has an astronomically large number of possible combinations and the actual decimal (base 10) value they represent is--well--huge.  Unlike earlier encryption methods, the security of PGP encryption lies entirely with the key.  Earlier encryption methods relied on "security through obscurity" (ie: keeping secret the method used to do the encryption).  The methods used to do PGP encryption are known and documented.  It is PGP's selection of the complex keys used to do an encryption that makes it next to impossible to crack.

The size of the key can be increased whenever necessary to stay one step ahead of advances in technology.  Time alone will tell if PGP can stand the test of time, but for now it's one of the best encryption technologies you'll find.

If you would like to read the history of encryption and understand the origins of Zimmermann's PGP program, an excellent account is given in Simon Singh's CODE BOOK (Doubleday, New York, NY, 1999).  Find out more about PGP at the International PGP home page.  The CryptoRights Foundation is another good website for information regarding privacy issues.  You might also like to join the PGP-BASICS User group where you can find speedy and informed answers to questions that might arise as you get started using PGP.  Once you're more experienced with the program, you can join the PGP Users Mailing List so you can keep in touch with issues related to privacy.

Once the download is complete, you'll have the zipped version of the PGP program on your hard drive.  Now you have to unzip it.  For this, your best bet is to use the shareware WinZip which you'll need to have installed on your computer.  You may already have this program from when you had to install other software.  You can check if you have the WinZip program by simply double clicking on the file you just downloaded (PGPFW658Win32.zip).  If you don't have WinZip installed on your computer, or if you're in doubt, you can go get it (download it) from the web.  The best place to do this is at http://www.winzip.com/ddchomea.htm.  Follow the directions to install the WinZip software on your computer.  With a program such as WinZip installed on your computer, you are now ready to unzip and install PGP.  Here are the steps to follow:

1. Now locate the PGP zip file PGPFW658Win32.zip wherever you downloaded it on your computer and double click on it to unzip it.

2. Next you'll be prompted to run the PGP Setup program, which will begin immediately.  You'll be presented right away with the PGP Freeware 6.5.8 Setup Wizard.

3. Follow the Wizard's step-by-step directions, clicking on the Next button as you go along.  The first three screens contain info about PGP (licensing, etc.).  Read them before clicking on the Next button.

4. The 4th screen asks you to enter your name and the name of the company you work for.  Next you're asked to confirm the folder where you want the PGP Wizard to install the program.  Unless you have other ideas, accept the default for this item.

5. Keep your wits about you on the next screen, which asks you which PGP components you want to install.  You do NOT need to install PGPnet Virtual Private Networking, since for most people it's unnecessary and, as Steve Kinney points out, can create nasty network configuration problems.  So Deselect this item by removing the check mark next to it before clicking on the Next button.

6. On each of the ensuing screens, read what the Wizard has to say.  When asked, accept the defaults and let the Wizard do all the setup for you.  

7. Once the PGP software is installed, you will have to reboot your system.  PGP will prompt you to go ahead and Restart.

8. After your system has been restarted, you are ready to create your Public and Private Keys.

Now that you have the PGP software installed on your computer, you need to create a Public and Private Key pair.  This you can do at any time.  Remember as you complete the steps that follow that your Public Key is so-called because you will willingly share it with others so that they can use it to send you secret information.  Your Private Key is so-called because it alone will decode any information encoded with your Public Key.  As long as you alone have knowledge of your Private Key, your privacy is assured.  Here are the steps to follow:

1. Open PGPkeys by selecting Start/Programs/PGP/PGPkeys or by clicking on the PGPtray icon in the lower right corner of your screen and selecting PGPkeys in the pop up menu.

2. The PGPkeys window opens up, listing various people's Public Keys, among which in a short while will be yours and any others (your correspondents) that you choose to add to the list.

3. In the PGPkeys menu bar, click on the Generate New Keypair icon to bring up the PGP Key Generation Wizard.  Read the introductory dialog, then click on Next.

4. The PGP Key Generation Wizard now asks you to enter your name and e-mail address.  Do this now.  You can use any name you like and it's a good idea to use a genuine e-mail address so you can take advantage of the PGP feature which will look up the correct key for you when you are writing to a particular correspondent.  Click Next when you're done entering your name and e-mail address.

5. Now the PGP Key Generation Wizard asks you to select a key type.  Accept the default (Diffie-Hellman/DSS) and click Next.

6. The PGP Key Generation Wizard next asks you to specify a size for your new keys.  Again accept the default (2048 bits, which will give you a key so large that it would be well nigh impossible to figure out even by the most powerful computer in the world) and click Next.

7. Now the PGP Key Generation Wizard asks you when you want your key pair to expire.  Accept the default (Key pair never expires) and click Next again.

