Re: libpq compression

On Jun16, 2012, at 17:15 , Tom Lane wrote:
> Magnus Hagander <magnus(at)hagander(dot)net> writes:
>> On Sat, Jun 16, 2012 at 12:55 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>> It's not obvious to me that we actually *need* anything except the
>>> ability to recognize that a null-encrypted SSL connection probably
>>> shouldn't be treated as matching a hostssl line; which is not something
>>> that requires any fundamental rearrangements, since it only requires an
>>> after-the-fact check of what was selected.
>
>> Maybe I spelled it out wrong. It does require it insofar that if we
>> want to use this for compression, we must *always* enable openssl on
>> the connection. So the "with these encryption method" boils down to
>> "NULL encryption only" or "whatever other standards I have for
>> encryption". We don't need the ability to change the "whatever other
>> standards" per subnet, but we need to control the
>> accept-NULL-encryption on a per subnet basis.
>
> After sleeping on it, I wonder if we couldn't redefine the existing
> "list of acceptable ciphers" option as the "list of ciphers that are
> considered to provide encrypted transport". So you'd be allowed to
> connect with SSL using any unapproved cipher (including NULL), the
> backend just considers it as equivalent to a non-SSL connection for
> pg_hba purposes. Then no change is needed in any configuration stuff.

Would we still tell openssl to only negotiate ciphers in the configured
list of available ciphers + NULL? If not, what happens if a connection
happens to use a cipher that is actually stronger than any cipher on
the "list of acceptable ciphers" list? The DBA wouldn't necessarily be
aware that such a cipher even exists, since it could have been made
available by an openssl upgrade…

But if we restrict the negotiable ciphers to the configure list + NULL,
then we're good I think.

best regards,
Florian Pflug