CS 417 Exam 3
Spring 2009
- 4 points
List the steps that Alice and Bob have to take to communicate with each other via a hybrid cryptosystem. Assume that Alice and Bob have each other's public keys. Be sure to specify types of encryption (public key or symmetric) and the keys being used at each step where applicable. - 6 points
Alice gives Bob a signed document along with her digital certificate, which was issued by VeriSign. Bob already has VeriSign's digital certificate. List the steps that Bob takes to validate Alice's certificate and signed document. - 4 points
List the steps that Bob would take to authenticate Alice using a nonce and public key cryptography. Assume that Alice has Bob's public key and Bob has Alice's public key. - 4 points
How come "key explosion" is not a problem with Kerberos even though it is based on symmetric cryptography? - The two-phase commit protocol uses two phases in order to:
(a) Obtain consensus from the group before directing everyone to commit or abort.
(b) Ensure that a transaction first gets all the locks on resources before it releases any.
(c) Partition the growing phase from the shrinking phase of a transaction.
(d) Ensure reliable message delivery: if the message does not get to the clients in the first phase, it will get to them in the second phase. - If a machine dies during phase 2 in the two-phase commit protocol but has already sent a commit response during phase 1, the machine must:
(a) Send an abort to the coordinator so it can inform others to now abort the transaction.
(b) Do nothing and wait for the next set of instructions from the coordinator.
(c) Let the other machines know of the situation via a multicast.
(d) Reconstruct the transaction state from the log and still be prepared to commit. - The Diffie-Hellman algorithm:
(a) Uses exponents to generate a public encryption key and a private decryption key.
(b) Is a way to adopt the DES symmetric cipher into a public key cipher.
(c) Is a public key encryption algorithm that creates two encryption keys for each user: a public key, which is shared, and a private key.
(d) Uses one-way functions to allow two parties to come up with a shared secret key. - Which statement is NOT true? RSA public key cryptography:
(a) Is designed for authentication, not data encryption.
(b) Has its security based on a one-way function.
(c) Requires the use of a different key to decrypt than to encrypt.
(d) Requires longer keys for the same level of security as symmetric ciphers. (e) Is considerably slower than DES symmetric cryptography. - Which is NOT a factor of authentication?
(a) Something you know.
(b) Something you have.
(c) Something you've seen.
(d) Something you are. - Every once in a while, my cellphone would die. It turned out that the battery was not making a reliable connection with the contact. This was an example of:
(a) A byzantine fault.
(b) An intermittent fault.
(c) A permanent fault.
(d) A transient fault. - The challenge authentication handshake protocol works on an insecure network because:
(a) The challenge data is encrypted with a shared secret key before the data is sent.
(b) The challenge data is encrypted with a private key before the data is sent.
(c) The password and challenge data are encrypted with a public key before the data is sent.
(d) The password and challenge data are hashed before the data is sent. - Alice uses Kerberos authentication to talk to Bob. Kerberos gives her a sealed envelope, or ticket. This ticket contains the session key and is encrypted so that:
(a) Only Bob and Kerberos can read it.
(b) Only Alice and Kerberos can read it.
(c) Only Bob, Alice, and Kerberos can read it.
(d) Only Kerberos can read it. - CAPTCHA is used to:
(a) Identify a user.
(b) Authenticate a user.
(c) Both identify and authenticate a user.
(d) Ensure that the response is not generated by a computer. - A null cipher is:
(a) A restricted cipher that takes no key.
(b) In programming, a generic container for cryptographic operations.
(c) Any result of an encryption where the key as all bits set to zero.
(d) A technique for hiding the existence a message. - The two-army problem tells us that:
(a) TCP/IP can never be fully reliable since IP is not reliable.
(b) The retransmission mechanism of TCP/IP allows it to be reliable even though IP itself is not reliable.
(c) TCP/IP can be reliable only if there are at least O(2n2/3) exchanges between a pair of hosts.
(d) TCP/IP needs to support message sequencing as well as retransmission to achieve reliability. - A software bug that lets an attacker change the return address of a function is an example of:
(a) Phishing.
(b) SYN flooding.
(c) Buffer overflow.
(d) A rootkit. - A hypervisor is:
(a) An instance of a virtual machine.
