decrypting server cookie

So to insert the key value into the rule, I'd use something like this, but insert the actual key value in place of "key_value":

when RULE_INIT {
   set ::key "key_value"
}

and then reference the key for decryption like this:

[AES::decrypt $::key $encryptedCookie]

???

Seems like that might raise a security policy violation flag, since the server's private key would be clearly visible in the GUI even for Read-Only users, and also exposed in cleartext in the config files/tech.outs, no?

thanks for the assist!

/deb