code: public boolean setTxMasterKey(byte[] key) {
  		boolean res = false;
  		if ((key.length == MASTER_KEY_SIZE_32_BYTES)
  				|| (key.length == MASTER_KEY_SIZE_16_BYTES)) {
  			txMasterKey = null;
  			txMasterKey = platform.getUtils().copy(key);
  			res = true;
  			logDebug("setTxMasterKey "
  					+ platform.getUtils().byteToHexString(txMasterKey));
  		} else {
  			logError("Wrong length iTxMasterKey: " + key.length);
  		}
  		return res;
  	}
docs: Sets the Master Key to be used for generating the Transmit session keys
  (only 256 bit keys supported - see PrivateGSM Tech Spec, 5.4.3)
  
  @param key
  Master Key string
  @return true if successfully set, false otherwise (invalid key length)