Introduction to Database CHAPTER 8 Application Design and

Introduction to Database CHAPTER 8 Application Design and Development n n n n Edited: Wei-Pang Yang, IM. NDHU, 2006 User Interfaces and Tools Web Interfaces to Databases Web Fundamentals Servlets and JSP Building Large Web Applications Triggers Authorization in SQL Application Security Source: Database System Concepts, Silberschatz etc. 2001 1

8. 1 User Interfaces and Tools n Most database users do not use a query language like SQL, but use 1. Forms and Graphical user interfaces 2. Report generators 3. Data analysis tools (see Chapter 18) n Many interfaces are Web-based n Back-end (Web server) uses such technologies as n Java servlets n Java Server Pages (JSP) n Active Server Pages (ASP) Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 2

The World Wide Web n n n The Web is a distributed information system based on hypertext. Most Web documents are hypertext documents formatted via the Hyper. Text Markup Language (HTML) HTML documents contain n text along with font specifications, and other formatting instructions hypertext links to other documents, which can be associated with regions of the text. forms, enabling users to enter data which can then be sent back to the Web server Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 3

A formatted report Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 4

8. 2 Web Interfaces to Databases Why interface databases to the Web? 1. Web browsers have become the de-facto standard user interface to databases n n n Enable large numbers of users to access databases from anywhere Avoid the need for downloading/installing specialized code, while providing a good graphical user interface Examples: banks, airline and rental car reservations, university course registration and grading, an so on. Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 5

Web Interfaces to Database (Cont. ) 2. Dynamic generation of documents n n Limitations of static HTML documents • Cannot customize fixed Web documents for individual users. • Problematic to update Web documents, especially if multiple Web documents replicate data. Solution: Generate Web documents dynamically from data stored in a database. • Can tailor the display based on user information stored in the database. • § E. g. tailored ads, tailored weather and local news, … Displayed information is up-to-date, unlike the static Web pages § E. g. stock market information, . . Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 6

8. 3 Web Fundamentals Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 7

8. 3. 1 Uniform Resources Locators n n n In the Web, functionality of pointers is provided by Uniform Resource Locators (URLs). URL example: http: //www. bell-labs. com/topics/book/db-book n The first part indicates how the document is to be accessed • “http” indicates that the document is to be accessed using the Hyper Text Transfer Protocol. n The second part gives the unique name of a machine on the Internet. n The rest of the URL identifies the document within the machine. The local identification can be: • The path name of a file on the machine, or • An identifier (path name) of a program, plus arguments to be passed to the program § E. g. http: //www. google. com/search? q=silberschatz Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 8

8. 3. 2 Hyper Text Markup Language n n n Hyper Text Markup Language (HTML) HTML provides formatting, hypertext link, and image display features. HTML also provides input features • Select from a set of options § Pop-up menus, radio buttons, check lists • Enter values § Text boxes n n Filled in input sent back to the server, to be acted upon by an executable at the server Hyper. Text Transfer Protocol (HTTP) used for communication with the Web server Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 9

Figure 8. 2: An HTML Source Text <html> <body> <table border cols = 3> <tr> <td> A-101 </td> <td> Downtown </td> <td> 500 </td> </tr> … </table> <center> The <i>account</i> relation </center> <form action=“Bank. Query” method=get> Select account/loan and enter number <select name=“type”> <option value=“account” selected> Account <option> value=“Loan”> Loan </select> <input type=text size=5 name=“number”> <input type=submit value=“submit”> </form> </body> </html> Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 10

8. 3. 3 Client-Side Scripting and Applets n n Browsers can fetch certain scripts (client-side scripts) or programs along with documents, and execute them in “safe mode” at the client site n Javascript n Macromedia Flash and Shockwave for animation/games n VRML n Applets Client-side scripts/programs allow documents to be active n E. g. , animation by executing programs at the local site n E. g. ensure that values entered by users satisfy some correctness checks n Permit flexible interaction with the user. • Executing programs at the client site speeds up interaction by avoiding many round trips to server Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 11

