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THE BEGINNER'S GUIDE TO PRETTY GOOD PRIVACY
Version 1.1 (April 13, 1995)

by Bill Morton <[email protected]>



This version is for the following users:
PGP 2.6.2 or 2.6i


Table of contents:
I. The beginner's guide to pretty good privacy.
   A. Table of Contents
   B. Information about this edition.
   C. DISCLAIMER
   D. Permisson to distribute.
II. Introduction.
   A. Hello there!
   B. Definitions
   C. Of front ends and easy approaches
   D. The PGP command line.
   E. Playing for perfection
III. Some installation tips.
   A. Where to install it.
   B. Of drives and directories
   C. Generating a secret key
IV. Key Management.
   A. Sign your own public key.
   B. Extracting a public key
   C. Adding a public key to your public key ring.
   D. Key verification.
   E. Signing someone else's key
   F. The use of Secret Keys and Public Keys.
V. Preparing a text for encryption.
   A. The basics
VI. Encrypting a text.
   A. Basic encryption
   B. ASCII armor
   C. Signing a ciphertext
   D. Wiping and deleting a file
   E. A Brief note on file extensions
VII. Mailing a ciphertext.
   A. Cut and paste
   B. File size
   C. Enclosing a file
VIII. Decrypting a ciphertext.
IX. Editing the config.txt and autoexec.bat files.
   A. AUTOEXEC.BAT
   B. CONFIG.TXT
   C. Congratulations!
X. Some other interesting PGP uses
   A. Signing and clear-signing
   B. Other kinds of files
   C. Signature certificates
   D. The -c option
XI. Some ways to get into trouble
   A. Improper keyring security
   B. Accepting uncertified keys
   C. Plaintext insecurity
   D. Spy stuff
   E. When NOT to use PGP.
XII. Conclusion.


B. Information about this edition.

    This document was written with the DOS user in mind. If
you use a Mac or another operating system you will find it
necessary to adapt some of the practises described here to
your situation. However, no matter what system you use you
can read this document and benefit from it.

    This text is provided in ASCII format without page
breaks or any other printer characters inserted.

    Thank you William Evans for your diligent proof reading
and suggestions which have been heeded, mostly.

C. DISCLAIMER

You have been asked to read the documents which came with
your PGP package, especially the volume of ESSENTIAL TOPICS
and you should do this at the first possible moment. This
document will attempt to introduce you to the basic use of
PGP; the basic concepts of key management, and the basic
concepts of text security. This is to get you "up and
running" in PGP as safely as possible. Perhaps after a few
days of PGP use you will be able to go back to the original
documentation and read it more clearly.

Until then use this BEGINNER'S GUIDE.

HOWEVER, neither the author of this document, or any of its
distributors are liable for any loss, damage, or breach of
security which results from your failure to understand and
use PGP properly.

D. Permisson to distribute and other legal stuff.

    This document may be freely distributed under the
following conditions:
    This document, THE BEGINNER'S GUIDE TO PRETTY GOOD
PRIVACY, may be distributed by any electronic means; e-mail,
ftp archive, Web page, BBS file, floppy disk. The author
reserves all rights to any hard copy distribution.
Individual users may make a hard copy for their own private
use.
    When distributing this edition of THE BEGINNER'S GUIDE
TO PRETTY GOOD PRIVACY, the attached PGP signature must
remain attached and the PGP signed document and the signature
must remain unaltered.
    To obtain my public key to verify the signature on this
document please e-mail me: [email protected]
    Don't send me any money! If you find that this document
has made your use of PGP easier then all I ask is that you
help one other person to begin using PGP.
    Finally, the mention of any copyrighted software in this
document does not imply an endorsement of PGP by the
software authors.

II. Introduction.

A. Hello there!

    Welcome to the wonderful world of encryption. You
have decided for whatever reason to use encryption to
protect your e-mail and other data stored or transmitted
electronically. Good decision.

    Many people think that people who encrypt their e-mail
have "something to hide." Well they do. Just like you they
choose to keep their private thoughts to themselves and
share them only with the people with whom they choose to
share them. Or, just like you, they have information which
they wish to e-mail or store that needs to be hidden from
business competitors or even competitors in their own
office.

    The beginning of this document is going to be rather
terse. We will begin by defining a few terms and introducing
a few concepts and then get right down to installing PGP and
using it. For those of you out there who are real sticklers
for technical precision I would advise you to tune out right
now. If you want hard core information read the PGP
documentation.

    As a general rule, if a description given below is
brief that's because the technical nuts and bolts are
described in the documents and if you want to know why I'm
telling you to do something then read the documents. If a
description is long and it seems like I'm hammering the same
point over and over it's because it's a really important
point. Usually it something that's also described in detail
in the PGP documents but it's probably a point where if you
make a mistake you will compromise the security of PGP and
probably get yourself into trouble.

B. Definitions

PGP: Pretty Good Privacy, a program developed by Philip
Zimmermann which uses public key encryption. It enables two
people to communicate by e-mail, whether interoffice or
intercontinental, with the greatest probability that no one
but the sender and the receiver can read the text.

Plaintext: The actual message, text, data, program, GIF
file, or whatever. It can be read, run or viewed by anyone.
PGP can encrypt any type of data but for the purposes of
this document we will refer to the plaintext as a text or
message.

Ciphertext: What the plaintext looks like after it is
encrypted. Unreadable, unrunable, unviewable except by the
person with the key to decrypt it.

Encryption: Taking plaintext and turning it into ciphertext.

Decryption: Taking ciphertext and turning it into plaintext.