8. The PGP Key Generation Wizard now asks you to enter a passphrase.  Think about this before you proceed.  Choose a passphrase that has at least eight (8) characters (that's a minimum of 8 characters as a requirement), with a mix of upper and lowercase letters or other characters.  The greater the mix of characters and the longer the passphrase, the better.  As Herb Kanner explains, "The size of the passphrase, and the inclusion of mixed case and non-alphabetics is to increase the difficulty of a brute force attack on your passphrase."  So, if you use a longer passphrase (Herb's is 15 characters long, and Bernie's is 33!!) even if someone used a supercomputer, it would take an intolerably long time for it to try all combinations till it hit on your passphrasse.  If you'd like to read more about this important subject of Passphrases, take a look at The Passphrase FAQ.  Arnold G. Reinhold's DiceWare Passphrase HomePage is another excellent resource.

9. Enter your passphrase once you've decided what it will be, hit Tab, and re-enter it for confirmation. Then click Next again.

10. If you have entered an inadequate passphrase, the PGP Wizard will warn you and ask you to go back and re-enter another passphrase.  But if all is well, the PGP Key Generation Wizard will now go ahead and generate your key pair.  You may be prompted to move your mouse around or hit random keys on the keyboard to help the Wizard create a more secure key.  Click Next when the Wizard has finished generating your key.

11. You'll now be asked if you want to send your new Public Key to a server where others around the globe can find it and use it when they want to encrypt data they wish to send you.  This is optional, so click in the box only if you wish to do this, then click on Next once more.

That's it!  You're done creating your PGP Public and Private Keys.  Now all you have to do is share your Public Key with anyone with whom you wish to exchange secure information.  The next sections tell you how to do this, and how to use your key and those of your correspondents to encrypt and decrypt the data that you exchange.

When you want to exchange Public Keys with a particular individual or group of individuals with whom you intend to exchange encrypted information, the best way to do this is to send it as an e-mail to whoever you want to have it.  Read what follows carefully, however, so you understand how PGP works.

The recipient of your Public Key will have to have PGP installed on their own computer if they want to be able to add your Public Key to their keyring and use it to encrypt the data they want to send you.  Likewise, you must have anyone else's Public Key on your keyring in PGPKeys if you want to send them encrypted data.  This is a bit tricky to understand at first, but think about it.  Anyone who uses PGP has two keys, a Public Key and a Private Key.  Your Public Key is used by other people to encrypt information they want to send you so no one else but you can know what the information contains.  When you receive an encrypted message from someone (could be any kind of data, not just text), you use your Private Key to decrypt it.  The neat thing is that you're the only person who can decrypt the secret message because you're the only person who has the Private Key, with the passphrase that unlocks it (unless you share your Passphrase and Private Key with someone else, which would defeat the purpose of PGP!).

If you want to, you can put your Public Key on one or more servers that form an international server chain.  Effectively, this makes your Public Key available to anyone anywhere who would like to exchange secure communications with you.  Step 6 below explains how to do this.

To include your Public Key in an e-mail message, here's all you do:

1. Open PGPkeys by selecting Start/Programs/PGP/PGPkeys or by clicking again on the PGPtray icon in the lower right corner of your screen and selecting PGPkeys in the pop up menu.

2. Locate your keypair among the list of keys in the dialog box and select it (by clicking once on it).  Then copy it (Edit/Copy or control-C)

3. Start a new message in your e-mail editor, in the To: box enter the e-mail address of the recipient, and type a subject header such as "My Public Key"

4. Now click to put the cursor in the body of the e-mail, Paste your Public Key (Edit/Paste or control-V) into the body of the e-mail, and send it.

Back to the Table of Contents

It's a good idea eventually to place your Public Key(s) on what's called a public certificate server.  This is a server where anyone can access your Public Key and use it to send you encrypted messages.  You'll still be the only one who can decrypt the message because you alone have the Private Key, so you never need worry that your privacy will be compromised just because you made your Public Key public.  After all, that's why it's called a Public Key.  However, as a beginner to PGP, you may not want to do this right away, since you may well decide to change your Public Key at a later date for one reason or another.  The thing is that, once you put your Public Key on a certificate server, you can't remove it--ever, and there's no point littering the server with keys that are never going to be used.  So keep this section of the tutorial in mind for later, after you've got used to using the program and have settled into using a particular Public Key.

Here, then, are the simple steps to make your Public Key available through the certificate server at MIT.  It doesn't matter which server you post your Public Key to, by the way, since they are all interlinked.  Wherever you post your Public Key, it will be available worldwide.

