Granted -- you'll have to find a way of doing the above securely.
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I use MD5 strings as cookies for that kind of thing. Two cookies, one with the user's name, then one with the MD5 of "<
string><privateknownconstant>". It is more secure if the private constant is <string> dependent.
For example, say I want to pass the string "johndoe", and know for sure I passed it. I will set one cookie as "johndoe". I will set another cookie as the md5 of "123johndoes-privatekey". On the recieving side, I put "johndoe" through md5 with string value of the "private key" and see if they match. It they match, then I know I set the cookie, and the value is probably ok.
-Pete