Lecture 5: Security, PhP

• Security and Authorization – Discretionary Access Control • Grant, Revoke, Authorization Graph, Views – Mandatory Access Control – Internet-oriented Security – Statistical Database Security CS3/586 Some slides copied from Kim Howard, with permission.

• Getting started in UNIX • Overview of PHP and HTML • PHP Basics • PHP and Databases – Postgres and MySQL – Database Abstractions – Connecting via Java or Perl • Security • References 5/1/2020 Lecture 5 Slide 1

Learning Objectives

• LO5.1 Identify the active privileges of GRANT and REVOKE after a sequence commands on tables and/or views • LO5.2 Derive information in a database despite statistical security measures .

• Be able to write a web application using a back end database Slide 2

Security and Authorization, Chapter 21

• Objectives: – Secrecy: Users should not be able to see things they are not supposed to see.

• E.g., A student can’t see other students’ grades.

– Integrity: Users should not be able to modify things they are not supposed to modify.

• E.g., Only instructors can assign grades.

– Availability: Users should be able to see and modify things they are allowed to see and modify.

• OS, Network security issues also relevant – Only database issues discussed here Slide 3

Access Controls

• 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 Slide 4

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 automatically gets all privileges on it.

– DMBS 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.

Slide 5

GRANT Command*

GRANT privileges ON object TO auth [WITH GRANT OPTION] • The following privileges can be specified:     SELECT: Can read all columns (including those added later via ALTER TABLE command).

 SELECT(col-name(s)) means can read these columns.

INSERT : Can insert tuples.

 INSERT(col-name(s)) means can insert non-null values into these columns.

DELETE: Can delete tuples.

REFERENCES (col-name): Can define foreign keys (in other tables) that refer to this column.

 Auth is a group of users.

• If a user has a privilege with the GRANT OPTION , can pass privilege on to other users (with or without passing on the GRANT OPTION ).

• Only owner can execute CREATE, ALTER, and DROP.

Slide 6

REVOKE Command

REVOKE privileges ON object FROM auth [RESTRICT|CASCADE] • Must be issued by a user who granted “privileges” on “object” to “auth”.

• CASCADE: –

abandon

anyone granted this privilege by auth, and so on recursively.

– “abandon”: If an auth’s privilege is abandoned and this is the last possible abandonment, then revoke auth’s privilege – “and so on recursively”: Abandon anyone granted the privilege by the auth just abandoned.

• RESTRICT: If CASCADE would cause anyone to be abandoned, then cancel the command.

Slide 7

Examples of Grant, Revoke

• Suppose Len has created the author table, then these commands are executed in this order – Len : GRANT UPDATE, SELECT ON author – Len : GRANT UPDATE ON author OPTION – Parisa : GRANT UPDATE ON author TO Yingjin TO Parisa WITH GRANT TO Yingjin – Len : REVOKE UPDATE ON author FROM Parisa CASCADE – Len : REVOKE SELECT ON author FROM Yingjin CASCADE • What privileges does Parisa have on author ?

• What privileges does Yingjin have on author ? • Can Yingjin issue UPDATE author A SET A.age=25 ?

• Can Yingjin issue UPDATE author A SET A.age=A.age+1 ?

Slide 8

REVOKE more precisely

• • In some cases we need a more precise definition of REVOKE.

Steps to be taken after “REVOKE P ON O FROM A” – First consider the case CASCADE 1. Draw an authorization graph of current state (cf. next page) 2.

Delete the arc corresponding to “GRANT P ON O TO A” 3. Also delete any arc not accessible from SYSTEM via grants of the privilege P on O 4. If an auth has no incoming arcs granting P on O, then auth loses the privilege P on O.

