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