《Fundamentals of Database Systems.ppt》由会员分享，可在线阅读，更多相关《Fundamentals of Database Systems.ppt（66页珍藏版）》请在三一办公上搜索。
1、,Chapter 23Database Security andAuthorization,Copyright 2004 Pearson Education,Inc.,Chapter 23-3,Chapter Outline,1 Database Security and Authorization1.1 Introduction to Database Security Issues 1.2 Types of Security1.3 Database Security and DBA1.4 Access Protection,User Accounts,and Database Audits
2、2 Discretionary Access Control Based on Granting Revoking Privileges2.1 Types of Discretionary Privileges2.2 Specifying Privileges Using Views2.3 Revoking Privileges2.4 Propagation of Privileges Using the GRANT OPTION2.5 Specifying Limits on Propagation of Privileges,Chapter 23-4,Chapter Outline(con
3、td.),3 Mandatory Access Control and Role-Based Access Control for Multilevel Security3.1 Comparing Discretionary Access Control and Mandatory Access Control3.2 Role-Based Access Control3.3 Access Control Policies for E-Commerce and the Web 4 Introduction to Statistical Database Security,Chapter 23-5
4、,Chapter Outline(contd.),5 Introduction to Flow Control 5.1 Covert Channels6 Encryption and Public Key Infrastructures6.1The Data and Advanced Encryption Standards6.2 Public Key Encryption6.3 Digital Signatures,Chapter 23-6,1 Introduction to Database Security Issues,Types of SecurityLegal and ethica
5、l issuesPolicy issuesSystem-related issuesThe need to identify multiple security levels,Chapter 23-7,Introduction to Database Security Issues(2),Threats to databases-Loss of integrity-Loss of availability-Loss of confidentialityTo protect databases against these types of threats four kinds of counte
6、rmeasures can be implemented:access control,inference control,flow control,and encryption.,Chapter 23-8,Introduction to DatabaseSecurity Issues(3),A DBMS typically includes a database security and authorization subsystem that is responsible for ensuring the security portions of a database against un
7、authorized access.Two types of database security mechanisms:Discretionary security mechanismsMandatory security mechanisms,Chapter 23-9,Introduction to DatabaseSecurity Issues(4),The security mechanism of a DBMS must include provisions for restricting access to the database as a whole;this function
8、is called access control and is handled by creating user accounts and passwords to control login process by the DBMS.,Chapter 23-10,Introduction to DatabaseSecurity Issues(5),The security problem associated with databases is that of controlling the access to a statistical database,which is used to p
9、rovide statistical information or summaries of values based on various criteria.The countermeasures to statistical database security problem is called inference control measures.,Chapter 23-11,Introduction to DatabaseSecurity Issues(6),Another security is that of flow control,which prevents informat
10、ion from flowing in such a way that it reaches unauthorized users.Channels that are pathways for information to flow implicitly in ways that violate the security policy of an organization are called covert channels.,Chapter 23-12,Introduction to DatabaseSecurity Issues(7),A final security issue is d
11、ata encryption,which is used to protect sensitive data(such as credit card numbers)that is being transmitted via some type communication network.The data is encoded using some coding algorithm.An unauthorized user who access encoded data will have difficulty deciphering it,but authorized users are g
12、iven decoding or decrypting algorithms(or keys)to decipher data.,Chapter 23-13,1.2 Database Security and the DBA,The database administrator(DBA)is the central authority for managing a database system.The DBAs responsibilities include granting privileges to users who need to use the system and classi
13、fying users and data in accordance with the policy of the organization.The DBA has a DBA account in the DBMS,sometimes called a system or superuser account,which provides powerful capabilities:1.Account creation2.Privilege granting3.Privilege revocation4.Security level assignmentThe DBA is responsib
14、le for the overall security of the database system.Action 1 is access control,whereas 2 and 3 are discretionary and 4 is used to control mandatory authorization.,Chapter 23-14,1.3 Access Protection,User Accounts,and Database Audits,Whenever a person or group of person s need to access a database sys
15、tem,the individual or group must first apply for a user account.The DBA will then create a new account number and password for the user if there is a legitimate need to access the database.The user must log in to the DBMS by entering account number and password whenever database access is needed.,Ch
16、apter 23-15,1.3 Access Protection,User Accounts,and Database Audits(2),The database system must also keep track of all operations on the database that are applied by a certain user throughout each login session.To keep a record of all updates applied to the database and of the particular user who ap