1. Start by connecting to the internet, so that PGP can access the web site (in our case a server at MIT) where your Public Key can be sent and included in the database of Public Keys.

2. Open PGPkeys by selecting Start/Programs/PGP/PGPkeys or by clicking on the PGPtray icon in the lower right corner of your screen and selecting PGPkeys in the pop up menu.

3. In the PGPKeys window, among the list of keys you see there, click on the icon representing your Public Key.  This is the key you want to post to the certificate server at MIT.

4. Now pull down the Server menu, select Send to and then select the link to the MIT server at http://pgpkeys.mit.edu:11371.

5. PGP will now access the server for you and post your Public Key there.  When it's done, it'll inform you that the key was posted successfully.

Step 7: Obtaining and Adding someone else's Public Key to your keyring

Once again this is simple enough.  There are two ways to do this.  You can either have someone send you their key in an e-mail and then paste it into your keyring from their e-mail or, if they have their key already posted to a certificate server, you can go get it yourself.  Here is all you do if you get someone's public key in an e-mail:

1. First you tell your friend or friends to follow Step 5 above to send you their Public Key in an e-mail message.  

2. Open the e-mail message containing the Public Key you wish to add to your keyring.

3. Drag to select from -----BEGIN PGP PUBLIC KEY BLOCK----- all the way down to -----END PUBLIC KEY BLOCK-----.

4. Then copy it (Edit/Copy or control-C)

5. Open PGPkeys by selecting Start/Programs/PGP/PGPkeys or by clicking again on the PGPtray icon in the lower right corner of your screen and selecting PGPkeys in the pop up menu.

6. In the PGPkeys window, paste the Public Key you wish to add to your keyring (Edit/Paste or control-V).

Voil�!  Check the keys in your keyring to verify that the new key has been added to the list.

For the record, and for practice, the following are the Public Keys of the authors of this tutorial. Add these Public Keys to your keyring now.

Netiva Caftori's Public Key:

