On Wed, 16 Mar 2005, Marc Sherman wrote:
> After writing the answer to Guy De Leeuw's question about TLS, I got to
> thinking; why is STARTTLS after connection on ports 25/587 preferred to
> tls_on_connect_ports on port 465?
It's because of IETF policy. Protocols should only be run on one port and
should have built-in security, rather than having a separate secure
version of the protocol on a different port.
> It seems to me that with tls_on_connect_ports, you get a slightly more secure
> session, because the HELO/EHLO doesn't travel in the clear, reducing the info
> available for traffic analysis by an attacker.
Actually the information in the HELO command is completely uninteresting
to an attacker. The real reason that TLS-on-connect is more secure than
STARTTLS is because it is more resistant to downgrade attacks. However
this is mostly to do with the bad quality of implementation of most SMTP
clients - they encourage users to make security optional rather than
required, which makes the attacker's job much easier.
Tony.
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