May be explicitly stated or implied by the practics statement or associated informative material 这些直接证据,在实践活动的陈述或说明部分可能被明确的或暗示性的规定了。
William , stallings, cryptography and network security,-principles and practics, second edition, prentice hall international, inc ., 2000 杨明等译,《密码编码学与网络安全:原理与实践》(第二版),电子工业出版社,北京,2001。