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<H1>Note: THIS INFORMATION ONLY APPLIES TO PRE-1.0 VERSIONS OF GNUPG</H1>
<H1>Moving from PGP to <a HREF="http://www.d.shuttle.de/isil/gnupg/">GnuPG</a></H1>
<B>Arghhh! How do I switch to GnuPG when I (and my friends) already use PGP?</B>
<HR>
<P>I recently had my old PGP 5.0 key brought back from the dead when a
colleague of mine wanted to send me some private info and all he had available
was PGP 5.5. Luckily I had created a DSS key under 5.0 and so I figured I
may be able to make use of my old keys. I regret not setting an expiration
date on my old key as it would have been very useful in this case. I now have
four keys that I must deal with. Two RSA (PGP 2.6), one DSS/Diffie-Hellman
(PGP 5.0) and
one DSA/ElGamal (GnuPG 3.6).
<P>Always set an expiration date on your keys.</P>
<P>That said, there are several issues at hand. First, I have a pair of
DSS/Diffie-Hellman keys that my friend is using PGP 5.5 to communicate
with me. Second, I have a DSS/Diffie-Hellman public key that my friend
is using. Thirdly, I have a copy of gnupg 0.4.0.

<P>This document has two parts. The first describes how to prepare to
<EM>encrypt</EM> messages to a user of PGP5.x. The second details how
to take a PGP5.x KEY and install it on your GnuPG keyring so you may
<EM>decrypt</EM> messages from a PGP5.x user.</P>

<P>If these instructions do or do not work for you I would like to
hear about it. Thanks to all the people on the GnuPG mailing list who
have unwittingly provided most of the information I used in creating
this.</P>

<HR WIDTH="90%">

<CENTER><H2>Encrypting TO a user of PGP 5.0+</H2></CENTER>
<HR WIDTH="90%">
<H3>Fetch user's key from remote key server</H3>
<P>In order to encrypt mail to my friend, I must be able to use GnuPG
to encrypt against a DSS/Diffie-Hellman key. I used PGP to retrieve
his public key from the keys.pgp.com public key server.
<BLOCKQUOTE>
<CODE>
$ <font color="#008080">pgpk -a hkp://keys.pgp.com/friend@sample.com</FONT><BR>
</CODE>
<PRE>
Looking up host keys.pgp.com
Establishing connection
Sending request
Receiving data
Cleaning up
Complete.

Adding keys:

Key ring: 'hkp://keys.pgp.com/taylor@technocage.com'
Type Bits KeyID Created Expires Algorithm Use
pub 1024 0x01234567 1998-10-10 ---------- DSS Sign & Encrypt
sub 2048 0x89ABCDEF 1998-10-10 ---------- Diffie-Hellman
uid Friend &lt;friend@sample.com&gt;

1 matching key found

Add these keys to your keyring? [Y/n] <FONT COLOR="#008080">y</FONT>

Keys added successfully.

</PRE>
</BLOCKQUOTE>
<H3>Verify key actually belongs to friend</H3>
<P>First, I printed out the key ID and fingerprint of each of the keys
so I can ask my friend if they match.</P>
<BLOCKQUOTE>
<CODE>
$ <font color="#008080">pgpk -ll friend@sample.com</FONT><BR>
<PRE>
Type Bits KeyID Created Expires Algorithm Use
pub 1024 <FONT COLOR="#F00000">0x01234567</FONT> 1998-10-10 ---------- DSS Sign & Encrypt
f20 Fingerprint20 = <FONT COLOR="#F00000">0123 4567 89AB CDEF FEDC BA98 7654 3210 DEAD BEEF</FONT>
sub 2048 <FONT COLOR="#F00000">0x89ABCDEF</FONT> 1998-10-10 ---------- Diffie-Hellman
f20 Fingerprint20 = <FONT COLOR="#F00000">FFFF DDDD 8888 5555 3333 2222 1111 0000 BAEF FADE</FONT>
uid Friend &lt;friend@sample.com&gt;
sig 0x01234567 1998-10-10 Friend &lt;friend@sample.com&gt;
</PRE>
</CODE>
</BLOCKQUOTE>


