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From "Phil Endecott" <>
Subject [users@httpd] Best practice for mod_authn_dbd + postgresql; really SHA1?
Date Thu, 10 Aug 2017 13:44:43 GMT
Dear Experts,

I'm trying to determine the best way to implement Apache
authentication using mod_authn_dbd and PostgrSQL; my starting
point has been this documentation: (F.25.2)

It looks like my choices are:

1: Do the crypto in PostgreSQL.  For example, I could insert
new password hashes:

   INSERT INTO passwords (username, pwhash)
     VALUES ('phil', crypt('passw0rd', gen_salt('bf',8)));

And check them:

   SELECT * FROM passwords WHERE username='phil'
     AND pwhash = crypt('passw0rd', pwhash);

The trouble is that this returns a pass/fail response, but at the
Apache end I don't see a way to make mod_authn_dbd (or anything else)
use that; that module wants to receive a password hash that it will
check itself.  So:

2. Do the crypto in Apache.  I could simply:

   SELECT pwhash FROM passwords WHERE username='phil';

But getting the passwords into PostgreSQL in the first place is
not so easy.  pgcrypto's blowfish implementation doesn't seem to
be quite the same as what Apache uses ($2a$ vs $2y$, whatever that
means...), so it looks like I would probably need to invoke the
htpasswd utility somewhere between my e.g. create_user.cgi /
change_password.cgi scripts and the SQL.  So:

3. Use SHA1.  This is described as "probably the most useful format
for DBD authentication" in the Apache docs, since the Apache and
PostgreSQL implementations are the same:

   INSERT INTO passwords (username, pwhash)
     VALUES ('phil', '{SHA}'||encode(digest('passw0rd','sha1'),'base64'));

   SELECT pwhash FROM passwords WHERE username='phil';

But the disadvantage is that this is relatively insecure; there is no
salt and the SHA1 algorithm is quick enough that it could be brute-forced.
I could of course add a salt before hashing, but I don't think there is
a way to make mod_authn_dbd compare against the same salted password.

I find this all a bit surprising.  Isn't this a common scenario?  Am
I missing something?  What do other people do?

Many thanks for any advice.

Regards, Phil.

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