I'm seeing some statements which are causing me to ask "What is the
architecture and method of encryption used by SSH/SFTP?"
http://www.ford-hutchinson.com/~fh-1-pfh/ftps-ext.html points out that
sftp and ftps are very different and refers to
http://www.enterprisedt.com/products...answers.html#2 for
more details. The latter site states

'SFTP uses keys rather than certificates. This means that it can't take
advantage of the "chains of trust" paradigm facilitated through
Certificate Authorities. This paradigm makes it possible for two
entities to establish a trust relationship without directly exchanging
security information, which is important for some applications. FTPS
uses certificates and therefore can take advantage of this paradigm.
SFTP clients must install keys on the server.'

They obviously have a bias in favor of ftps. I'm not concerned with
trying to decide whether one is superior to the other, what I'm trying
to understand is the technology.

If sftp uses keys instead of certificates, what kind of keys are used
and why can't they take advantage of chains of trust? If this statement
isn't true please explain what's wrong with it.

The other question concerns "SFTP clients must install keys on the
server". (Again, if this is true) What are they talking about? I've
done some reading in the SSH RFCs and, as best as I can tell, the client
is the one accepting and verifying the server key (I'm not so sure I
have a firm grasp on all that the RFCs are saying). If this is true why
are clients installing keys on the server?

Final question: Is there a document which has a high level explanation
of what happens in ssh communication? Something like:

client does this
server does that
client next does this
server next does that

Thanks for any replies or information.