As distinct from the type of signature generated by the SSH server
itself from the host key, this lets you exclude (and by default does
exclude) the old "ssh-rsa" SHA-1 signature type from the signature of
the CA on the certificate.
This will allow the central host_ca_new function to pre-populate the
structure with default values for the fields, so that once I add more
options to CA configuration they can take their default values when
loading a saved record from a previous PuTTY version.
As well as eliminating the null-pointer dereference, I also now
realise that the format-translation code depended on leaving the final
translated string in 'otherstr' in order to pass the host key check
afterwards (if they match).
I've also now realised that this only applies to *SSH-1* RSA keys, so
it's even more obsolete than I thought before. Perhaps I should just
remove this code instead of spending all this effort on fixing it. But
I've done the fix now, so I'll commit it, and then maybe we can remove
it afterwards (and have a working version of it available to resurrect
if ever needed!).
A user points out that in commit 6143a50ed2, when I converted all
use of the registry to functions that return a newly allocated buffer
instead of allocating a buffer themselves beforehand, I overlooked
that one use of the old idiom was reusing the preallocated buffer as
work space.
I _hope_ nobody still needs this code - the 'old-style' host key cache
format it handles was replaced in 2000. If anyone has a PuTTY host key
cache entry that's survived 22 years without either having to be
reinitialised on a new system or changed when the machine's host key
was upgraded, they're doing better than I am!
But if it's still here, it should still work, obviously. Replaced the
reused buffer with a strbuf, which is more robust anyway.
Now we offer the OpenSSH certificate key types in our KEXINIT host key
algorithm list, so that if the server has a certificate, they can send
it to us.
There's a new storage.h abstraction for representing a list of trusted
host CAs, and which ones are trusted to certify hosts for what
domains. This is stored outside the normal saved session data, because
the whole point of host certificates is to avoid per-host faffing.
Configuring this set of trusted CAs is done via a new GUI dialog box,
separate from the main PuTTY config box (because it modifies a single
set of settings across all saved sessions), which you can launch by
clicking a button in the 'Host keys' pane. The GUI is pretty crude for
the moment, and very much at a 'just about usable' stage right now. It
will want some polishing.
If we have no CA configured that matches the hostname, we don't offer
to receive certified host keys in the first place. So for existing
users who haven't set any of this up yet, nothing will immediately
change.
Currently, if we do offer to receive certified host keys and the
server presents one signed by a CA we don't trust, PuTTY will bomb out
unconditionally with an error, instead of offering a confirmation box.
That's an unfinished part which I plan to fix before this goes into a
release.
All the fiddly business where you have to check that a thing exists,
make sure of its type, find its size, allocate some memory, and then
read it again properly (or, alternatively, loop round dealing with
ERROR_MORE_DATA) just doesn't belong at every call site. It's crying
out to be moved out into some separate utility functions that present
a more ergonomic API, so that the code that decides _which_ Registry
entries to read and what to do with them can concentrate on that.
So I've written a fresh set of registry API wrappers in windows/utils,
and simplified windows/storage.c as a result. The jump-list handling
code in particular is almost legible now!
Correcting a source file name in the docs just now reminded me that
I've seen a lot of outdated source file names elsewhere in the code,
due to all the reorganisation since we moved to cmake. Here's a giant
pass of trying to make them all accurate again.
marshal.h now provides a macro put_fmt() which allows you to write
arbitrary printf-formatted data to an arbitrary BinarySink.
We already had this facility for strbufs in particular, in the form of
strbuf_catf(). That was able to take advantage of knowing the inner
structure of a strbuf to minimise memory allocation (it would snprintf
directly into the strbuf's existing buffer if possible). For a general
black-box BinarySink we can't do that, so instead we dupvprintf into a
temporary buffer.
For consistency, I've removed strbuf_catf, and converted all uses of
it into the new put_fmt - and I've also added an extra vtable method
in the BinarySink API, so that put_fmt can still use strbuf_catf's
more efficient memory management when talking to a strbuf, and fall
back to the simpler strategy when that's not available.
Previously, checking the host key against the persistent cache managed
by the storage.h API was done as part of the seat_verify_ssh_host_key
method, i.e. separately by each Seat.
Now that check is done by verify_ssh_host_key(), which is a new
function in ssh/common.c that centralises all the parts of host key
checking that don't need an interactive prompt. It subsumes the
previous verify_ssh_manual_host_key() that checked against the Conf,
and it does the check against the storage API that each Seat was
previously doing separately. If it can't confirm or definitively
reject the host key by itself, _then_ it calls out to the Seat, once
an interactive prompt is definitely needed.
The main point of doing this is so that when SshProxy forwards a Seat
call from the proxy SSH connection to the primary Seat, it won't print
an announcement of which connection is involved unless it's actually
going to do something interactive. (Not that we're printing those
announcements _yet_ anyway, but this is a piece of groundwork that
works towards doing so.)
But while I'm at it, I've also taken the opportunity to clean things
up a bit by renaming functions sensibly. Previously we had three very
similarly named functions verify_ssh_manual_host_key(), SeatVtable's
'verify_ssh_host_key' method, and verify_host_key() in storage.h. Now
the Seat method is called 'confirm' rather than 'verify' (since its
job is now always to print an interactive prompt, so it looks more
like the other confirm_foo methods), and the storage.h function is
called check_stored_host_key(), which goes better with store_host_key
and avoids having too many functions with similar names. And the
'manual' function is subsumed into the new centralised code, so
there's now just *one* host key function with 'verify' in the name.
Several functions are reindented in this commit. Best viewed with
whitespace changes ignored.
This gets rid of all those annoying 'win', 'ux' and 'gtk' prefixes
which made filenames annoying to type and to tab-complete. Also, as
with my other recent renaming sprees, I've taken the opportunity to
expand and clarify some of the names so that they're not such cryptic
abbreviations.
