rsync and SSL

Cameron Simpson cs at
Thu Sep 20 11:11:18 EST 2001

On Thu, Sep 20, 2001 at 01:00:46AM +0000, M. Drew Streib <dtype at> wrote:
| On Thu, Sep 20, 2001 at 10:47:15AM +1000, Cameron Simpson wrote:
| > That way we could do SMTP over SSL etc etc transparently: clients connect,
| > say "SSL", if rejected either fall back or fall out, and if accepted
| > then away we all go.
| > 
| > Is there some technical reason for not doing things this way?
| Other than an extra couple tcp transmissions, not too many. It does
| probably break about all existing protocols though, at least as written,
| since the SSL handshake would fall outside of the bounds of the protocol.
| Implementing this on SMTP, for instance, would require more than SMTP,
| but would be SMTP+SSLoption, which _may_ be fully backwards compatible,
| but certainly not "compliant", as it implements non-standard behavior.

Yeah, but a server not implementing the request should return a 5xx error.
It's not like the client should proceed with the SSL stuff unless it
gets a "2xx Yeah I speak SSL." and therefore nothing should break.

| Even if the initial request were inside of the bounds of the protocol,
| as in "Renegotiate: SSL" as an http header, the followup
| handshake and subsequent transmission certainly wouldn't be standard.

For HTTP you'd return a 4xx or 5xx error of some kind, surely?

| This may not bother you from a technical perspective, but might upset
| people that are purists at the wire protocol level.

Shouldn't if the spec makes sure things don't ascend (descend?) into SSL
without acceptance on both ends...

| It is something
| that certainly could be debated, either for an individual protocol,
| or across the spectrum. Nothing to stop rsync from implementing something
| like this, since it is sort of in charge of its own protocol development...

Well, it'd be handy in rsync if only as a proof of concept.

| I'd be interested in seeing an IETF proposal for something like this,
| just for public debate.

I'll try to find out how to write one and submit it then...
Cameron Simpson, DoD#743        cs at

Will Hack Perl for Fine Food and Fun.
	- Tom Christiansen <tchrist at>

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