17、plied each update,we can modify system log,which includes an entry for each operation applied to the database that may be required for recovery from a transaction failure or system crash.If any tampering with the database is suspected,a database audit is performed,which consists of reviewing the log
18、 to examine all accesses and operations applied to the database during a certain time period.A database log that is used mainly for security purposes is sometimes called an audit trail.,Chapter 23-16,Discretionary Access Control Based on Granting and Revoking Privileges,The typical method of enforci
19、ng discretionary access control in a database system is based on the granting and revoking privileges.,Chapter 23-17,2.1Types of Discretionary Privileges,The account level:At this level,the DBA specifies the particular privileges that each account holds independently of the relations in the database
20、.The relation(or table level):At this level,the DBA can control the privilege to access each individual relation or view in the database.,Chapter 23-18,2.1Types of Discretionary Privileges(2),The privileges at the account level apply to the capabilities provided to the account itself and can include
21、 the CREATE SCHEMA or CREATE TABLE privilege,to create a schema or base relation;the CREATE VIEW privilege;the ALTER privilege,to apply schema changes such adding or removing attributes from relations;the DROP privilege,to delete relations or views;the MODIFY privilege,to insert,delete,or update tup
22、les;and the SELECT privilege,to retrieve information from the database by using a SELECT query.,Chapter 23-19,2.1Types of Discretionary Privileges(3),The second level of privileges applies to the relation level,whether they are base relations or virtual(view)relations.The granting and revoking of pr
23、ivileges generally follow an authorization model for discretionary privileges known as the access matrix model,where the rows of a matrix M represents subjects(users,accounts,programs)and the columns represent objects(relations,records,columns,views,operations).Each position M(i,j)in the matrix repr
24、esents the types of privileges(read,write,update)that subject i holds on object j.,Chapter 23-20,2.1Types of Discretionary Privileges(4),To control the granting and revoking of relation privileges,each relation R in a database is assigned and owner account,which is typically the account that was use
25、d when the relation was created in the first place.The owner of a relation is given all privileges on that relation.In SQL2,the DBA can assign and owner to a whole schema by creating the schema and associating the appropriate authorization identifier with that schema,using the CREATE SCHEMA command.
26、The owner account holder can pass privileges on any of the owned relation to other users by granting privileges to their accounts.,Chapter 23-21,2.1Types of Discretionary Privileges(5),In SQL the following types of privileges can be granted on each individual relation R:SELECT(retrieval or read)priv
27、ilege on R:Gives the account retrieval privilege.In SQL this gives the account the privilege to use the SELECT statement to retrieve tuples from R.MODIFY privileges on R:This gives the account the capability to modify tuples of R.In SQL this privilege is further divided into UPDATE,DELETE,and INSERT
28、 privileges to apply the corresponding SQL command to R.In addition,both the INSERT and UPDATE privileges can specify that only certain attributes can be updated by the account.,Chapter 23-22,2.1Types of Discretionary Privileges(6),REFERENCES privilege on R:This gives the account the capability to r
29、eference relation R when specifying integrity constraints.The privilege can also be restricted to specific attributes of R.Notice that to create a view,the account must have SELECT privilege on all relations involved in the view definition.,Chapter 23-23,2.2 Specifying Privileges Using Views,The mec
30、hanism of views is an important discretionary authorization mechanism in its own right.For example,if the owner A of a relation R wants another account B to be able to retrieve only some fields of R,then A can create a view V of R that includes only those attributes and then grant SELECT on V to B.T
31、he same applies to limiting B to retrieving only certain tuples of R;a view V can be created by defining the view by means of a query that selects only those tuples from R that A wants to allow B to access.,Chapter 23-24,2.3 Revoking Privileges,In some cases it is desirable to grant a privilege to a
32、 user temporarily.For example,the owner of a relation may want to grant the SELECT privilege to a user for a specific task and then revoke that privilege once the task is completed.Hence,a mechanism for revoking privileges is needed.In SQL,a REVOKE command is included for the purpose of canceling pr
33、ivileges.,Chapter 23-25,2.4 Propagation of Privileges using the GRANT OPTION,Whenever the owner A of a relation R grants a privilege on R to another account B,privilege can be given to B with or without the GRANT OPTION.If the GRANT OPTION is given,this means that B can also grant that privilege on
