WebApp Sec mailing list archives
RE: Using SSL private key for cookie's HMAC
From: "Michael Silk" <michaels () phg com au>
Date: Mon, 6 Sep 2004 12:10:26 +1000
Hi, I probably would not be re-using the SSL key; consider if your SSL certificate updates but you still have people with the old SSL-Private key-encrypted cookie waiting to connect to your site. They browse back, after your SSL update, only to discover an error message, because your app can no longer decrypt, or match, or whatever, their cookie data. Further, consider another situation where you may have different SSL certificates for different sub-domains, but one cookie for the entire domain; which SSL cert do you use to encrypt your cookie? There doesn't seem to be any benefit at all using the same key, only headaches, so just generate your own :) -- Michael -----Original Message----- From: Jeff Williams [mailto:jeff.williams () aspectsecurity com] Sent: Tuesday, 31 August 2004 11:38 PM To: Simon Zuckerbraun; webappsec () securityfocus com Subject: Re: Using SSL private key for cookie's HMAC Simon, I'm curious too. Assuming you use the private key properly, are there any risks associated with using the private key for purposes other than SSL. Could the SSL private key be safely used as a "master key" for encrypting and signing other things on the web server? I suspect the reasons to use a separate key are for better key management. You'll want to change keys periodically and it might just be easier if you don't have to change the site's SSL cert as well. So I think it's an interesting idea, but it's probably just as easy to have a separate key for purposes other than SSL. --Jeff Jeff Williams Aspect Security, Inc. http://www.aspectsecurity.com ----- Original Message ----- From: "Simon Zuckerbraun" <szucker () sst-pr-1 com> To: <webappsec () securityfocus com> Sent: Friday, August 27, 2004 12:42 AM Subject: Using SSL private key for cookie's HMAC
I'm pondering a design question regarding a web application that is to operate over SSL. We want to include an HMAC in our cookies to prevent tampering. To produce an HMAC, the server must be configured with a private key. Since the website operates with SSL, the server already *has* a
private
key available: the private key of its SSL certificate. Is there any
harm
in using this same private key for producing the HMACs as well? Thanks, Simon
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Current thread:
- Re: Using SSL private key for cookie's HMAC, (continued)
- Re: Using SSL private key for cookie's HMAC Andrew Steingruebl (Sep 05)
- Re: Using SSL private key for cookie's HMAC Jeff Williams (Sep 05)
- Re: Using SSL private key for cookie's HMAC Adam Shostack (Sep 05)
- Re: Using SSL private key for cookie's HMAC Jason Coombs PivX Solutions (Sep 05)
- Re: Using SSL private key for cookie's HMAC Peter Conrad (Sep 06)
- Re: Using SSL private key for cookie's HMAC Jason Coombs PivX Solutions (Sep 07)
- Re: Using SSL private key for cookie's HMAC Peter Conrad (Sep 07)
- Webserver problems John Fisher (Sep 09)
- RE: Webserver problems Dinis Cruz (Sep 10)
- Re: Webserver problems Mike Kalinovich (Sep 11)
- Re: Using SSL private key for cookie's HMAC Peter Conrad (Sep 06)