Client Side Scripting and Security n Security mechanisms needed to ensure that malicious scripts do not cause damage to the client machine n n Easy for limited capability scripting languages, harder for general purpose programming languages like Java E. g. Java’s security system ensures that the Java applet code does not make any system calls directly n n Disallows dangerous actions such as file writes Notifies the user about potentially dangerous actions, and allows the option to abort the program or to continue execution. Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 12

8. 3. 4 Web Servers and Sessions n n A Web server can easily serve as a front end to a variety of information services. The document name in a URL may identify an executable program, that, when run, generates a HTML document. n n n The Web client can pass extra arguments with the name of the document. To install a new service on the Web, one simply needs to create and install an executable that provides that service. n n When a HTTP server receives a request for such a document, it executes the program, and sends back the HTML document that is generated. The Web browser provides a graphical user interface to the information service. Common Gateway Interface (CGI): a standard interface between web and application server Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 13

Three-Tier Web Architecture Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 14

Two-Tier Web Architecture n Multiple levels of indirection have overheads H Alternative: two-tier architecture Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 15

HTTP and Sessions n The HTTP protocol is connectionless n n In contrast, Unix logins, and JDBC/ODBC connections stay connected until the client disconnects • retaining user authentication and other information Motivation: reduces load on server • operating systems have tight limits on number of open connections on a machine Information services need session information n n That is, once the server replies to a request, the server closes the connection with the client, and forgets all about the request E. g. user authentication should be done only once per session Solution: use a cookie Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 16

Sessions and Cookies n A cookie is a small piece of text containing identifying information n n Sent by server to browser on first interaction Sent by browser to the server that created the cookie on further interactions • part of the HTTP protocol Server saves information about cookies it issued, and can use it when serving a request • E. g. , authentication information, and user preferences Cookies can be stored permanently or for a limited time Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 17

8. 4 Servlets and JSP n Java Servlet specification defines an API for communication between the Web server and application program n n n E. g. methods to get parameter values and to send HTML text back to client Application program (also called a servlet) is loaded into the Web server n Two-tier model n Each request spawns a new thread in the Web server • thread is closed once the request is serviced Servlet API provides a get. Session() method n Sets a cookie on first interaction with browser, and uses it to identify session on further interactions n Provides methods to store and look-up per-session information • E. g. user name, preferences, . . Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 18

8. 4. 1 A Servlet Example Public class Bank. Query(Servlet extends Http. Servlet { public void do. Get(Http. Servlet. Request request, Http. Servlet. Response result) throws Servlet. Exception, IOException { String type = request. get. Parameter(“type”); String number = request. get. Parameter(“number”); …code to find the loan amount/account balance … …using JDBC to communicate with the database. . …we assume the value is stored in the variable balance result. set. Content. Type(“text/html”); Print. Writer out = result. get. Writer( ); out. println(“<HEAD><TITLE>Query Result</TITLE></HEAD>”); out. println(“<BODY>”); out. println(“Balance on “ + type + number + “=“ + balance); out. println(“</BODY>”); out. close ( ); } } Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 19

8. 4. 5 Server-Side Scripting n Server-side scripting simplifies the task of connecting a database to the Web n n Define a HTML document with embedded executable code/SQL queries. Input values from HTML forms can be used directly in the embedded code/SQL queries. When the document is requested, the Web server executes the embedded code/SQL queries to generate the actual HTML document. Numerous server-side scripting languages n n JSP, Server-side Javascript, Cold. Fusion Markup Language (cfml), PHP, Jscript General purpose scripting languages: VBScript, Perl, Python Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 20

8. 5 Building Large Web Applications Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 21

8. 5. 3 Improving Application Performance is an issue for popular Web sites n n May be accessed by millions of users every day, thousands of requests per second at peak time Caching techniques used to reduce cost of serving pages by exploiting commonalities between requests n At the server site: • Caching of JDBC connections between servlet requests • Caching results of database queries § Cached results must be updated if underlying database changes • Caching of generated HTML n At the client’s network • Caching of pages by Web proxy Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 22

