![Revoking Authorization in SQL
The revoke statement is used to revoke authorization.
revoke<privilege list>
on <relation name or view name> from <user list> [restrict|cascade]
Example:
revoke select on branch from U1, U2, U3 cascade
Revocation of a privilege from a user may cause other users also
to lose that privilege; referred to as cascading of the revoke.
We can prevent cascading by specifying restrict:
revoke select on branch from U1, U2, U3 restrict
With restrict, the revoke command fails if cascading revokes
are required.](https://image.slidesharecdn.com/databasemanagementsystemsecurity-240410114040-91408f21/85/Database-Management-System-Security-pptx-19-320.jpg)
Database Management System Security.pptx
- 1. Access Control •A security policy specifies who is authorized to do what. •™ A security mechanism allows us to enforce a chosen security policy. ™ •Two main mechanisms at the DBMS level: – Discretionary access control – Mandatory access control
- 2. Discretionary Access Control ™ Based on the concept of access rights or privileges for objects (tables and views), and mechanisms for giving users privileges (and revoking privileges). ™ Creator of a table or a view automatically gets all privileges on it. – DBMS keeps track of who subsequently gains and loses privileges, and ensures that only requests from users who have the necessary privileges (at the time the request is issued) are allowed
- 3. Mandatory Access Control ™ Based on system-wide policies that cannot be changed by individual users. – Each DB object is assigned a security class. – Each subject (user or user program) is assigned a clearance for a security class. – Rules based on security classes and clearances govern who can read/write which objects. ™ Most commercial systems do not support mandatory access control. Versions of some DBMSs do support it; used for specialized (e.g., military) applications.
- 4. Why Mandatory Control? ™ Discretionary control has some flaws, e.g., the Trojan horse problem: – Dick creates Horsie and gives INSERT privileges to Justin (who doesn’t know about this). – Dick modifies the code of an application program used by Justin to additionally write some secret data to table Horsie. – Now, Justin can see the secret info. ™ The modification of the code is beyond the DBMSs control, but it can try and prevent the use of the database as a channel for secret information.
- 5. Security and Authorization The data stored in the database need protection from a. Unauthorized access b. Malicious destruction or alteration c. Accidental introduction of inconsistency that integrity constraints provide Among the forms of malicious access are: a. Unauthorized reading of data (theft of information) b. Unauthorized modification of data c. Unauthorized destruction of data
- 6. Security Security - protection from malicious attempts to steal or modify data. Database system level Authentication and authorization mechanisms to allow specific users access only to required data We concentrate on authorization in the rest of this chapter Operating system level Operating system super-users can do anything they want to the database! Good operating system level security is required. Network level: must use encryption to prevent Eavesdropping (unauthorized reading of messages) Masquerading (pretending to be an authorized user or sending messages supposedly from authorized users)
- 7. Security (Cont.) Physical level Physical access to computers allows destruction of data by intruders; traditional lock-and-key security is needed Computers must also be protected from floods, fire, etc. Human level Users must be screened to ensure that an authorized users do not give access to intruders Users should be trained on password selection and secrecy
- 8. Authorization Forms of authorization on parts of the database: Read authorization - allows reading, but not modification of data. Insert authorization - allows insertion of new data, but not modification of existing data. Update authorization - allows modification, but not deletion of data. Delete authorization - allows deletion of data
- 9. Authorization (Cont.) Forms of authorization to modify the database schema: Index authorization - allows creation and deletion of indices. Resources authorization - allows creation of new relations. Alteration authorization - allows addition or deletion of attributes in a relation. Drop authorization - allows deletion of relations.
- 10. Authorization and Views Users can be given authorization on views, without being given any authorization on the relations used in the view definition Ability of views to hide data serves both to simplify usage of the system and to enhance security by allowing users access only to data they need for their job A combination of relational-level security and view-level security can be used to limit a user’s access to precisely the data that user needs.
- 11. View Example Suppose a bank clerk needs to know the names of the customers of each branch, but is not authorized to see specific loan information. Approach: Deny direct access to the loan relation, but grant access to the view cust-loan, which consists only of the names of customers and the branches at which they have a loan. The cust-loan view is defined in SQL as follows: create view cust-loan as select branch-name, customer-name from borrower, loan where borrower.loan-number = loan.loan-number
- 12. View Example (Cont.) The clerk is authorized to see the result of the query: select * from cust-loan When the query processor translates the result into a query on the actual relations in the database, we obtain a query on borrower and loan. Authorization must be checked on the clerk’s query before query processing replaces a view by the definition of the view.