-----BEGIN PGP PUBLIC KEY BLOCK-----

Version: PGPfreeware 6.5.8 for non-commercial use <http://www.pgp.com>

mQGiBDp1yy0RBADVlyDewVwltBs7HnHCG3bXlVUODFkn/00TdbM2SPnOAIkj4giB

ylOP7Mg+Hr5y7FIBvmPWx06In6JjNQiSbpshP5YHv57UfE79nEJdWuSTQt/7j7IJ

GkHYtBRHQMIAHMgT8IB5d3gFq52jSa8hw/ixMP09a0Rw8RP9+kOE4s9UrQCg/zVH

IHswdc/mb50PjdeXwnjxQbkD/3lJYEzz8eUlFHB4rVaC1yRi21Lypf0DIMfQg5j9

xBxY4odFJKyf22PeuAjp9roURRIbGIkIGH8eXF+Mav9OqEdD80JbEn1hZuaLk1RF

k1XJjmFRdKXz+Q7JmRdbs3zXXav2cYwalgzEXT5kuXuNlThLTnLoEFop8Hl3xM4/

PdqMBACkkHb07vPY5l429tdXqL00lE6LedlBW4FLjI534QgselsrUxq5U5y0Wg1Z

//a66l5QkyaMrpsHKfkLHdaPOVCs/WeG6eLwD/cUBEM1Y9Yb5DaB0njdZB3Yxcm8

W23hpKjDanb7SbaSA16gBIWRlvrB/qU+MZAj+EXRDJmwMJq2y7QjbmV0aXZhIGNh

ZnRvcmkgPG5ldGl2YWNAb25lYm94LmNvbT6JAE4EEBECAA4FAjp1yy0ECwMCAQIZ

AQAKCRDFpFclYzXzSwiRAJ0S3djCkJJPUalRyE+vWnfnhvJmDgCfTEBN2N6GlGWO

mrOg1tQlZoWbd5q5Ag0EOnXLLRAIAPZCV7cIfwgXcqK61qlC8wXo+VMROU+28W65

Szgg2gGnVqMU6Y9AVfPQB8bLQ6mUrfdMZIZJ+AyDvWXpF9Sh01D49Vlf3HZSTz09

jdvOmeFXklnN/biudE/F/Ha8g8VHMGHOfMlm/xX5u/2RXscBqtNbno2gpXI61Brw

v0YAWCvl9Ij9WE5J280gtJ3kkQc2azNsOA1FHQ98iLMcfFstjvbzySPAQ/ClWxiN

jrtVjLhdONM0/XwXV0OjHRhs3jMhLLUq/zzhsSlAGBGNfISnCnLWhsQDGcgHKXrK

lQzZlp+r0ApQmwJG0wg9ZqRdQZ+cfL2JSyIZJrqrol7DVekyCzsAAgIH+wVFKD3A

FEdEBHqDZuKjLdLJIKHk4gloKeQ60R9NLLFynfIgSvgsii5uWLY9+gZ2FIGnP3Yc

GxZH1HASv+pG1sw0MnhutxZui3E3Mt69Uv1KTlTGYkfS+mXBw4Qr7hXavCkF45we

f/9Qlj6hSKVjy4YcewdvpopM9S4gVcBq+EdTp1negsCyj3YhFiEo0JEL40mnoHX7

HudJBbiBmknmBZOjxzBBeDPcu7fWV/LDCWiFoGg9uWy2KOcIt7sNXVJbukbSGYg2

hzOB2JPaqCqI5+4YfUCumNLd0lktT7S1V3/6xszEnybQL7tMtmrZZFAFHFAwLNPA

bLxdF/b26GbrTT+JAEYEGBECAAYFAjp1yy0ACgkQxaRXJWM180ttbQCg98c40J41

iXkP9CuqGR0LBJ46VNAAnj+5dH9N226fBp5TN0rAyxwBveTK

=0VvA

-----END PGP PUBLIC KEY BLOCK-----

Bernie Poole's Public Key:

-----BEGIN PGP PUBLIC KEY BLOCK-----

Version: PGPfreeware 6.5.8 for non-commercial use <http://www.pgp.com>

mQGiBDrlpg0RBADQIOANoihULVTQ3sddrU7XObaNMtgFY7fEpybl0fqQStPyqXHY

nMdeHQQA/d9vEviuN5kbLXW2m1Zf67mAajDc8jP/lElYQg8lv8C6XXBkVH/7i7gC

mFteHDbXCsh8Eqwh2okC3frYPpAx1I0z1VtmOGz2jFfxjVBNfuuBPhaRHQCg/0v8

TEi/i/vY7ALLMPcPCAnPgk8EAMKlb/mBTqbahBjCBWx/CLpEQQ/qVDQmlEk/BBKz

ms6t0OQXtqwcf5+kxre2Xf3XDYRYZPL9mS5oSjSLk2vma+5/Z59Xg39tWke7GULs

hle9wA8Bta/ak6t3fxCr/4MyS2BSpYsIfA+6AlPAs2rOF7EX6jOZkfhHvyS1jCBV

4Y0jA/0VoX+TaDNDZotbMT5INGMkIQS9PD8B3/ynjRdRnDpjOIVscEp0A2tyZ853

9w7TkiVoFtBg5XcM5H1j9FZBfhPg/aZGz0ofJlnvhxGiNVUE2Zxr1PwftTFUJUBu

7RqnliUsYCL00aFoEDXIJ4T18dB8a/KO9Jh520+RXOUOMe0G4rQkQmVybmllIFBv

b2xlIDxiZXJuaWVwb29sZUB5YWhvby5jb20+iQBOBBARAgAOBQI65aYNBAsDAgEC

GQEACgkQ+JGoqOuWpYh1fQCffB+5AYS1tGBpTBn8ILTGfJNZfkkAmwYgG8PbHJKG

MR2ip6RXYxqk6HfUuQINBDrlpg0QCAD2Qle3CH8IF3KiutapQvMF6PlTETlPtvFu

uUs4INoBp1ajFOmPQFXz0AfGy0OplK33TGSGSfgMg71l6RfUodNQ+PVZX9x2Uk89

PY3bzpnhV5JZzf24rnRPxfx2vIPFRzBhznzJZv8V+bv9kV7HAarTW56NoKVyOtQa

8L9GAFgr5fSI/VhOSdvNILSd5JEHNmszbDgNRR0PfIizHHxbLY7288kjwEPwpVsY

jY67VYy4XTjTNP18F1dDox0YbN4zISy1Kv884bEpQBgRjXyEpwpy1obEAxnIByl6

ypUM2Zafq9AKUJsCRtMIPWakXUGfnHy9iUsiGSa6q6Jew1XpMgs7AAICB/9fLWJk

MxqlKPuP4nfcDXxjYu5yYrtgTxnEA8LjwHILFHC6dS+TruOBehDWWq07PEihRVdK

3vY/oOSV70Du4yO2/siau4xUNhrP2dw1AKgDW1gNvQbeXYuxhs7vKDQGHDgYhUKm

z5E6hX5Z3HesujXnHWe8NtTqa1gM+SP3LF6oFkzTpuIoogRRULy6HUbis1v+Um4i

WI1EXchfauNwy6IzFYOTw41MExKtDyxTLjzBz/PfsncQc2zWpFAih8ZcqQkiOg8B

a+h7xp0hrPzXT0ewxb3aiELI+2oq6m0uwprWJE09REWgwe78gRwbiwlPDH4P/uL9

/tUA2PaCPaEkM7+EiQBGBBgRAgAGBQI65aYNAAoJEPiRqKjrlqWIZv0AoK/IfMGB

Pk7ZKtEr64R8NAArXBoQAJ9E90U+eHZzVN9jG/MVuJKwiNRYZw==

=xI2U

-----END PGP PUBLIC KEY BLOCK-----

Pranav Lal's Public Key:

