Internet Security Professional Reference:PGP

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Adding Someone Else’s Key

Before you can encrypt a message for someone else, you first need to have all the recipient’s keys on the public key ring. Through various key management methods, you can obtain other users’ keys and, after they are obtained, the keys can be added to the public key ring. For example, a user could add this key block:

Assume that this is in a file called warlord.asc. This file can then be added to the public key ring using the command:

~> pgp -ka warlord.asc
Pretty Good Privacy(tm) 2.6.2 - Public-key encryption for the masses.
(c) 1990-1994 Philip Zimmermann, Phil’s Pretty Good Software. 11 Oct 94
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc.
Distributed by the Massachusetts Institute of Technology.
Export of this software may be restricted by the U.S. government. \
Current time: 1995/11/19 05:36 GMT

Looking for new keys...
pub   709/C1B06AF1 1992/09/25  Derek Atkins <warlord@MIT.EDU>

Checking signatures...

Keyfile contains:
   1 new key(s)

One or more of the new keys are not fully certified.
Do you want to certify any of these keys yourself (y/N)? No

Now the public key ring looks like this:

Type bits/keyID    Date       User ID
pub   709/C1B06AF1 1992/09/25 Derek Atkins <warlord@MIT.EDU>
pub  1024/D0C6326D 1995/11/14 Ruth Thomas <tara@mail.Free.NET>

Encrypting a Message

When someone else’s key is on the key ring, it is simple to encrypt a message to that user. If the file message, for example, contains the plaintext to encrypt, you can encrypt the file to the user “warlord” by using this command:

~> pgp -eat message warlord
Pretty Good Privacy(tm) 2.6.2 - Public-key encryption for the masses.
(c) 1990-1994 Philip Zimmermann, Phil’s Pretty Good Software. 11 Oct 94
Uses the RSAREF(tm) Toolkit, which is copyright RSA Data Security, Inc.
Distributed by the Massachusetts Institute of Technology.
Export of this software may be restricted by the U.S. government.
Current time: 1995/11/19 05:39 GMT

Recipients’ public key(s) will be used to encrypt.
Key for user ID: Derek Atkins <warlord@MIT.EDU>
709-bit key, Key ID C1B06AF1, created 1992/09/25

WARNING:  Because this public key is not certified with a trusted
signature, it is not known with high confidence that this public key
actually belongs to: “Derek Atkins <warlord@MIT.EDU>”.

Are you sure you want to use this public key (y/N)? yes
.
Transport armor file: message.asc

The dot (.) on a line by itself is printed by PGP to inform the user that the RSA encryption has proceeded. Because RSA is a slow operation, PGP prints the dot to inform you that it is still processing the message. Otherwise, users might incorrectly believe that PGP is not working. After PGP has finished with the RSA encryption, it writes the output file, message.asc, which can be sent to your recipients:

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