单项选择题
Which of these is the best way to provide sender non-repudiation？（）
A. pre-sharedkey B. secure hash C. SSL D. RSA signature
单项选择题 WhatgroupinCiscoIOSdoes1536-bitDiffie-Hellmanprimemodulusequivalenttoo？（）
单项选择题 Whataretheheadersizesforpoint-to-pointandmulti-pointGRE（alsoknownasmGRE）withtunnelkey？（）
单项选择题 Whichonesarethetwotypeofciphers？（）
