Hi Gawel,

The encryption/decryption variables that Forms Authentication use are
configured in the <machineKey> entry (see machine.config file or your
web,config file as well).
The "decryptionKey" attribute drives the key management as well as the
symmetric algorithm used. The default values "Autogenerate" set the 3DES
algorithm and a random key is generated and stored in the Local Security
Authority (LSA). You may specify your own key if you change this attribute
with the hexadecimal encoded value of your random generated key. For further
info search for "machineKey" on the MSDN Library.

Hernan de Lahitte
http://weblogs.asp.net/hernandl
http://www.lagash.com/english/index.html

"An expert is one who knows more and more about less and less until he knows
absolutely everything about nothing".