Bob Rosenberg's Public Key:

If  your friend or friends have a Public Key (or Keys) already posted to a certificate server, you can go get it yourself.  Here are the steps to do this:

1. Open PGPkeys by selecting Start/Programs/PGP/PGPkeys or by clicking on the PGPtray icon in the lower right corner of your screen and selecting PGPkeys in the pop up menu.

2. Pull down the Server menu and select Search.

3. In the search dialog box, type the name of the person whose key you are looking for and hit OK.  PGP will go to the international certificate server and find the key or keys for you (many people have more than one Public Key on the certificate server).  If a Public for your friend exists on the certificate server, you'll soon see it displayed on your screen.

4. Click on the Public Key you want so as to highlight it, and then copy it (Edit/Copy or control-C).

5. Go back to your PGPkeys window where you see all the keys on your keyring.  If one of the keys is highlighted by default, click anywhere off the list of keys to make sure no key is currently selected.

6. Finally, in the PGPkeys window, paste the Public Key you wish to add to your keyring (Edit/Paste or control-V).

Back to the Table of Contents

There's something you need to know right away about PGP encryption: once you encrypt a message using the Public Key of the person to whom you're sending it, you won't be able subsequently to decrypt it and read it yourself since you don't have your correspondent's Private Key.  Most of the time this doesn't matter because you may not need to keep a copy of every message you sent.  But sometimes (maybe often, if you consider it necessary) you want to keep your own encrypted copy of a message for the record and you need to be able to decrypt it, if and when you want to read it at a later date.  The best thing to do is tell PGP to encrypt all your messages using your correspondent's Public Key as well as one of your own Public Keys (called the Default Public Key).  Here's how you do this:

1. Open PGPkeys by selecting Start/Programs/PGP/PGPkeys or by clicking on the PGPtray icon in the lower right corner of your screen and selecting PGPkeys in the pop up menu.

2. In the Edit menu select Options..., then in the Options dialog box make sure the General tab is selected

3. Click to put a check mark in the small box next to Always encrypt to default key, then click on OK.

That takes care of the problem of saving an encrypted copy of all your messages that you can readily decipher (decrypt) at a later date. Now for the steps you'll take to send (sign) and receive (verify) Clear Signed e-mails.  The following section (Step 10) explains how to do this.

Back to the Table of Contents

Sometimes you won't want to use encryption when communicating.  For example, when contributing to a listserv, posting notes that are shared with a community of folks where you can't be sure every member is using encryption, you won't encrypt your posting.  But you can sign your posting with your PGP encrypted signature which any other PGP user will be able to verify as a way of ensuring that the note is genuinely sent by you.  This notion of providing added assurance about the source of communication is part of what is known as the "Web of Trust", where people carefully validate/verify and sign each others' Public Keys so that others can find reassurance that the originator of an e-mail is who he or she appears to be.  You can read more about this concept at http://www.rubin.ch/pgp/weboftrust.en.html where Patrick Feisthammel provides a fuller explanation along with an encouragement for all users of PGP to sign each others' keys.  The concept of the Web of Trust is further explained by Hal Finney at http://www.sandelman.ottawa.on.ca/spki/html/1996/spring/msg00120.html.  For now, here are the simple steps to sign your own unencrypted mail.

1. After you have finished writing your message or e-mail, right click on the PGPtray icon in the lower right corner of your screen, then in the pop up menu choose Current Window/Sign.  The message is fed into a routine called a HASH Function (a function that converts one string of characters into a fixed length string).

2. You will be prompted to enter your Passphrase (unless you have selected the option for PGP to recall your Passphrase from what's called the "cache"--which is not a good idea unless you know what you're doing (see Step 14), so for the time being we'll assume that you will be prompted to enter your Passphrase).  In Step 14 you'll learn how to extend the time that your Passphrase is kept in the cache, along with warnings about how you should clear the cache when you leave your computer unattended for any period of time.

3. Go ahead and type your Passphrase and hit OK.

That's all there is to signing your unencrypted e-mails.  Unfortunately, signing your unencrypted mail does not, in and of itself, reliably guarantee to the receiver of your note that you are who you say you are, so you should have your Public Key signed by at least one other trusted person who trusts you and can bear witness to your integrity within the context of the Web of Trust.  This signing links your "real world"/"Offline" identity with your "Electronic"/"Online" persona.  So long as all messages are signed with the same key, that (even in the absence of any other signatures) is enough "proof" of electronic identity.

