3 # Monkeysphere Documentation #
8 * Monkeysphere relies on [GnuTLS](http://gnutls.org/) version 2.4.0 or later.
12 * Getting started as a [user](/getting-started-user)
13 * Getting started as a [server admin](/getting-started-admin)
17 * [Initial specifications at CMRG](http://cmrg.fifthhorseman.net/wiki/OpenPGPandSSH)
18 * [OpenPGP (RFC 4880)](http://tools.ietf.org/html/rfc4880)
19 * [Secure Shell Authentication Protocol (RFC 4252)](http://tools.ietf.org/html/rfc4252)
20 * [URI scheme for SSH, RFC draft](http://tools.ietf.org/wg/secsh/draft-ietf-secsh-scp-sftp-ssh-uri/)
22 ## Similar Projects ##
24 The monkeysphere isn't the only project intending to implement a PKI
25 for OpenSSH. We provide links to these other projects because they're
26 interesting, though we have concerns with their approaches.
28 All of the other projects we've found so far require a patched version
29 of OpenSSH, which makes adoption more difficult. Most people don't
30 build their own software, and simply overlaying a patched binary is
31 associated with significant maintenance (and therefore security)
32 problems. A PKI becomes more useful the more people participate in
33 it, so widespread adoption is important.
37 [openssh-gpg](http://www.red-bean.com/~nemo/openssh-gpg/) is a patch
38 against OpenSSH to support OpenPGP certificates. According to its
39 documentation, it is intended to support [`pgp-sign-rsa` and
40 `pgp-sign-dss` public key algorithms for hosts, as specified by the
41 IETF](http://tools.ietf.org/html/rfc4253#section-6.6).
43 Some concerns with `openssh-gpg`:
45 * This patch is significantly old; it doesn't appear to have been
46 maintained beyond OpenSSH 3.6p1. As of this writing, OpenSSH is on
49 * It only provides infrastructure in one direction: the user
50 authenticating the host by name. There doesn't seem to be a
51 mechanism for dealing with identifying users by name, or allowing
52 users to globally revoke or update keys.
54 * The choice of User ID (`anything goes here (and here!)
55 <ssh@foo.example.net>`) for host keys overlaps with the current use
56 of the User ID space. While it's unlikely that someone actually
57 uses this e-mail address in the web of trust, it would be a nasty
58 collision, as the holder of that key could impersonate the server
59 in question. The monkeysphere uses [User IDs of the form
60 `ssh://foo.example.net`](http://tools.ietf.org/wg/secsh/draft-ietf-secsh-scp-sftp-ssh-uri/)
61 to avoid collisions with existing use.
63 * It's not clear that `openssh-gpg` acknowledges or respects the
64 usage flags on the host keys.
66 * It requires patching OpenSSH.
69 ### Perspectives OpenSSH client ###
71 [The Perspectives project](http://www.cs.cmu.edu/~perspectives/) at
72 CMU has released an [openssh client that uses network
73 notaries](http://www.cs.cmu.edu/~perspectives/openssh.html) to bolster
74 your confidence in new keys. This offers a defense against a narrow
75 MITM attack (e.g. by someone who controls your local gateway) by
76 simply verifying that other machines from around the network see the
77 same keys for the remote host that you're seeing.
79 This is quite useful, but doesn't take the system as far as it could
80 go, and doesn't tie into the existing web of trust.
82 Some concerns with the Perspectives OpenSSH client:
84 * This client won't help if you are connecting to machines behind
85 firewalls, on NAT'ed LANs, with source IP filtering, or otherwise
86 in a restricted network state.
88 * There is still a question of why you should trust these particular
89 notaries during your verification. Who are the notaries? How
90 could they be compromised?
92 * It only provides infrastructure in one direction: the user
93 authenticating the host by name. There is no mechanism for dealing
94 with identifying users by name, or allowing users to globally
95 revoke or change keys.
97 * It requires patching OpenSSH
99 ### OpenSSH with X.509v3 certificates ###
101 Roumen Petrov [maintains a patch to OpenSSH that works with the X.509
102 PKI model](http://www.roumenpetrov.info/openssh/). This is the
103 certificate hierarchy commonly used by TLS (and SSL before that).
105 Some concerns about OpenSSH with X.509v3:
107 * the X.509 certificate specification itself [encourages corporate
108 consolidation and centralized global "trust" because of its
109 single-issuer architectural
110 limitation](http://lair.fifthhorseman.net/~dkg/tls-centralization/).
111 This results in an expensive and cumbersome system for smaller
112 players, and it also doesn't correspond to the true distributed
113 nature of human-to-human trust. Furthermore, centralized global
114 "trusted authorities" create a tempting target for attack, and a
115 single-point-of-failure if an attack is successful.
117 Depending on how you declare your trust relationships, OpenPGP is
118 capable of providing the same hierarchical structure as X.509, but
119 it is not limited to such a structure. The OpenPGP Web of Trust
120 model is more flexible and more adaptable to represent real-world
121 trust than X.509's rigid hierarchy.
123 * It requires patching OpenSSH.