KeyEnvelope
                    class KeyEnvelope
                
                Represents the envelope key details JSON schema stored on the service.
            In the envelope technique, a securely generated content encryption key (CEK) is generated
            for every encryption operation. It is then encrypted (wrapped) with the user-provided key
            encryption key (KEK), using a key-wrap algorithm. The wrapped CEK is stored with the
            encrypted data, and needs the KEK to be unwrapped. The KEK and key-wrapping operation is
            never seen by this SDK.
            
                
The algorithm used to wrap the content encryption key.
            
The encrypted content encryption key.
            In V2, the content encryption algorithm is wrapped in with the key,
            authenticating the selected decryption algorithm.
            
The key identifier string.
            
public KeyEnvelope()