Access Control. Ed Crowley

Transcription

1 Access Control Ed Crowley 1

2 ISC 2 Key Areas of Knowledge Control access by applying the following concepts/methodologies/techniques 1. Policies 2. Types of controls (preventive, detective, corrective ) 3. Techniques (e.g., non-discretionary, discretionary and mandatory) 4. Identifcation and Authentication 5. Decentralized/distributed access control techniques 6. Authorization mechanisms 7. Logging and monitoring 2

3 ISC2 Key Areas of Knowledge Understand access control attacks Assess, effectiveness of access controls 3

4 Topics Access Control Defined Access control terms and best practices Access Control Principles Access Control models MAC, DAC, and NDAC Access control types Authentication Methods Passwords Tokens Identification Methods Biometrics Passwords and attacks Kerberos and other SSOs Auditing and Monitoring Intrusion Detection Object reuse 4

5 Access Control Defined Collection of mechanisms that permit system managers to exercise a directing or restraining influence over the behavior, use, and content of a system. Permits specification of: What users can do Which resources they can access What operations they can perform on a system. CISSP Study Guide 5

6 An Access Control Model Butler Lampson, Computer Security in the Real World SecurityRealIEEE/69-SecurityRealIEEE.htm 6

7 Access Control Systems Include procedures that: Identify users and processes Process and log access requests Grant or deny access Monitor system access Applications Include AAA services Authentication Authorization Accounting 7

8 Access Controls Components could be Hardware (physical) and/or Software (logical). Pertain to systems that are: Context Distributed or Centralized. Effective access control requires a secure physical infrastructure and a secure computer base. Specific goals depend on your specific environment. i.e. dependent on your Risk Assessment 8

9 Typical Goals Maintain data and system Confidentiality Integrity Availability Utilize appropriate fault tolerance and recovery processes. Support services include accountability Provide Auditing Services Users Processes Resources 9

10 Related Integrity Goals Data consistency (integrity): Internal External Internal consistency assures that data is consistent with itself. For example, changes in inventories are congruent with purchase orders. External consistency ensures that data stored in the database is consistent with the real world. For example, inventory records are congruent with physical inventories. Requires a method for comparing computer and physical inventories. 10

11 Access Access A specific type of interaction between a subject and an object that results in the flow of information from one to the other. Subject An active entity, generally in the form of a person, process, or device, that causes information to flow among objects or changes the system state. Technically, a process/domain pair. Aqua Book (NCSC-TG ) 11

12 Object Passive entity that contains or receives information. Access to an object potentially implies access to the information it contains. Examples of objects include: records, blocks, pages, segments, files, directories, directory trees, and programs, as well as bits, bytes, words, fields, processors, video displays, keyboards, clocks, printers, and network nodes. Aqua Book (NCSC-TG ) 12

13 Reference Monitor mediates all access between a subject and an object. 13

14 Logical and Physical Controls Involve the restriction of access to systems. Encryption, smart cards, anti-virus software, audit trails and ACLs. Physical controls incorporate, file backup, guards, gates, and building security. 14

15 Access Control Terms Identify a User with a Username Authenticate a User with a: Password Token, or Biometric Authorize access to a resource 15

16 Access Control Best Practices Utilize Groups or Roles Job Function, Department, Location Centralized vs. Decentralized Single-sign-on (centralized) vs. local logins for each system Vulnerability: One compromise all access 16

17 Access Control Principles Separation of Duties Developer does not sign off tests and promote to production Admin does not sign off on log reviews of own servers Financial transactions processed are reviewed approved by a manager in a line of higher authority. Collusion is a deliberate agreement to subvert controls 17

18 Access Control Principles Rotate job duties to detect and prevent fraud; learn new skills, refresh staff 18

19 Access Control Principles Need to Know Principle: Given only access rights needed to perform job Implicit deny to resources unless authorized and granted access 19

