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Computer Security

In: Computers and Technology

Submitted By redzacalypse
Words 578
Pages 3
Assignment 1 Solution 1. Compare and contrast symmetric encryption with public-key encryption, including the strengths and weaknesses of each. Solution Scalability: with public-key encryption, multiple users can send encrypted messages to Alice using her public key and these messages can be decrypted only by Alice; thus, a linear number of publicprivate key pairs need to be established, distributed and protected to allow pairwise confidential communication between any two users; instead, symmetric encryption requires a quadratic number of secret keys. Efficiency: existing symmetric encryption methods are much faster and use much shorter keys than existing public-key encryption methods. Usability: symmetric-key encryption is easier to understand by a non-expert than public-key encryption.

2. Give an example of the false sense of security that can come from using the “security by obscurity" approach. Solution There are many examples. One possibility would be to use a weak encryption algorithm, like the Caesar cipher and try to keep secret the type of algorithm that you are using, in addition to keeping the key secret. The problem with this approach is that if someone guesses you are using such an algorithm or is able to reverse engineering your software, then they will discover your algorithm. From there it is a simple matter to break your weak encryption scheme.

3. Benny is a thief who tried to break into an Automated Teller Machine (ATM) using a screwdriver, but was only able to break five different keys on the numeric keypad and jam the card reader, at which point he heard Alice coming, so he hid. Alice walked up, put in her ATM card, successfully entered her 4-digit PIN, and took some cash. But she was not able to get her card back, so she drove off to find help. Benny then went back to the ATM, and started entering numbers to try to discover Alice's PIN and steal money from her account. What is the worst-case number of PINs that Benny has to enter before correctly discovering Alice's PIN? Solution Since Benny broke 5 different keys and Alice was still able to enter her PIN, it must only use the 5 remaining keys. So the total number of possible keys is now 54 = 625. In the worst case, Benny will have to enter 625 before he enters the correct one.

9. Discuss whether barcodes are more or less secure than magnetic stripe cards. Solution Both barcodes and magnetic stripe cards store information but cannot perform computations. They have similar security against an adversary who reads the data on them and tries to decrypt it. Also, Both barcodes and magnetic strip cards can be easily cloned. Barcodes can be captured from a distance using a camera while reading a magnetic strip card requires a device that comes in contact with the card.

Barcodes are usually printed on paper, which is more fragile than a magnetic stripe card, typically made of plastic. On the other hand, paper barcodes do not have the risk of becoming demagnetized.

10. A salesperson at a high-end computer security firm wants to sell you a protective cover for your passport, which contains an RFID tag inside storing your sensitive information. The salesperson's solution costs “only" $79.99 and protects your passport from being read via radio waves while it is in your pocket. Explain how you can achieve the same thing for under $3.00. Solution Wrap your passport in aluminum foil.

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