I downloaded the Old CCAvenue plugin from Nopcommerce.
As I was using Nopcommerce 3.0 ; I modified the 3.0 's Plugins directory.
The old API code was using Helper classes to encrypt the post data for API using Working key.
Now CCAvenue has asked for access code which is a hash and generated for a Specific URL which needs to be provided in order to redirect to their New api viz. https://secure.ccavenue.com/transaction/transaction.do?command=initiateTransaction
Also you need to use CCAvenues Dll to encrypt and decrypt the post data and return data from CCAvenue.