quiz107key - public key with the principal that possesses...

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Quiz 7 Key CNT 5106C 15 April 2010 Instructions: Write your last name, then first initial in upper righthand corner of answer sheet, and write “Quiz 5” centered at top. Answer all questions. 1. What is the fundamental challenge in use of symmetric key cryptography? What is the fundamental challenge in the use of asymmetric key cryptography? Explain. 2. What is the most common combination of IPSEC protocol and transport mode? Describe. Why is it the most popular combination? KEY 1. The basic challenge in symmetric key cryptography is key distribution. If the channel is not secure, then the key cannot be distributed over the channel for which it is to be used, so a secure channel has to be used. This may be out of band (e.g., face-to-face distribution) or in-band using another mechanism to provide security (e.g., public key cryptography). In asymmetric (Public Key) cryptography, the basic issue is reliable association of a
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Unformatted text preview: public key with the principal that possesses the corresponding private key. While it is perfectly OK to advertise the public key, it is critical to know to whom the key belongs, or else a third party can spoof the identity of a given principal, possibly engaging in a man-in-the-middle attack. 2. The most common IPSEC protocol is ESP (Encapsulating Security Payload) , as opposed to AH (Authentication Header). This is because ESP also provides authentication capability, whereas AH does not provide for confidentiality, which is generally desirable. Tunneling Mode is the most common transport mode, because the end stations do not have to be IPSEC aware, and only the certificate and session keys for the IPSEC gateway need to be managed, as opposed to certificates for every host behind the gateway and for every pair of communicating hosts....
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