Security & Robustness

Question 1

What are the 4 pillars of security?

Answer 1

• Authentication
• Authorisation
• Integrity & Non-repudiation
• Confidentiality

Question 2

Name 3 forms of authentication

Answer 2

• password controlled access
• pre-registration scheme
• self-registration scheme

Question 3

Briefly describe 4 different types of authorisation (access control)

Answer 3

• Mandatory: for high security systems, permissions given by security manager for threads to touch certain data
• Discretionary - users set access rights to files
• Role-based - users are granted certain roles, which have certain access permissions
• Lattice-based - users mst exceed access level of object

Question 4

What are the 5 security elements of the Java security manager?

Answer 4

• Permissions; actions code can perform
• Code sources; origins of code
• Protection domains; maps permissions to code sources
• Key stores; digital signatures
• Policy files; lists permissions

Question 5

What are the main technolgoies associated with secure transmission of data?

Answer 5

• digital signatures
• digital certificates
• message digests (digital fingerprints)

Question 6

What is a cryptographic hash?

Answer 6

• Function that converts a string into a limited length hashcode
• keyless algorithm; easy to compute
• hard to recover original message
• hard to obtain collisions (meesages that have same hashcode)
• discontinuous mapping; similar messages dont have similar hashcodes

Question 7

Describe what happens during a simple message digest and its weakness

Answer 7

• sender sends message m and digest d = h(m)
• reciever computes d’=h(m) and then checks if d = d’
• if not message has been tampered

weakness is if d and m are both modified during transit

Question 8

Describe what a message authentication code is? (complex message digest)

Answer 8

• users have shared password P
• sender computes digest d = h(p||m)
• sender computes mac = h(p||d)
• sends message m and mac
• reciever computes digest d’ = h(p||m)
• reciever checks mac’ = h(p||d’)

Question 9

What is symmetric key encryption? What are its issues?

Answer 9

• both parties use same key for encryption and decryption

issues:

• key sharing
• key management

Question 10

What is public/private key encryption? How does it solve issues of symmetric key encryption?

Answer 10

use 2 related prime keys

• sender encrypts with public key
• reciever decrypts with private key
• no key transmission issues
• no key management issues

Question 11

What is a digital signature?

Answer 11

• comibination of message digest & extra encryption
• authenticates sender, and message integrity
• sender encrypts digest with own private key
• reciever decrypts digest with senders public key

Question 12

What is a digital certificate?

Answer 12

Certifying authority vouches for a 3rd party by issuing a digital certificate

Question 13

What do we look at to see if systems are robust?

Answer 13

• if a system is distributed & has redundancy
• available under stress
• failsafe transactions
• penetration resistant

Question 14

What is meant by physical protection of data?

Answer 14

• multiple copies of database in speparate locations
• regular backups of whole dataset to remote locations
• data storage in the cloud
• use RAID architecture (redundant array of independent disks)

Question 15

What is an SQL view?

Answer 15

• derived table; computed from other tables
• enhances usability and security in large databases
• can be inefficient as it hides a complex subquery

Question 16

How do we control access to data to make databases more penetration resistant?

Answer 16

• ensreu users have restricted views of data
• prohibit arbitrary free-data entry where possible
  
  • provide restricted choice selections

Question 17

How do we make databases more resistant to penetration?

Answer 17

• control access to data

- validate all inputs

Question 18

What is a failsafe transaction?

Answer 18

• set of updates wrapped up in one transaction, whic fails or succeeds as a whole to protect against loss of service
• upon failure database must rollback or revert

Question 19

What are 3 possible strategies to prevent data loss during transaction interruption?

Answer 19

• deffered update; write changes to temp file and commit all at once or rollback if failed
• immediate update; log old values and revert if transactions fial
• shadow paging; dynamic pointers to blocks of current data; merge or revert if fail.

Question 20

What are 4 issues with concurrent database access?

Answer 20

• dirty read; read data out of date
• non-repeatable read; inconsistent queries
• phantom read; queries return extra data
• lost update; simulatenous updates mean one is lost

Question 21

Describe different types of concurrency control (7)

Answer 21

• serialize all transactions +all transactions execute in sequence BUT bottleneck reduces performace
• Row locking +transactions locked out while row updates BUT possible deadlock
• Deadlock avoidance +aborts transactions if locks cant be obtained BUT aborts valid transactions
• Deadlock detection to break circular deadlocks resulting in fewer aborts
• Shared & Exclusive locks; locks shared for reading but not for writing
• Phantom & Intent locks; phantom lock reserves empty row for insertion, intent lock declares intent to commit changes
• Timestamping