Unit 10 Security Flashcards
What type of interference is taking place if, Alice alters Bob’s file without permission?
(Type 2) Modification
What type of interference is taking place if, a hacker deploys software to observe packets travelling on a network?
(Part 2) Interception
What type of interference is taking place if, a website receives a flood of requests for a web page, preventing callers from viewing the site?
(Part 2) Interruption
What type of interference is taking place if, a user receives an e-mail appearing to be from his supervisor, who did not send the e-mail?
(Part 2) Fabrication
How would each class of security threat (normal operation, interruption, interception, modification, fabrication) would apply to a file on a hard disk?
(Part 2)
- Normal operation - no interference to file access
- Interruption - an attacker has prevented authorised access to the file
- Interception - an unauthorised party has obtained access to the file
- Modification - an unauthorised party has altered the file
- Fabrication - a fake file has been constructed
What security services might be at fault in a click-fraud case in which fake clicks are generated on an online advertisement?
(Part 2) Non-repudiation may be at fault if the clicks cannot be associated with particular parties. It is likely that the clicks cannot be easily traced, because the most likely form of identification in this case is an IP address, and IP addresses can be fabricated by a program.
In a click-fraud case in which fake clicks are generated on an online advertisement, what class of threat is this?
(Part 2) The class of threat is fabrication.
How many possible Caesar ciphers are there in English?
(Part 3) Assuming a 26-character alphabet there are 25 possible substitutions.
What advantages does a cipher involving modulo arithemetic have?
(Part 3) The output of a modulus function is always within a certain range, which can be easily mapped to the desired character set. It is also easily implemented and computationally cheap.
Which is stonger under a brute-force attack?
- using a password of five characters from the character set {a, b, c, d, e, f}
- or using a password of ten characters in length from the character set {a, b, c}
(Part 3)
- six characters with a password length of 5 gives a key space of 65 = 7776
- three characters with a password length of ten gives a key space of 310 = 59049
The longer password is stronger, because it results in a larger key space. However even a long password that appears in a dictionary is relatively weak as it is vulnerable to a dictionary attack.
Why is public key cryptography called asymmetric and private key cryptography called symmetric?
(Part 3) In public key cryptography there are two different keys, the public key and private key, one used for encryption and the other for decryption. In private key cryptography there is only one key, the secret key suitable for both encryption and decryption.
What is an example of a middle-person attack on public key cryptography?
(Part 3) Alice wants to send a message to Bob, susing Bob’s public key. Alice is tricked into using Eve’s public key instead - now Eve is able to impersonate Bob and read messages intended for Bob. (Bob will not be able to decipher these messages even if he receives them)
Does Alice really know that a messagedeciphered by Bob’s public key came from Bob?
(Part 3) This depends on how Alice received the key. If she did not receive the key in a secure fashion (ex. face to face) she only knows the public key comes from someone claiming to be Bob.
What are three reasons why keys might have expiry dates?
(Part 3)
- Reusing a key may give an attacker more data to work with and so a better chance of cracking the code
- Keys that previously were considered secure might not be any more due to increasing computing power and new methods of attack
- If a key has become compromised, it cannot be used indefinitely
What is an example of how an attacker might exploit a collision?
(Part 3) The message “Transfer £5 to A Bank” might have the same hash as “Transfer £1000 to A Bank”. The attacker might be able to intercept and substitute the second message for the first.
Likewise, a program could be altered in such a way that its hash is unaltered, so that an integrity check does not detect tampering, and a malicious program can be substituted for a valid one.
