Bài giảng Bảo mật cơ sở dữ liệu: Security models - Trần Thị Kim Chi

Bài giảng Bảo mật cơ sở dữ liệu: Security models trình bày các nội dung: Access control, types of Access control, mandatory access control, rules based access control, authentication methods, operating system authentication,... Mời các bạn cùng tham khảo.

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d Database Application Security Models

Discretionary/mandatory access control

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© FPT Software 3

Access control

• Access control is a security technique that can

be used to regulate who or what can view or use resources in a computing environment.

• Access control systems perform authorization

identification, authentication, access approval,

and accountability of entities through login

credentials includingpasswords, personal

identification numbers (PINs), biometric scans,

and physical or electronic keys.

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Types of Access control

• There are two main types of access control:

– Physical,

– logical

• Physical access control limits access to campuses, buildings, rooms and physical IT assets

• Logical access limits connections to computer networks, system files and data.

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Types of Access control

The four main categories of access control are:

• Mandatory access control

• Discretionary access control

• Role-based access control

• Rule-based access control

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Mandatory access control (MAC)

system-controlled policy restricting access to resource

objects (such as data files, devices, systems,

etc.) based on the level of authorization or

clearance of the accessing entity, be it person,

process, or device.

• http://

searchsecurity.techtarget.com/definition/mandatory-access-control-MAC

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Discretionary access control (DAC)

• Discretionary access control (DAC) is a type of

access control defined by the Trusted Computer System Evaluation Criteria "as a means of restricting access to objects based on the identity of subjects and/or groups to which they belong The controls are discretionary in the sense that a subject with a certain access permission is capable of passing that permission (perhaps indirectly) on to any other subject (unless restrained by mandatory access control )".

• Discretionary access control is commonly discussed in contrast to mandatory access control (MAC, sometimes

termed non-discretionary access control)

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Role-based access control (RBAC)

• Role-based access control (RBAC) is a method of

regulating access to computer or network resources

based on the roles of individual users within an

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Rules Based Access Control

• Rules Based Access Control is a strategy for managing

user access to one or more systems, where business

changes trigger the application of Rules, which specify

access changes.

• Implementation of Rules Based Access Control systems

is feasible so long as the number of triggering business

events and the set of possible actions that follow those

events are both small.

• - See more at:

http://hitachi-id.com/concepts/rules_based_access_control.html#sthas h.TJMhLiGM.dpuf

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Authentication Methods

– Verifies user identity

– Permits access to the operating system

– Allows physical entrance to company property

– Magnetic cards and biometric measures

means

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verifies holder of certificate

– Small electronic device

– Displays a number unique to the token holder; used with the

holder’s PIN as a password

– Uses a different password each time

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– Also known as a security card or smart card

– Similar to a credit card; uses an electronic circuit instead of a

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– Developed by the University of Michigan

– A centralized directory database stores:

• Users (user name and user ID)

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– Developed and used by Microsoft

– Employs a challenge/response authentication protocol

– User keeps a private key

– Authentication firm holds a public key

– Encrypt and decrypt data using both keys

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centralized authentication mechanism

information is transmitted over the network in an

encrypted form

– Password is not stored locally

– Invulnerable to brute force or dictionary attacks

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Authorization

perform the functions they request

authenticated

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Operating System Authentication

Microsoft SQL Server 2000)

depend on OS to

authenticate users

– Once an intruder is inside the

OS, it is easier to access the

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User Administration

– Use a consistent naming convention

– Always provide a password to an account and force the user to

change it at the first logon

– Protect passwords

– Do not use default passwords

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Creating a SQL Server User

system

SECURITYADMIN)

– Windows Integrated (trusted) login

– SQL Server login

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Creating Windows Integrated Logins

– SP_GRANTLOGIN system stored procedure

– Can be associated local, domain, group usernames

– Use the Security container

– Logins -> New Login

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Creating Windows Integrated Logins

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Creating SQL Server Logins

– SP_ADDLOGIN system stored procedure

– Password is encrypted by default

– Specify a default database

– Security container

– Logins -> New Login

– SQL Server Authentication option

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Removing Users

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– Highlight the desired login