Text editor: A plain vanilla ASCII text editor is unlike a
word processor. You can encrypt word processor files but you
should be aware of some of the security drawbacks. Word
processors use swap files and automatic back-up files to
make it almost impossible for you to lose your text. This
is a good thing unless you don't want people to read your
text, either by accident or on purpose.
    For example, this document is being written with MS-
Word. When I quit for the night and save the uncompleted
manuscript in the file PGPBEGIN.DOC MS-Word automatically
saves a copy in PGPBEGIN.BAK. If I work on this document for
more than a few moments MS-Word also saves the file in an
autoback-up file in case the power goes off. Also, whenever
I edit the file MS-Word saves chunks of this file in case I
want to undo my edits. This is great for making sure I don't
lose my text, terrible for security. Certainly I could go
through my entire hard disk and delete each file but even
then a simple DOS command like UNDELETE could bring them back
to life. So for the purposes of PGP security always use a
text editor like MS-Editor that comes with MS-DOS and then
use the -w command option with PGP. (More about this later.)

Public Key: This is the part of PGP which is used to encrypt
text. This is the key that you give to other people so that
they can send ciphertext to you which only you can read.

Secret Key: This is the part of PGP which is used to decrypt
text. This is the key which allows you and only you to read
the ciphertext that was made by your public key. It is
protected by your pass phrase.

Key id: A hexadecimal number assigned to each key generated
which may be used instead of the user id to identify a key.

Key Fingerprint: A long string of hexadecimal numbers which
is diplayed when you use the PGP command:

pgp -kvc john

The key fingerprint is used to authenticate PGP public keys.

User id: This is also attached to the secret and public keys
when the keys are generated. It is the name (and e-mail
address) of the person to whom the key belongs.

Public Keyring: A file called pubring.pgp where you keep
your public key and the public keys of the people to whom
you want to send ciphertext.

Secret Keyring: A file called secring.pgp where your secret
key (or keys) is stored.

Command line: A line typed at the DOS prompt which sets a
program in action.

C. Of front ends and easy approaches

    In this document I will not be detailing how to
physically install PGP on your machine. The central focus of
this document is enabling you to use PGP with the greatest
ease with the greatest security.
    And now a word about "front ends." The term "front end"
(sometimes referred to as a "shell") refers to a program which
acts as an easy user interface for another program . Front
ends have been designed for the Amiga, MS-Windows,
Macintosh, and MS-DOS environments and to work with various
e-mail and newsreader programs. The advantage to using a
front end program is that PGP becomes easier to use. The
major disadvantage, from the aspect of learning PGP, is that
front ends hide the operation of PGP from the user. If you
learn to use PGP from the command line and develop some
understanding of what is going on, you are less likely to
make a mistake which will compromise the effectiveness of PGP
and your security. Later you may wish to take advantage of
one of the front ends which are available. That can be your
decision. However, I believe that after you work your way
through the following document you will find PGP so easy to
use that you won't need to make it any easier.

D. The PGP command line.

    The PGP command line is simple to construct because it
is made up of some basic parts. A PGP command line that you
will encounter later in this document looks like this:

pgp -seatw intro.doc John -u Mary

    Right now it may look like gibberish but by the time
you read one third of this document you will understand the
simplicity of the command line. For now let's look at the
parts and give them general names and describe each part's
use.

"pgp" These letters start Pretty Good Privacy. They will be
the first three characters that you type every time you use
PGP.

"-seatw" The command options. There are a variety of command
options that tell PGP what to do. When a command option is
being described individually it will be referred to as a
single character with a dash preceding it: "-w". However, on
the command line only one dash is needed before the command
options. Therefore to use the command options -s, -e,-a, -t,
and -w you would type

pgp -seatw

not

pgp -s-e-a-t-w

"intro.doc" This is the name of the file that is to be
encrypted. Any file can be encrypted by PGP as long as you
put its name here. The name of the document can even include
the path to the document. (This saves the necessity of
copying the document.) For example, if PGP is installed in a
directory on your hard drive called C:\PGP and the file you
want to encrypt, sales.txt is in a directory called
C:\REPORTS you could use the following command line while in
the PGP directory:

pgp -seaw c:\reports\sales.txt.

In this example PGP will create an encrypted file called
sales.asc and place it in the REPORTS directory.

"John" This is the user id attached to the public key that
you want to use to encrypt the file. This is the "name" of
the person to whom you are sending the ciphertext and the
only person who will be able to read the text.
    The user id's attached to public keys usually include
the name of the person to whom the key belongs and some
other piece of information, usually their e-mail address.
They typically look like this:

John Qwerty <[email protected]>

    The nice thing about PGP is that you don't have to type
out the complete user id to make use of the public key
attached to it. To encrypt a file using John's public key I
could type at the command line any of the following:

pgp -seaw intro.doc John
pgp -seaw intro.doc qwerty
pgp -seaw intro.doc "John Qwerty"
[The only time you must use quotes around the user id is if
there is a space included.]

    There is one "however" to include here. If you have
more than one public key on your public key ring with the
name "John" in the user id PGP will automatically pick the
first "John" it comes to. You may have to use the last name
or the full user id to pick the key you want. If you use the
full user id remember to enclose it in quotes.
    PGP public keys are also identified by a key id which
may be used to identify the public key you want to use. This
is described in the PGP documentation.
    Another nice thing is if you forget this piece of
information in the command line PGP will ask you for it.

"-u Mary" This is the user id of the person using PGP to
send the document. As you will see later this form is used
with the -s option. This is the name you used on your secret
key. If you use the -s option  and forget the -u part PGP
will use the last secret key you created.

E. Playing for perfection

    There are many ways to learn. There's memorization
which is great if you want to remember the multiplication
table but it won't work for PGP. Then there's the old "Learn
from your mistakes" method. Great if you're working on a BMW
but in the world of personal security one mistake can be
costly.
    The only way you can learn PGP safely and quickly is
through play. In the course of this guide you will create
keys for two fictional people. Then you can play a game of
sending encrypted e-mail back and forth between the two of
them.

