git.distorted.org.uk Git - u/mdw/putty/blob - doc/pgpkeys.but

   1 \define{versionidpgpkeys} \versionid $Id$
   2
   3 \A{pgpkeys} PuTTY download keys and signatures
   4
   5 \cfg{winhelp-topic}{pgpfingerprints}
   6
   7 \I{verifying new versions}We create \i{PGP signatures} for all the PuTTY
   8 files distributed from our web site, so that users can be confident
   9 that the files have not been tampered with. Here we identify
  10 our public keys, and explain our signature policy so you can have an
  11 accurate idea of what each signature guarantees.
  12 This description is provided as both a web page on the PuTTY site, and
  13 an appendix in the PuTTY manual.
  14
  15 As of release 0.58, all of the PuTTY executables contain fingerprint
  16 material (usually accessed via the \i\c{-pgpfp} command-line
  17 option), such that if you have an executable you trust, you can use
  18 it to establish a trust path, for instance to a newer version
  19 downloaded from the Internet.
  20
  21 (Note that none of the keys, signatures, etc mentioned here have
  22 anything to do with keys used with SSH - they are purely for verifying
  23 the origin of files distributed by the PuTTY team.)
  24
  25 \H{pgpkeys-pubkey} Public keys
  26
  27 We supply two complete sets of keys. We supply a set of RSA keys,
  28 compatible with both \W{http://www.gnupg.org/}{GnuPG} and PGP2,
  29 and also a set of DSA keys compatible with GnuPG.
  30
  31 In each format, we have three keys:
  32
  33 \b A Development Snapshots key, used to sign the nightly builds.
  34
  35 \b A Releases key, used to sign actual releases.
  36
  37 \b A Master Key. The Master Key is used to sign the other two keys, and
  38 they sign it in return.
  39
  40 Therefore, we have six public keys in total:
  41
  42 \b RSA:
  43 \W{http://www.chiark.greenend.org.uk/~sgtatham/putty/keys/master-rsa.asc}{Master Key},
  44 \W{http://www.chiark.greenend.org.uk/~sgtatham/putty/keys/release-rsa.asc}{Release key},
  45 \W{http://www.chiark.greenend.org.uk/~sgtatham/putty/keys/snapshot-rsa.asc}{Snapshot key}
  46
  47 \lcont{
  48 Master Key: 1024-bit; \I{PGP key fingerprint}fingerprint:
  49 \cw{8F\_15\_97\_DA\_25\_30\_AB\_0D\_\_88\_D1\_92\_54\_11\_CF\_0C\_4C}
  50 }
  51
  52 \b DSA:
  53 \W{http://www.chiark.greenend.org.uk/~sgtatham/putty/keys/master-dsa.asc}{Master Key},
  54 \W{http://www.chiark.greenend.org.uk/~sgtatham/putty/keys/release-dsa.asc}{Release key},
  55 \W{http://www.chiark.greenend.org.uk/~sgtatham/putty/keys/snapshot-dsa.asc}{Snapshot key}
  56
  57 \lcont{
  58 Master Key: 1024-bit; fingerprint:
  59 \cw{313C\_3E76\_4B74\_C2C5\_F2AE\_\_83A8\_4F5E\_6DF5\_6A93\_B34E}
  60 }
  61
  62 \H{pgpkeys-security} Security details
  63
  64 The various keys have various different security levels. This
  65 section explains what those security levels are, and how far you can
  66 expect to trust each key.
  67
  68 \S{pgpkeys-snapshot} The Development Snapshots keys
  69
  70 These keys are stored \e{without passphrases}. This is
  71 necessary, because the snapshots are generated every night without
  72 human intervention, so nobody would be able to type a passphrase.
  73
  74 The actual snapshots are built on a team member's home Windows box.
  75 The keys themselves are stored on an independently run Unix box
  76 (the same one that hosts our Subversion repository). After
  77 being built, the binaries are uploaded to this Unix box and then
  78 signed automatically.
  79
  80 Therefore, a signature from one of the Development Snapshots keys
  81 \e{DOES} protect you against:
  82
  83 \b People tampering with the PuTTY binaries between the PuTTY web site
  84 and you.
  85
  86 But it \e{DOES NOT} protect you against:
  87
  88 \b People tampering with the binaries before they are uploaded to the
  89 independent Unix box.
  90
  91 \b The sysadmin of the independent Unix box using his root privilege to
  92 steal the private keys and abuse them, or tampering with the
  93 binaries before they are signed.
  94
  95 \b Somebody getting root on the Unix box.
  96
  97 Of course, we don't believe any of those things is very likely. We
  98 know our sysadmin personally and trust him (both to be competent and
  99 to be non-malicious), and we take all reasonable precautions to
 100 guard the build machine. But when you see a signature, you should
 101 always be certain of precisely what it guarantees and precisely what
 102 it does not.
 103
 104 \S{pgpkeys-release} The Releases keys
 105
 106 The Release keys have passphrases and we can be more careful about
 107 how we use them.
 108
 109 The Release keys are kept safe on the developers' own local
 110 machines, and only used to sign releases that have been built by
 111 hand. A signature from a Release key protects you from almost any
 112 plausible attack.
 113
 114 (Some of the developers' machines have cable modem connections and
 115 might in theory be crackable, but of course the private keys are
 116 still encrypted, so the crack would have to go unnoticed for long
 117 enough to steal a passphrase.)
 118
 119 \S{pgpkeys-master} The Master Keys
 120
 121 The Master Keys sign almost nothing. Their purpose is to bind the
 122 other keys together and certify that they are all owned by the same
 123 people and part of the same integrated setup. The only signatures
 124 produced by the Master Keys, \e{ever}, should be the signatures
 125 on the other keys.
 126
 127 We intend to arrange for the Master Keys to sign each other, to
 128 certify that the DSA keys and RSA keys are part of the same setup.
 129 We have not yet got round to this at the time of writing.
 130
 131 We have collected a few third-party signatures on the Master Keys,
 132 in order to increase the chances that you can find a suitable trust
 133 path to them. We intend to collect more. (Note that the keys on the
 134 keyservers appear to have also collected some signatures from people
 135 who haven't performed any verification of the Master Keys.)
 136
 137 We have uploaded our various keys to public keyservers, so that
 138 even if you don't know any of the people who have signed our
 139 keys, you can still be reasonably confident that an attacker would
 140 find it hard to substitute fake keys on all the public keyservers at
 141 once.