Introduction to Database CHAPTER 8 Application Design and Development n n n n Edited: Wei-Pang Yang, IM. NDHU, 2006 User Interfaces and Tools Web Interfaces to Databases Web Fundamentals Servlets and JSP Building Large Web Applications Triggers Authorization in SQL Application Security Source: Database System Concepts, Silberschatz etc. 2001 23

8. 6 Triggers n 啟動 A trigger is a statement that is executed automatically by the system as a side effect of a modification to the database. create trigger setnull-trigger before update on r referencing new row as nrow for each row when nrow. phone-number = ‘ ‘ set nrow. phone-number = null n n To design a trigger mechanism, we must: n Specify the conditions under which the trigger is to be executed (when). n 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. Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 24

8. 6. 1 Need for Trigger n Suppose that instead of allowing negative account balances, the bank deals with overdrafts by n n n 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. 3. account 5. loan n Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 25

8. 6. 2 Trigger in SQL n An Example: overdraft in Bank create trigger overdraft-trigger after update on account referencing new row as nrow 6. borrower for each row when nrow. balance < 0 begin atomic insert into borrower (select customer-name, account-number from depositor where nrow. account-number = depositor. account-number); insert into loan values (n. row. account-number, nrow. branch-name, – nrow. balance); update account set balance = 0 where account-number = nrow. account-number end Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 26

Trigger in SQL (cont) n n Triggering event can be insert, delete or update Triggers on update can be restricted to specific attributes e. g. balance n E. g. create trigger overdraft-trigger after update of balance on account n n n Values of attributes before and after an update can be referenced n referencing old row as: for deletes and updates n referencing new row as: for inserts and updates Triggers can be activated before an event E. g. Convert blanks to null. create trigger setnull-trigger before update on r referencing new row as nrow for each row when nrow. phone-number = ‘ ‘ //blank set nrow. phone-number = null Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 27

8. 6. 3 When Not To Use Triggers n n n Triggers were used earlier for tasks such as n maintaining summary data (e. g. total salary of each department) n 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: n Databases today provide built in materialized view facilities to maintain summary data n Databases provide built-in support for replication Encapsulation facilities can be used instead of triggers in many cases n Define methods to update fields n Carry out actions as part of the update methods instead of through a trigger Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 28

8. 7 Authorization in SQL n Privileges in SQL n Roles n Grant n with grant option n Revoke Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 29

8. 7. 1 Granting of Privileges n n Authorization Graph: The passage of authorization from one user to another may be represented by graph. n The nodes of this graph are the users. n The root of the graph is the database administrator. Consider graph for update authorization U 1 DBA U 2 U 4 U 5 U 3 Fig. 8. 11 Authorization-Grant Graph n Revoke • DBA revoke from U 1, then … Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 30

Granting of Privileges (cont. ) 打破 Fig. 8. 12 Attempt to Defeat Authorization Revocation Fig. 8. 13 Authorization Graph Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 31

8. 7. 2 Granting Privileges in SQL n The grant statement is used to confer authorization grant <privilege list> on <relation name or view name> to <user list> is: • a user-id • public, which allows all valid users the privilege granted • A role (more on this later) Example: grant users U 1, U 2, and U 3 select authorization on the branch relation: n n grant select on branch to U 1, U 2, U 3 n Grant with option DBA: grant select on branch to U 1 with grant option U 1 : grant select on branch to U 2 with grant option Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 32

8. 7. 3 Roles n n Role: 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 n Roles can be assigned to users, and even to other roles n Example: Bank Database n Roles: teller, branch-manager, auditor, system administrator U 1 DBA U 2 U 4 U 5 U 3 Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 33

Roles (cont. ) n Privileges can be granted to or revoked from roles, just like user n Roles can be assigned to users, and even to other roles n 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 alice, bob grant manager to avi Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 34

8. 7. 4 Revoking of Privileges with grant option: allows a user who is granted a privilege to pass the privilege on to other users. n n Example: grant select on branch to U 1 with grant option gives U 1 the select privileges on branch and allows U 1 to grant this privilege to others Revoke n U 1 DBA U 2 U 4 revoke select on branch from U 1, U 2, U 3 cascade default U 5 revoke select on branch from U 1, U 2, U 3 restrict U 3 Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 35