– Choose Delete from the Action menu

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– Increasing a storage quota

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SQL Server: Modifying Windows

Integrated Login Attributes

– SP_DEFAULTDB system stored procedure

– SP_DEFAULTLANGUAGE stored procedure

– Expand the security container

– Select desired login

– Properties (on the Action Menu)

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Default Users

– SYS, owner of the data dictionary

– SYSTEM, performs almost all database tasks

– ORAPWD, creates a password file

– SA, system administrator

– BUILT_IN\Administrators

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Remote Users

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Linked Servers

– Object Linking and Embedding Database (OLEDB)

– Open Database Connectivity (ODBC)

the linked database

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Best Practices

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Best Practices

– Mimic Oracle’s recommended installation for UNIX

– Use local Windows or domain Windows accounts

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Best Practices

– Mimic Oracle’s recommended installation for UNIX

– Use local Windows or domain Windows accounts

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Password Policies

– Matches your company missions

– Enforced at all level of the organization

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Defining and Using Profiles

– Describes limitation of database resources

– Defines database users behavior

– Prevents users from wasting resources

– Oracle does

– Microsoft SQL Server 2000 does not

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Creating Profiles in SQL Server

2000 or 2005

application level within OLEDB

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Designing and Implementing

Password Policies

passwords are harder to break

– Training

– Education

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What Is a Password Policy?

– Enhances the robustness of a password

– Reduces the likelihood of password breaking

– Complexity

– Change frequency

– Reuse

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Importance of Password Policies

strengthen authentication by adopting technological

measures that protect their assets

the company and raises employee awareness of

password protection

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Designing Password Policies

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Implementing Password Policies

– Integrated server system

– Windows authentication mode

– Challenge/response methodology

– Challenge is eight bytes of random data

– Response is a 24-byte DES-encrypted hash

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– Integrated server system

– Windows authentication mode

– Challenge/response methodology

– Challenge is eight bytes of random data

– Response is a 24-byte DES-encrypted hash

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– A key known by client and server encrypts handshake data

– Requires a Key Distribution Center (KDC)

– Tickets

– Time must be synchronized networkwide

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Granting and Revoking User Privileges

operations

– System privileges:

• Granted only by a database administrator

• Granted by a user with administration privileges

– Object privileges:

• Granted to a user by the schema owner

• Granted by a user with GRANT privileges

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– Grant permission using the GRANT statement

– Revoke permission using the REVOKE statement

– Enterprise Manager

– Deny permission using the DENY statement

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– Table and database objects privileges:

• GRANT, REVOKE, and DENY

• EXECUTE permission

• Enterprise Manager (3 methods)

– Column privileges:

• GRANT, REVOKE, and DENY

• Enterprise Manager (2 methods)

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Creating, Assigning, and Revoking User

Roles

– Used to organize and administer privileges

– It is like a user, except it cannot own object

– Can be assigned privileges

– Can be assigned to users

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Roles

– Standard and application

– Create roles using SP_ADDROLE system-stored procedure

– Add members to a role using SP_ADDROLEMEMBER stored

procedure

– Drop members from a role using SP_DROPROLEMEMBER

stored procedure

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Roles

– User-defined roles (continued):

• Drop roles using SP_DROPROLE stored procedure

• Use Enterprise Manager

– Fixed server roles:

• Cannot be modified or created

• Add member to a role using SP_ADDSRVROLEMEMBER stored procedure

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Roles

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Roles

– Fixed server roles (continued):

• Drop members from a role using SP_DROPSRVROLEMEMBER stored procedure

– Fixed database roles:

• Cannot be modified

• Give access to database administrative tasks

• Add members to a role using SP_ADDROLEMEMBER stored procedure

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Roles

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Roles

– Fixed database roles (continued):

• Drop members from a role using SP_DROPROLEMEMBER stored procedure

– Public database role:

• Cannot be dropped

• Users automatically belong to this role

• Users cannot be dropped

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Best Practices

– Never store passwords for an application in plaintext

– Change passwords frequently

– Use passwords at least eight characters long

– Pick a password that you can remember

– Use roles to control and administer privileges

– Report compromise or loss of a password

– Report any violation of company guidelines

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Best Practices

– Never give your password to anyone

– Never share your password with anyone

– Never give your password over the phone

– Never type your password in an e-mail

– Make sure your password is complex enough

– Use Windows integrated security mode

– In Windows 2000/3 domain use domain users and take

advantage of Kerberos

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Best Practices

– Require complex passwords with special characters in the first

seven bytes

– Require a password length of at least eight

– Set an account lockout threshold

– Do not allow passwords to automatically reset

– Expire end-user passwords

– Do not expire application-user passwords

– Enforce a password history

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– Enhances password robustness

– Reduces likelihood of password breaking

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Best Practices

– Organize and administer privileges in an easy manner

– Role is like a user but cannot own objects

– Role can be assigned privileges

– GRANT and REVOKE

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E-mail Security

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– Do not configure e-mail server on the same machine were

sensitive data resides

– Do not disclose technical details about the

e-mail server

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and writing actions

protects data

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the Security tab on a

file’s Properties dialog

box

– Allow indicates grant

– Deny indicates revoke

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File Permissions

– Three permission settings: owner; group to which owner

belongs; all other users

– Each setting consist of rwx

• r for reading, w for writing, and x for executing

– CHMOD command used to change file permissions

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File Transfer

– Internet service for transferring files from one computer to

another

– Transmits usernames and passwords in plaintext

– Root account cannot be used with FTP

– Anonymous FTP: ability to log on to the FTP server without

being authenticated

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File Transfer

– Use Secure FTP utility if possible

– Make two FTP directories:

• One for uploads with write permissions only

• One for downloads with read permissions only

– Use specific accounts with limited permissions

– Log and scan FTP activities

– Allow only authorized operators

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Sharing Files

over the Internet

– Malicious code

– Adware and spyware

– Privacy and confidentiality

– Pornography

– Copyright issues

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Memory

– Stop using the program

– Apply a patch (service pack) to fix it

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Covert channels

• MLS designed to restrict legitimate channels of

communication

• May be other ways for information to flow

• For example, resources shared at different

levels may signal information

• Covert channel : “communication path not

intended as such by system’s designers”

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Covert Channel Example

• Alice has TOP SECRET clearance, Bob has

CONFIDENTIAL clearance

• Suppose the file space shared by all users

• Alice creates file FileXYzW to signal “1” to

Bob, and removes file to signal “0”

• Once each minute Bob lists the files

– If file FileXYzW does not exist, Alice sent 0

– If file FileXYzW exists, Alice sent 1

• Alice can leak TOP SECRET info to Bob!

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Alice:

Time:

Create file Delete file Create file Delete file

Bob: Check file Check file Check file Check file Check file

Data: 1 0 1 1 0

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• Other examples of covert channels

– Print queue

– ACK messages

– Network traffic, etc., etc., etc.

• When does a covert channel exist?

1. Sender and receiver have a shared resource

2. Sender able to vary property of resource that

receiver can observe

3. Communication between sender and receiver can

be synchronized

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• Covert channels exist almost everywhere

• Easy to eliminate covert channels…

– Provided you eliminate all shared resources and all

communication

• Virtually impossible to eliminate all covert

channels in any useful system

– DoD guidelines: goal is to reduce covert channel

capacity to no more than 1 bit/second

– Implication is that DoD has given up trying to

eliminate covert channels!

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• Consider 100MB TOP SECRET file

– Plaintext version stored in TOP SECRET place

– Encrypted with AES using 256-bit key, ciphertext

stored in UNCLASSIFIED location

• Suppose we reduce covert channel capacity

to 1 bit per second

• It would take more than 25 years to leak

entire document thru a covert channel

• But it would take less than 5 minutes to leak

256-bit AES key thru covert channel!

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Inference Control Example

• Suppose we query a database

– Question: What is average salary of female CS

• Specific information has leaked from

responses to general questions!

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