QUESTION: 3

If you receive a RST packet while doing an ACK scan, it indicates that the port is open.(True/False).

True
False

Answer(s): A

Explanation:

When and ACK is sent to an open port, a RST is returned.

Symmetric encryption algorithms are known to be fast but present great challenges on the key management side. Asymmetric encryption algorithms are slow but allow communication with a remote host without having to transfer a key out of band or in person. If we combine the strength of both crypto systems where we use the symmetric algorithm to encrypt the bulk of the data and then use the asymmetric encryption system to encrypt the symmetric key, what would this type of usage be known as?

Symmetric system
Combined system
Hybrid system
Asymmetric system

Answer(s): C

Explanation:

Because of the complexity of the underlying problems, most public-key algorithms involve operations such as modular multiplication and exponentiation, which are much more computationally expensive than the techniques used in most block ciphers, especially with typical key sizes. As a result, public-key cryptosystems are commonly "hybrid" systems, in which a fast symmetric-key encryption algorithm is used for the message itself, while the relevant symmetric key is sent with the message, but encrypted using a public-key algorithm. Similarly, hybrid signature schemes are often used, in which a cryptographic hash function is computed, and only the resulting hash is digitally signed.

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QUESTION: 3

What is the best means of prevention against viruses?

Assign read only permission to all files on your system.
Remove any external devices such as floppy and USB connectors.
Install a rootkit detection tool.
Install and update anti-virus scanner.

Answer(s): D

Explanation:

Although virus scanners only can find already known viruses this is still the best defense, together with users that are informed about risks with the internet.

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QUESTION: 3

RC4 is known to be a good stream generator. RC4 is used within the WEP standard on wireless LAN. WEP is known to be insecure even if we are using a stream cipher that is known to be secured.
What is the most likely cause behind this?

There are some flaws in the implementation.
There is no key management.
The IV range is too small.
All of the above.
None of the above.

Answer(s): D

Explanation:

Because RC4 is a stream cipher, the same traffic key must never be used twice. The purpose of an IV, which is transmitted as plain text, is to prevent any repetition, but a 24-bit IV is not long enough to ensure this on a busy network. The way the IV was used also opened WEP to a related key attack. For a 24-bit IV, there is a 50% probability the same IV will repeat after 5000 packets.
Many WEP systems require a key in hexadecimal format. Some users choose keys that spell words in the limited 0-9, A-F hex character set, for example C0DE C0DE C0DE C0DE. Such keys are often easily guessed.

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