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diff --git a/website/similar.mdwn b/website/similar.mdwn deleted file mode 100644 index aef9c6f..0000000 --- a/website/similar.mdwn +++ /dev/null @@ -1,135 +0,0 @@ -[[!meta title="Similar Projects"]] - -The monkeysphere isn't the only project intending to implement a PKI -for OpenSSH. We provide links to these other projects because they're -interesting, though we have concerns with their approaches. - -[[toc ]] - -All of the other projects we've found so far require a patched version -of OpenSSH, which makes adoption more difficult. Most people don't -build their own software, and simply overlaying a patched binary is -associated with significant maintenance (and therefore security) -problems. - -While ultimately contributing a patch to -[OpenSSH](http://openssh.com/) (or -[any](http://mina.apache.org/sshd/) -[free](http://www.chiark.greenend.org.uk/~sgtatham/putty/) -[SSH](http://www.lysator.liu.se/~nisse/lsh/) -[implementation](http://matt.ucc.asn.au/dropbear/dropbear.html)) is -not a bad thing, we hope to be able to better establish the use of a -PKI without resorting to source modification. - -## openssh-gpg ## - -[openssh-gpg](http://www.red-bean.com/~nemo/openssh-gpg/) is a patch -against OpenSSH to support OpenPGP certificates. According to its -documentation, it is intended to support [`pgp-sign-rsa` and -`pgp-sign-dss` public key algorithms for hosts, as specified by the -IETF](http://tools.ietf.org/html/rfc4253#section-6.6). - -Some concerns with `openssh-gpg`: - - * This patch is old; it doesn't appear to have been maintained beyond - OpenSSH 3.6p1. As of this writing, OpenSSH 5.1p1 is current. - - * It only provides infrastructure in one direction: the user - authenticating the host by name. There doesn't seem to be a - mechanism for dealing with identifying users by name, or allowing - users to globally revoke or update keys. - - * The choice of User ID (`anything goes here (and here!) - <ssh@foo.example.net>`) for host keys overlaps with the current use - of the User ID space. While it's unlikely that someone actually - uses this e-mail address in the web of trust, it would be a nasty - collision, as the holder of that key could impersonate the server - in question. The monkeysphere uses [User IDs of the form - `ssh://foo.example.net`](http://tools.ietf.org/wg/secsh/draft-ietf-secsh-scp-sftp-ssh-uri/) - to avoid collisions with existing use. - - * It's not clear that `openssh-gpg` acknowledges or respects the - [usage flags](http://tools.ietf.org/html/rfc4880#section-5.2.3.21) - on the host keys. This means that it could accept a "sign-only" - key as suitable for authenticating a host, despite the - clearly-marked intentions of the key-holder. - -## Perspectives OpenSSH client ## - -[The Perspectives project](http://www.cs.cmu.edu/~perspectives/) at -CMU has released an [openssh client that uses network -notaries](http://www.cs.cmu.edu/~perspectives/openssh.html) to bolster -your confidence in newly-seen keys. This offers a defense against a -narrow MITM attack (e.g. by someone who controls your local gateway) -by simply verifying that other machines from around the network see -the same keys for the remote host that you're seeing. - -This tactic is quite useful, but doesn't take the system as far as it -could go, and doesn't tie into any existing web of trust. - -Some concerns with the Perspectives OpenSSH client: - - * This client won't help if you are connecting to machines behind - firewalls, on NAT'ed LANs, with source IP filtering, or otherwise - in a restricted network state, because the notaries won't be able - to reach it. - - * There is still a question of why you should trust these particular - notaries during your verification. Who are the notaries? How - could they be compromised? - - * It only provides infrastructure in one direction: the user - authenticating the host by name. There is no mechanism for dealing - with identifying users by name, or allowing users to globally - revoke or change keys. - - * It doesn't provide any mechanism for key rotation or revocation: - Perspectives won't help you if you need to re-key your machine. - - * The most common threat which Perspectives protects against (a - narrow MITM attack, e.g. the attacker controls your gateway) often - coincides with the ability of the attacker to filter arbitrary - traffic to your node. But in this case, the attacker could filter - out your traffic to the notaries (or the responses from the - notaries). Such filtering (rejecting unknown UDP traffic, as - Perspectives appears to use UDP port 15217) is unfortunately - common, particuarly on public networks, even when the gateway is - not malicious. This reduces the utility of the Perspectives - approach. - -## OpenSSH with X.509v3 certificates ## - -Roumen Petrov [maintains a patch to OpenSSH that works with the X.509 -PKI model](http://www.roumenpetrov.info/openssh/). This is the -certificate hierarchy commonly used by TLS (and SSL). - -Some concerns about OpenSSH with X.509v3: - - * the X.509 certificate specification itself [encourages corporate - consolidation and centralized global "trust" because of its - single-issuer architectural - limitation](http://lair.fifthhorseman.net/~dkg/tls-centralization/). - This results in an expensive and cumbersome system for smaller - players, and it also doesn't correspond to the true distributed - nature of human-to-human trust. Furthermore, centralized global - "trusted authorities" create a tempting target for attack, and a - single-point-of-failure if an attack is successful. - - Depending on how you declare your trust relationships, OpenPGP is - capable of providing the same hierarchical structure as X.509, but - it is not limited to such a structure. The OpenPGP Web of Trust - model is more flexible and more adaptable to represent real-world - trust than X.509's rigid hierarchy. - - * X.509 certificates can identify hosts by name, but not by - individual service. This means that a compromised web or e-mail - server with access to the X.509 key for that service could re-use - its certificate as an SSH server, and it would be able to - masquerade successfully. - - The monkeysphere uses [User IDs of the form - `ssh://foo.example.net`](http://tools.ietf.org/wg/secsh/draft-ietf-secsh-scp-sftp-ssh-uri/), - so they are not by-default shared across services on the same host - (you can still share a key across services on the same host if you - like, but the service User IDs can be certified independently of - one another). |