III. Some installation tips.

A. Where to install it.

    One possible way to compromise the security of PGP is
to install it in a place where people have access to your
keyrings. You keyrings are in the files labeled SECRING.PGP,
SECRING.BAK, PUBRING.PGP, and PUBRING.BAK. These files need
to be protected from prying eyes. Therefore, installing PGP
on your machine at work which is networked to every other
machine in the office or in your account on the mainframe is
not a good idea.
    The files SECRING.BAK and PUBRING.BAK are automatic
back-up files of your keyrings. I will not mention them
again but all of the security precautions you would take for
the files ending with .PGP apply to these files. For more
information on the usefulness of the .BAK files and how to
use them please read the PGP documentation.
    Ideally, you will install PGP on a machine which is not
accessible to any other user. If you want more security,
install PGP on a floppy disk and only put that floppy into
the drive when you want to use it.
    I have installed PGP on the hard drive of my personal
computer. It is not connected to any networks and no other
users have access to it. This setup could be made extra
secure by putting my keyrings on a floppy and storing them
under lock and key somewhere else.
    If you want to use PGP in the office or any other
environment where security is an issue here's a few
suggestions:
    You could install PGP on your home computer, produce
the ciphertexts at home then move them to a floppy which you
take to your work computer, copy and send. At the end of the
day you copy all of the ciphertexts that you have received,
take them home and decipher them.
    Take PGP to work with you on a floppy, only run it when
your computer is not on the network and always take the
floppy out of the drive and lock it away. (Especially when
you go to the bathroom.)
    For a further discussion of the physical security
aspects of PGP see the PGP documentation.
    By now you should have the idea that under no
circumstances should your keyrings be placed where someone
else can have access to them. Although your secret key is
protected from the casual passerby by your pass phrase you
must understand that the pass phrase is one of the weaker
links in the PGP chain. A person with unlimited access to
your secret key and a little time could crack your pass
phrase (if you have a weak pass phrase) and begin to read
your incoming mail and send mail signed by you.

Answer this question:

Does anyone whom I would not want to read my mail have
access or could potentially have access to this machine?

If you answered yes then only run PGP from a floppy.
If you answered no then install it on your hard drive.

B. Of drives and directories

    Put PGP in a directory labeled PGP unless you're
putting it on a floppy. When using PKunzip use the -d option
so that the documentation is put in a separate directory.
Read the documents. Later versions of PGP have been designed
not to run without the documents present unless you twiddle
with the program. If you want to do that then read the
documents and find out how to do it there.
    At this point you may be tempted to add some lines to
the autoexec.bat file. Some of these additions make PGP
easier to use but they are not necessary. You may also be
tempted to edit the mysterious config.txt file. Resist the
temptation. We will discuss editing config.txt and the
autoexec.bat files later to make PGP easier to use but for
the sake of your security do the following exercises in the
directory in which PGP is installed.
    Once you have PGP in a directory type the following
command line:

pgp -h

This will give you a list of all the command options for
PGP. This will also prove that you have something that runs.

C. Generating a secret key

    For practise start by generating two secret keys. We
will begin with two casual grade keys and then you can later
apply all of the principles learned by a few hours of
practise to generate larger keys with greater security.

At the command prompt type:

pgp -kg

1. Key size

    You will be asked to select a key size. For these
practise sessions pick 1. Casual grade. When you get to
generating keys for real select 3. Military grade which
produces a 1024 bit key.

2. User Id

    You will then be asked for your user id. This usually
consists of your name and e-mail address and it's how
everyone will remember that this key belongs to you. For the
practice session type the following:

John Qwerty <[email protected]>

    Of course your user id can be anything you want it to
be. For example, if you only use PGP on a BBS and you only
want to be know by your alias you could enter just your
alias.

3. Pass Phrase

    The next request is for the pass phrase. The pass
phrase will be used to unlock the secret key to use it to
sign texts and decrypt messages. This is one of the points
where you have to be security conscious. The shorter the
pass phrase the easier it will be for someone to crack it.
Also, do not use your name, your spouse's name, the name of
your first born child, your dog's name, your telephone
number (work, home, or any combination there of).
    Use something which is reasonably long and yet something
that you can remember. If you want to spice it up you can
use unusual spacing, capitalization, and odd characters.
For example:

Example 1: Willy Wonka meets the Terminator
Example 2: willywoNKA meet$ the^ terMIN@tor

    Both examples are 32 characters long. Technically
example #2 would be harder for a machine to guess because it
uses odd ASCII characters but #1 has the advantage of being
easily remembered. (Tech point: "Willy" is not the same as
"willy" and both are different than "wiLLy". Remember, if
you capitalize it once it's forever.)

         NEVER WRITE YOUR PASS PHRASE DOWN!

    Most of the major security breaches of the 20th century
have been the result of people writing their pass phases,
PIN's or passwords down.

[Note: For the purposes of this exercise use simple pass
phrases. When it comes time to make your own secret key pick
a good strong pass phrase.]

4. Typing random bytes

    PGP will now ask you to type for awhile depending on
the size of the key you are making.
    The reason for this is covered in the documents. Just
type one of your favorite poems. (Don't sit there and hit
the same key again and again.) The bigger the key the more
you will be asked to type. Just type until you hear the
beep. Then you'll be asked to wait and the program will
generate your secret and public key for "John Qwerty". The
bigger the key the longer the wait. Take heart though, you
only have to generate one secret/public key pair so a little
time now pays off later.

    Congratulations, you have just created a public key and
a secret key. Do it one more time for the following
fictitious user id:

Mary Asdfg <[email protected]>

Give Mary a different pass phrase than the one you used for
John. For normal use you would create only one secret/public
key set with your name on it.

    For the rest of this tutorial we will use the names
John and Mary to signify two PGP users who are using PGP to
protect their privacy.

