Chapter 9: Database Security: An Introduction Outline Introduction to Database Security Issues • Types of Security • Threats to databases • Database Security and DBA • Access Protection, User Accounts, and Database Audits Discretionary Access Control • Types of Discretionary Privileges • Specifying Privileges Using Views • Revoking Privileges • Propagation of Privileges Using the GRANT OPTION • An example • Weakness Mandatory Access Control • Bell-LaPudula Model • Comparing DAC and MAC RBAC (Role-Based Access Control) Encryption & PKI (Public Key Infrastructure) 2 Introduction to Database Security Issues Types of Security • Legal and ethical issues • Policy issues • System-related issues • The need to identify multiple security levels 3 Three Basic Concepts Authentication: a mechanism that determines whether a user is who he or she claims to be Authorization: the granting of a right or privilege, which enables a subject to legitimately have access to a system or a system’s objects Access Control: a security mechanism (of a DBMS) for restricting access to a system’s objects (the database) as a whole 4 4 Introduction to Database Security Issue(2) Threats • Any situation or event, whether intentional or unintentional, that will adversely affect a system and consequently an organization • Threats to: • Computer systems • Databases 5 Threats to Computer Systems 6 Scope of Data Security Needs •Must protect databases & the servers on which they reside •Must administer & protect the rights of internal database users •Must guarantee the confidentiality of ecommerce customers as they access the database •With the Internet continually growing, the threat to data traveling over the network increases exponentially 7 Introduction to Database Security Issues (3) Threats to databases • Loss of integrity • Loss of availability • Loss of confidentiality To protect databases against these types of threats four kinds of countermeasures can be implemented: • Access control • Inference control • Flow control • Encryption 8 Introduction to Database Security Issues (4) A DBMS typically includes a database security and authorization subsystem that is responsible for ensuring the security portions of a database against unauthorized access. Two types of database security mechanisms: • Discretionary security mechanisms • Mandatory security mechanisms 9 Introduction to Database Security Issues 5) The security mechanism of a DBMS must include provisions for restricting access to the database as a whole • This function is called access control and is handled by creating user accounts and passwords to control login process by the DBMS. 10 Introduction to Database Security Issues (6) The security problem associated with databases is that of controlling the access to a statistical database, which is used to provide statistical information or summaries of values based on various criteria. • The countermeasures to statistical database security problem is called inference control measures.
11 Introduction to Database Security Issues (7) Another security is that of flow control, which prevents information 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. 12 Introduction to Database Security Issues (8) A final security issue is data 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 encoding algorithm.
• An unauthorized user who access encoded data will have difficulty deciphering it, but authorized users are given decoding or decrypting algorithms (or keys) to decipher data. 13 Database Security and the DBA The database administrator (DBA) is the central authority for managing a database system. • The DBA’s responsibilities include • granting privileges to users who need to use the system • classifying users and data in accordance with the policy of the organization The DBA is responsible for the overall security of the database system. 14 Database Security and the DBA (2) The DBA has a DBA account in the DBMS • Sometimes these are called a system or superuser account • These accounts provide powerful capabilities such as: • 1.
Security level assignment • Action 1 is access control, whereas 2 and 3 are discretionarym and 4 is used to control mandatory authorization 15 Access Protection, User Accounts, and Database Audits Whenever a person or group of person s need to access a database system, the individual or group must first apply for a user account. • The DBA will then create a new account id and password for the user if he/she deems there is a legitimate need to access the database The user must log in to the DBMS by entering account id and password whenever database access is needed. 16 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 applied 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.
17 Access Protection, User Accounts, and Database Audits(3) If any tampering with the database is suspected, a database audit is performed • A database audit consists of reviewing the log 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. 18 Outline Introduction to Database Security Issues • Types of Security • Threats to databases • Database Security and DBA • Access Protection, User Accounts, and Database Audits Discretionary Access Control • Types of Discretionary Privileges • Specifying Privileges Using Views • Revoking Privileges • Propagation of Privileges Using the GRANT OPTION • Examples • Weakness Mandatory Access Control • Bell-LaPudula Model • Comparing DAC and MAC RBAC (Role-Based Access Control) Encryption & PKI (Public Key Infrastructure) 19 Discretionary Access Control User can protect what they own. Owner may grant access to other.
Owner can define the type of access (read/write/execute/…) given to others. The typical method of enforcing discretionary access control in a database system is based on the granting and revoking privileges. 20 Types 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. The relation level (or table level): • At this level, the DBA can control the privilege to access each individual relation or view in the database.
21 Types of Discretionary Privileges(2) The privileges at the account level apply to the capabilities provided to the account itself and can include • 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 tuples; • and the SELECT privilege, to retrieve information from the database by using a SELECT query. 22 Types of Discretionary Privileges(3) The second level of privileges applies to the relation level • This includes base relations and virtual (view) relations. The granting and revoking of privileges 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) • The columns represent objects (relations, records, columns, views, operations). • Each position M(i,j) in the matrix represents the types of privileges (read, write, update) that subject i holds on object j.
23 Types of Discretionary Privileges(4) To control the granting and revoking of relation privileges, for each relation R in a database: • The owner of a relation is given all privileges on that relation. • The owner account holder can pass privileges on any of the owned relation to other users by granting privileges to their accounts. • The owner account holder can also take back the privileges by revoking privileges from their accounts. 24 Types of Discretionary Privileges(5) In SQL the following types of privileges can be granted on each individual relation R: • SELECT (retrieval or read) privilege on R: • This gives the account retrieval privilege.
• The SELECT statement is used 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 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.
25 Types of Discretionary Privileges(6) In SQL the following types of privileges can be granted on each individual relation R (contd.): • REFERENCES privilege on R: • This gives the account the capability to reference 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. 26 Specifying Privileges Using Views The mechanism 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. • The 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. 27 Revoking Privileges In some cases it is desirable to grant a privilege to a 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 privileges. 28 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 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 granted to B, all the privileges that B propagated based on that privilege should automatically be revoked by the system. 29 Limiting the horizontal propagation 30 Limiting the vertical propagation 31 An Example Suppose that the DBA creates four accounts • A1, A2, A3, A4 and wants only A1 to be able to create base relations.
Then the DBA must issue the following 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 SCHEMA EXAMPLE AUTHORIZATION A1; 32 An Example(2) User account A1 can create tables under the schema called EXAMPLE.