(b) Control software for coordinating virtual machines.
(c) A form of single queue workload distribution.
(d) The use of HTTP REDIRECT for load balancing. - Signed software does NOT ensure that:
(a) The code is from a known publisher.
(b) The code has not been modified after installation.
(c) Buffer overflow attacks will not work.
(d) The code has not been infected with a virus. - A DMZ:
(a) Hosts internal services.
(b) Hosts Internet-visible services.
(c) Is a protected subnet for non-secured internal machines.
(d) Is a firewall between the internal network and the Internet. - A packet filter cannot screen against:
(a) Data from the external network that is masqueraded with a source address from the internal network.
(b) Mail messages with executable files as attachments.
(c) External hosts trying to connect to your FTP server.
(d) Internal users not being allowed to access specific external web sites. - A buffer overflow attack is designed to:
(a) Take a machine out of service.
(b) Inject new code into a running program.
(c) Extract a user's password.
(d) Redirect a URL to another site. - A virtual machine monitor does NOT:
(a) Present a set of virtual devices to the operating systems under its control.
(b) Intercept system calls to the operating system.
(c) Intercept privileged instructions.
(d) Coordinate access to physical devices on the computer. - On the Internet, a VPN tunnel appears as a stream of IP packets:
(a) From one source to one destination.
(b) From multiple sources to one destination.
(c) From one source to multiple destinations.
(d) From multiple sources to multiple destinations. - A heartbeat network is used to:
(a) Enable multiple machines in a cluster to share one disk.
(b) Elect a cluster coordinator to manage cluster resources.
(c) Synchronize operations within the cluster.
(d) Allow machines in a cluster to determine if other machines are alive. - The technique of winnowing and chaffing relies on:
(a) Sending slightly different messages to different recipients.
(b) Sending encrypted messages that only authorized recipients can decrypt.
(c) Sending multiple messages, with some messages containing invalid signatures.
(d) Hiding messages within a document. - Compared with two-phase locking, strict two-phase locking:
(a) Avoids having transactions read uncommitted data.
(b) Maximizes concurrency among multiple transactions.
(c) Ensures that deadlock will not occur.
(d) Ensures that the result from concurrent execution is the same as that from serial execution. - Which of the following is NOT an advantage of hybrid cryptosystems? Hybrid cryptosystems:
(a) Are faster than public-key cryptography.
(b) Easily facilitate communication between multiple parties.
(c) Eliminate the need for a trusted third-party.
(d) Provide increased security because each message has two levels of encryption. - Wide-mouth frog authentication relies on which mechanism to provide security against attackers when passing a session key?
(a) Trusted third-party.
(b) Nonces.
(c) Public-key cryptography.
(d) X.509 digital certificates. - The four As of security are Authentication, Authorization, Accounting, and Auditing. Which one is not properly defined?
(a) Authentication - the process of asking the user to provide his or her identity.
(b) Authorization - determining whether a user is allowed to access certain resources or programs.
(c) Accounting - logging system activity so that all system breaches are recorded, identified, and available for further analysis.
(d) Auditing - Inspecting the software and system configurations for security flaws. - Dual-homed hosts are:
(a) Machines that verify requests from an untrusted network to access services within a trusted network.
(b) Machines with two separate network interfaces: one connected to an untrusted network and the other connected to a trusted network.
(c) Stripped-down machines that provide proxy services with as few tools as possible so as to limit an intruder's potential to illegally access a trusted network.
(d) Machines that act as routers in order to manage access to both the DMZ subnet and the trusted network. - Storage Area Networks (SAN) provide which one of the advantages?
(a) SANs are fault-tolerant since all disks have a back-up copy in case of failure.
(b) SANs eliminate the need for a distributed lock manager in a cluster.
(c) SANs use network switches to allow specific machines to read and/or write to specific disks.
(d) SANs reconstruct data from a failed disk using neighboring disks and error-correcting codes. - Restarting a failed application from a checkpoint is known as a:
(a) Cold failover.
(b) Cascading failover.
(c) Warm failover.
(d) Hot failover.
Part I – 22 Points
PART II – 78 points – 3 points each
For each statement, select the most appropriate answer. You may omit two questions. Please clearly indicate the questions you choose to omit.
