[problems]

A quick overview of how SSH key authentication works:

> SSH client: I support key auth

> SSH server: Let's use key auth

> SSH client: Do you take this public key hash: XXXXXX?

> SSH server: Yes I do

or

> SSH server: No I don't

Repeat for as many keys as you like.

You can therefore grab a list of known public keys for a given person and ask a given ssh server if it knows about the given public key. Given a few days you could even scan the entire IPv4 space for servers taking a given public key. Username must match, etc of course, but it's an attack many people might not consider.

[bdamm]

Expanding this to the tor case that the GGP outlined, even if the server isn't compromised the use of the same key in two very different contexts (for git and for your silkroad command console) reveals that the client is one and the same. I believe just packet sniffing can ascertain this.

[bogomipz]

Sure, you would still need a Linux userid on that host (I'm assuming that PermitRootLogin is set to No.) Although that's probably easy to guess considering a person's name is often available in from Github or even the default comment field that ssh-keygen adds.