Re: Firewall best practices

The firewall needs to know the cert at one end of the connection (it can 
be either end, so if it knows the client cert you are using it will work 
as well)

In some cases the firewall makes up a cert on the fly, with the browser 
set to trust any cert the firewall signs, and the firewall is a full 
man-in-the-middle proxy.

In other cases the firewall works on a copy of the traffic and decrypts it 
with the known certs (there are some PKI modes this will not work on)

David Lang

On Tue, 27 Apr 2010, John Morrison wrote:

> My understanding of https (and other PKI-based encryption) is that
> only the holder of the private key can decrypt the data encrypted with
> the other (public) key in the pair. My view is that the firewall can
> only decrypt and inspect https traffic if it is acting as the server
> to the external client. It can't intercept and decrypt https traffic
> destined for another device - the real server. If it did https would
> be worthless. Any hacker could buy such a firewall to sniff and
> decrypt all https traffic.
>
> On 23 April 2010 20:18,  <[email protected]> wrote:
>> On Fri, 23 Apr 2010, Martin Barry wrote:
>>
>>> $quoted_author = "Marcus J. Ranum" ;
>>>>
>>>> That's why firewalls need to go back to doing what they
>>>> originally did, and parsing/analyzying the traffic that
>>>> flows through them, rather than "stateful packet
>>>> inspection" (which, as far as I can tell, means that
>>>> there's a state-table entry saying "I saw SYN!")
>>>
>>> Marcus, are you referring to DPI or proxies or both or something else
>>> entirely?
>>>
>>>
>>>> If the firewall doesn't understand the data it's passing,
>>>> it's not a firewall, it's a hub.
>>>
>>> If an application emulates HTTPS traffic and is proxy aware, how do you
>>> tell
>>> the difference?
>>
>> There are firewalls on the market that can decrypt HTTPS traffic (and I
>> believe be configured to block any traffic that they can't decrypt)
>>
>> David Lang
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