5. Another World

    At this point some of you are asking, "Why do John and
Mary want to use PGP? They must be up to something! <nudge,
nudge, wink, wink> To keep your mind out of the gutter and
to provide you with a practical use for PGP I'll tell you
why they are using PGP.
    John and Mary work for the same company. John is in the
New York office and Mary works in the San Francisco office.
They are working very hard on a presentation to the Board of
Directors concerning the future of the company they work
for: Glomabyte Inc. The information they are exchanging
could compromise the financial situation of the company if
it fell into the competitor's hands.
    That's reason #1. Reason #2 has to do with the manager
of the NY office, Judy Putz, and the manager of the SF
office, Vinny Brick. Both have advanced their careers by
appropriating ideas from others. In the past they have just
cruised by their victim's desk while the victim was on a
break and quickly copied all the files on the victim's
computer onto a floppy and then went to their own office to
read them at their leisure. John and Mary have already taken
the precaution of installing security systems on their PC's
at work. However, as managers both Judy and Vinny can
monitor e-mail. Most of this stuff is just nasty rumor but
there have been too many coincidences. John and Mary have
installed fairly good security systems on their personal
computers but they know that their e-mail is vulnerable.
    For both these reasons John and Mary have decided to
use PGP. They have both installed PGP on floppy and keep the
floppy under their possession at all times.

    For Mary to be able to send ciphertext to John that
only he can read she needs a copy of John's public key. For
John to send ciphertext to Mary that only she can read he
needs a copy of Mary's public key. The next step is PGP key
management.

    Every time you use the -kg command option you generate
a unique key pair. If you generate two key pairs with the
same user id they will be different keys with different key
id's and plaintext which is encrypted with one key will not
be able to be read with a differnt key. For example, we
could generate another key for John Qwerty using the same
user id so that we now have two keys for John Qwerty
distinguishable by the key id number and fingerprint. Let's
call them key A and key B and I'll show you how John can get
into trouble.
    John distributes the public key component of key A to
all of his associates who then use it to encrypt mail and
send it to him. John decides to use key B for his friends.
So far, fine and good. However, the only way that John can
distinguish between the two keys is with the key id number.
He must remember when sending a ciphertext to his friends
that he must sign with key 0x45F6 and when he sends a
ciphertext to his associates he must sign with key 0x3FC6.
Sometimes he gets the keys mixed up and the recipients of
his messages get an "Unknown Signature" message which causes
some concern.
    Also, if you generate a key pair and then delete the
file SECRING.PGP there is no way to reconstruct your secret
key. You would not be able to read any mail sent to you which
was encrypted with the public key that matched the now
missing secret key. Keep a back-up copy of your keyring
files in a safe place.

IV. Key Management.

A. Sign your own public key.

    Signing a public key is saying, I know who this person
is and trust that this key belongs to them. You know who you
are so sign your own public key. This also makes it next to
impossible for someone to tamper with your public key.
    Sign John's public key with John's secret key with the
following command:

pgp -ks John -u John

    Sign Mary's public key with Mary's secret key with the
following command:

pgp -ks Mary -u Mary

    For all signing procedures you will be asked for the
pass phrase for your secret key. Your secret key is used to
sign things like other people's public keys and to sign
texts. Since you are the only one with your secret key then
the message must have come from you. Right?

B. Extracting a public key

    John sits down at his computer and types the following
command:

pgp -kxa John

PGP asks him: "Extract key to which file:?"
He types "john"

He ends up with a file called JOHN.ASC. He then mails the
file JOHN.ASC to Mary. Mary does the same thing with her
public key and sends the results, MARY.ASC, to John. (More
on actually sending PGP files later.) You, of course, have
actually created these files. Take a look at them with a
text editor.

C. Adding a public key to your public key ring.

    John types the following command:

pgp mary.asc

    PGP "reads" the file, notes that it is a public key,
asks John if he wants to add it to the public key ring, and
then asks a few more questions. (More on those later.)
    (At this point you will not be able to "add" these keys
because you already have them on you public keyring.)
    After Mary has added John's public key to her public
keyring they are now ready to send PGP encrypted material
back and forth. However, there is one way that Vinny or Judy
could compromise the security of John and Mary's PGP keys.
It involves a complicated switching of keys but it can be
done. John and Mary must make sure that the public keys in
their possession are actually the public keys of the person
whose name appears in the user id.

D. Key verification.

    It should have occurred to you by now that you could
create a key with any user id on it. Let's say you create a
key with the user id: Bill Clinton <[email protected]>.
Unless I can verify that this key actually does or does not
belong to Mr. Clinton then I might be fooled into thinking
that I was sending mail to the "real" Mr. Clinton. PGP
provides a method for key verification.
    John and Mary have each other's home telephone numbers
and they have had enough telephone conversations to
recognize each others voice. They have also met several
times. They arrange a mutually convenient time and meet on
the telephone. John is sitting at his computer and Mary is
sitting at hers.
    John types the command:

pgp -kvc mary

    This shows him the "PGP fingerprint" of Mary's public
key. At the same time Mary has typed the same command. Then
John reads to her the list of numbers and letters. If it
matches the fingerprint that Mary has then they both know
that John has received a copy of Mary's public key and that
it is safe to use it with confidence. They repeat the
procedure for John's key.
    Right now John and Mary are ready to begin sending
texts back and forth in the security of PGP.

E. Signing someone else's key

    John now types the command:

pgp -ks mary -u john

    Mary types:

pgp -ks john -u mary

    In answering the questions presented by PGP they are
"telling" PGP that the key in question actually belongs to
the person whose user id is attached and the level of trust
accorded to that person's ability to manage keys.
    In order for Mary to have a copy of her public key with
John's signature on it John must do the following:

pgp -kxa mary

and creates a file called MARY.ASC which he then mails to
Mary. When Mary receives the file she types the command:

pgp mary.asc

PGP reads the file and automatically adds John's signature
to her public key. Mary repeats the procedure with John's
public key.