The signing is only needed if you need to do the real world linking.  The Signing of an Email serves an additional purpose beyond showing that the message was written by the owner of the key, namely that the message has not been altered between the time the owner signed it and the time you verify the signature.  So long as the Signature verifies, you know that the message has not been altered.  The verification also shows when the message was signed; thus it shows the latest time that it could have been written. This is only in theory since there is no way to prove the validity of the time stamp.  In other words: Was the user's computer set to the correct time and what time zone were they in?.  When the proof of the accuracy of the time of creation is important, there needs to be some external function applied (such as a Digital Notary signing the message or Digital Signature).  Ways in which this can be done is beyond the scope of this tutorial.  The actual signing process works as follows:

• The message is fed into a routine called a HASH Function (a function that converts one string of characters into another), that produces a string that represents the contents of the message (called a Message Digest).  Any change in the formatting of the message (such as moving a letter/word between the end of one line to the start of the next) is enough to create a different string.  Thus, altering the actual contents and not just its formatting will also generate a different Message Digest.

• The Message Digest (along with the time stamp and some other control information) is then encrypted with the Sender's Private Key to create the Digital Signature which is placed after the message text.  In an encrypt&sign operation, it is this signed text not just the message which is encrypted.

• Upon receipt (or after decrypting, if the message is not clear signed but was encrypted&signed), the Digital Signature is then decrypted with the recipient's Public Key (remember that Encryption with a Private Key allows Decrypting with the corresponding Public Key) to recover the Message Digest.

• The message itself is then fed through the Hash Function to produce another Message Digest.

• If the two Message Digests match, this proves not only that the message has not been altered but that it was signed by the Key Owner (otherwise the decrypt of the Signature would not have recovered the correct Message Digest [and control information] to compare with the newly created copy).

Warning: After you do the Verify Step, the message will be altered to contain a block of text that shows the status of the verify operation. You will be offered the chance to replace the received signed (or encrypted and signed) copy with the verified copy.  Do NOT do this replace if you want to be able to show that the text was not altered AFTER receipt and verification.  Leaving it in its (Encrypted and) Signed/Un-Verified form allows you to Re-verify it anytime you need to.

This is a sample of what a Clear Signed Message looks like:

And this is what the clear signed message looks like after being verified:

Here is a comment from a respected member of the Public Key Encryption community (Nick Andriash) in response to a request he received to sign a cyberfriend's Public Key.  "With respect to signing each other's Public Keys," Nick replied, "I have already done so with a non-exportable signature, because we have been in constant communication, and I obtained your Public Key from your web site; I am confident enough in knowing the messages are coming from the same person at the same address...  I just don't know who that person is, and that is why I cannot sign your Public Key with an exportable signature, where it will always travel with the Public Key.  For that, I insist on face to face meetings, along with an exchange of photo ID, etc., as this is the only way to maintain the integrity of one's own Web of Trust.  All of the people who have signed my Key, I have met personally, and that is as it should always be, unless we are introduced to each other by a Trusted Introducer whose signature appears on both our Public Keys."

When you sign someone else's Public Key, you are verifying that it belongs to the person who claims to own it.  You are stating that you know this individual and that the key really belongs to him or her.  As it states in the PGP dialog box for signing a key: "By signing the selected user ID(s), you are certifying based on your own direct first-hand knowledge that the key(s) and attached user ID(s) actually belong to the identified user(s)."  Then, before signing, you're asked to remember if you received the key in a secure manner (you know where it came from) or if you have verified the fingerprint with the owner.  The dialog box includes the owner's fingerprint so you could, if you wanted to, go over the fingerprint with the owner in person ideally, or at the very least over the phone, just to make sure everything's kosher.

In this way, you are able to give a key greater authenticity.  Under normal circumstances, you may think it unnecessary to validate someone else's key in this way.  You might even think it seems like overkill.  But suppose someone were to masquerade as someone else (say, as you) and put a Public Key in that person's (or your) name on an internationally available certificate server.  Then suppose that other people were to encrypt messages using that Public Key, thinking the message could be decrypted and read only by the person they THINK they're sending it to (say, you).  All the masquerader has to do now is intercept those messages and easily decrypt them because the masquerader has the Passphrase and corresponding Private Key.

As Nick points out above, there are two ways to sign someone else's Public Key.  There is a non-exportable signature, which is good for communication between familiar friends who already know and trust each other informally.  Then there is an exportable signature, based on careful, if necessary face-to-face identification and verification, which is a much stronger form of reassurance about the integrity of the owner of the Public Key.

