Integrity and Security.pdf

Integrity and Security IT 311 – Advanced Database Management System Topics: o Domain Constraints o Referential Integrity o Triggers o Security o Authorization o Authorization in SQL Data Security vs Data Integrity Data security refers to the prevention of data from unauthorized users. It is only...

Integrity and Security IT 311 – Advanced Database Management System Topics: o Domain Constraints o Referential Integrity o Triggers o Security o Authorization o Authorization in SQL Data Security vs Data Integrity Data security refers to the prevention of data from unauthorized users. It is only allowed to access the data to the authorized users. In database, the DBA or head of department can access all the data. Some users are only allowed to retrieve data, whereas others are allowed to retrieve as well as to modify the data. Data integrity is defined as the data contained in the database is both correct and consistent. For this purpose, the data stored in the database must satisfy certain types of procedures (rules). The data in a database must be correct and consistent. So, data stored in the database must satisfy certain types of procedure (rules). DBMS provides different ways to implement such types of constraints (rules). This improves data integrity in a database. Difference between Data Security and Data Integrity # Data Security Data Integrity 1 Data security refers to the Data integrity refers to the quality of prevention of data corruption data, which assures the data is through the use of controlled complete and has a whole structure. access mechanisms. 2 Its motive is the protection of Its motive is the validity of data. data. 3 Its work is to only the people who Its work is to check the data is should have access to the data are correct and not corrupt. the only ones who can access the data. Difference between Data Security and Data Integrity # Data Security Data Integrity 4 It refers to making sure that data is It refers to the structure of the data and accessed by its intended users, thus how it matches the schema of the ensuring the privacy and protection database. of data. 5 Some of the popular means of data Some of the means to preserve integrity security are are backing up, error detection, authentication/authorization, designing a suitable user interface and masking, and encryptions. correcting data. 6 It relates to the physical form of data It relates to the logical protection against accidental or intentional loss (correct, complete and consistence) of or misuse and destruction. data. Difference between Data Security and Data Integrity # Data Security Data Integrity 7 It avoids unauthorized access of data. It avoids human error when data is entered. 8 It can be implemented through : It can be implemented by following rule user accounts (passwords) : authentication schemes Primary Key Foreign Key Relationship Domain Constraints A table in DBMS is a set of rows and columns that contain data. Columns in table have a unique name, often referred as attributes in DBMS. A domain is a unique set of values permitted for an attribute in a table. e.g. a domain of month-of-year can accept January, February….December as possible values, a domain of integers can accept whole numbers that are negative, positive and zero. Domain constraints are user defined data type and we can define them like this: Domain Constraint = data type + Constraints (NOT NULL / UNIQUE / PRIMARY KEY / FOREIGN KEY / CHECK / DEFAULT) Example: MariaDB Constraint Numeric constraints and comparisons: CREATE TABLE t1 (a CHECK (a>2), b CHECK (b>2), CONSTRAINT a_greater CHECK (a>b)); INSERT INTO t1(a) VALUES (1); ERROR 4022 (23000): CONSTRAINT `a` failed for `test`.`t1` INSERT INTO t1(a,b) VALUES (3,4); ERROR 4022 (23000): CONSTRAINT `a_greater` failed for `test`.`t1` INSERT INTO t1(a,b) VALUES (4,3); Query OK, 1 row affected (0.04 sec) Referential Integrity Referential integrity refers to the relationship between tables. Because each table in a database must have a primary key, this primary key can appear in other tables because of its relationship to data within those tables. When a primary key from one table appears in another table, it is called a foreign key. Foreign keys join tables and establish dependencies between tables. tables can form a hierarchy of dependencies in such a way that if you change or delete a row in one table, you destroy the meaning of rows in other tables. Example: Referential integrity in the demonstration database For example, the following figure shows that the customer_num column of the customer table is a primary key for that table and a foreign key in the orders and cust_calls tables. Customer number 106, George Watson, is referenced in both the orders and cust_calls tables. If customer 106 is deleted from the customer table, the link between the three tables and this particular customer is destroyed. Referential integrity is the logical dependency of a foreign key on a primary key. Referential Integrity in SQL Primary and candidate keys and foreign keys can be specified as part of the SQL create table statement: o The primary key clause lists attributes that comprise the primary key. o The unique key clause lists attributes that comprise a candidate key. o The foreign key clause lists the attributes that comprise the foreign key and the name of the relation referenced by the foreign key. By default, a foreign key references the primary key attributes of the referenced table foreign key (account-number) references account Short form for specifying a single column as foreign key account-number char (10) references account  Reference columns in the referenced table can be explicitly specified o but must be declared as primary/candidate keys foreign key (account-number) references account(account-number) Referential Integrity in SQL – Example create table customer (customer-name char(20), customer-street char(30), customer-city char(30), primary key (customer-name)) create table branch (branch-name char(15), branch-city char(30), assets integer, primary key (branch-name)) create table account (account-number char(10), branch-name char(15), balance integer, primary key (account-number), foreign key (branch-name) references branch) create table depositor (customer-name char(20), account-number char(10), primary key (customer-name, account-number), foreign key (account-number) references account, foreign key (customer-name) references customer) Cascading Actions in SQL create table account... foreign key(branch-name) references branch on delete cascade on update cascade...) Due to the on delete cascade clauses, if a delete of a tuple in branch results in referential-integrity constraint violation, the delete “cascades” to the account relation, deleting the tuple that refers to the branch that was deleted. Cascading updates are similar.  If there is a chain of foreign-key dependencies across multiple relations, with on delete cascade specified for each dependency, a deletion or update at one end of the chain can propagate across the entire chain. If a cascading update to delete causes a constraint violation that cannot be handled by a further cascading operation, the system aborts the transaction. o As a result, all the changes caused by the transaction and its cascading actions are undone. Referential integrity is only checked at the end of a transaction o Intermediate steps are allowed to violate referential integrity provided later steps remove the violation o Otherwise it would be impossible to create some database states, e.g. insert two tuples whose foreign keys point to each other e.g. spouse attribute of relation marriedperson(name, address, spouse)  Alternative to cascading: o on delete set null o on delete set default Null values in foreign key attributes complicate SQL referential integrity semantics, and are best prevented using not null o if any attribute of a foreign key is null, the tuple is defined to satisfy the foreign key constraint! Example: Foreign key constraints ALTER TABLE `tbl_order` ADD CONSTRAINT `fk_product_id` FOREIGN KEY (`product_id`) REFERENCES `tbl_product`(`id`) ON DELETE RESTRICT ON UPDATE SET NULL; Triggers A trigger is a statement that is executed automatically by the system as a side effect of a modification to the database. To design a trigger mechanism, we must: Specify the conditions under which the trigger is to be executed. Specify the actions to be taken when the trigger executes. Triggers introduced to SQL standard in SQL:1999, but supported even earlier using non-standard syntax by most databases. Trigger: Example Suppose that instead of allowing negative account balances, the bank deals with overdrafts by ◦ setting the account balance to zero ◦ creating a loan in the amount of the overdraft ◦ giving this loan a loan number identical to the account number of the overdrawn account The condition for executing the trigger is an update to the account relation that results in a negative balance value. Triggering Events and Actions in SQL Triggering event can be insert, delete or update Triggers on update can be restricted to specific attributes e.g. create trigger overdraft-trigger after update of balance on account Values of attributes before and after an update can be referenced o referencing old row as : for deletes and updates o referencing new row as : for inserts and updates Triggers can be activated before an event, which can serve as extra constraints. E.g. convert blanks to null. Statement Level Triggers Instead of executing a separate action for each affected row, a single action can be executed for all rows affected by a transaction ◦ Use for each statement instead of for each row ◦ Use referencing old table or referencing new table to refer to temporary tables (called transition tables) containing the affected rows ◦ Can be more efficient when dealing with SQL statements that update a large number of rows External World Actions We sometimes require external world actions to be triggered on a database update e.g. re-ordering an item whose quantity in a warehouse has become small, or turning on an alarm light, Triggers cannot be used to directly implement external-world actions, BUT o Triggers can be used to record actions-to-be-taken in a separate table o Have an external process that repeatedly scans the table, carries out external-world actions and deletes action from table External World Actions e.g. Suppose a warehouse has the following tables o inventory(item, level): How much of each item is in the warehouse o minlevel(item, level) : What is the minimum desired level of each item o reorder(item, amount): What quantity should we re-order at a time o orders(item, amount) : Orders to be placed (read by external process) Example: MariaDB Trigger Syntax: CREATE [OR REPLACE] [DEFINER = { user | CURRENT_USER | role | CURRENT_ROLE }] TRIGGER [IF NOT EXISTS] trigger_name trigger_time trigger_event ON tbl_name FOR EACH ROW [{ FOLLOWS | PRECEDES } other_trigger_name ] trigger_stmt; Example: CREATE DEFINER=`root`@`localhost` TRIGGER increment_animal AFTER INSERT ON animals FOR EACH ROW UPDATE animal_count SET animal_count.animals = animal_count.animals+1; When Not To Use Triggers ▪ Triggers were used earlier for tasks such as o maintaining summary data (e.g. total salary of each department) o Replicating databases by recording changes to special relations (called change or delta relations) and having a separate process that applies the changes over to a replica ▪ There are better ways of doing these now: o Databases today provide built in materialized view facilities to maintain summary data o Databases provide built-in support for replication ▪ Encapsulation facilities can be used instead of triggers in many cases o Define methods to update fields o Carry out actions as part of the update methods instead of through a trigger Security Security - protection from malicious attempts to