1. The Web of Trust

    PGP is unique in that it relies on the users to a great
extent for the security of public keys. When you sign a
public key you make two evaluations.
    The first and most important one is "Does this key
belong to the person to whom the user id says it belongs?"
For example, if Mr. Clinton comes to my house with a disk
containing his PGP key and someone I really trust, like
Melissa my barber, comes along and says "That really is Bill
Clinton," then I might sign his key. However, if I get a
piece of e-mail with a note saying, "Hi Bill. I want to get
my key signed by all the Bills in the world. Signed Bill
Clinton," I am definitely not going to sign the key.
    The second evaluation that is made is my trust of that
person's ability to sign keys. For example, Let's say Mr.
Clinton did drop by for coffee and I did sign his key. Let's
also say that you have met me and signed my public key and
placed it on your key ring and indicated to PGP that you
completely trust my key management abilities. When you
receive Mr. Clinton's key you are more likely to accept it
as genuine.
    Once you evaluate a person's key management ability PGP
automatically evaluates every key that person signs. And
this evaluation never leaves your Public Keyring. So if you
have a friend whose key you feel comfortable signing but you
know that they are a bit of a ditz when it comes to signing
other people's keys you can still sign their key but set the
trust parameter low.

F. The use of Secret Keys and Public Keys.

    When you use the PGP command -kg you actually generate
a key pair. Both keys have the same user id attached. The
Secret Key is the key you use to unlock ciphertext that is
made with your Public Key. Your Public Key is the key that
other people must have if they are to send ciphertext to
you. When you use the PGP command option -kxa PGP
automatically makes a copy of your Public Key for you to e-
mail to a friend or associate. You never have to worry about
"accidently" mailing your secret key. The only way someone
could get their hands on your Secret Key is if they get a
copy of SECRING.PGP and they manage to break your pass
phrase that is used to lock the key.


V. Preparing a text for encryption.

A. The basics

    The first thing that Mary wants to send John is a copy
of the introduction to the report they are working on. They
have both been using MS-Word and so she can send the file in
MS-Word format. The first thing Mary does is get to the DOS
prompt. Because she uses Windows she clicks on the icon for
the DOS prompt. (Another option would be to exit Windows
completely.) She then copies the file she wants to send,
called INTRO.DOC, to the PGP floppy which she has already
installed in the A drive of her computer.
    [If Mary had installed PGP on the hard drive of her
computer she would have copied the text into the PGP
directory. Earlier I mentioned that you can include the full
path of the file you want to encrypt in the PGP command
line. This is true but for the purpose of keeping the
example simple I've had Mary copy the file.]
    She is now ready to encrypt the file for sending.

VI. Encrypting a text.

    Mary has several options which she can choose from to
enhance the security of her text in transmission.

A. Basic encryption

    By typing the command

pgp -e intro.doc john

Mary will produce a file encrypted with John's public key.
Only John can decrypt the contents of INTRO.PGP and read it
but that's not good enough.
    The file INTRO.PGP contains some odd characters and
because of the way e-mail works it may not make the journey
from coast to coast intact. If even one piece of the file
INTRO.PGP is changed John will not be able to read it.
Therefore, another option must be used to make the file e-
mailable.

B. ASCII armor

    ASCII characters are recognized by almost every computer
in the world. They like ASCII characters and will pass them on
unchanged but they may not like some of the characters that
they find in a file which ends with the letters "pgp".
Therefore it is necessary to wrap the PGP file in ASCII
characters. PGP does this easily and automatically when
the -a command option is included.
    There is also another technical consideration. Some
computers use a carriage return and a line feed command at
the end of each line, some do not. If Mary was using a MAC
and John had an IBM PC this could cause some problems. PGP
can automatically compensate for this with the -t command
option.
    Mary might have typed this command:

pgp -eat intro.doc john

which would have produced a file called INTRO.ASC. Now the
file can be e-mailed but that's still not good enough.

C. Signing a ciphertext

    First, a demonstration of why this option is important.
    Remember Vinny? He has realized early on that John and
Mary are going to use PGP and he knows that he will not be
able to read their mail anymore. (Vinny has been using PGP
for some time because he knows just how important security
is.) So he decides to throw a monkey wrench into their
working relationship.
    Vinny captures a copy of John's public key as it goes
out in e-mail and adds it to his public key ring. He still
can't read John's PGP mail but he does do the following:
    He writes a nasty note on his word processor and puts
Mary's name to it. He then encrypts it using John's public
key and sends it to John using Mary's account. (Stranger
things have happened in the world of office politics.) John
receives the ciphertext, decrypts it, and is startled for a
moment. Then he realizes that the message is not signed with
Mary's secret key. Mary always signs her messages therefore
the message probably doesn't come from her.
    Signing a message with your secret key means that the
message could only have come from you since only you could
have a copy of your secret key.
    Therefore Mary encrypts the file INTRO.DOC with the
following command:

pgp -seat intro.doc john -u mary

    This produces a file named INTRO.ASC which has been
signed with Mary's secret key. To sign the file Mary will be
asked to enter the pass phrase for her secret key so that
PGP can unlock her secret key and use it. Therefore, if her
pass phase is long enough and unguessable even if someone
were to steal her secret keyring they still could not read
her mail and sign ciphertexts with her secret key. (Now do
you see why I went on about pass phrases earlier!)
    Mary is now ready to send the ciphertext to John but
there is one more security issue that she wants PGP to deal
with automatically.