20 File Security Directory hierarchies, and inherited permissions in subdirectories and files (Windows NTFS, Unix umask) Finance may view accounting data and reports but not change Often remove Domain admins from HR/Personnel/Payroll data access Employees can see the Company Policies, but not change them Secretary vs. Manager vs. Analyst doing work on credit reporting Secretary no access Manager view Analyst update Admin full control Watch for bosses delegating to secretary; Secretary keeping access to old dept 20

21 File and Print Permissions 21

22 Print Security Most printers are set to allow anyone to print to them Most will also allow redirection or redundant direction of output Restrict redirect, mainly in sensitive areas or from sensitive systems Set auditing on printers. Review appropriate use 22

23 Logical Access Control Logical Access Control Methods: Software-based components that authenticate users and allow them to access resources Often built into operating system, application, or module 23

24 Logical Access Control Methods Password policies: length, strength, rotation, age, failed logins count/lock Domain passwords should not match local username/password due to risk of pass-through authentication. Single-signon via LDAP source allows use of both domain and local systems via one single-source 24

25 To download 62,000 random logons and passwords click below The Lulz Boat 25

26 Logical Access Control Methods User account policies: naming conventions, disable unused accounts Token use (RSA SecurID, Cryptocard / Proximity card / RFID chip Time and machine use restrictions (rare now, due to remote access) 26

27 Access Control Model A framework that defines how subjects access objects. Controlling access by a subject to an object involves establishing access rules. Three common frameworks: Mandatory Access Controls (MAC) Discretionary Access Control (DAC) Non-Discretionary Access Control aka role based (NDAC) 27

28 MAC Subject s access to an object depends upon labels. A label indicate subject s clearance and classification or sensitivity of the object. Every subject and object must have a label. Based upon rules System makes access decisions. Administrator makes access rules. Military standard. Note that historically, the military has been primarily interested in confidentiality. 28

29 DAC May be user directed or identity based. System makes access decisions. Enables a resource owner to specify what subjects can access what objects. Often implemented as a matrix utilizing Access Control Lists (ACLs). Role based access control is a form of DAC. Commercial standard. 29

30 MAC and DAC MAC DAC with ACL 30

31 Non-Discretionary Access Control aka Role Based Control Useful in high turnover areas. Based on the organizational security policy, a central authority determines, by group, what subjects can have access to what objects. Lattice based access control models are considered Non- Discretionary. Lattice based models utilize pairs of elements that have the least upper bound of values and the greatest lower bound. Subject s role, or task, determines access. 31

32 MAC, DAC, and NDAC Summary Discretionary Access Control User decides what objects are shared with what subjects. Mandatory Access Control Centralized framework decides what objects are shared with what subjects. Non Discretionary Access Control Centralized with predefined roles determining access based upon users role or task. 32

33 Identification and Authentication Professing an identity to a system. Logon ID Facilitates user accountability. Authentication Verification that claimed identity is valid. User password. Note authentication establishes a subject s identity, does not grant access to a specific resource. 33

34 Three Possible Authentication Criteria Something you know. Username, password Something you have. Token, key Something you are. Biometrics 34

35 Two-factor Authentication Requires two of the three authentication factors. ATM card & PIN Credit Card & Signature Username & password 35

36 Password Problems Vulnerable Password files must be protected. Inconvenient Users forget them. Reputable Users tell them to other people. Expensive When users forget, enterprise has to pay people to reset password, staff help desk, investigate password compromises 36

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38 Sample Password Issues Composition Length Lifetime Source Ownership Distribution Storage Entry Transmission Authentication period. 38

39 Password Attack Methods Brute force Try every possible combination. Dictionary Run an encrypted dictionary. Brute Force and Dictionary attacks are also available in a smart form Trojan horse Capture password on system. Key logger Capture all keystrokes on system. Social Engineering If password passes over a network, then protocol call analyzers will also capture them. 39

40 Password Countermeasures Time of day restrictions. Length restrictions. Limit unsuccessful logons. Limit concurrent connections. Enable auditing. Put last login date into banner. 40

