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Assignment - 4 Database Security

Assignment – 4     Database Security   Submission Date : 13-Apr-2011  

Q.1	Explain the Following Questions in detail.
	1.    What is database security? Explain the goal of database security? 2.    Describe the Granting & Revoking privileges using SQL with syntax and example. Explain account level, table level and column level privileges. 3.    Explain concept of audit train in detail 4.    Explain the Mandatory Access Control with Bell-Lapadulla model. 5.    What is statistics database security? 6.    What do you mean by firewall? What are firewall techniques that are used in database Security? 7.    Explain data encryption with different schemes. 8.   Using Polyalphabetic substitution method and encryption key, “SECURITY”, encrypt the plaintext message “SELL ALL STOCKS”
Q.2	Differentiate the following :
	1.    Security Vs integrity 2.    Discretionary Access Control Vs Mandatory Access Control 3.    Authorization Vs Authentication. 4.    Simple Property Vs Star Property 5.    Audit Trail Vs Transaction Log 6.    Simple Substitution Method Vs Polyalphabetic Substitution Method

Starvation Vs Deadlock

Starvation	Deadlock
Starvation happens if same transaction is always choosen as victim.	A deadlock is a condition in which two or more transaction are waiting for each other.
It occurs if the waiting scheme for locked items in unfair, giving priority to some transactions over others.	A situation where two or more transactions are unable to proceed because each is waiting for one of the other to do something.
Starvation is also known as lived lock.	Deadlock is also known as circular waiting.
Avoidance: ->switch priorities so that every thread has a chance to have high priority. -> Use FIFO order among competing request.	Avoidance: ->Acquire locks are predefined order. ->Acquire locks at once before starting.
It means that transaction goes in a state where transaction never progress.	It is a situation where transactions are waiting for each other.
Example :	Example :

Lost Update Vs Uncommitted Data

Lost Update	Uncommitted Data
This problem is also known as “Multiple Update problem”	This problem is also known as “Dirty Read”
In the multiple update problem, the data written by one transaction is being overwritten by another transaction.	In Dirty read, data written by one transaction is read by another transaction before that transaction commits.
Two transaction accessing the same database item have their operations interleaved in a way that makes the database item incorrect.	This problem occurs when one transaction is allowed to see the intermediate result of the another transaction before it is committed.
Example : Connection A Connection B    ………    ……… SELECT Row1    ………    ………    ………    ……… SELECT Row1    ………    ……… UPDATE Row1    ………    ………    ………    ……… UPDATE Row1	Example : Connection A Connection B    ………    ………    ………  UPDATE Row1    ………    ……… SELECT Row1    ………    ………    ………    ………  ROLLBACK
Situation : Connection A and B both read a record and then update it, the effect of the first update will be overwritten by the second update.	Situation : Connection A reads an object that has been modified by Connection B but Connection B has not committed yet. Here, Connection B rollback transaction and uncommitted data is already read by Connection A. This is known as “Uncommitted Dependency”
Problem : Connection A and B both reading old value. Here Connection A updates row after some time Connection B updates that row. So, changes made by Connection A would be lost.	Problem : Connection A was permitted to read the intermediate result of Connection B before the Connection B was terminated.
Solution : Prohibit a shared lock Use batch processing Implementing locking scheme Two phase locking also solve this problem	Solution : Prevent Connection A from reading the account balance until the Connection B is terminated. i.e. either committed or rollback.