Re: reducing our reliance on MD5

On 02/11/2015 11:30 PM, Claudio Freire wrote:
> On Wed, Feb 11, 2015 at 5:25 PM, Heikki Linnakangas
> <hlinnakangas(at)vmware(dot)com> wrote:
>> On 02/11/2015 06:35 AM, Claudio Freire wrote:
>>>
>>> Usually because handshakes use a random salt on both sides. Not sure
>>> about pg's though, but in general collision strength is required but
>>> not slowness, they're not bruteforceable.
>>
>> To be precise: collision resistance is usually not important for hashes used
>> in authentication handshakes. Not for our MD5 authentication method anyway;
>> otherwise we'd be screwed. What you need is resistance to pre-image attacks.
>
> AFAIK, if I find a colliding string to the MD5 stored in pg_authid, I
> can specify that to libpq and get authenticated.
>
> Am I missing something?

If you know the MD5 stored in pg_authid, you can use that directly to
authenticate. No need to find the original password, or another
colliding string, that hashes to the same MD5.

- Heikki