– RESTRICT is the same as before: If CASCADE would cause any arc other than “GRANT ON P TO A” to be deleted, then abort the command. Slide 9

Authorization Graph

System

( * on Sailors,Yes)

Joe

1 (Select on Sailors,Yes) 4 (Select on Sailors,Yes) 6 (Revoke, Cascade) 3 (Select on Sailors,Yes)

Art

2 (Select on Sailors,Yes) 5 (Select on Sailors,Yes)

Cal Bob

Slide 10

GRANT/REVOKE on Views

• The creator of a view only has a privilege on the view if s/he has it on every component of the view.

– In particular, must have SELECT on all components to create the view – If the creator of a view loses the SELECT privilege on an underlying table, the view is dropped!

• If the creator of a view loses a privilege held with the grant option on an underlying table, (s)he loses the privilege on the view as well; so do users who were granted that privilege on the view!

Slide 11

View Example

• Len is the creator of author. Suppose these statements are executed.

– Len: GRANT SELECT ON author TO Vijay WITH GRANT OPTION – Len: GRANT SELECT ON author TO Pratibha OPTION WITH GRANT – Pratibha: GRANT SELECT ON author TO Vijay WITH GRANT OPTION – Vijay: CREATE VIEW ta AS SELECT * FROM AUTHOR A WHERE A.age < 30 – Len: REVOKE SELECT ON author FROM Vijay CASCADE – Len: REVOKE SELECT ON author FROM Pratibha RESTRICT • What privileges does Vijay have on author, ta?

• What privileges does Pratibha have on author, ta?

Slide 12

Role-Based Authorization

• In SQL-92, privileges are actually assigned to authorization ids , which can denote a single user or a group of users.

• In SQL:1999 privileges are assigned to roles .

– – – Roles can then be granted to users and to other roles.

Reflects how real organizations work.

Illustrates how standards often catch up with “de facto” standards embodied in popular systems.

Slide 13

Security to the Level of a Field!

• Can create a view that only returns one field of one tuple. (How?) • Then grant access to that view accordingly.

• Allows for

arbitrary

granularity of control,

but

: – – Clumsy to specify, though this can be hidden under a good UI Performance is unacceptable if we need to define field granularity access frequently. (Too many view creations and look-ups.) Slide 14

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 security class.

for a – 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.

Slide 15

Why Mandatory Control?

• Discretionary control has some flaws, e.g., the

Trojan horse

problem: – – – Justin has access to secret information that Dick wants to know.

Dick creates a table called Secret and gives INSERT privileges to Justin (who doesn’t know about this).

Dick modifes the code of a database application program used by Justin to additionally write some secret data to table Secret.

• This requires hacking the OS security system a bit.

– Now, Dick can see the secret data. • 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.

Slide 16

Bell-LaPadula Model

• Objects (e.g., tables, views, tuples) • Subjects (e.g., users, user programs) • Security classes: – Top secret (TS), secret (S), confidential (C), unclassified (U): TS > S> C > U • Each object and subject is assigned a class.

– – Subject S can read object O only if class(S) >= class(O) (Simple Security Property) Subject S can write object O only if class(S) <= class(O) (* Property) Slide 17

Intuition

• I dea is to ensure that information can never flow from a higher to a lower security level.

• E.g., If Dick is cleared for security class C, Justin for class S, and the secret information has class S: – – Dick’s table, Secret, has Dick’s clearance, C.

Justin’s application has his clearance, S.

– So, the database application cannot write into table Secret.

• The mandatory access control rules are applied in addition to any discretionary controls that are in effect.

Slide 18

Multilevel Relations

bid 101 102 bname Salsa Pinto color Red Brown class S C • Users with S and TS clearance will see both rows; a user with C will only see the 2 nd row; a user with U will see no rows.

• If user with C tries to insert <101,Pasta,Blue,C>: – – Allowing insertion violates key constraint Disallowing insertion tells user that there is another object with key 101 that has a class > C!

– Problem resolved by treating class field as part of key.

Slide 19

Polyinstantiation

• Consider previous table with <101,Pasta,Blue,C> inserted.

• What is the color of boat with bid=101?

– Only the highest visible security level exists.

