Last Revision 1.0 12/16/98
Written by: Vinne Moscaritolo
THIS IS SAMPLE CODE!
--------------------
This is the first public release, It is pretty
stable for everyday use, but I am aware of a few bugs. I
have listed them below..
This sample is a good example of what can be done with the
AppleShare IP UAM sdk and also provides some useful authenication
on the Macintosh.
WHAT IS IT?
------------
PGPuam is an enhancement to the standard AppleShare IP User Access
Methods (UAM) that enables a user to perform two-way strongly
authenticated logins to an AppleShare IP server from a Mac OS client.
The PGPuam system consists of two major components, a client and a
server plug-in.
WHY DO I WANT IT?
-----------------
Tired of remembering and keeping track of Appleshare passwords?
Did you know that same digital signature technology that is used to
guarantee the identity of e-mail can also be used to strongly authenticate
users of network services. This provides three significant advantages over
password based user authentication systems:
- Since the same key and passphrase used to sign e-mail messages is
also used for server access, you only need to remember one passphrase.
- Strong user authentication is provided by cryptographic digital
signatures.
- Since the user maintains the only secret material in the system,
compromising a server's user database results in limited damage.
HOW DOES IT WORK?
-----------------
Authentication with Cryptographic Signatures
E-mail communication on the Internet faces a security challenge similar to
network user authentication. Since e-mail packets are broadcast through
public networks, these messages can also be eavesdropped on and
counterfeited by unauthorized individuals. However e-mail vendors have
been able to address this problem by leveraging public key cryptography to
digitally sign and authenticate e-mail messages.
In a public key cryptosystem, each user or principle generates a pair of
mathematically-related cryptographic keys. These keys are created in such
a way that it is computationally infeasible to derive one key from the
other. One of the keys is made publicly available to anyone who wishes to
communicate with that user. The other key is kept private and never
revealed to anyone else. This private key is secured by either placing it
in a hardware token or further encrypting it to a passphrase, or both. The
private key is then used by the principal to digitally sign data. This
digital signature can later be checked with the matching public key to
ensure that the data has not been tampered with and that it originated
from the holder of the private key.`
Since the holder of the private key is the only entity who can create a
digital signature that verifies with the corresponding public key, there
is a strong correlation between a user's identity and the ability to sign
with that private key. Thus the public key can function as a principle's
identity in cyberspace .
Because they provide such strong testimony to the authenticity of the
sender, public-key cryptographic systems are becoming very popular among
today's Internet e-mail users.
The same digital signature technology that guarantees the identity of the
e-mail sender can be used to strongly authenticate users of network
services, too. By having the user sign a random challenge message from the
server at login, the server can verify the identity of the user with his
public key. The server randomly creates the challenge message to prevent
replay attacks. This process is illustrated in the following scenario :
1. The user initiates network service access.
2. The server looks up the user's public key in its authentication
database. The server then generates a random challenge string and sends
the challenge to the client.
3. The client digitally signs the challenge string and returns the
cryptographic signature to the server. The client also sends a counter
challenge string which is used to verify the server's authenticity.
4. The server then checks the client's signature and, if successful,
grants access. It also signs and returns the client's counter-challenge.
This process provides several significant advantages over password based
user authentication systems:
- Since the same key and passphrase used to sign e-mail messages is also
used for server access, the user need only remember one passphrase. This
is done without the risks associated with passphrase caches.
- Strong user authentication is provided by cryptographic digital
signatures.
- Since the user maintains the only secret material in the system,
compromising a server's user database results in limited damage.
While similar systems have been proposed by a number of researchers they
lacked the availability of a widely-accepted key infrastructure. Since PGP
already has a large key infrastructure, I have chosen to exploit this by
building a challenge-response system using the PGP software developers kit
(PGPsdk), which is avilable from the pgp website .
WHAT DOES IT RUN ON?
-------------------
I have tested the client on MacOS 8.5 PPC only. I have no reason to belive
that it would not run on 8.1 PPC . It requires AppleShare Client 3.8.1 (or
newer, it comes with 8.5). The server works with AppleShare 6.1. Most
important, you must have a copy of PGP 6.0 or better on the client, manager
and servers machines.
EXPORT ISSUES
--------------
PGPuam does not contain any crypto code. It is purely for
authentication use only. (In fact all Signatures and Random
number generation is done via the PGPsdk) Therefor this code
does not fall under jusidiction of ITAR. Feel free to enjoy
it.
ABOUT THE CODE.
-------------------
PGPuam is a Metrowerks Codewarrior PRO 4 project. The code
is considered sample code for now. It uses a bunch of
technologies such as: CFM, Appearance Manager, Collections
Manager, PGPsdk etc. So there is a lot to learn by examining
the code itself.
HOW DO I BUILD IT?
-------------------
1) Before starting, you must get a copy of the PGPsdk. You
can download it from http://www.pgp.com/sdk/. Place the
Library and the Headers in the PGPsdkMac folder.
2) Build the "PGPuam Client" Project.
- - Move the result, a file called "PGPuam" into either the
Extensions folder or optionaly create folder titled
"AppleShare Folder" place it in either the Extensions folder
or System Folder and place the PGPuam file in that folder.
3) Build the "PGPuam Server" Project.
HOW DO I SET IT UP?
-------------------
Server:
0) Install PGP 6.0 (or better) on the server (or at least drop the approp
PGP libraries into the Extension folder)
1) Drop the "PGPuam Server" file in the "AppleShare IP UAM" folder found in
the server's extension folder.
2) - Unfortunately you must also Modify the SIZE resource of the
"AppleShare IP Registry" file in server's extension folder to
allocate a bit more memory then the stock configuration. I suggest
adding at least 1K more space. Yes this is a bug in the ASIP design
and yes they are working on a fix for the future, but for now you
can correct this using your favorite resource editor. I have taken
the liberty of enclosing a copy of a modified one with this
distribution.
3) Reboot the server.
Manager:
0) Install PGP 6.0 (or better) and make sure it runs, you'll need to at
least setup the default keychains.
1) Launch the PGPuam Manager program
2) Select a server in the "Connect.." Dialog (This must be done on a
machine remote to the server for now, must also have appletalk
connectivity) and enter the Admin Name/password.
3) Select "Server Settings" from the Server menu. and Press "Generate" to
create a server key. (it might ask you to move the mouse around) then
save the key..
4) Drag out a copy of the new public key to the desktop and save this, you
will need this for users later.
5) Close the window.
6) Go to the User List window and open a test user up, drag in a copy of
that users's public Key (From PGPkeys or whatever) and save. Do this
for each user you want to test with.
Clients:
0) Install PGP 6.0 (or better) and make sure it runs, you'll need to at
least setup the default keychains. Each client will need their own
keys, it can (should be) be an existing key.
1) If you are not already running "AppleShare" client 3.8.1 (comes with
macOS 8.5) then update now. You should be able to find a copy at
the Appleshare IP website at
Cool, download It.Comments (vinnie@vmeng.com)
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