1. Virtual Private Databases Dr. Gabriel

2. 2 Overview of Virtual Private Databases A VPD deals with data access VPD controls data access at the row or column level SQL Server 2005: use VIEW data object Oracle10g: –Specific functions

3. 3 Overview of Virtual Private Databases (continued)

4. 4 Shared database schema: –Containing data that belongs to different users –User view or update only data he or she owns Purposes/benefits: –Security requirements necessitate data access be restricted at row or column level –One database schema serves multiple unrelated groups or entities

5. 5 Implementing Row- and Column-level Security with SQL Server SQL Server 2000 does not support VPDs; you can mimic their functionality Use views and expand security models

6. 6 Implementing a VPD Using Views View object limits what users can see and do with existing data: hides columns or rows from users CREATE VIEW statement: creates data views

7. 7 Hiding Rows Based on the Current User System function USER: –Returns database user –Used to implement row-based security Implementing row-based security with views: –Need a column in your tables for the row’s owner –Preface it with “CTL”

8. 8 Hiding Rows Based on the Current User Example: Create table customers ( ID int not null primary key, LName varchar(50) not null, …, CtlUpdUser varchar(200) not null default user) Create view vcustomer As Select id, lname From customers Where CtlUpdUser =user

9. 9 Row-based Security Using Access Levels Variation of both: –Application table-based security model –Application function-based security model Access levels: –0 = No access –1 = select –2 = select, insert –3 = select, insert, update

10. 10 Row-based Security Using Access Levels (continued) Access levels (continued): –4 = select, insert, update, delete –5 = administrator access Steps: –Create the APPLICATION USERS table –Alter the CUSTOMER table to include the ACCESS CONTROL column –With the security structure in place use a view to retrieve data

11. 11 Row-based Security Using Application Functions Steps (continued): apply privileges Drawbacks: it allows insertion, update, and deletion of records Alternatives: –Use stored procedures –Use application functions: access table list a function instead of a level

12. 12 Row-based Security Using Application Functions create table tappusersaccess ( username varchar(200) not null primary key, AccessLevel int not null default 0 ) create table tcustomers ( ID int not null primary key, LName varchar(200) not null,..., AccessLevel int not null default 0 ) create view vcustomer as select id, lname from tcustomers where accesslevel>0 and accesslevel <=(select isnull(accesslevel,0) from tappusersaccess where username=user)

13. 13 Row-based Security Using Application Functions create procedure pcustomerselect as select id,lname from tcustomers where accesslevel>0 and accesslevel <=(select isnull(accesslevel,0) from tappusersaccess where username=user) create procedure pcustomerdelete @id int as declare @level int select @level=select isnull(accesslevel,0) from tappusersaccess where username=user if @level>=4 begin delete from tcustomers where id=@id and accesslevel>=@level end

14. 14 Column-based Security (continued) Access-level control with SQL Server steps: –Create the APP_TABLES table –Create the APP_COLUMNS columns –All access to the tables must be performed with stored procedures

15. 15 Column-based Security (continued) create table tapptables ( tableid int not null primary key, tablename varchar(200) not null ) create table tapptablecolumns ( columnid int not null primary key, tableid int not null, columnname varchar(200) not null, AccessLevel int not null default 0 ) create table tappuseraccess ( username varchar(200), accesslevel int )

16. 16 Column-based Security (continued) alter proc pcustomerselect as declare @qry varchar(max), @level int, @col varchar(128),@ct int; select @level=(select isnull(accesslevel,0) from tappuseraccess where username=user); declare cur cursor for select columnname from tapptablecolumns a inner join tapptables b on a.tableid=b.tableid where b.tablename='tcustomers' and a.accesslevel<=@level select @qry='select ' select @ct=0 open cur fetch next from cur into @col while @@fetch_status=0 begin if @ct=0 begin select @qry=@qry+@col end else begin select @qry=@qry+', '+@col end select @ct=@ct+1 fetch next from cur into @col end close cur deallocate cur select @qry=@qry + ' from tcustomers' print @qry execute (@qry)

17. 17 Column-based Security (continued) Column Privileges with SQL Server –set update permissions for a user/role on a particular column in a particular table Ex. grant update on customer(phone) to abc

18. 18 Questions?