<P>I then phoned my friend and asked him to
verify the key fingerprint and ID over the telephone. As luck would have
it, the information matched up.
<H3>Export key to ascii file</H3>
After verifying that the key was his, I exported it like so:</P>
<BLOCKQUOTE>
<CODE>
$ <font color="#008080">pgpk -xa friend &gt; friend.key</FONT><BR>
<PRE>
</PRE>
</CODE>
</BLOCKQUOTE>
<H3>Import key to GnuPG</H3>
<P>I then used gnupg to import that key.</P>
<BLOCKQUOTE>
<CODE>
$ <font color="#008080">gpg --import &lt; friend.key</FONT>
</CODE>
<PRE>
gpg (GNUPG) 0.4.0; Copyright (C) 1998 Free Software Foundation, Inc.
This program comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to redistribute it
under certain conditions. See the file COPYING for details.

gpg:[stdin]: key ABCDEFGH: public key imported
</PRE>
</BLOCKQUOTE>
<P>I could have used the following command as well.</P>
<BLOCKQUOTE>
<CODE>
$ <font color="#008080">pgpk -xa friend | gpg --import</FONT>
</CODE>
<PRE>
gpg (GNUPG) 0.4.0; Copyright (C) 1998 Free Software Foundation, Inc.
This program comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to redistribute it
under certain conditions. See the file COPYING for details.

gpg:[stdin]: key ABCDEFGH: public key imported
</PRE>
</BLOCKQUOTE>

<H3>Create test message for friend</H3>
<P>Now that I have loaded my friends key onto my GnuPG keyring, I can make
a little test message for him to try decrypting.</P>
<BLOCKQUOTE>
<CODE>
$ <font color="#008080">echo 'Hello Friend!' | gpg -ear friend </FONT>
</CODE>
<PRE>
-----BEGIN PGP MESSAGE-----
Version: GNUPG v0.4.0 (GNU/Linux)
Comment: Get GNUPG from ftp://ftp.guug.de/pub/gcrypt/
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=xYcK
-----END PGP MESSAGE-----
</PRE>
</BLOCKQUOTE>
<P>I take the resulting cyphertext and paste it into an email addressed
to my friend. Now we wait....</P>

<P>We wait some more (my friend is notoriously slow to respond to messages).</P>

<P>Finally after a long (long) time, my friend responds that he was
able to read my message. Of course, he is kind enough to use my PGP
key to send this. Thus we segue into the next section on using GnuPG
to decrypt messages sent by users of PGP5.0 to DSS/DH keys generated
by PGP5.0.
</P>
<P>One important note is that my friend was using PGP5.5, not 5.0. In
later tests with pgp 5.0i I discovered that you must add two more parameters
to the encryption command. Specifically <CODE>--no-armor --no-comment</CODE>
<BLOCKQUOTE>
<CODE>
$ <font color="#008080">echo 'Hello Friend!' | gpg -ear --no-armor --no-comment friend &gt; mesg </FONT>
</CODE>
</BLOCKQUOTE>
<P>Remember that <CODE>gpg --no-armor</CODE> will produce 'binary' output and so you
are wise to stick it in a file and then attach that file to an email.
</P>

<HR WIDTH="90%">
<CENTER><H2>Decrypting with a PGP DSS/Diffie-Hellman key</H2></CENTER>
<HR WIDTH="90%">

<P>Now the problem is, how do I make it so that my friend can use my GPG key
to send me messages? Is this even possible?</P>

<P>I must now import my old DSS/Diffie-Hellman key onto
my GnuPG key ring. This is not as easy as one may think. It is complicated
by the fact that the PGP key utility <CODE>pgpk</CODE> does not have a
parameter for exporting a private key. As luck would have it, superior
software packages such as GnuPG are capable of solving this problem for us.
<P>It is important to note that <B>this procedure puts your private key
at risk</B> for a short period of time and therefore <B>should not be done
on a multi-user or public system</B></P>