8. 7. 5 Authorization and Views n n n 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 or relational-level security and view-level security can be used to limit a user’s access to precisely the data that user needs. Edited: Wei-Pang Yang, IM. NDHU, 2006 SQL View V 1 View V 2 Base Table B 1 Base Table B 2 Base Table B 3 Base Table B 4 Data Set D 1 D 2 D 3 D 4 Source: Database System Concepts, Silberschatz etc. 2001 36

Authorization and Views (cont. ) n Suppose a bank clerk needs to know the names of the customers of each branch, but is not authorized to see specific loan information. n 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 n The cust-loan view is defined in SQL as follows: create view cust-loan as select branchname, customer-name from borrower, loan where borrower. loan-number = loan-number § The clerk is authorized to see the result of the query: select * from cust-loan Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 37

8. 7. 6 Limitations of SQL Authorization n SQL standard does not support authorization at a tuple level n E. g. we cannot restrict students to see only their own grades In web database, the authorization task falls on the application program, with no support from SQL n 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 n Benefit: fine grained authorizations, such as to individual tuples, can be implemented by the application. n Drawback: Authorization must be done in application code, and may be dispersed all over an application 成粒狀 Fine grained authorizations n Oracle Virtual Private Database (VPD) • Automatically add --where depositor. name = syscontext. user-id() Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 38

8. 7. 7 Audit Trails n 足跡 Audit Trail: 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. Dishonest trick 詐騙 n n Used to track erroneous (mistake) or fraudulent updates. Can be implemented using triggers, but many database systems provide direct support. Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 39

8. 8 Application Security n n Forms of Malicious Access: 蓄意的; 惡意的 n Unauthorized reading of data n Unauthorized modification of data n Unauthorized destruction of data Security Levels: to protect the database 1. Database system level • Authorization mechanisms to allow specific users access only to required data • We concentrate on authorization in the rest of this chapter 2. Operating system level • Operating system super-users can do anything they want to the database! Good operating system level security is required. Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 40

Application Security (cont. ) 加密 3. Network level: • must use encryption to prevent 4. Physical level • Physical access to computers allows destruction of data by 闖入者 intruders; traditional lock-and-key security is needed • Computers must also be protected from floods, fire, etc. § More in Chapter 17 (Recovery) 5. 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 保密能力 Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 41

Integrity vs. Security n Integrity: n n Integrity constraints guard against accidental damage to the database, by ensuring that authorized changes to the database do not result in a loss of data consistency. They test values inserted in the database, and test queries to ensure that the comparisons make sense. Costly to test Security: n Protect database from unauthorized access and malicious 惡意的 destruction or alteration Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 42

Statistical Databases (補) n n Problem: how to ensure privacy of individuals while allowing use of data for statistical purposes (e. g. , finding median income, average bank balance, sum, count, etc. ) Solutions: n System rejects any query that involves fewer than some predetermined number of individuals. Still possible to use results of multiple overlapping queries to deduce data about an individual 污染 n n n Data pollution -- random falsification of data provided in response 竄改 to a query. Random modification of the query itself. There is a tradeoff between accuracy and security. Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 43

8. 8. 1 Encryption Techniques n n Data may be encrypted when database authorization provisions do not offer sufficient protection. Properties of good encryption technique: n n n 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 the encryption key. Extremely difficult for an intruder to determine the encryption key. Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 44

Encryption Techniques (cont. ) n Data Encryption Standard (DES) n n n substitutes characters and rearranges their order on the basis of an encryption key which is provided to authorized users via a secure mechanism. • E. g. I LOVE YOU + 2 K NQXG AQW Scheme is no more secure than the key transmission mechanism since the key has to be shared. Advanced Encryption Standard (AES) n is a new standard replacing DES, and is based on the Rijndael algorithm, but is also dependent on shared secret keys Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 45

最早有關密碼的書 (1920) (補) Source: http: //www. nsa. gov/museum/ Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 46

