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d515e4f1a3
This is a heavily edited (by me) version of a patch originally due to Nico Williams and Viktor Dukhovni. Their comments: * Don't delegate credentials when rekeying unless there's a new TGT or the old service ticket is nearly expired. * Check for the above conditions more frequently (every two minutes by default) and rekey when we would delegate credentials. * Do not rekey with very short service ticket lifetimes; some GSSAPI libraries may lose the race to use an almost expired ticket. Adjust the timing of rekey checks to try to avoid this possibility. My further comments: The most interesting thing about this patch to me is that the use of GSS key exchange causes a switch over to a completely different model of what host keys are for. This comes from RFC 4462 section 2.1: the basic idea is that when your session is mostly bidirectionally authenticated by the GSSAPI exchanges happening in initial kex and every rekey, host keys become more or less vestigial, and their remaining purpose is to allow a rekey to happen if the requirements of the SSH protocol demand it at an awkward moment when the GSS credentials are not currently available (e.g. timed out and haven't been renewed yet). As such, there's no need for host keys to be _permanent_ or to be a reliable identifier of a particular host, and RFC 4462 allows for the possibility that they might be purely transient and only for this kind of emergency fallback purpose. Therefore, once PuTTY has done a GSS key exchange, it disconnects itself completely from the permanent host key cache functions in storage.h, and instead switches to a _transient_ host key cache stored in memory with the lifetime of just that SSH session. That cache is populated with keys received from the server as a side effect of GSS kex (via the optional SSH2_MSG_KEXGSS_HOSTKEY message), and used if later in the session we have to fall back to a non-GSS key exchange. However, in practice servers we've tested against do not send a host key in that way, so we also have a fallback method of populating the transient cache by triggering an immediate non-GSS rekey straight after userauth (reusing the code path we also use to turn on OpenSSH delayed encryption without the race condition).
PuTTY README
============
This is the README file for the PuTTY installer distribution. If
you're reading this, you've probably just run our installer and
installed PuTTY on your system.
What should I do next?
----------------------
If you want to use PuTTY to connect to other computers, or use PSFTP
to transfer files, you should just be able to run them from the
Start menu.
If you want to use the command-line-only file transfer utility PSCP,
you will probably want to put the PuTTY installation directory on
your PATH. On Windows 7 and similar versions, you can do this at
Control Panel > System and Security > System > Advanced system
settings > Environment Variables.
Some versions of Windows will refuse to run HTML Help files (.CHM)
if they are installed on a network drive. If you have installed
PuTTY on a network drive, you might want to check that the help file
works properly. If not, see http://support.microsoft.com/kb/896054
for information on how to solve this problem.
What do I do if it doesn't work?
--------------------------------
The PuTTY home web site is
https://www.chiark.greenend.org.uk/~sgtatham/putty/
Here you will find our list of known bugs and pending feature
requests. If your problem is not listed in there, or in the FAQ, or
in the manuals, read the Feedback page to find out how to report
bugs to us. PLEASE read the Feedback page carefully: it is there to
save you time as well as us. Do not send us one-line bug reports
telling us `it doesn't work'.