steal or modify data. Levels of Security Database system level o Authentication and authorization mechanisms to allow specific users access only to required data Operating system level o 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 o Eavesdropping (secretly listen to a conversation) o Masquerading (pretending to be an authorized user or sending messages supposedly from authorized users) Levels of Security 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 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 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. Authorization and Views Users can be given authorization on views, without being given any authorization on the relations used in the view definition n 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 or relational-level security and view-level security can be used to limit a user’s access to precisely the data that user needs. 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. 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: o H Grant must be revoked from U4 since U1 no longer has authorization o H 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: o DBA grants authorization to U7 o U7 grants authorization to U8 o U8 grants authorization to U7 o 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. Security Specification in SQL The grant statement is used to confer authorization grant on to ▪ is: o a user-id o public, which allows all valid users the privilege granted o 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). 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 Privilege To Grant Privileges with grant option: allows a user who is granted a privilege to pass the privilege on to other users. Example: grant select on branch to U1 with grant option gives U1 the select privileges on branch and allows U1 to grant this privilege to others 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 grant teller to alice, bob grant manager to avi Revoking Authorization in SQL The revoke statement is used to revoke authorization. revoke on from [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.  may be all to revoke all privileges the revoke may hold. ▪ If includes public all users lose the privilege except those granted it explicitly. ▪ If the same privilege was granted twice to the same user by different grantees, the user may retain the privilege after the revocation. ▪ All privileges that depend on the privilege being revoked are also revoked. 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 ▪ With the growth in Web access to databases, database accesses come primarily from application servers. ▪ End users don't have database user ids, they are all mapped to the same database user id o All end-users of an application (such as a web application) may be mapped to a single database user o The task of authorization in above cases falls on the application program, with no support from SQL ▪ Benefit: fine grained authorizations, such as to individual tuples, can be implemented by the application. ▪ Drawback: Authorization must be done in application code, and may be dispersed all over an application ▪ Checking for absence of authorization loopholes becomes very difficult since it requires reading large amounts of application code Audit Trails An audit trail is a log of all changes (inserts/deletes/updates) to the database along with information such as which user performed the change, and when the change was performed. Used to track erroneous/fraudulent updates. Can be implemented using triggers, but many database systems provide direct support. Encryption Data may be encrypted when database authorization provisions do not offer sufficient protection. Properties of good encryption technique: o Relatively simple for authorized users to encrypt and decrypt data. o Encryption scheme depends not on the secrecy of the algorithm but on the secrecy of a parameter of the algorithm called the encryption key. o Extremely difficult for an intruder to determine the encryption key. 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 secure 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: o public key – publicly published key used to encrypt data, but cannot be used to decrypt data o 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 RSA public-key encryption scheme is based on the hardness of factoring a very large number (100's of digits) into its prime components. Authentication Password based authentication is widely used, but is susceptible to sniffing on a network Challenge-response systems avoid transmission of passwords o DB sends a (randomly generated) challenge string to user o User encrypts string and returns result. o DB verifies identity by decrypting result o 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 o E.g. use private key (in reverse) to encrypt data, and anyone can verify authenticity by using public key (in reverse) to decrypt data. o Only holder of private key could have created the encrypted data. o Digital signatures also help ensure nonrepudiation: sender cannot later claim to have not created the data Digital Certificates Digital certificates are used to verify authenticity of public keys. Problem: when you communicate with a web site, how do you know if you are talking with the genuine web site or an imposter? Solution: use the public key of the web site Problem: how to verify if the public key itself is genuine? Solution: Every client (e.g. browser) has public keys of a few root-level Certification authorities A site can get its name/URL and public key signed by a certification authority: signed document is called a certificate Client can use public key of certification authority to verify certificate Multiple levels of certification authorities can exist. Each certification authority o presents its own public-key certificate signed by a higher level authority, and o Uses its private key to sign the certificate of other web sites/authorities Thank You!