– Both exist – The proper policy is chosen according to the semantics of the application • Notice that the answer to the question depends on your clearances. This is called

polyinstantiation

.

Slide 20

Internet-Oriented Security

• Key Issues: User authentication and trust.

– When DB must be accessed from a secure location, password based schemes are usually adequate.

• For access over an external network, trust is hard to achieve.

– If someone with Sam’s credit card wants to buy from you, how can you be sure it is not someone who stole his card?

– How can Sam be sure that the screen for entering his credit card information is indeed yours, and not some rogue site spoofing you (to steal such information)? How can he be sure that sensitive information is not “sniffed” while it is being sent over the network to you?

• Encryption is a technique used to address these issues.

Slide 21

Encryption

• “Masks” data for secure transmission or storage – Encrypt(data, encryption key) = encrypted data – Decrypt(encrypted data, decryption key) = original data – Without decryption key, the encrypted data is meaningless gibberish • Symmetric Encryption: – Encryption key = decryption key; all authorized users know decryption key (a weakness).

– DES, used since 1977, has 56-bit key; AES has 128-bit (optionally, 192-bit or 256-bit) key • Public-Key Encryption: Each user has two keys: – User’s public encryption key: Known to all – Decryption key: Known only to this user – Used in RSA scheme (Turing Award!) Slide 22

Certifying Servers

• If Amazon distributes their public key , Sam’s browser will encrypt his credit card information using it.

– So, only Amazon can decipher Amazon’s private key .

the credit card information , since no one else has • • But how can Sam (or his browser) know that the public key is genuine? for Amazon – Amazon contracts with, say, Verisign, to issue a certificate – This certificate is stored in encrypted form, encrypted with Verisign’s

private

known only to Verisign.

key, – Verisign’s public key is known to all browsers, which can therefore decrypt the certificate and obtain Amazon’s public key, and be confident that it is genuine.

– Your browser then generates a temporary

session key,

encodes it using Amazon’s public key, and sends it to Amazon. – All subsequent msgs between the browser and Amazon are encoded using symmetric encryption (e.g., DES), which is more efficient than public-key encryption.

This solves the problem of you trusting Amazon, but not the problem of Amazon trusting you.

Slide 23

Statistical DB Security

• Statistical DB: Contains information about individuals, but allows only aggregate queries (e.g., average age, rather than Joe’s age).

• New problem: It may be possible to infer some secret information!

– E.g., If I know Joe is the oldest sailor, I can ask “How many sailors are older than X?” for different values of X until I get the answer 1; this allows me to infer Joe’s age.

• Idea: Insist that each query must involve at least N rows, for some N. Will this work? Slide 24

Challenge Question

• You can ask queries which aggregate data (no GROUP BY) from at least 6 tuples. Find the age of Len with as few queries as possible. Your answer should work for any instance of the table with more than 6 entries.

Name

Len Dave Xavier Kyu Olgay Vachara Tabor

Age

61 45 25 20 19 22 24 Slide 25

Creating your UNIX Workspace

• Login to your CS UNIX account – mkdir ~/public_html – chmod 755 public_html • Place all web files in public_html • All files must be world readable – chmod 644 index.html

• If you enter this address to a browser – http://www.cs.pdx.edu/~username • The browswer will display a default index file if one exists – index.html, index.php, index.cgi

Slide 26

What is PHP?

• Recursive acronym for “PHP: Hypertext Preprocessor” • Widely used Open Source general-purpose scripting language – Scripting language: programing language that controls software applications.

• Specially suited for Web development • Can be embedded into HTML • There may well be better scripting languages, but I think PHP is the easiest to learn.

