Re: difference between SSL, SSH and VPN

From: Per Hedeland (per_at_hedeland.org)
Date: 05/16/03 

Date: Fri, 16 May 2003 19:04:16 +0000 (UTC)

In article <87he7xjq0m.fsf@blarg.net> Eric Hanchrow <offby1@blarg.net> writes:
>>>>>> "Joss" == Joss <joss@pleasereplytogroup.com> writes:
>
> Joss> What are the differences between SSL, SSH and VPN?
>
>Different goals.
>
>* SSL is a library that provides encryption, authentication, and other
> stuff to applications.

More specifically, applications that use TCP sessions - and the library
is just the most common implementation of course, from a communications
standpoint I guess SSL should be considered a "layer".

>* SSH is an application (that happens to use SSL) that lets you
> securly log in to remote systems, copy files, and forward ports.

SSH doesn't use SSL at all.

> OK, strictly speaking, there are a number of implementations of
> SSH. But they all offer more or less the same features.

SSH is a protocol (or rather two), with a number of implementations,
several of which are called SSH:-) - the features are pretty much
defined by the specification of the protocol(s).

>* VPN is a class of applications that lets you securely connect to a
> remote network as if it were a local network.

I'd be hard pressed to call VPN an "application", at least in the
"standard" case (e.g. IPSec).

> Thus there is
> certainly some overlap with SSH, but VPN is more general -- any
> program that communicates over the network will, once you set up a
> VPN, be able to securely communicate with the remote system. SSH's
> port-tunneling feature is sort of a poor man's version of VPN -- it
> only works for TCP connections, for example, whereas I think VPN can
> secure UDP as well.

Port forwarding itself cannot reasonably be called VPN (there are more
limitations as you suggest) - but on top of port forwarding (or rather
on top of SSH) you can put e.g. PPP and on top of that IP, and *then*
you have a "poor man's VPN".

--Per Hedeland
per@hedeland.org

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