D. Wiping and deleting a file.

    Mary still has a copy of INTRO.DOC on the floppy she
was using. She wants to get rid of that copy just in case
the worst happens and she loses the disk or accidently
leaves the disk in the machine and Vinny comes along and
makes a copy of it.
    Deleting a file just won't cut it in the world of
security. When you use the command to delete a file what
happens is the "address" of the file is removed from
the operating system and its name no longer appears in the
file lists. However, the data itself, the contents of the
file, remain on the disk and can be restored to a readable
state by a simple command.
    It is necessary to wipe the file first with the PGP -w
command option and then delete it. When PGP "wipes" a file
it smears it with a bunch of electronic gobble-de-gook. Any
attempt to look at the file would only yield a screen full
of meaningless characters. Then PGP deletes the file.
    Therefore Mary uses the following command to encrypt
the file she is sending to John:

pgp -seatw intro.doc john -u mary

    Except for a few exceptions Mary always uses the
command options -seatw to encrypt her mail. So should you.
There are some exceptions and we will touch on them later
but for now get into the habit of typing "pgp -seatw"

    A word of caution. When you use the -w option make sure
you really don't want the plaintext around. If Mary had
referred to the original copy of INTRO.DOC in the PGP
command line like this:

pgp -seatw c:\project\intro.doc john -u mary

then the next time she went to look for INTRO.DOC it would
be gone. She would have to send the file INTRO.ASC to John,
have him decrypt it and then encrypt it with her public key
and send it back.

    Mary is now ready to mail a ciphertext to John.

E. A Brief note on file extensions

    File extensions are the three letter tags on the end of
file names. For example "sample.txt" has a file extension
".txt" which generally indicates that it is a text file. PGP
uses two file extensions:

".pgp" indicates that the file is PGP encrypted in binary
format.

".asc" indicates that the file is PGP encrypted AND wrapped
in ASCII armor.

    While these are the file extensions PGP uses they
are not necessary. If I PGP encrypt a file called SAMPLE.TXT
into a file called SAMPLE.ASC I can rename the file
BINKY.TXT. As long as the PGP headers remain in the
ciphertext all I need to do to read the file is type:

pgp binky.txt

    PGP will automatically detect the PGP encryption, and
if I have the proper secret key, it will decrypt the file.


VII. Mailing a ciphertext.

    There are a variety of e-mail packages around which
make it next to impossible to give detailed instructions.
Therefore, we will describe in general terms the methods for
getting a ciphertext to its destination. You will have to
experiment with your system.

A. Cut and paste

1. Open the encrypted file with a text editor.

    It is important that you use the text editor with your
mailer or some other text editor. Some word processors add
special formatting characters automatically to files that
they open and save. They may also change the line length or
use word wrap to change the shape of the text. A PGP
encrypted message must retain its integrity to be useful at
the other end.

2. Select all the text in the file.
    Everything from
         -----BEGIN PGP MESSAGE-----
    to
         -----END PGP MESSAGE-----
must be included.

3. Cut it.

4. Paste it into the message area of your e-mail
    Be sure not to change the least smallest character in
the ciphertext. You should also be aware of the line length
in the e-mail window. An ASCII armored file is 65 characters
wide. If your line length is set to 60 then your program may
attempted to split the lines and thereby corrupt the
ciphertext. The can also cause problems for clearsigned texts.

B. File size

    If you use the cut and paste method for sending your
encrypted files then you may run into a technical glitch.
Most e-mail systems have a maximum size for the message
being sent, sometimes around 50 Kb or 720 lines of text.
PGP can automatically compensate for this. One of the settings
in the config.txt file (which we are soon going to begin
looking at) tells PGP to break long files into shorter
files.
    Let's say that Mary's file, INTRO.DOC, when encrypted
produces a file 98 K long. Instead of producing a large file
labeled INTRO.ASC, PGP automatically produces two files
labeled INTRO.AS1 and INTRO.AS2. Mary would then send both
files in separate e-mail.

C. Enclosing a file

    Most e-mail programs have an "enclose" function. This
allows you to send a file along with a message. Mary could
type a brief note saying: "Here's the material we talked
about," and then send the file INTRO.ASC as an enclosure.

Either method works so pick the one you like. If you
can try sending yourself some encrypted e-mail using both
methods.

VIII. Decrypting a ciphertext.

    Mary chooses to use the enclosure method and so John
receives a brief note with a file attached which is placed
in the directory c:\mail\incoming. When he sees the .ASC
file extension he knows it's a PGP file so he puts his PGP
disk into drive A and switches to DOS. He copies the file to
the PGP disk, (or directory if he has installed it in a
directory on his hard drive) and types the following at the
command line:

pgp intro.asc

    PGP asks him for the pass phrase to unlock his secret
key. PGP announces that the file has a good signature from
Mary and then produces a plaintext file called "INTRO". At
this point John can read the file with his word processor or
text editor. It's that simple.
    If John is using a word processor like MS-WORD to read
the file then he may want to rename the file "INTRO.DOC" but
that's his choice.
    If the file is too big to be e-mailed and PGP has
broken INTRO.ASC into INTRO.AS1 and INTRO.AS2 then the only
change John has to make to his command line is

pgp intro.as1

PGP automatically reassembles the file and places it under
one file name.
    If Mary had used the cut and past method and placed the
PGP file into the message area of her e-mail John would
simply save the e-mail to a file. In her subject header Mary
would give some indication as to what file name to use.
Either,
"Save this as intro.asc" or "Save this as intro.as1".
    The one time that the file extension is important is
when a large file has been broken into smaller files. Then
the numbered file extensions are used to reassemble the
original text. Therefore if plaintxt.doc has been PGPed into
plaintxt.as1, plaintxt.as2, plaintext.as3 it is important
that the file extension be affixed.
    If John wanted to automatically restore the original
file name he would have used the following command line:

pgp -p intro.asc

The -p command option automatically restores the original
filename to the document.

IX. Editing the config.txt and autoexec.bat files.

    One of the files that popped into existence when you
installed PGP was a file labeled CONFIG.TXT. This file
allows you to store some of your preferences and makes using
PGP even easier. In this part of the Beginner's Guide to PGP
we will explore modifying that file (it's easy!) and the
AUTOEXEC.BAT file (even easier!). Then we will look at some
other PGP options you might use.

