[Zope] Reversible encryption on passwords?

Terry Hancock hancock@anansispaceworks.com
Thu, 20 Mar 2003 09:15:37 -0800

Hi all,

I've been thinking about the pros and cons of using encrypted
passwords, and I've realized that there are actually some
additional choices.

Normally "encrypted password" means you run a secure hash
(non-reversible) on a password and then you  actually 
compare the hashes.  But there are drawbacks:

1) You can't remind the user of their password, because you
don't have it.

2) Certain password-checking schemes (design for plain-text
may not be easily implemented this way.

But then I started thinking about *actual* encryption and things
like GnuPG encryption and signing.

Suppose I use a private key to encrypt/decrypt the password
data for storage in the database.  The key might be stored on
the server's filesystem or be retrieved from a more secure computer,
but it would be used to encrypt the data for storage and then
to decrypt it for authentication.  You could do this with public-key
cryptography, too, but it's not clear to me that there is an
advantage to that.

Anyway, in the authentication process, the password would
posted in "plain text" -- but if the connection is via SSL (HTTPS), then it
is actually encrypted on the way to the server.

So, in this scenario, my database contains password fields which
can only be read with the right key, but can be decrypted, and
the connection to the user is protected by SSL's public-key
cryptography.  (The idea being that should the database be
compromised, the passwords would not be exposed -- at least
not in plain text, you'd need to get both the database and the

It seems to me that this offers most of the security of normal
encrypted passwords, but with fewer drawbacks.  It does mean
that the site owner can read the passwords, but that's supposed
to be the advantage.

Presumeably I'm not the first person to think of this -- is it used by
some sites or not?  If not, why not?  I'm wondering what the faults
are and whether it'd be a good strategy for us.

Thanks for any comments,

Terry Hancock ( hancock at anansispaceworks.com )
Anansi Spaceworks  http://www.anansispaceworks.com