\A{pgpkeys} PuTTY download keys and signatures

\cfg{winhelp-topic}{pgpfingerprints}

\I{verifying new versions}We create \i{PGP signatures} for all the PuTTY
files distributed from our web site, so that users can be confident
that the files have not been tampered with. Here we identify
our public keys, and explain our signature policy so you can have an
accurate idea of what each signature guarantees.
This description is provided as both a web page on the PuTTY site, and
an appendix in the PuTTY manual.

As of release 0.58, all of the PuTTY executables contain fingerprint
material (usually accessed via the \i\c{-pgpfp} command-line
option), such that if you have an executable you trust, you can use
it to establish a trust path, for instance to a newer version
downloaded from the Internet.

(Note that none of the keys, signatures, etc mentioned here have
anything to do with keys used with SSH - they are purely for verifying
the origin of files distributed by the PuTTY team.)

\H{pgpkeys-pubkey} Public keys

We supply two complete sets of keys. We supply a set of RSA keys,
compatible with both \W{http://www.gnupg.org/}{GnuPG} and PGP2,
and also a set of DSA keys compatible with GnuPG.

In each format, we have three keys:

\b A Development Snapshots key, used to sign the nightly builds.

\b A Releases key, used to sign actual releases.

\b A Master Key. The Master Key is used to sign the other two keys, and
they sign it in return.

Therefore, we have six public keys in total:

\b RSA:
\W{http://www.chiark.greenend.org.uk/~sgtatham/putty/keys/master-rsa.asc}{Master Key},
\W{http://www.chiark.greenend.org.uk/~sgtatham/putty/keys/release-rsa.asc}{Release key},
\W{http://www.chiark.greenend.org.uk/~sgtatham/putty/keys/snapshot-rsa.asc}{Snapshot key}

\lcont{
Master Key: 1024-bit; \I{PGP key fingerprint}fingerprint:
\cw{8F\_15\_97\_DA\_25\_30\_AB\_0D\_\_88\_D1\_92\_54\_11\_CF\_0C\_4C}
}

\b DSA:
\W{http://www.chiark.greenend.org.uk/~sgtatham/putty/keys/master-dsa.asc}{Master Key},
\W{http://www.chiark.greenend.org.uk/~sgtatham/putty/keys/release-dsa.asc}{Release key},
\W{http://www.chiark.greenend.org.uk/~sgtatham/putty/keys/snapshot-dsa.asc}{Snapshot key}

\lcont{
Master Key: 1024-bit; fingerprint:
\cw{313C\_3E76\_4B74\_C2C5\_F2AE\_\_83A8\_4F5E\_6DF5\_6A93\_B34E}
}

\H{pgpkeys-security} Security details

The various keys have various different security levels. This
section explains what those security levels are, and how far you can
expect to trust each key.

\S{pgpkeys-snapshot} The Development Snapshots keys

These keys are stored \e{without passphrases}. This is
necessary, because the snapshots are generated every night without
human intervention, so nobody would be able to type a passphrase.

The actual snapshots are built on a team member's home Windows box.
The keys themselves are stored on an independently run Unix box
(the same one that hosts our Git repository). After
being built, the binaries are uploaded to this Unix box and then
signed automatically.

Therefore, a signature from one of the Development Snapshots keys
\e{DOES} protect you against:

\b People tampering with the PuTTY binaries between the PuTTY web site
and you.

But it \e{DOES NOT} protect you against:

\b People tampering with the binaries before they are uploaded to the
independent Unix box.

\b The sysadmin of the independent Unix box using his root privilege to
steal the private keys and abuse them, or tampering with the
binaries before they are signed.

\b Somebody getting root on the Unix box.

Of course, we don't believe any of those things is very likely. We
know our sysadmin personally and trust him (both to be competent and
to be non-malicious), and we take all reasonable precautions to
guard the build machine. But when you see a signature, you should
always be certain of precisely what it guarantees and precisely what
it does not.

\S{pgpkeys-release} The Releases keys

The Release keys have passphrases and we can be more careful about
how we use them.

The Release keys are kept safe on the developers' own local
machines, and only used to sign releases that have been built by
hand. A signature from a Release key protects you from almost any
plausible attack.

(Some of the developers' machines have cable modem connections and
might in theory be crackable, but of course the private keys are
still encrypted, so the crack would have to go unnoticed for long
enough to steal a passphrase.)

\S{pgpkeys-master} The Master Keys

The Master Keys sign almost nothing. Their purpose is to bind the
other keys together and certify that they are all owned by the same
people and part of the same integrated setup. The only signatures
produced by the Master Keys, \e{ever}, should be the signatures
on the other keys.

We intend to arrange for the Master Keys to sign each other, to
certify that the DSA keys and RSA keys are part of the same setup.
We have not yet got round to this at the time of writing.

We have collected a few third-party signatures on the Master Keys,
in order to increase the chances that you can find a suitable trust
path to them. We intend to collect more. (Note that the keys on the
keyservers appear to have also collected some signatures from people
who haven't performed any verification of the Master Keys.) 

We have uploaded our various keys to public keyservers, so that
even if you don't know any of the people who have signed our
keys, you can still be reasonably confident that an attacker would
find it hard to substitute fake keys on all the public keyservers at
once.