The important rule of thumb is this:  Never, ever sign someone else's Public Key with an exportable signature UNLESS you are able to say categorically that you know who he or she is and have a strong assurance that he or she will not belie your trust.  If you follow this rule of thumb, you will be able, over time, to build up your own personal Web of Trust while extending the larger, global Public Key encryption Web of Trust.  The GNU Privacy Handbook has an excellent section on Trust, Validity and the concept behind the Web of Trust.

Here then are the simple steps to sign someone else's Public Key.  First as a non-exportable signature:

1. Open PGPkeys by selecting Start/Programs/PGP/PGPkeys or by clicking on the PGPtray icon in the lower right corner of your screen and selecting PGPkeys in the pop up menu.

2. In the list of keys in the PGPkeys window, right click on the key you wish to sign.

3. In the pop up menu, select the item Sign....  Immediately PGP presents a dialog box which lists the key you wish to sign, along with its fingerprint (a long string of hexadecimal characters).  The text in the dialog box advises you to ensure that the key you are about to sign was given to you in a secure manner, and if you're not absolutely sure, you should verify the fingerprint with the owner of the Public Key.  At the very least, unless you are quite sure the key belongs to the person who owns it, you should phone the individual and have them repeat to you the characters of the fingerprint by way of validation.

4. You'll notice a small check box next to "Allow signature to be exported" and you are advised that "others may rely upon your signature."  DON'T check this box if all you want to do is add a non-exportable signature to the Public Key.

5. Click on OK to complete the non-exportable signing of the Public Key.

Then as an exportable signature:

1. Open PGPkeys by selecting Start/Programs/PGP/PGPkeys or by clicking on the PGPtray icon in the lower right corner of your screen and selecting PGPkeys in the pop up menu.

2. In the list of keys in the PGPkeys window, right click on the key you wish to sign.

3. In the pop up menu, select the item Sign....  Immediately PGP presents a dialog box which lists the key you wish to sign, along with its fingerprint (a long string of hexadecimal characters).  The text in the dialog box advises you to ensure that the key you are about to sign was given to you in a secure manner, and if you're not absolutely sure, you should verify the fingerprint with the owner of the Public Key.  For an exportable signature, this means literally meeting with the individual face-to-face and verbally and/or visually validating that the Public Key you wish to sign with an exportable signature really and truly belongs to the person to whom you believe it belongs.  This might sound like overkill, but the fact is that an exportable signature has absolutely no value without this face-to-face guarantee.

4. You'll notice a small check box next to "Allow signature to be exported" and you are advised that "others may rely upon your signature."  For an exportable signature, check this box before you click OK to complete to exportable signature of the Public Key.

Step 12: Using the PGP encryption software to protect (encrypt) your personal documents

On your computer in the office or at home, you may well have private documents that you do not want others to be able to read.  You can use your own Public Key to encrypt these documents.  You can easily and quickly encrypt a single file or a set of files.  To decrypt the files, you simply reverse the process that follows by selecting the option to Decrypt instead of Encrypt from the PGP menu.  Here are the steps to follow to encrypt a single file or document:

1. Right click on the Start menu in the lower left corner of your Windows screen, select the Explore option in the pop-up menu, then in the left hand column of the Explore window select the C drive, for example, and you'll see the contents of your C drive listed in the right hand side of the Exploring window.

2. Right click on any document you have listed there (in the right hand side of the Exploring window) and you'll see a new item (PGP) in the pop-up menu.

3. Select PGP in the pop-up menu and then you'll see the sub-menu option to Encrypt the document you've highlighted.  Click on Encrypt.

4. Now you're presented with the Key Selection dialog box.  Double click on your own Public Key (or drag it down to the Recipients box below) and click on OK.  PGP has now created a second, encrypted, version of the document with a .pgp extension.

5. All you need do now is delete the original, non-encrypted document, so that all you have left on your disk is the encrypted file which only you can read.  Do this right away by right clicking on the original and selecting Delete from the pop-up menu.

And here are the steps to follow to encrypt a selected set of files or all the files or documents in a folder:

1. Right click on the Start menu in the lower left corner of your Windows screen, select the Explore option in the pop-up menu, then in the left hand column of the Explore window select the C drive, for example, and you'll see the contents of your C drive listed in the right hand side of the Exploring window.

2. If necessary, open the folder in which you  have saved the files you want to encrypt, and either drag across them all to select them as a group, or click to select the first file in the list, and hold down the shift key while you click on the last of the files you want to encrypt.

3. Now Right click on any document you have highlighted in the list of files you selected (in the right hand side of the Exploring window) and you'll see the new item (PGP) in the pop-up menu.