<H3>Step one: import your public key</H3>
<P>This is the easy part. We use pgpk to extract your public key from
your keyring and import it into GnuPG.</P>
<BLOCKQUOTE>
<CODE>
$ <font color="#008080">pgpk -x 7BBD08DC | gpg --import</FONT><BR>
<PRE>
gpg (GNUPG) 0.4.0; Copyright (C) 1998 Free Software Foundation, Inc.
This program comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to redistribute it
under certain conditions. See the file COPYING for details.

gpg:[stdin]: key 7BBD08DC: not changed
gpg:[stdin]: key 00000000: no valid user ids
gpg: this may be caused by a missing self-signature
gpg:[stdin]: key 0809AD24: no valid user ids
gpg: this may be caused by a missing self-signature
</PRE>
</CODE>
</BLOCKQUOTE>
<P>A quick check of the gnupg keyring shows that my key has, in fact
been imported properly. I don't entirely understand the output of the
import however nothing in it seems troublesome. Perhaps someone who
knows more than I do can explain it to me.</P>
<BLOCKQUOTE>
<CODE>
$ <font color="#008080">gpg --list-keys</FONT><BR>
<PRE>
gpg (GNUPG) 0.4.0; Copyright (C) 1998 Free Software Foundation, Inc.
This program comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to redistribute it
under certain conditions. See the file COPYING for details.

pub 1024D/7BBD08DC 1997-07-23 Caskey L. Dickson <caskey@one.sample.com>
uid Caskey L. Dickson <caskey@two.sample.com>
uid Caskey L. Dickson <caskey@three.sample.com>
sub 4096g/2B65D18B 1997-07-23
</PRE>
</CODE>
</BLOCKQUOTE>
<P>That certainly does look like my key.</P>

<H3>Remove passphrase from private PGP key</H3>
<P>This is the <B>dangerous part</B>. Depending upon your paranoia
level you can do everything from a simple <CODE>w</CODE> in order to
see who else is on your machine to unplugging your network card and
modem from the wall. It all depends upon the environment you operate
in and how much you trust the sytem you are using.
<BLOCKQUOTE>
<CODE>
$ <font color="#008080">pgpk -e 0x7BBD08DC</FONT><BR>
<PRE>
sec+ 1024 0x7BBD08DC 1997-07-23 ---------- DSS Sign & Encrypt
sub 4096 0x2B65D18B 1997-07-23 ---------- Diffie-Hellman
uid Caskey L. Dickson &lt;caskey@one.sample.com&gt;
uid Caskey L. Dickson &lt;caskey@two.sample.com&gt;
uid Caskey L. Dickson &lt;caskey@three.sample.com&gt;

1024 bits, Key ID 0x7BBD08DC, created 1997-07-23
"Caskey L. Dickson &lt;caskey@one.sample.com&gt;"
"Caskey L. Dickson &lt;caskey@two.sample.com&gt;"
"Caskey L. Dickson &lt;caskey@three.sample.com&gt;"


Do you want to unset this key as axiomatic [y/N]? <font color="#008080">N</FONT>

Do you want to unset this key as axiomatic [y/N]? <font color="#008080">N</FONT>

Do you want to add a new user ID [y/N]? <font color="#008080">N</FONT>

Do you want to change your pass phrase (y/N)? <font color="#008080">Y</FONT>
Need old passphrase. Enter pass phrase: <font color="#008080">passphrase</FONT>
Need new passphrase. Enter pass phrase: <font color="#008080">*nothing*</FONT>
Enter it a second time. Enter pass phrase: <font color="#008080">*nothing*</FONT>
Changing master key passphrase...
Changing subkey passphrase...