A. AUTOEXEC.BAT

    The AUTOEXEC.BAT file sets up some of the options which
make using programs on your computer easier. You can add a
couple of items to AUTOEXEC.BAT which will make using PGP
easier. Here's a step by step guide:

1. Open AUTOEXEC.BAT with a text editor.

    You cannot use a word processor like MS-WORD or
WORDPERFECT to edit this file. You must use something like
MS-EDITOR or NOTEPAD in MS-WINDOWS.
    Before making any changes save your current
AUTOEXEC.BAT as AUTOEXEC.OLD just in case. (You should have
created a back-up boot disk long ago.)

2. Put PGP in the PATH

    Find the line which starts with the word PATH. It will
look something like this:

PATH=C:\;C:\DOS;C:\GMOUSE;C:\WORD

    If you have installed PGP on your hard drive add the
following to the end of the above line: ;C:\PGP so that it
now looks like this:

PATH=C:\;C:\DOS;C:\GMOUSE;C:\WORD;C:\PGP

3. Set PGPPATH

    The environment variable PGPPATH tells PGP where to
look for the files it needs to operate. Just below the line
which starts with PATH add this line:

PGPPATH=C:\PGP

    I am assuming that you have installed PGP in a
directory named PGP on your hard drive. If it's elsewhere
then put the path to elsewhere here and in the PATH line.

4. Re-boot

    To get all the modifications that you have added to
take effect save your new AUTOEXEC.BAT, exit the text
editor, and reboot. Simple.
    These changes will allow you to use PGP in any
directory and on any disk. Instead of copying files around
just go to the directory or disk where the file you want to
encrypt is and use the PGP command line. The encrypted file
will be created in the same directory.

B. CONFIG.TXT

    CONFIG.TXT is a file of PGP options which can be set by
the user. It is mostly self explanatory and all you need to
do is open it with a text editor and make the changes which
you want. I am going to suggest four specific changes which
will make your use of PGP more effective and explain one of
the other options. As for the other options included in
CONFIG.TXT you can make up your mind about them after
reading the PGP documents.

1. MYNAME
    The first option you will encounter is
#MyName = "John Q. Public"
    Normally PGP will use the last key added to your secret
key ring to decrypt and sign things or it will prompt you
for the key you want to use. Setting your user id in the
quotes will select the key you want to use automatically.
You may include your name, your name and your e-mail
address, or any item in your user id. Set this one if you
have more than one secret key but use one key more than the
other. John makes the following change:

MyName = "John Qwerty"

2. ARMORLINES = 720
    Don't change this setting unless your e-mail system is
a little quirky. It affects the size of ASCII armor files.
If the big files which you PGP get chopped up into smaller
files that are still to big to e-mail than make this number
smaller. If you wish to store a big file in ASCII armor with
out it being chopped up you can use the following command
line:

pgp -seaw intro.doc john +armorlines=0

3. #ARMOR = ON
    If you are going to use PGP mostly for e-mail then
remove the "#" from the front of this line. Now you no
longer have to use the -a option in the command line.

4. #TEXTMODE = ON
    Again, if you're using e-mail, PGP will automatically
take care of things like translating from one machine to
another. Remove the "#" and you no longer have to use the -t
option in the command line.

5. #CLEARSIG=ON
    This is handy if you are posting to USENET groups or if
you want to send a plaintext note and still have the
security of having signed it so that the text cannot be
altered without detection. (As well as indicating to
everyone who reads the news group and has your key that the
note really came from you!) Remove the "#".
    Another example of clear signing is this document.

C. Congratulations!

    Save the modifications you've made to CONFIG.TXT and
you are well on your way to being an effective PGP user.
Remember the command line that Mary used to get the text
ready to send to John?

pgp -seatw intro.doc john -u Mary

Now all she needs to type is:

pgp -sew intro.doc john

See how easy it gets?

X. Some other interesting PGP uses

    This section discusses some of the interesting uses of
PGP. Right now you are set to produce all of the encrypted
e-mail that you want. If you can do that you can do
everything listed below.

A. Signing and clear-signing

    Authentication is one of the considerations of any
security system. Is the person who sent the text the person
whom they say they are? Is the file that has been received
actually the file that they intended to send? PGP
authenticates not only ciphertext but plaintext and binary
files as well.
    Using the PGP command

pgp -s plaintext.txt

if you have activated the clearsig and armor options in
CONFIG.TXT, will produce a file called PLAINTEXT.ASC. It
will be readable by anyone but it will also contain a PGP
signature. Anyone with your public key will know if the text
came from you and if the text has been tampered with. This
is helpful if you intend to post something to a Usenet
newsgroup or to a BBS message board and you want to make
sure that no one changes what you have said.
    If you want to send a binary file PGP can also be
useful. Using the PGP command

PGP -sb binary.exe

will leave the file BINARY.EXE untouched but will also
create a signature certificate, BINARY.ASC. A person who has
your public key, the files BINARY.EXE and BINARY.ASC can now
detect any tampering attempt made against BINARY.EXE. This
is useful if you are planning to post a binary file, perhaps
a program you have written, at an ftp site or on a BBS.
    PGP signatures, whether clear signed or on ciphertext
cannot be forged. In other words, if you clear sign a text
the signature cannot be cut from the text and pasted onto
something else. The signature depends not just on your
secret key be on the contents of the text as well.

B. Other kinds of files

    As mentioned earlier, PGP can be used to sign a variety
of files, it can also be used to encrypt a variety of files.
For example, if you are using a compression utility to
archive important documents into a zipped file you could
protect those files in one of two ways. You could encrypt
each file and then include them in the zipped file. This
might take awhile if you have 1000 files to archive. A
quicker method, and one which is just as secure, is to
archive all of the files in the zipped file first and then
encrypt the zipfile.
    PGP is also an execellent choice for e-mailing binary
files like gif, jpeg, exe. Because PGP also compresses the
file which it encrypts it also leaves you with fewer bytes to
transfer.
    Basically, if there is a file on your computer PGP can
encrypt it.