Slide 27

Some Advantages of PHP

• Runs on all major OS ’s: MS Windows, Solaris, major UNIX and Linux variants, Mac OS’s • Runs on all major web servers : Apache, MS IIS, iPlanet, … • Has support for all major DBMS s: My SQL, Postgres, Oracle, SQL Server, DB2, … • Simple to learn basics, especially for those knowing other languages like C/C++ • Lots of advanced features for professional programmers • Also available for command line applications (PHP-GTK) scripting and gui Slide 28

HTML

• HTML Hyper Text Markup Language • Way to explain document structure (not presentation!) – Structure is title, paragraph, section – Use CSS for presentation, e.g., font size, bold, bullets, margins • Tries to be device independent • Outside the scope of this lecture • HTML Tutorials: http://w3.org/MarkUp/#tutorials • A Caveman's Introduction to HTML and Related Tools: http://www.cat.pdx.edu/~johnj/talks/show.php/introHTML Slide 29

HTML Requests

• Client sends HTTP request from browser to web server • Server locates pages and transmit back to client • Browser renders webpage from html Slide 30

PHP Requests

• PHP executed by server and HTML sent back to server Slide 31

PHP is a Server-Side Language

• PHP code is surrounded by start and end tags • Preprocessing jumps in and out of PHP “mode” – Replaces ALL PHP with HTML • Finally, HTML is sent back to browser Slide 32

Example of Server Side Processing

• If your HTML/PHP file contains: • Then the PHP processor sends this HTML text back to your browser (see it with “view source”): Hello World • Try it, and remember – The HTML/PHP file must end in .php, e.g., test.php

• It is just a text file, edit it with pico, vi, emacs, etc.

– The file must reside in public_html,e.g., public_html/test.php

– The file must have world-readable permission – Address it from any browser with http://www.cs.pdx.edu/~username/test.php

Slide 33

My First PHP Page

System Build Date Configure Command Server API Virtual Directory Support Configuration File (php.ini) Path …truncated… PHP Version 4.4.0

SunOS scalpel.cat.pdx.edu 5.9 Generic_117171-07 sun4u Aug 22 2005 08:43:09 '…omitted… Apache disabled /pkgs/webservers/apache-1.3.33/etc Slide 34

PHP Language Basics

• Tutorial: http://us2.php.net/tut.php

• Language Reference: http://us2.php.net/manual/en/langref.php

Slide 35

Language Basics

• Type decided at runtime by PHP depending on the context in which that variable is used • null, boolean, integer, float, string, array, object

$foo = 1; // integer $bar = "Testing"; // string $xyz = 3.14; // float $foo = $foo + 1; // still an integer ?> Slide 36

Basic Data Types

• Numbers (integers and real), Strings

$a = 1234; $b = 0777; $c = 0xff; $d = 1.25; echo "$a $b $c $d
\n"; ?> • Output: 1234 511 255 1.25

$name = 'Rasmus $last'; // Single-quoted $str = "Hi $name\n"; // Double-quoted echo $str; ?> • Output: Hi Rasmus $last Slide 37

More Basic Data Types, Dynamic Typing

• Booleans

$greeting = true; while ($greeting) { echo "Hi Carl"; $greeting = false; } ?> • Output: Hi Carl • Dynamic Typing – Don't have to declare types – Automatic conversion done

echo 5 + "1.5" + "10e2"; ?> • Output: 1006.5

Slide 38

Arrays

• Useful for many things besides an array: list (vector), hashtable, dictionary, collection, stack, queue, and more

$arr[1] = 1; $arr["stuff"] = "more stuff"; // always use quotes //around string literal array indexes $arr2[1][2] = 3; ?> • Useful array functions built-in • array_push, array_pop, array_rand, array_shift, array_search, sort, ...

Slide 39

Predefined Variables*

• $_SERVER : array containing information such as headers, paths, and script locations • $_GET : associative array of variables passed to the current script via the HTTP GET method • $_POST : associative array of variables passed to the current script via the HTTP POST method

echo "script: $_SERVER[SCRIPT_NAME]
\n"; ?> echo "user-agent: $_SERVER[HTTP_USER_AGENT]
\n"; • Output script: /~len/test.php user-agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; InfoPath.1; .NET CLR 2.0.50727; .NET CLR 1.1.4322) Slide 40

C-like syntax

" . print_r($arr) . "