pg_hba.conf and crypt

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

On Thu, 6 May 1999, Oliver Elphick wrote:

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.

Thank you very much. This helped to clear up quite a bit and I've now got
crypt'ed passwords working. Normally I would prefer not to have to
utilize such passwords, but I'm trying to setup a basic distributed "push"
database where a bunch of client databases get their information from a
central repository and I want the databases as secure as possible so that
only the central server can update the clients.

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Louis Zirkel III (lzirkel@cleverly.com) System Admin/Programmer
"We're living on the Edge of the Century" -- Styx

Oliver Elphick wrote:

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.

Hi, Oliver,

I follow your instructions to do on my local machine, edit the file
pg_hba.conf:

local all password
host all 127.0.0.1 255.255.255.255 crypt

then I connect with psql, use the -u option, I got the following errors:

% psql -u
Username: postgres
Password:

User authentication failed
Connection to database 'postgres' failed.
User authentication failed

If I don't edit the file pg_hba.conf, I can connect template1
with no problem. I have run createuser and have created the user 'postgres'.
Would you like to tell me how to solve this problem, thanks.

-Kevin.

Kevin Lo wrote:

Hi, Oliver,

I follow your instructions to do on my local machine, edit the file
pg_hba.conf:

local all password
host all 127.0.0.1 255.255.255.255 crypt

then I connect with psql, use the -u option, I got the following errors:

% psql -u
Username: postgres
Password:

User authentication failed
Connection to database 'postgres' failed.
User authentication failed

You must set a password for postgres before you change pg_hba.conf, using
`ALTER USER postgres WITH PASSWORD xxxxx'. It sounds as if you haven't
done this.

--
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