C. Signature certificates

    There was an earlier mention of signature certificates.
These are generated withthe PGP command:

pgp -sb text.txt

and they have a variety of uses already mentioned. Here's a
use that you may not have thought of yet. You can make a
signature certificate of any file on your computer.
    For example, let's say that I made signature
certificates for every executable file on my machine and
stored them on a floppy somewhere safe. Anytime I wished I
could retrieve the signature certificates and compare them
to the files. I would know immediately if the files had been
altered. While this might not replace virus scanning
utilities it is a protection if there is any danger of your
system being maliciously hacked.

D. The -c option

    The PGP command option -c enables you to use the IDEA
algorythm for encryption without the RSA keys. Each time you
use -c you will be asked for a pass phrase. This pass phrase
is unique to the file you are encrypting and can change each
time you want it to. All you have to do is remember the pass
phrase.
    This is an excellent option for storing files on your
hard drive or encrypting stuff to yourself. Because PGP
compresses files as it encrypts them is is also an excellent
archive format.

XI. Some ways to get into trouble.

A. Improper keyring security

    Your keyrings are kept in two files. Your secret key is
kept in the file SECRING.PGP and your public keys as well as
the public keys of the people you encrypt to are kept in
PUBRING.PGP.
    Both of these files should be backed up on a secure
medium and kept in a safe place. If you lose SECRING.PGP
and don't have a secure copy then you are stuck. You will
need to generate a new key pair and re-distribute the
matching public key to all your correspondents.
    SECRING.PGP is protected by your pass phrase. Don't
write the pass phrase down, anywhere. Also, do not use PGP
on a multiuser system. There are just too many ways for
someone to monitor your keystrokes, capture your pass
phrase, and use your secret key.
    Keeping these two files safe and tamper free is your
major security concern with the use of PGP.

B. Accepting uncertified keys
    PGP allows you to use any public key in your possession
to encrypt files. You do not need to sign a key to use it
nor do you need to accord it any level of trust. However,
you must remember that these keys are used "as is"; there is
no guarantee that the key belongs to the person whose name
is in the user id. Read the PGP docs to learn about how this
could cause you a problem.

C. Plaintext insecurity
    One sure way to compromise your security is by sloppy
handling of your plaintext.
    First of all, unless you use the -w command option,
your plaintext remains on your disk. If you've just written
a nasty note about your boss he or she cannot read the
encrypted copy but if the plaintext is still in existence
you may be in trouble.
    The same problem may occur at the other end. Your buddy
who decrypts your nasty note may leave the plaintext out in
full view.
    One way to check this is to use the -m command option
when encrypting your nasty note.

pgp -sewm nastnote.txt john

When John decrypts NASTNOTE.ASC PGP will not create a
plaintext file. Instead it will print the file to screen
only.
    There is a very simple way to short circuit the -m
command option and create a plaintext file but at least
using the -m option will alert the receiver that the
material is sensitive.

    You can also use the -m option when decrypting a file.
You will be able to preview the text before deciding whether
or not to create a permanent plaintext file. Simply type

pgp -m ciphertext.asc


D. Spy stuff

    In the documents which come with PGP there is a section
that describes some of the tactics used by very determined
opponents to compromise your security. Even if you are a
perfect user of PGP, securing your keyrings, wiping your
plaintext, using a strong pass phrase, etc., there are
tatics which can be used by the determined opponent. Some of
these tactics require some sophistication like Tempest
technology. Other tactics are as simple as a hidden camera
pointed at the screen of your terminal. [Hidden cameras are
becoming a tool of management with increasing frequency.]
    The other point to remember is that you can be as
security conscious as you could possibly be only to have all
your precautions compromised by the recipient of your
ciphertext.
    What it all boils down to is this: PGP provides an
excellent protection against random invasions of privacy.
Used properly PGP protects your e-mail from any intrusion
while in transit or any file PGP encypted while on your
machine (provided you have a strong pass phrase and/or
SECRING.PGP is not on your hard drive as well.) When it
comes to security be as paranoid as you want to be but
always remember to have fun.
    With all of the people who want to examine the details
of everything you do personal privacy is one of the major
issues of the late 20th century. PGP is a tool to enhance
your personal freedom by securing your personal information.
It will only work as well as you choose to use it.

E. When NOT to use PGP.

    There are some circumstances when using PGP might not
be a wise idea, or if you do use it you might want to
consider the risks.
    Currently PGP is legal to use in Canada, the United
States, and many other countries. However, there are some
countries which restrict the use of encryption. France is
one example. If you are not sure about the encryption laws
in the country in which you live get a discreet legal
opinion from a lawyer. (Never trust a "legal" opinion posted
in a newsgroup.)
    You may want to exercise some prudence when using PGP
at your place of employment. Sending an encrypted file to a
co-worker in another department is one thing. However,
sending an encrypted message through the firewall to a
friend who works at an other company might set off some
alarms especially if you work for a major corporation.

XII. Conclusion.
    Congratulations, you are now a new and productive
member of the world of encryption. If you have made no
modifications to the PGP config.txt file or the autoexec.bat
file you can use PGP in just the way that has been outlined
in this document. All you have to do is remember to copy the
file which you want to encrypt to the directory or disk in
which you have installed PGP.
    Before you go any further delete the John and Mary
keys. Use the following commands:

pgp -kr john
pgp -kr mary

    It might be the case that you have started using PGP
before you read this document and now want to make some
changes. If you want to change your pass phrase or user id
use the following command:

pgp -ke (your user id here)

    For more information on the nuts and bolts of PGP and
some of the issues involved please read the documents that
came with your copy of PGP.


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