Which of the following statements are true regardinghashing？ （）

多项选择题WhichtwostepsdoesareceiverperformtovalidateamessageusingHMAC？（）

A. decrypts the received MAC using a secret key
B. compares the computed MAC vs. the MAC received
C. authenticate the receivedmessage using the sender’s public key
D. look up the sender’s public key
E. extracts the MAC from the receivedmessage thenencrypts the received message with a secret keyto producethe MAC
F. Computes the MAC using the receivedmessage and a secret key as inputs to the hash function

单项选择题Whichofthefollowingbestdescribesahashfunction？（）

A.An irreversible fast encryption method
B.A reversible fast encryption method
C.A reversible value computed from a piece of data and used to detect modifications
D.An irreversible value computed froma piece of data and used to detect modifications
E.A table inwhich values are stored for efficient retrieval.

单项选择题Whatdoesqospre-classifyprovidesinregardtoimplementingQoSoverGRE IPSecVPNtunnels？（）

A. enables IOS to copy the ToS field from the inner （original） IPheader to theouter tunnel IP header
B. enables IOS to make a copy of the inner （original） IP header and to run a QoS classification before encryption， based on fields in the inner IP header.
C. enables IOS to classify packets based on the ToS field in the inner （original） IP header
D. enables IOS to classify packets based on the ToS field in the outer tunnel IP header
E. enables the IOS classification engine to only see a single encrypted and tunneledflow to reduce classification complexity

多项选择题Asymmetricandsymmetricciphersdifferinwhichofthefollowingway（s）？（）

A.Asymmetric ciphers use pre-shared keys
B.Symmetric ciphers are faster to compute
C.Asymmetric ciphers are faster to compute
D.Asymmetric ciphers use public and private

单项选择题WhichofthefollowingisthemosteffectivetechniquetopreventsourceIPAddressspoofing？（）

A. policy based routing （PBR）
B. unicast reverse path forwarding （uRPF）
C. lock and keyACL
D. RFC 1918filtering
E. IP source routing