encrypt specified attributes in a Set-Cookie response to be stored in a client,
then decrypt and forward the Cookie request only to the originator
of the Cookie.
An attribute in a Cookie is specified as "attribute@host"
In the former case, a cookie generated by a host is encrypted
and echoed to host only.
In the latter case, a cookie generated by hosts in the domain
can be echoed to hosts in the domain.
The special string "%a" in cryptKey is substituted by
the IP-address of the client. This makes the crypted Cookie be usable
only by clients on the host of the IP-address.