virtual private databases dr. gabriel. 2 overview of virtual private databases a vpd deals with data...

Virtual Private DatabasesVirtual Private Databases

Dr. Gabriel

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Overview of Virtual Private DatabasesOverview 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

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Overview of Virtual Private Databases Overview of Virtual Private Databases (continued)(continued)

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Overview of Virtual Private Databases Overview of Virtual Private Databases (continued)(continued)

• 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

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Implementing Row- and Column-level Implementing Row- and Column-level Security with SQL ServerSecurity with SQL Server

• SQL Server 2000 does not support VPDs; you can mimic their functionality

• Use views and expand security models

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Implementing a VPD Using ViewsImplementing 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

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Hiding Rows Based on the Current Hiding Rows Based on the Current UserUser

• 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”

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Hiding Rows Based on the Current Hiding Rows Based on the Current UserUser

• Example:Create table customers (ID int not null primary key,LName varchar(50) not null,…,CtlUpdUser varchar(200) not null default user)

Create view vcustomerAsSelect id, lnameFrom customers Where CtlUpdUser =user

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Row-based Security Using Access Row-based Security Using Access LevelsLevels

• 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

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Row-based Security Using Access Row-based Security Using Access Levels (continued)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

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Row-based Security Using Application Row-based Security Using Application FunctionsFunctions

• 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

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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 vcustomerasselect id, lnamefrom tcustomerswhere accesslevel>0 and accesslevel <=(select isnull(accesslevel,0) from

tappusersaccess where username=user)

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create procedure pcustomerselectasselect id,lnamefrom tcustomers where accesslevel>0 and accesslevel <=(select isnull(accesslevel,0) from

tappusersaccess where username=user)

create procedure pcustomerdelete@id int asdeclare @level intselect @level=select isnull(accesslevel,0) from tappusersaccess where username=userif @level>=4 begin delete from tcustomers where id=@id and accesslevel>=@level end

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Column-based Security (continued)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

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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

)

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Column-based Security (continued)Column-based Security (continued)alter proc pcustomerselectasdeclare @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.tableidwhere b.tablename='tcustomers' and a.accesslevel<=@level

select @qry='select 'select @ct=0open curfetch next from cur into @colwhile @@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 endclose curdeallocate curselect @qry=@qry + ' from tcustomers'print @qryexecute (@qry)

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• 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

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Questions?Questions?

virtual private databases dr. gabriel. 2 overview of virtual private databases a vpd deals with data...

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