code: public final void init(Key key)
              throws InvalidKeyException, ExemptionMechanismException {
          done = false;
          initialized = false;
  
          keyStored = key;
          exmechSpi.engineInit(key);
          initialized = true;
      }
docs: Initializes this exemption mechanism with a key.
  
  <p>If this exemption mechanism requires any algorithm parameters
  that cannot be derived from the given <code>key</code>, the
  underlying exemption mechanism implementation is supposed to
  generate the required parameters itself (using provider-specific
  default values); in the case that algorithm parameters must be
  specified by the caller, an <code>InvalidKeyException</code> is raised.
  
  @param key the key for this exemption mechanism
  
  @exception InvalidKeyException if the given key is inappropriate for
  this exemption mechanism.
  @exception ExemptionMechanismException if problem(s) encountered in the
  process of initializing.