Peer to Peer instead of Client to Server

John Stevens john at
Mon Apr 7 13:11:56 EDT 2008


I'm working on a project where the services are distributed, thus
they need "peer to peer" authentication.

Currently a client authenticates to any of the hosts running one of
the servers that are part of the distributed service, but for that
server to be able to contact a peer I've had to use a trick where I
kinit as a user, then start the server as a process owned by that

Guessing wildly, there appears to be two possible ways to solve
this problem: copy a forwardable TGT through the network of
service servers, or to have individual servers authenticate
themselves to other servers.

The first solution, (forwardable TGT) seems to add quite a
bit to the network traffic, while having the advantage of
authenticating all work done as being done for the user of
the client.  The second seems more "correct" as each server
is part of a distributed service, so in effect having
servers authenticate to other servers is "part of the service
authenticating itself to another part of the same service".

If I may solicit input: are both methods possible (there is
very little documentation, developer's guides, etc. for
forwardable tickets . . . in fact, there is very little
Kerberos developers documentation period)?  If both
are, is there one you see as being better for some
reason (more secure, etc.)?  Finally, besides the raw
code, is there any documentation or simple examples you
can point me at that suggest which functions to use, and
how to string them together to implement either?

I did find the code that seems to forward a TGT in the
telnet code in the MIT Kerberos source, but I couldn't find
anything to suggest how to use said ticket (though I'm guessing
that the correct process would be to receive said TGT, create
a new cache on the server side, stick this TGT into it, then
use that cache in a "client" to server authentication in
pretty much the exact same way as you would in any client to
server authentication.

The server to server authentication is a bit trickier, though
something like requesting a TGT for the server principal, then
using that to get server tickets in the same way as a client
does, except that the very begining of that process requires
the input of a password, and If I go storing passwords on the
servers, I might as well use the service password, yes?  In other
words, is there any way to use the server keytable as a means for
getting a TGT?

Finally, the telnet code seems to basically copy the TGT to the
other host in the clear.  Is this secure?  Or did I miss an encryption
step along the way?  The telnet code uses a function I can't find
documentation for, as well, so I'm not sure what it does or is
supposed to do.

Any pointers to documentation, suggestions, criticism, etc. would
be deeply appreciated.

John S.

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