Re: Postgres: pg_hba.conf, md5, pg_shadow, encrypted passwords

* Eliot Simcoe (esimcoe@mac.com) wrote:
> On Apr 21, 2005, at 8:59 PM, Stephen Frost wrote:
> >The intention of the 'md5' method in pg_hba.conf is to avoid having
> >the
> >password go over the network in the clear, yes.  Unfortunately, this
> >pretty much requires that the database have something which is
> >password-equivilant stored on disk.
>
> Wouldn't it be possible for postgres to rehash the md5 checksum of the
> password before storing it in pg_shadow? This seems preferable if not
> optimal.
> Does anyone know why this is not being done?

Well, let's consider what's happening with that:

server- user added 'with encrypted password'
server- generate random salt
server- perform md5(md5(password+username)+salt) into hash
server- store hash and salt in pg_shadow

client- contact server
server- randomly generate challenge
server- send challenge to client
client- perform md5(md5(password+username)+challenge) into response
client- send response to server
server- retrive hash and salt from pg_shadow
server- perform md5(hash+salt) into expected
server- compare response from client to expected
server- nope, they don't match...

Whoops, that doesn't work, trying to compare:

md5(md5(password+username)+challenge) to
md5(md5(password+username)+salt)

Challenge and salt aren't the same, nor should they be (if they were
then they'd have to be constant and you would have to send it over the
wire).

If I missed something in this, please let me know.
Stephen