Certificate and RSACryptoServiceProvider

//===
RSACryptoServiceProvider rsa ...

Bob rsa.Encrypt(): use Alice's public key to encrypt the msg sent for the receiver Alice;

Bob rsa.Decrypt():  use Bob's private key to decrypt the received msg target for Bob from ...;


Henceforth, in order to sign the hash, have to use rsa.Decrypt() (i.e. pirvate key) !?
to verify the crypted sig , have to use rsa.Encrypt()
but they failed for hash/sig verify/creation

*** use rsa.VerifyHash() / rsa.SignHash() instead


//=== another trouble
exception: Key not valid for use in specified state.
input data to long?