ASE decryption & MD5 hash

Question

Hi,

I need a solution for the problem i am having in ASE decryption.

in my Querystring I am exepcting 4 parameters - Param1, Param2, Param3, Param4

Param1,Param2 - Are normal parameters which i will be using
Param3 -  ASE Encrypted data
Param4 - MD5 hash value

I dont have much knowledge about ASE encryption.
Only infomation I got from MSDN is about Machine-key config settings

http://msdn2.microsoft.com/en-us/library/ms998288.aspx

I am not getting how i will be applying ASE decryption for my 3rd parameter and MD5 hash for 4th parameter in my URL

Can someone provide me any help about -

Decrypting the 3rd parameter
and how to deal with hash value i will be getting.

Thanks in advance.
Sup