RE: Transferring a Session

[Noah Gray <NGray () worldrelief net>]

It sounds like you're close, I would make suggestions regarding 
method #3: 
1) Consider HMAC-SHA-1 has a synchronous-key message hashing alg.
2) Add a timestamp in the posted message that is also signed with the user's
identity to prevent replay attacks.
3) It's also possible to check the HTTP referrer at server B to validate the
script at server A signing the data, but this IS NOT certain security. It
would just be a great thing to log, as it will always be right on valid
attempts, and would hilight a replay attack against server B in the logs.
You could also temporarily block the IP of these failed attempts.


-----Original Message-----
From: David Robert
To: webappsec () securityfocus com
Sent: 5/3/04 6:33 PM
Subject: Transferring a Session

Hello all,

I have a problem I would like some input on. I need to implement a
solution
that allows one website to securely transfer 'logged in' state to
another
website.

I know this problem must have been solved 100 times before but I have
not
found a simple 'open' standard procedure for solving this. Maybe it's
just
too simple? In any case, suggestions appreciated. Further details below.

Requirements/Constraints:
1) System A authenticates users.
2) System A needs to present a link/form to the user that brings them to
a
logged in session on System B.
3) System B is written in Java and uses SSL, form based,
username/password
authentication.
4) Users are created on System B from System A data that identifies the
user
on System A (System A identifiers). This data is unique and unchanged
over
time. System B creates a tentative user (and generates a
username/password)
from this information. An administrator on System B will later authorize
this creation. The System B username/password is never changed.
5) We are looking for a system that is easy to implement and consistent
with
the level of security already present - i.e. open to man in the middle
attacks, etc.

Solutions:
There are 3 solutions I have been considering. They involve ensuring
that:
a) The link/POST the user uses to get to System B really came from
System A.
b) System A identifiers on the request have been unchanged.

The solutions I am considering are:
1) Sign the parameters of the request generated on System A with a
private
key. Use the public key on system B to verify the sender and contents.
2) Create a service on system B that will create a time-dependent token.
System A validates itself with B and gets a token. It includes it on the
generated link/POST for the user. The token is used by system B to
verify
the request.
3) Like #1 but use a common secret key for both system A and B. Request
parameters will be signed by this key. Recommendations on the signing
algorithm to use?
Of course, all requests between system A, B and the user are SSL.

The 'time dependent' nature of the last two are at the request of the
client. They are concerned that the link can be read from the browser's
cache by an attacker. Is this really a problem if the page on system A
is
set to not be cached?

Any input appreciated,
-David

-----Original Message-----
From: dave kleiman [mailto:dave () isecureu com]
Sent: Sunday, May 02, 2004 1:08 AM
To: webappsec () securityfocus com
Subject: ISAPI


Hello,

Is there a timeout setting anywhere for and ISAPI.dll in IIS5.

We have an issue where the ISAPI request is made, the sever is trying to
write it to the client and it is timing out.



_____________________________________
Dave Kleiman, CISSP, MCSE, CISM, CIFI
www.SecurityBreachResponse.com