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24 January 2014

Comments

We are looking into options for adding hmac protection to Cookie data. The trick here is that the data leaving the web app in the Set-Cookie response header is not exactly the same as the data returned in request Cookie headers.

Look at this example Set-Cookie from Google -

Set-Cookie: PREF=ID=45f40e8097a0ef03:FF=0:TM=1391003789:LM=1391003789:S=dHIbLYQBaCTU01tL; expires=Fri, 29-Jan-2016 13:56:29 GMT; path=/; domain=.google.com

Out of this data, only the "PREF" Cookie data would be sent back in subsequent requests. The expires, path and domain Set-Cookie elements instruct the browser what to do with the Cookie data but it is not included within the response. The end result is that we can not simply hash the entire Set-Cookie header like we can do with HTML elements. We would need to only hash the first Cookie data section. This is where we are researching.

Excellent and illustrative article, thanks.

I am guessing that is possible to add a HMAC to cookie variables. Any pointers on how?

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