(補) World War II Enigma (德國) Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: http: //www. nsa. gov/museum/ Big machine (美國) Source: Database System Concepts, Silberschatz etc. 2001 47

(補) Three-Rotor Machine Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: http: //www. nsa. gov/museum/ Source: Database System Concepts, Silberschatz etc. 2001 48

新時代 (補) 特殊IC Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: http: //www. nsa. gov/museum/ Supercomputer: Cray-XMP Source: Database System Concepts, Silberschatz etc. 2001 49

Public Encryption: RSA 公開金鑰 (補) • e. g. Painttext P = 13; public-key: e=11, r=15 Ciphertext C = modulo r = modulo 15 = 1792160394037 modulo 15 =7 Decryption P = modulo r = modulo 15 = 343 modulo 15 = 13 乙: e, 甲: e, r C= mod r Edited: Wei-Pang Yang, IM. NDHU, 2006 P= r, d mod r Source: Database System Concepts, Silberschatz etc. 2001 51

Public Encryption: RSA 公開金鑰 (cont. ) n (補) The scheme of : [Rivest 78] 1. Choose, randomly, two distinct large primes p and q, and compute the product r=p*q e. g. p=3, q=5, r=15 2. Choose, randomly, a large integer e, such that gcd (e, (p-1)*(q-1) ) = 1 Note: any prime number greater than both p and q will do. (p-1)*(q-1)= 2*4 = 8, e = 11 3. Take the decryption key, d, corresponding to e to be the unique "multiplicative inverse" of e, modulo (p-1)*(q-1); i. e. d*e = 1, modulo(p-1)*(q- 1) Note: The algorithm for computing d is straight forward. d*11=1, mod 8, ==> d=3 Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 52

Public Encryption: RSA 公開金鑰 (cont. ) (補) · Exercise: Suppose we have r = 2773, e = 17, try to find d = ? Answer: 1. 50*50 = 2500 ~ 2773 2. 47*53 2773 3. 47*59 = 2773 so p = 47, q = 59 4. (p-1)(q-1) = 2668 5. d*17 = 1, modulo (p-1)*(q-1) => d*17 = 1, modulo 2668 d = 1: 17 + 2667 2668 x d = 2: 4 + 2667. . . 2668 x d = 157: (157*17) / (2668) = 2 Edited: Wei-Pang Yang, IM. NDHU, 2006 r: 50 digits => 4 hrs 75 digits => 100 days 100 digits => 74 years 500 digits => 4*10^25 years Source: Database System Concepts, Silberschatz etc. 2001 53

Encryption Techniques: RSA n Public-key Encryption: n n 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. Keys 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. Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 54

8. 8. 2 Encryption Support in Databases Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 55

8. 8. 3 Authentication n n 確定 證明 Forms of authorization on parts of the database: n Read authorization n Insert authorization n Update authorization n Delete authorization Forms of authorization to modify the database schema: n Index authorization - allows creation and deletion of indices. n Resources authorization - allows creation of new relations. n n Alteration authorization - allows addition or deletion of attributes in a relation. Drop authorization - allows deletion of relations. Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 56

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8. 8. 3. 1 Challenge-Response System n n Password-based Authentication n is widely used by OS and database n Drawback: easy to “sniff” the password on a network Challenge-response systems: n No passwords travel across the network n DB sends a (randomly generated) challenge string to user n User encrypts string and returns result. n DB verifies identity by decrypting result Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 59

8. 8. 3. 2 Digital Signatures n Digital Signatures (數位簽章) n are used to verify authenticity of data n n 確定 證明文件 Method: • 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) Repudiation: refuse to accept, 否認 Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 60

8. 8. 3. 3 Digital Certificates數位憑證 n n n 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? 正統的 vs. 詐騙者 n 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 憑證授權 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 n § presents its own public-key certificate signed by a higher level authority, § Uses its private key to sign the certificate of other web sites/authorities Edited: Wei-Pang Yang, IM. NDHU, 2006 Source: Database System Concepts, Silberschatz etc. 2001 61

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