Do you really need to determine today's password?

One approach I've used in the past is calculate a new password (with the
date not an input to your algorithm -- though I have found the microsecond
counter of the Time of Day clock to be handy starting point, especially when
manipulated a tad), encrypt "some data" using the password as a key (in your
case I would suggest part of "some data" is the issuers current date), and
store the returned encrypted value. For validation within the application
re-encrypt the "some data" (now using the application current date as part
of "some data") using the user provided password. Compare the generated
value with the stored value. If the same then it's today's password. If it's
not the same then it may or may not be a previous password, but it sure
isn't todays password. The drawback of course is that you can't determine
today's password. You can though verify that it's today's password (which
I've usually found close enough).

Hope this helps,
On Fri, Jun 11, 2010 at 5:05 PM, Simon Coulter <shc@xxxxxxxxxxxxxxxxx>wrote:

Looking for suggestions:

I want to protect access to an application via a password. I want the
password to automatically change daily. I want the application to be
able to determine today's password without having to read it from an
external source (i.e., algorithmically/programmatically derived). This
last requirement means:

o no special profile with password changed daily
o no validation list use
o no encrypted password stored in external object such as *FILE or

I envisage:
o Application objects are *PUBLIC *EXCLUDE
o Application objects are authorised to a specific group profile
o Password generator is *PUBLIC *EXCLUDE
o Password generator is authorised to a specific profile (different
from the above)

In actual use a user who is a member of the application group AND who
needs to use this particular application will request the password
from an authorised issuer. The issuer will use the password generator
to determine today's password. The user will then use the application.

The "automatic daily change" requirement means the password generation/
validation is tied to the date but obviously simple encryption linked
to the date will not be very secure nor will each daily password be
sufficiently different from the previous one.

I have some ideas but thought I would see what others suggest--always
presuming you think this sufficiently interesting to bother with :)

Simon Coulter.
FlyByNight Software OS/400, i5/OS Technical Specialists
Phone: +61 2 6657 8251 Mobile: +61 0411 091 400 /"\
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