mirror of
https://git.tartarus.org/simon/putty.git
synced 2025-04-13 00:58:06 -05:00
42740a5455
In the case where a server presents a host key signed by a different certificate from the one you've configured, it need not _always_ be evidence of wrongdoing. I can imagine situations in which two CAs cover overlapping sets of things, and you don't want to blanket-trust one of them, but you do want to connect to a specific host signed by that one. Accordingly, PuTTY's previous policy of unconditionally aborting the connection if certificate validation fails (which was always intended as a stopgap until I thought through what I wanted to replace it with) is now replaced by fallback handling: we present the host key fingerprint to the user and give them the option to accept and/or cache it based on the public key itself. This means that the certified key types have to have a representation in the host key cache. So I've assigned each one a type id, and generate the cache string itself by simply falling back to the base key. (Rationale for the latter: re-signing a public key with a different certificate doesn't change the _private_ key, or the set of valid signatures generated with it. So if you've been convinced for reasons other than the certificate that a particular private key is in the possession of $host, then proof of ownership of that private key should be enough to convince you you're talking to $host no matter what CA has signed the public half this week.) We now offer to receive a given certified host key type if _either_ we have at least one CA configured to trust that host, _or_ we have a certified key of that type cached. (So once you've decided manually that you trust a particular key, we can still receive that key and authenticate the host with it, even if you later delete the CA record that it didn't match anyway.) One change from normal (uncertified) host key handling is that for certified key types _all_ the host key prompts use the stronger language, with "WARNING - POTENTIAL SECURITY BREACH!" rather than the mild 'hmm, we haven't seen this host before'. Rationale: if you expected this CA key and got that one, it _could_ be a bold-as-brass MITM attempt in which someone hoped you'd accept their entire CA key. The mild wording is only for the case where we had no previous expectations _at all_ for the host to violate: not a CA _or_ a cached key.
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.