41 Password Terms One time password provides maximum security. Tokens can be used to facilitate one time passwords. May be credit card size memory cards or smart cards. Static password is the same for each log-on. Passphrase Sequence of characters that is usually longer than the allotted number for a password. Converted into a virtual password. 41

42 Tokens Static or dynamic Synchronous dynamic password tokens Time based e.g. secret key encryption of the system time. Asynchronous Dynamic password tokens No time dependency Challenge-response tokens. System generates a random challenge string and the owner enters the string into the token along with the proper PIN. 42

43 Biometrics Automated means of identifying and/or authenticating the identity of a person based on physiological or behavioral characteristics. Three performance measures False Rejection Rate (FRR) -- Type I error False Acceptance Rate (FAR) -- Type II error Crossover Error Rate (CER) Expressed as a percentage, false acceptance rate equals the false rejection rate. (lower is better) 43

44 Biometric Issues Enrollment Time Acceptable rate is 2 minutes per person Throughput Time Acceptable rate is 10 people per minute Acceptability Issues Privacy Physical Psychological 44

45 Potential Biometric Criteria Fingerprints Retina scans Iris scans Facial scans Palm scans Hand geometry Voice Handwritten signature dynamics 45

46 Biometrics Summary Advantages Can not be forgotten Lasts forever Makes login & authentication easier Possible long term cost advantages when compared to passwords Disadvantages Initial expense Not mature Problematic user acceptance 46

47 Access Control Methodologies Centralized For dial up users, Radius, CHAP, TACUS, and TACUS + TACUS+ can use 2 part authentication Open Radius Decentralized Utilizes Database Hybrid 47

48 Single Sign On (SSO) Addresses problem of logging on multiple times to access different resources. Each user has one password for all enterprise resources. Difficult to implement. Examples include: Kerberos SESAME KryptoKnight 48

49 Kerberos Defacto SSO standard for heterogeneous networks. Assumes that messages are not secure. Specifically designed to eliminate the need to transmit passwords over the network. Centralized access control methodology. Utilizes symmetric key cryptography. Kerberos authenticates clients to other entities on a network from which a client requires services. 49

50 Kerberos Fundamentals KDC provides security services to principles. Principles may be users or processes KDC initially uses secret keys to exchange information with the client and server. Issues temporary symmetric session keys for communications between: Client and KDC (share a secret key) Server and the KDC (share a different key) Client and server. Security unit called a realm. Realm is a logical grouping of resources. 50

51 Kerberos Operational Overview 51

52 Kerberos Logical Components Key Distribution Center (KDC) Hold all secret keys Initially uses secret keys to exchange information with the client and server KDC Logical Components Authentication Service (AS) Authenticates network entities Ticket granting Service (TGS) Generates temporary session keys 52

53 Kerberos Issues All software must be kerberized. Time clocks must be synchronized. Uses UDP KDC is a single point of failure. 53

54 Kerberos Vulnerabilities Kerberos addresses confidentiality and integrity. Does not directly address availability. Kerberos servers are vulnerable to both physical attacks and attacks from malicious code. Password guessing can be used to impersonate a client. A client s secret key is stored temporarily on the client workstation and can be compromised as well as the session keys that are stored at the client s computer and at the servers. Network monitor could initiate a replay attack. 54

55 Security Domain (Realm) Decentralized access control methodology. Realm of trust. Defines the objects a subject can access. Ensures that random activities do not damage system resources. 55

56 Monitoring IDS Logs Audit trails Network tools 56

57 Auditing Ensures that users are accountable for their actions. Verifies that security policies are enforced. Works as a deterrence to improper actions. Used as an investigative tool. 57

58 TEMPEST Study and control of electrical signals emitted by systems. If not controlled, these signals can function as covert channels. For PCs, normally implemented by placing system within a Faraday Cage. 58

59 Object Reuse Ensures that magnetic media must not have any remanence of previous data. Erased magnetic data can often be recovered. 59

60 Questions? 60