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In recent months I've had two requests from different people to build support into PuTTY for automatically handling complicated third-party auth protocols layered on top of keyboard-interactive - the kind of thing where you're asked to enter some auth response, and you have to refer to some external source like a web server to find out what the right response _is_, which is a pain to do by hand, so you'd prefer it to be automated in the SSH client. That seems like a reasonable thing for an end user to want, but I didn't think it was a good idea to build support for specific protocols of that kind directly into PuTTY, where there would no doubt be an ever-lengthening list, and maintenance needed on all of them. So instead, in collaboration with one of my correspondents, I've designed and implemented a protocol to be spoken between PuTTY and a plugin running as a subprocess. The plugin can opt to handle the keyboard-interactive authentication loop on behalf of the user, in which case PuTTY passes on all the INFO_REQUEST packets to it, and lets it make up responses. It can also ask questions of the user if necessary. The protocol spec is provided in a documentation appendix. The entire configuration for the end user consists of providing a full command line to use as the subprocess. In the contrib directory I've provided an example plugin written in Python. It gives a set of fixed responses suitable for getting through Uppity's made-up k-i system, because that was a reasonable thing I already had lying around to test against. But it also provides example code that someone else could pick up and insert their own live response-provider into the middle of, assuming they were happy with it being in Python.
This is the README for PuTTY, a free Windows and Unix Telnet and SSH
client.
PuTTY is built using CMake <https://cmake.org/>. To compile in the
simplest way (on any of Linux, Windows or Mac), run these commands in
the source directory:
cmake .
cmake --build .
Then, to install in the simplest way on Linux or Mac:
cmake --build . --target install
On Unix, pterm would like to be setuid or setgid, as appropriate, to
permit it to write records of user logins to /var/run/utmp and
/var/log/wtmp. (Of course it will not use this privilege for
anything else, and in particular it will drop all privileges before
starting up complex subsystems like GTK.) The cmake install step
doesn't attempt to add these privileges, so if you want user login
recording to work, you should manually ch{own,grp} and chmod the
pterm binary yourself after installation. If you don't do this,
pterm will still work, but not update the user login databases.
Documentation (in various formats including Windows Help and Unix
`man' pages) is built from the Halibut (`.but') files in the `doc'
subdirectory using `doc/Makefile'. If you aren't using one of our
source snapshots, you'll need to do this yourself. Halibut can be
found at <https://www.chiark.greenend.org.uk/~sgtatham/halibut/>.
The PuTTY home web site is
https://www.chiark.greenend.org.uk/~sgtatham/putty/
If you want to send bug reports or feature requests, please read the
Feedback section of the web site before doing so. Sending one-line
reports saying `it doesn't work' will waste your time as much as
ours.
See the file LICENCE for the licence conditions.