Which of these is the best way to provide sender non-repudiation？（）

单项选择题WhatgroupinCiscoIOSdoes1536-bitDiffie-Hellmanprimemodulusequivalenttoo？（）

A. group 3
B. group 1
C. group 5
D. group 7

单项选择题Whataretheheadersizesforpoint-to-pointandmulti-pointGRE（alsoknownasmGRE）withtunnelkey？（）

A. 4 bytes for both
B. 4 bytes， and 8 bytes respectively
C. 8 bytes for both
D. 24 bytes for both

单项选择题Whichonesarethetwotypeofciphers？（）

A. Blocking cipher andnon-blocking cipher
B. CBC cipher and EBC cipher
C. Block cipher and Stream cipher
D. Blocker cipher and Streamer cipher
E. 3DES cipher and AES cipher

单项选择题WhichSSLprotocoltakesanapplicationmessagetobetransmitted，fragmentsthedataintomanageableblocks，optionallycompressesthedata，appliesaMAC，encrypts，addsaheader，andtransmitstheresultingunitinaTCPsegment？（）

A. SSL Handshake Protocol
B. SSLAlert Protocol
C. SSL Record Protocol
D. SSL Change CipherSpec Protocol

单项选择题ForaroutertoobtainacertificatefromaCA，whatisthefirststepofthecertificateenrollmentprocess？（）

A. the router generates a certificate request and forwards it tothe CA
B. the router generates an RSA key pair
C. the router sends its public key to the CA
D. the CA sends its public key to the router
E. the CA verifies the identity of the router
F. the CA generates a certificate request and forwards it to the router