4. Select PGP in the pop-up menu and then you'll see the sub-menu option to Encrypt the document(s) you've highlighted.  Click on Encrypt.

5. Now you're presented with the Key Selection dialog box.  Double click on your own Public Key (or drag it down to the Recipients box below) and click on OK.  PGP will now go ahead and create a second, encrypted, version of each of the files or documents you selected.

6. All you need do now is delete the original, non-encrypted documents, so that all you have left on your disk are the encrypted files which only you can read.  Do this right away.  The original documents still should be selected as a block, though if they aren't, just click on the Type header at the top of the Explore window to sort the files as encypted and non-encrypted.  Now, with all the originals selected (highlighted), right click on any one of them, then select Delete from the pop-up menu.

You can also encrypt and decrypt the entire contents of a folder by simply right clicking on the folder and selecting Encrypt from the PGP sub menu.  But this is not as convenient as opening the folder first and selecting the files as a list before encrypting them since, after PGP has finished the encryption process, you'll have to delete the original files one by one.

Deleting files on your disks raises another issue, which you can learn about in the next section...

We'll be adding explanations for more PGP Options over the next few weeks.  For now, here is an explanation of how you can tweak the time frame of the cache that PGP uses to remember your Passphrase.  You'll also find out here how to Purge your Passphrase cache, a simple task which is very important to remember to do when you leave your computer unattended.  Finally, for your convenience, we've added a table listing the hotkeys available in PGP.

As mentioned above in Step 8, every time PGP needs access to the Private Key (to Decrypt an Encrypted Message or Sign an Outgoing Message or someone's Public Key) the corresponding Passphrase will need to be re-entered.  By default, PGP will remember--cache--your Passphrase for two minutes so that you do not have to re-enter it if needed more than once within this time frame.  A cache (which means "hidden" or "hiding place" in French) is a small area on your disk used by the computer to store data it needs to access quickly and frequently.  PGP's Passphrase caches are used to save you time by temporarily holding your Passphrases (you may have more than one) after you've typed them a first time in a session at the computer.  Unfortunately, two minutes is too short a time frame for most users, with the result that it's usually necessary to re-enter the Passphrase every time.  This is no problem if your Passphrase is short and easy to enter; but a short, simple Passphrase defeats the purpose of PGP which encourages the use of suitably large and complex Passphrases in order to foil attempts at cracking them, as explained above in Step 3 above.

• Altering the time that PGP keeps your Passphrase in the cache.  This will save you having to repeatedly re-enter your Passphrase every time you need access to the Private Key.  Just remember, before you leave your machine unattended, to tell PGP to forget the Passphrase [empty the Cache].  Here are the simple steps to extend the time that PGP keeps your Passphrase in the cache:

1. Click on the PGPtray icon in the lower right corner of your screen and select Options... in the pop-up menu.

2. Make sure the General tab is selected in the Options dialog box and notice the Passphrase caching options related to Single Sign-On.

3. Increase the default amount of time you want your Passphrase cached.  If you normally are at your computer for an hour or more, you might increase the time to one hour, for example.  If you always log off when you leave your computer, you might select the option to cache your Passphrase while logged on.

• Purging your Passphrase caches.

1. The simplest way to do this is to use the quick keyboard (hotkey) command: control-F12.  Hold down the control key while you press the F12 key.

The important thing is to err on the side of safety.  Don't cache your passphrase for a long period of time because if someone comes to your computer while you're away from the machine, your encrypted information will be able to be read if that person knows how to use PGP.  Depending on your circumstances (are you concerned that someone nearby might check out the contents of your computer?) you should get into the habit of purging your Passphrase caches whenever you leave your computer unattended.  Better safe than sorry.

• PGP's HotKeys.

Acknowledgements

We are grateful to the following folks who have kindly reviewed the tutorial and/or offered suggestions for improving it: Daniel Alvarez, Nick Andriash, Nathaniel Borenstein, Karen Coyle, Jim Davis, Steven Dickenson, John M. Dwyer, Harry Hochheiser, Herb Kanner, Steve Kinney, Pranav Lal, Tom McCune, Peter Meyns, Erik Nilsson, Charles Parlier, Steve Teicher, and Jacques Therrien.  If you have further suggestions to help us do a better job, please drop a line to Pranav, Netiva, Bob, or Bernie.

© Bernard Poole, Netiva Caftori, Pranav Lal, Bob Rosenberg, 2001-2009.  All rights reserved.  /  poole@pitt.edu, ncaftori@neiu.edu, pranav@softhome.net, robert.rosenberg@rarpsl.com  /  Revised June 14, 2019