34、R to other accounts.Suppose that B is given the GRANT OPTION by A and that B then grants the privilege on R to a third account C,also with GRANT OPTION.In this way,privileges on R can propagate to other accounts without the knowledge of the owner of R.If the owner account A now revokes the privilege
35、 granted to B,all the privileges that B propagated based on that privilege should automatically be revoked by the system.,Chapter 23-26,2.5 An Example,Suppose that the DBA creates four accounts-A1,A2,A3,and A4-and wants only A1 to be able to create base relations;then the DBA must issue the followin
36、g GRANT command in SQL:GRANT CREATETAB TO A1;In SQL2 the same effect can be accomplished by having the DBA issue a CREATE SCHEMA command as follows:CREATE SCHAMA EXAMPLE AUTHORIZATION A1;,Chapter 23-27,2.5 An Example(2),User account A1 can create tables under the schema called EXAMPLE.Suppose that A
37、1 creates the two base relations EMPLOYEE and DEPARTMENT;A1 is then owner of these two relations and hence all the relation privileges on each of them.Suppose that A1 wants to grant A2 the privilege to insert and delete tuples in both of these relations,but A1 does not want A2 to be able to propagat
38、e these privileges to additional accounts:GRANT INSERT,DELETE ON EMPLOYEE,DEPARTMENT TO A2;,Chapter 23-28,2.5 An Example(3),EMPLOYEE,DEPARTMENT,Chapter 23-29,2.5 An Example(4),Suppose that A1 wants to allow A3 to retrieve information from either of the two tables and also to be able to propagate the
39、 SELECT privilege to other accounts.A1 can issue the command:GRANT SELECT ON EMPLOYEE,DEPARTMENT TO A3 WITH GRANT OPTION;A3 can grant the SELECT privilege on the EMPLOYEE relation to A4 by issuing:GRANT SELECT ON EMPLOYEE TO A4;(Notice that A4 can not propagate the SELECT privilege because GRANT OPT
40、ION was not given to A4.),Chapter 23-30,2.5 An Example(5),Suppose that A1 decides to revoke the SELECT privilege on the EMPLOYEE relation from A3;A1 can issue:REVOKE SELECT ON EMPLOYEE FROM A3;(The DBMS must now automatically revoke the SELECT privilege on EMPLOYEE from A4,too,because A3 granted tha
41、t privilege to A4 and A3 does not have the privilege any more.),Chapter 23-31,2.5 An Example(6),Suppose that A1 wants to give back to A3 a limited capability to SELECT from the EMPLOYEE relation and wants to allow A3 to be able to propagate the privilege.The limitation is to retrieve only the NAME,B
42、DATE,and ADDRESS attributes and only for the tuples with DNO=5.A1 then create the view:CREATE VIEW A3EMPLOYEE ASSELECT NAME,BDATE,ADDRESSFROM EMPLOYEEWHERE DNO=5;After the view is created,A1 can grant SELECT on the view A3EMPLOYEE to A3 as follows:GRANT SELECT ON A3EMPLOYEE TO A3 WITH GRANT OPTION;,
43、Chapter 23-32,2.5 An Example(7),Finally,suppose that A1 wants to allow A4 to update only the SALARY attribute of EMPLOYEE;A1 can issue:GRANT UPDATE ON EMPLOYEE(SALARY)TO A4;(The UPDATE or INSERT privilege can specify particular attributes that may be updated or inserted in a relation.Other privilege
44、s(SELECT,DELETE)are not attribute specific.),Chapter 23-33,2.6 Specifying Limits on Propagation of Privileges,Techniques to limit the propagation of privileges have been developed,although they have not yet been implemented in most DBMSs and are not a part of SQL.Limiting horizontal propagation to a
45、n integer number i means that an account B given the GRANT OPTION can grant the privilege to at most i other accounts.Vertical propagation is more complicated;it limits the depth of the granting of privileges.,Chapter 23-34,3 Mandatory Access Control and Role-Based Access Control for Multilevel Secu
46、rity,The discretionary access control techniques of granting and revoking privileges on relations has traditionally been the main security mechanism for relational database systems.This is an all-or-nothing method:A user either has or does not have a certain privilege.In many applications,and additi
47、onal security policy is needed that classifies data and users based on security classes.This approach as mandatory access control,would typically be combined with the discretionary access control mechanisms.,Chapter 23-35,3 Mandatory Access Control and Role-Based Access Control for Multilevel Securi
48、ty(2),Typical security classes are top secret(TS),secret(S),confidential(C),and unclassified(U),where TS is the highest level and U the lowest:TS S C UThe commonly used model for multilevel security,known as the Bell-LaPadula model,classifies each subject(user,account,program)and object(relation,tup
49、le,column,view,operation)into one of the security classifications,TS,S,C,or U:clearance(classification)of a subject S as class(S)and to the classification of an object O as class(O).,Chapter 23-36,3 Mandatory Access Control and Role-Based Access Control for Multilevel Security(3),Two restrictions ar
50、e enforced on data access based on the subject/object classifications:A subject S is not allowed read access to an object O unless class(S)class(O).This is known as the simple security property.A subject S is not allowed to write an object O unless class(S)class(O).This known as the star property(or
