Re: [GENERAL] pg_hba.conf and crypt - Mailing list pgsql-general

Louis Zirkel III wrote:
  >I'm having trouble understanding how to get the crypt option working in
  >the pg_hba.conf file.  I can get cleartext passwords to be passed and they
  >work just fine, but I cannot figure out how in the heck to get the crypt
  >option working.  I've looked through the FAQ and found only a reference to
  >the pg_hba.conf man page which isn't all that clear to me.  Any help would
  >be greatly appreciated.

This is a document I wrote some time ago on this subject.  If any parts of
it are no longer accurate, please let me know.

=============================================================================
How to use clear or encrypted passwords for PostgreSQL access:
=============================================================

Use lines such as

  local        all                password
  host        192.137.23    255.255.255.0    crypt

in /etc/postgresql/pg_hba.conf; then you can use

   CREATE USER user WITH PASSWORD password...

to create a new user with the specified password, or

   ALTER USER user WITH PASSWORD password...

to change the password of an existing user.  ANY USER with create-user
privilege can ALTER a password for any user, *INCLUDING* the postgres
super-user.

If connecting with psql, use the -u option; the user is prompted for username
and password.  If you don't use -u, the connection fails.

If using your own program with libpq, it is up to you to collect the user name
and password from the user and send them to the backend with PQsetdbLogin().

Passwords are stored in pg_shadow in clear, but if `crypt' authentication is
specified, the frontend encrypts the password with a random salt and
the backend uses the same salt to encrypt the password in the database.
If the two encrypted passwords match, the user is allowed access. If the
authentication method is `password', the password is transmitted and
compared in clear.

If passwords are turned on, it becomes impossible to connect as
a user, if no password is defined for that user.  Neither can you use
\connect to change user within psql.

[Debian-specific section deleted]


Problems with password authentication
=====================================

1. There is no easy and secure way to automate access when passwords are
   in use.  It would be good if the postgres super-user (as identified by
   Unix on a Unix sockets connection) could bypass the authentication.

2. In general, passwords are insecure, because they are held in clear
   in pg_shadow.  Anyone with create-user privilege can not only alter but
   also read them.  They ought to be stored with one-way encryption, as
   with the Unix password system.

3. The postgres super-user's password can be changed by anyone with
   create-user privilege.  It ought to be the case that people can
   only change their own passwords and that only the super-user can change
   other peoples' passwords.

4. If passwords are turned on, the -u option must be supplied to psql. If
   it is not, psql merely says "Connection to database 'xxxx' failed.".  A
   more helpful error message would be desirable.

=============================================================================


--
Oliver Elphick                                Oliver.Elphick@lfix.co.uk
Isle of Wight                              http://www.lfix.co.uk/oliver
               PGP key from public servers; key ID 32B8FAA1
                 ========================================
     "If it is possible, as much as it depends on you, live
      peaceably with all men."        Romans 12:18