Do want to set this as your default key [y/N]? <font color="#008080">N</FONT>
Keyrings updated.
</PRE>
</CODE>
</BLOCKQUOTE>
<H3>Export private key into GnuPG</H3>
<P>Now that we have removed the passphrase from the key we can export
it using GnuPG.</P>
<BLOCKQUOTE>
<CODE>
$ <font color="#008080">mkdir ~/private</FONT><BR>
$ <font color="#008080">chmod 700 ~/private</FONT><BR>
$ <font color="#008080">chdir ~/private</FONT><BR>
$ <font color="#008080">gpg --armor --export-secret-keys --secret-keyring ~/.pgp/secring.skr 0x7BBD08DC &gt; mykey.sec</FONT><BR>
<PRE>
gpg (GNUPG) 0.4.0; Copyright (C) 1998 Free Software Foundation, Inc.
This program comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to redistribute it
under certain conditions. See the file COPYING for details.

gpg: key 456260DC: secret key without public key
gpg: failed to initialize the TrustDB: Public key not found
</PRE>
</CODE>
</BLOCKQUOTE>
<P>The messages about not having a TrustDB entry and a missing public
key are more or less normal as we did not specify the matching public
key ring on the GnuPG command line.</P>

<H3>Import secret key file to GnuPG</H3>
<P>We have a file named mykey.sec which contains an ascii armored
private key sans passphrase. Now we must quickly load it into our
keyring. </P>
<BLOCKQUOTE>
<CODE>
$ <font color="#008080">gpg --import &lt; mykey.sec</FONT><BR>
<PRE>
</PRE>
</CODE>
</BLOCKQUOTE>
<P>I don't have the output of this command (yet).</P>

<H3>Set passphrase on both keys <EM>IMMEDIATELY</EM></H3>
<P>We must quickly put the passphrases back onto *both* keyrings now.</P>
<P>Some of you have asked 'what the heck does the third instruction do?' It's actually
a rather simple trick. The <CODE>mykey.sec</CODE> file contains an un-protected
secret key. Obviously we want to get rid of it ASAP. If we were to just <CODE>rm</CODE>
the file, yes that would eliminate the file, however the now unused blocks would be floating around
on the disk somewhere with your secret key bytes still in it.
Not a terrible thing, but if you're going to jump off the building
from the 10th floor, why not make it the 100th and enjoy the view on the way down.
Seriously though, what we've done is take the GnuPG binary and overwritten the secret
key file. This (mostly) ensures that the data is gone. It isn't as strong as the
techniques used by the military (xor, 3 writes) but I'm assuming that you aren't worried
about someone disassembling your hard drive to find that file.</P>
<BLOCKQUOTE>
<CODE>
$ <font color="#008080">pgpk -e 0x7BBD08DC</FONT><BR>
$ <font color="#008080">gpg --edit-key 0x7BBD08DC</FONT><BR>
$ <font color="#008080">cat `which gpg` &gt; mykey.sec</FONT><BR>
$ <font color="#008080">rm mykey.sec</FONT><BR>
<PRE>
</PRE>
</CODE>
</BLOCKQUOTE>
<H3>Test key.</H3>
<P>Now we have our public and private DSS/Diffie-Hellman key on our
GnuPG key ring. We shall employ pgp to create a test message for us
to decrypt.</P>
<BLOCKQUOTE>
<CODE>
$ <font color="#008080">echo 'hello world' | pgpe -r 0x7BBD08DC |
gpg --decrypt</FONT><BR>
<PRE>
No files specified. Using stdin.

1024 bits, Key ID gpg (GNUPG) 0.4.0; Copyright (C) 1998 Free Software Foundation, Inc.
This program comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to redistribute it
under certain conditions. See the file COPYING for details.

7BBD08DC, Created 1997-07-23
"Caskey L. Dickson &lt;caskey@one.sample.com&gt;"
"Caskey L. Dickson &lt;caskey@two.sample.com&gt;"
"Caskey L. Dickson &lt;caskey@three.sample.com&gt;"

You need a passphrase to unlock the secret key for
user: "Caskey L. Dickson <caskey@technocage.com>"
(4096-bit ELG-E key, ID 2B65D18B, created 1997-07-23)

hello world
</PRE>
</CODE>
</BLOCKQUOTE>
<P>And thus, we have used gpg to decrypt a message encrypted with PGP5
and a PGP5 key.</P>

<P>Comments welcome.</P>
<HR>
<EM>Copyright &copy; 1998</EM><BR>
<cite><Img src="http://www.technocage.com/~caskey/email.gif"><BR>
<EM>Last modified: 1998-10-12</EM>
</cite>
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