- 13. Authorization on Views Creation of view does not require resources authorization since no real relation is being created The creator of a view gets only those privileges that provide no additional authorization beyond that he already had. E.g. if creator of view cust-loan had only read authorization on borrower and loan, he gets only read authorization on cust-loan
- 14. Granting of Privileges The passage of authorization from one user to another may be represented by an authorization graph. The nodes of this graph are the users. The root of the graph is the database administrator. Consider graph for update authorization on loan. An edge Ui Uj indicates that user Ui has granted update authorization on loan to Uj. U1 U4 U2 U5 U3 DBA
- 15. Authorization Grant Graph Requirement: All edges in an authorization graph must be part of some path originating with the database administrator If DBA revokes grant from U1: Grant must be revoked from U4 since U1 no longer has authorization Grant must not be revoked from U5 since U5 has another authorization path from DBA through U2 Must prevent cycles of grants with no path from the root: DBA grants authorization to U7 U7 grants authorization to U8 U8 grants authorization to U7 DBA revokes authorization from U7 Must revoke grant U7 to U8 and from U8 to U7 since there is no path from DBA to U7 or to U8 anymore.
- 16. Security Specification in SQL The grant statement is used to confer authorization grant <privilege list> on <relation name or view name> to <user list> <user list> is: a user-id public, which allows all valid users the privilege granted A role (more on this later) Granting a privilege on a view does not imply granting any privileges on the underlying relations. The grantor of the privilege must already hold the privilege on the specified item (or be the database administrator).
- 17. Privileges in SQL select: allows read access to relation,or the ability to query using the view Example: grant users U1, U2, and U3 select authorization on the branch relation: grant select on branch to U1, U2, U3 insert: the ability to insert tuples update: the ability to update using the SQL update statement delete: the ability to delete tuples. references: ability to declare foreign keys when creating relations. usage: In SQL-92; authorizes a user to use a specified domain all privileges: used as a short form for all the allowable privileges
- 18. Roles Roles permit common privileges for a class of users can be specified just once by creating a corresponding “role” Privileges can be granted to or revoked from roles, just like user Roles can be assigned to users, and even to other roles SQL:1999 supports roles create role teller create role manager grant select on branch to teller grant update (balance) on account to teller grant all privileges on account to manager grant teller to manager
- 19. Revoking Authorization in SQL The revoke statement is used to revoke authorization. revoke<privilege list> on <relation name or view name> from <user list> [restrict|cascade] Example: revoke select on branch from U1, U2, U3 cascade Revocation of a privilege from a user may cause other users also to lose that privilege; referred to as cascading of the revoke. We can prevent cascading by specifying restrict: revoke select on branch from U1, U2, U3 restrict With restrict, the revoke command fails if cascading revokes are required.
- 20. Limitations of SQL Authorization SQL does not support authorization at a tuple level E.g. we cannot restrict students to see only (the tuples storing) their own grades
- 21. Encryption Data may be encrypted when database authorization provisions do not offer sufficient protection. Properties of good encryption technique: Relatively simple for authorized users to encrypt and decrypt data. Encryption scheme depends not on the secrecy of the algorithm but on the secrecy of a parameter of the algorithm called the encryption key. Extremely difficult for an intruder to determine the encryption key.
- 22. Encryption and Decryption Data Encryption Standard (DES) substitutes characters and rearranges their order on the basis of an encryption key which is provided to authorized users via a secured mechanism. Scheme is no more secure than the key transmission mechanism since the key has to be shared. Advanced Encryption Standard (AES) is a new standard replacing DES, and is based on the Rijndael algorithm, but is also dependent on shared secret keys Public-key encryption is based on each user having two keys: public key – publicly published key used to encrypt data, but cannot be used to decrypt data private key -- key known only to individual user, and used to decrypt data. Need not be transmitted to the site doing encryption. Encryption scheme is such that it is impossible or extremely hard to decrypt data given only the public key. The public-key encryption scheme is based on the hardness of factoring a very large number (100's of digits) into its prime components.
- 23. Authentication Password based authentication is widely used, but is susceptible to sniffing on a network Challenge-response systems avoid transmission of passwords DB sends a (randomly generated) challenge string to user User encrypts string and returns result. DB verifies identity by decrypting result Can use public-key encryption system by DB sending a message encrypted using user’s public key, and user decrypting and sending the message back Digital signatures are used to verify authenticity of data E.g. use private key (in reverse) to encrypt data, and anyone can verify authenticity by using public key (in reverse) to decrypt data. Only holder of private key could have created the encrypted data. Digital signatures also help ensure nonrepudiation: sender cannot later claim to have not created the data