Computer Security Principles and Practice PDF

Computer Security: Principles and Practice Fourth Edition Chapter 1 Overview Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved The NIST Interna...

Computer Security: Principles and Practice Fourth Edition Chapter 1 Overview Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved The NIST Internal/Interagency Report NISTIR 7298 (Glossary of Key Information Security Terms , May 2013) Defines the Term Computer Security as Follows: “ Measures and controls that ensure confidentiality, integrity, and availability of information system assets including hardware, software, firmware, and information being processed, stored, and communicated.” Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 1.1 Essential Network and Computer Security Requirements Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Key Security Concepts Confidentiality – Preserving authorized restrictions on information access and disclosure, including means for protecting personal privacy and proprietary information Integrity – Guarding against improper information modification or destruction, including ensuring information nonrepudiation and authenticity Availability – Ensuring timely and reliable access to and use of information Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Levels of Impact Low – The loss could be expected to have a limited adverse effect on organizational operations, organizational assets, or individuals Moderate – The loss could be expected to have a serious adverse effect on organizational operations, organizational assets, or individuals High – The loss could be expected to have a severe or catastrophic adverse effect on organizational operations, organizational assets, or individuals Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Computer Security Challenges (1 of 2) 1. Computer security is not as simple as it might first appear to the novice 2. In developing a particular security mechanism or algorithm, one must always consider potential attacks on those security features 3. Procedures used to provide particular services are often counterintuitive 4. Physical and logical placement needs to be determined 5. Security mechanisms typically involve more than a particular algorithm or protocol and also require that participants be in possession of some secret information which raises questions about the creation, distribution, and protection of that secret information 6. Attackers only need to find a single weakness, while the designer must find and eliminate all weaknesses to achieve perfect security Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Computer Security Challenges (2 of 2) 7. Security is still too often an afterthought to be incorporated into a system after the design is complete, rather than being an integral part of the design process 8. Security requires regular and constant monitoring 9. There is a natural tendency on the part of users and system managers to perceive little benefit from security investment until a security failure occurs 10. Many users and even security administrators view strong security as an impediment to efficient and user-friendly operation of an information system or use of information Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 1.1 Computer Security Terminology, from RFC 2828, Internet Security Glossary, May 2000 (1 of 2) Adversary (threat agent) Individual, group, organization, or government that conducts or has the intent to conduct detrimental activities. Attack Any kind of malicious activity that attempts to collect, disrupt, deny, degrade, or destroy information system resources or the information itself. Countermeasure A device or techniques that has as its objective the impairment of the operational effectiveness of undesirable or adversarial activity, or the prevention of espionage, sabotage, theft, or unauthorized access to or use of sensitive information or information systems. Risk A measure of the extent to which an entity is threatened by a potential circumstance or event, and typically a function of 1) the adverse impacts that would arise if the circumstance or event occurs; and 2) the likelihood of occurrence. Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 1.1 Computer Security Terminology, from RFC 2828, Internet Security Glossary, May 2000 (2 of 2) Security Policy A set of criteria for the provision of security services. It defines and constrains the activities of a data processing facility in order to maintain a condition of security for systems and data. System Resource (Asset) A major application, general support system, high impact program, physical plant, mission critical system, personnel, equipment, or a logically related group of systems. Threat Any circumstance or event with the potential to adversely impact organizational operations (including mission, functions, image, or reputation), organizational assets, individuals, other organizations, or the Nation through an information system via unauthorized access, destruction, disclosure, modification of information, and/or denial of service. Vulnerability Weakness in an information system, system security procedures, internal controls, or implementation that could be exploited or triggered by a threat source. Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 1.2 Security Concepts and Relationships Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Assets of a Computer System Hardware Software Data Communication facilities and networks Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Vulnerabilities, Threats and Attacks Categories of vulnerabilities – Corrupted (loss of integrity) – Leaky (loss of confidentiality) – Unavailable or very slow (loss of availability) Threats – Capable of exploiting vulnerabilities – Represent potential security harm to an asset Attacks (threats carried out) – Passive – attempt to learn or make use of information from the system that does not affect system resources – Active – attempt to alter system resources or affect their operation – Insider – initiated by an entity inside the security parameter – Outsider – initiated from outside the perimeter Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Countermeasures Means used to deal with security attacks – Prevent – Detect – Recover May itself introduce new vulnerabilities Residual vulnerabilities may remain Goal is to minimize residual level of risk to the assets Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 1.2 Threat Consequences, and the Types of Threat Actions That Cause Each Consequence (1 of 2) Threat Consequence Threat Action (Attack) Unauthorized Disclosure Exposure: Sensitive data are directly released to an unauthorized A circumstance or event entity. whereby an entity gains Interception: An unauthorized entity directly accesses sensitive data access to data for which the traveling between authorized sources and destinations. entity is not authorized. Inference: A threat action whereby an unauthorized entity indirectly accesses sensitive data (but not necessarily the data contained in the communication) by reasoning from characteristics or by-products of communications. Intrusion: An unauthorized entity gains access to sensitive data by circumventing a system’s security protections. Deception Masquerade: An unauthorized entity gains access to a system or A circumstance or event that performs a malicious act by posing as an authorized entity. may result in an authorized Falsification: False data deceive an authorized entity. entity receiving false data and Repudiation: An entity deceives another by falsely denying believing it to be true. responsibility for an act. Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 1.2 Threat Consequences, and the Types of Threat Actions That Cause Each Consequence (2 of 2) Threat Consequence Threat Action (Attack) Disruption Incapacitation: Prevents or interrupts system operation by disabling a A circumstance or event that system component. interrupts or prevents the Corruption: Undesirably alters system operation by adversely correct operation of system modifying system functions or data. services and functions. Obstruction: A threat action that interrupts delivery of system services by hindering system operation. Usurpation Misappropriation: An entity assumes unauthorized logical or physical A circumstance or event that control of a system resource. results in control of system Misuse: Causes a system component to perform a function or service services or functions by an that is detrimental to system security. unauthorized entity. Based on RFC 4949 Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 1.3 Scope of Computer Security This figure depicts security concerns other than physical security, including control of access to computers systems, safeguarding of data transmitted over communications systems, and safeguarding of stored data. Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 1.3 Computer and Network Assets, with Examples of Threats Blank Availability Confidentiality Integrity Blank Hardware Equipment is stolen or An unencrypted USB disabled, thus denying drive is stolen. service. Software Programs are deleted, An unauthorized copy of A working program is denying access to users. software is made. modified, either to cause it to fail during execution or to cause it to do some unintended task. Data Files are deleted, denying An unauthorized read of Existing files are modified access to users. data is performed. An or new files are fabricated. analysis of statistical data reveals underlying data. Communication Messages are destroyed Messages are read. The Messages are modified, Lines and or deleted. Communication traffic pattern of delayed, reordered, or Networks lines or networks are messages is observed. duplicated. False rendered unavailable. messages are fabricated. Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Passive and Active Attacks Passive Attack Active Attack Attempts to learn or make use of Attempts to alter system information from the system but resources or affect their does not affect system resources operation Eavesdropping on, or monitoring Involve some modification of of, transmissions the data stream or the creation of a false stream Goal of attacker is to obtain information that is being Four categories: transmitted – Replay Two types: – Masquerade – Release of message contents – Modification of messages – Traffic analysis – Denial of service Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 1.4 Security Requirements (1 of 7) Access Control: Limit information system access to authorized users, processes acting on behalf of authorized users, or devices (including other information systems) and to the types of transactions and functions that authorized users are permitted to exercise. Awareness and Training: (i) Ensure that managers and users of organizational information systems are made aware of the security risks associated with their activities and of the applicable laws, regulations, and policies related to the security of organizational information systems; and (ii) ensure that personnel are adequately trained to carry out their assigned information security-related duties and responsibilities. Audit and Accountability: (i) Create, protect, and retain information system audit records to the extent needed to enable the monitoring, analysis, investigation, and reporting of unlawful, unauthorized, or inappropriate information system activity; and (ii) ensure that the actions of individual information system users can be uniquely traced to those users so they can be held accountable for their actions. Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 1.4 Security Requirements (2 of 7) Certification, Accreditation, and Security Assessments: (i) Periodically assess the security controls in organizational information systems to determine if the controls are effective in their application; (ii) develop and implement plans of action designed to correct deficiencies and reduce or eliminate vulnerabilities in organizational information systems; (iii) authorize the operation of organizational information systems and any associated information system connections; and (iv) monitor information system security controls on an ongoing basis to ensure the continued effectiveness of the controls. Configuration Management: (i) Establish and maintain baseline configurations and inventories of organizational information systems (including hardware, software, firmware, and documentation) throughout the respective system development life cycles; and (ii) establish and enforce security configuration settings for information technology products employed in organizational information systems. Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 1.4 Security Requirements (3 of 7) Contingency Planning: Establish, maintain, and implement plans for emergency response, backup operations, and postdisaster recovery for organizational information systems to ensure the availability of critical information resources and continuity of operations in emergency situations. Identification and Authentication: Identify information system users, processes acting on behalf of users, or devices, and authenticate (or verify) the identities of those users, processes, or devices, as a prerequisite to allowing access to organizational information systems. Incident Response: (i) Establish an operational incident-handling capability for organizational information systems that includes adequate preparation, detection, analysis, containment, recovery, and user-response activities; and (ii) track, document, and report incidents to appropriate organizational officials and/or authorities. Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 1.4 Security Requirements (4 of 7) Maintenance: (i) Perform periodic and timely maintenance on organizational information systems; and (ii) provide effective controls on the tools, techniques, mechanisms, and personnel used to conduct information system maintenance. Media Protection: (i) Protect information system media, both paper and digital; (ii) limit access to information on information system media to authorized users; and (iii) sanitize or destroy information system media before disposal or release for reuse. Physical and Environmental Protection: (i) Limit physical access to information systems, equipment, and the respective operating environments to authorized individuals; (ii) protect the physical plant and support infrastructure for information systems; (iii) provide supporting utilities for information systems; (iv) protect information systems against environmental hazards; and (v) provide appropriate environmental controls in facilities containing information systems. Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 1.4 Security Requirements (5 of 7) Planning: Develop, document, periodically update, and implement security plans for organizational information systems that describe the security controls in place or planned for the information systems and the rules of behavior for individuals accessing the information systems. Personnel Security: (i) Ensure that individuals occupying positions of responsibility within organizations (including third-party service providers) are trustworthy and meet established security criteria for those positions; (ii) ensure that organizational information and information systems are protected during and after personnel actions such as terminations and transfers; and (iii) employ formal sanctions for personnel failing to comply with organizational security policies and procedures. Risk Assessment: Periodically assess the risk to organizational operations (including mission, functions, image, or reputation), organizational assets, and individuals, resulting from the operation of organizational information systems and the associated processing, storage, or transmission of organizational information. Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 1.4 Security Requirements (6 of 7) Systems and Services Acquisition: (i) Allocate sufficient resources to adequately protect organizational information systems; (ii) employ system development life cycle processes that incorporate information security considerations; (iii) employ software usage and installation restrictions; and (iv) ensure that third-party providers employ adequate security measures to protect information, applications, and/or services outsourced from the organization. System and Communications Protection: (i) Monitor, control, and protect organizational communications (i.e., information transmitted or received by organizational information systems) at the external boundaries and key internal boundaries of the information systems; and (ii) employ architectural designs, software development techniques, and systems engineering principles that promote effective information security within organizational information systems. Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 1.4 Security Requirements (7 of 7) System and Information Integrity: (i) Identify, report, and correct information and information system flaws in a timely manner; (ii) provide protection from malicious code at appropriate locations within organizational information systems; and (iii) monitor information system security alerts and advisories and take appropriate actions in response. (FIPS 200) Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Fundamental Security Design Principles Economy of mechanism Isolation Fail-safe defaults Encapsulation Complete mediation Modularity Open design Layering Separation of privilege Least astonishment Least privilege Least common mechanism Psychological acceptability Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Attack Surfaces Consist of the reachable and exploitable vulnerabilities in a system Examples: – Open ports on outward facing Web and other servers, and code listening on those ports – Services available on the inside of a firewall – Code that processes incoming data, email, XML, office documents, and industry-specific custom data exchange formats – Interfaces, SQL, and Web forms – An employee with access to sensitive information vulnerable to a social engineering attack Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Attack Surface Categories Network Attack Surface Software Attack Surface – Vulnerabilities over an – Vulnerabilities in application, enterprise network, utility, or operating system wide-area network, or code the Internet – Particular focus is Web server – Included in this software category are network protocol vulnerabilities, Human Attack Surface such as those used for a denial-of-service – Vulnerabilities created by attack, disruption of personnel or outsiders, such communications links, as social engineering, human and various forms of error, and trusted insiders intruder attacks Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 1.4 Defense in Depth and Attack Surface Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 1.5 An Attack Tree for Internet Banking Authentication Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Computer Security Strategy (1 of 2) Security Policy – Formal statement of rules and practices that specify or regulate how a system or organization provides security services to protect sensitive and critical system resources Security Implementation – Involves four complementary courses of action: ▪ Prevention ▪ Detection ▪ Response ▪ Recovery Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Computer Security Strategy (2 of 2) Assurance – Encompassing both system design and system implementation, assurance is an attribute of an information system that provides grounds for having confidence that the system operates such that the system’s security policy is enforced Evaluation – Process of examining a computer product or system with respect to certain criteria – Involves testing and may also involve formal analytic or mathematical techniques Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Standards (1 of 2) Standards have been developed to cover management practices and the overall architecture of security mechanisms and services The most important of these organizations are: – National Institute of Standards and Technology (NIST)  NIST is a U.S. federal agency that deals with measurement science, standards, and technology related to U.S. government use and to the promotion of U.S. private sector innovation – Internet Society (ISOC)  ISOC is a professional membership society that provides leadership in addressing issues that confront the future of the Internet, and is the organization home for the groups responsible for Internet infrastructure standards Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Standards (2 of 2) – International Telecommunication Union (ITU-T)  ITU is a United Nations agency in which governments and the private sector coordinate global telecom networks and services – International Organization for Standardization (ISO)  ISO is a nongovernmental organization whose work results in international agreements that are published as International Standards Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Summary Computer security concepts Fundamental security design – Definition principles – Challenges Attack surfaces and attack trees – Model – Attack surfaces Threats, attacks, and assets – Attack trees – Threats and attacks Computer security strategy – Threats and assets – Security policy Security functional – Security implementation requirements – Assurance and evaluation Standards Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Copyright This work is protected by United States copyright laws and is provided solely for the use of instructors in teaching their courses and assessing student learning. Dissemination or sale of any part of this work (including on the World Wide Web) will destroy the integrity of the work and is not permitted. The work and materials from it should never be made available to students except by instructors using the accompanying text in their classes. All recipients of this work are expected to abide by these restrictions and to honor the intended pedagogical purposes and the needs of other instructors who rely on these materials. Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Computer Security: Principles and Practice Fourth Edition Chapter 2 Cryptographic Tools Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Symmetric Encryption The universal technique for providing confidentiality for transmitted or stored data Also referred to as conventional encryption or single-key encryption Two requirements for secure use: – Need a strong encryption algorithm – Sender and receiver must have obtained copies of the secret key in a secure fashion and must keep the key secure Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 2.1 Simplified Model of Symmetric Encryption Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Attacking Symmetric Encryption Cryptanalytic Attacks Brute-Force Attacks Rely on: Try all possible keys on – Nature of the algorithm some ciphertext until an intelligible translation into – Some knowledge of the general plaintext is obtained characteristics of the plaintext – On average half of all – Some sample plaintext-ciphertext possible keys must pairs be tried to achieve Exploits the characteristics of the success algorithm to attempt to deduce a specific plaintext or the key being used – If successful all future and past messages encrypted with that key are compromised Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 2.1 Comparison of Three Popular Symmetric Encryption Algorithms Blank DES Triple DES AES Plaintext block size (bits) 64 64 128 Ciphertext block size (bits) 64 64 128 Key size (bits) 56 112 or 168 128, 192, or 256 DES = Data Encryption Standard AES = Advanced Encryption Standard Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Data Encryption Standard (DES) Until recently was the most widely used encryption scheme – FIPS PUB 46 – Referred to as the Data Encryption Algorithm (DEA) – Uses 64 bit plaintext block and 56 bit key to produce a 64 bit ciphertext block Strength concerns: – Concerns about the algorithm itself ▪ DES is the most studied encryption algorithm in existence – Concerns about the use of a 56-bit key ▪ The speed of commercial off-the-shelf processors makes this key length woefully inadequate Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 2.2 Average Time Required for Exhaustive Key Search Key Size Number of Time Required at Time Required at 109 decryptions /  s 1013 decryptions /  s 10tot heninthpower d ecrypti o nsper microse conds 10tot he1 3power d ecrypti o nsper microse conds (bits) Cipher Alternative Keys 56 DES 256  7.2  1016 2tot h e56po wer ap proximatelyequ als7.2t imes1 0t othe1 6powe r 255  s = 1.125 years 2tot h e55po wer micr o second s=1.125years 1 hour 128 AES 2128  3.4  1038 2tot h e128p ower a pproximatelyeq uals3.4ti me s10tot h e38po wer 2127  s = 5.3  1021 years 2tot h e127p ower microse con ds=5.3ti mes1 0t othe2 1powe r ye ar s 5.3  1017 years5.3ti mes1 0t othe1 7powe r ye ar s 168 Triple DES 2168  3.7  1050 2tot h e168p ower a pproximatelyeq uals3.7ti me s10tot h e50po wer 2167  s = 5.8  1033 years 2tot h e167p ower microse con ds=5.8ti mes1 0t othe3powe r ye ar s 5.8  1029 years5.8ti mes1 0t othe2 9powe r ye ar s 192 AES 2192  6.3  1057 2tot h e192p ower a pproximatelyeq uals6.3ti me s10tot h e57po wer 2191  s = 9.8  10 40 years 2tot h e191p ower microse con ds=9.8ti mes1 0t othe4 0powe r ye ar s 9.8  1036 years9.8ti mes1 0t othe3 6powe r ye ar s 256 AES 2256  1.2  1077 2tot h e256p ower a pproximatelyeq uals1.2ti me s10tot h e77po wer 2255  s = 1.8  1060 years 2tot h e255p ower microse con ds=1.8ti mes1 0t othe6 0powe r ye ar s 1.8  1056 years1.8ti mes1 0t othe5 6powe r ye ar s Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Triple DES (3DES) Repeats basic DES algorithm three times using either two or three unique keys First standardized for use in financial applications in ANSI standard X9.17 in 1985 Attractions: – 168-bit key length overcomes the vulnerability to brute-force attack of DES – Underlying encryption algorithm is the same as in DES Drawbacks: – Algorithm is sluggish in software – Uses a 64-bit block size Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Advanced Encryption Standard (AES) Needed a replacement for 3DES – 3DES was not reasonable for long term use NIST called for proposals for a new AES in 1997 – Should have a security strength equal to or better than 3DES – Significantly improved efficiency – Symmetric block cipher – 128 bit data and 128/192/256 bit keys Selected Rijndael in November 2001 – Published as FIPS 197 Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Practical Security Issues Typically symmetric encryption is applied to a unit of data larger than a single 64-bit or 128-bit block Electronic codebook (ECB) mode is the simplest approach to multiple-block encryption – Each block of plaintext is encrypted using the same key – Cryptanalysts may be able to exploit regularities in the plaintext Modes of operation – Alternative techniques developed to increase the security of symmetric block encryption for large sequences – Overcomes the weaknesses of ECB Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 2.2 Types of Symmetric Encryption Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Block & Stream Ciphers Block Cipher – Processes the input one block of elements at a time – Produces an output block for each input block – Can reuse keys – More common Stream Cipher – Processes the input elements continuously – Produces output one element at a time – Primary advantage is that they are almost always faster and use far less code – Encrypts plaintext one byte at a time – Pseudorandom stream is one that is unpredictable without knowledge of the input key Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Message Authentication Protects against active attacks Verifies received message is authentic – Contents have not been altered – From authentic source – Timely and in correct sequence Can use conventional encryption – Only sender and receiver share a key Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Message Authentication Without Confidentiality Message encryption by itself does not provide a secure form of authentication It is possible to combine authentication and confidentiality in a single algorithm by encrypting a message plus its authentication tag Typically message authentication is provided as a separate function from message encryption Situations in which message authentication without confidentiality may be preferable include: – There are a number of applications in which the same message is broadcast to a number of destinations – An exchange in which one side has a heavy load and cannot afford the time to decrypt all incoming messages – Authentication of a computer program in plaintext is an attractive service Thus, there is a place for both authentication and encryption in meeting security requirements Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 2.3 Message Authentication Using a Message Authentication Code (MAC) Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 2.5 Message Authentication Using a One-Way Hash Function Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved To Be Useful for Message Authentication, a Hash Function H Must Have the Following Properties: Can be applied to a block of data of any size Produces a fixed-length output H( x ) is relatively easy to compute for any given x One-way or pre-image resistant – Computationally infeasible to find x such that H( x ) = h Computationally infeasible to find y  x such that H( y ) = H( x ) Collision resistant or strong collision resistance – Computationally infeasible to find any pair (x, y) such that H( x ) = H( y ) Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Security of Hash Functions There are two approaches to attacking a secure hash function: – Cryptanalysis ▪ Exploit logical weaknesses in the algorithm – Brute-force attack ▪ Strength of hash function depends solely on the length of the hash code produced by the algorithm SHA most widely used hash algorithm Additional secure hash function applications: – Passwords ▪ Hash of a password is stored by an operating system – Intrusion detection ▪ Store H(F) for each file on a system and secure the hash values Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Public-Key Encryption Structure Publicly proposed by Diffie and Hellman in 1976 Based on mathematical functions Asymmetric – Uses two separate keys – Public key and private key – Public key is made public for others to use Some form of protocol is needed for distribution Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 2.6 Public-Key Cryptography (1 of 2) Plaintext – Readable message or data that is fed into the algorithm as input Encryption algorithm – Performs transformations on the plaintext Public and private key – Pair of keys, one for encryption, one for decryption Ciphertext – Scrambled message produced as output Decryption key – Produces the original plaintext Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 2.6 Public-Key Cryptography (2 of 2) User encrypts data using his or her own private key Anyone who knows the corresponding public key will be able to decrypt the message Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 2.3 Applications for Public-Key Cryptosystems Symmetric Key Encryption of Algorithm Digital Signature Distribution Secret Keys RSA Yes Yes Yes Diffie–Hellman No Yes No DSS Yes No No Elliptic Curve Yes Yes Yes Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Requirements for Public-Key Cryptosystems Computationally easy to create key pairs Useful if either key Computationally easy can be used for each for sender knowing role public key to encrypt messages Computationally easy Computationally for receiver knowing infeasible for opponent private key to decrypt to otherwise recover ciphertext original message Computationally infeasible for opponent to determine private key from public key Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Asymmetric Encryption Algorithms (1 of 2) RSA (Rivest, Shamir, Adleman) – Developed in 1977 – Most widely accepted and implemented approach to public-key encryption – Block cipher in which the plaintext and ciphertext are integers between 0 and n − 1 for some n. Diffie-Hellman key exchange algorithm – Enables two users to securely reach agreement about a shared secret that can be used as a secret key for subsequent symmetric encryption of messages – Limited to the exchange of the keys Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Asymmetric Encryption Algorithms (2 of 2) Digital Signature Standard (DSS) – Provides only a digital signature function with SHA-1 – Cannot be used for encryption or key exchange Elliptic curve cryptography (ECC) – Security like RSA, but with much smaller keys Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Digital Signatures NIST FIPS PUB 186-4 defines a digital signature as: – ”The result of a cryptographic transformation of data that, when properly implemented, provides a mechanism for verifying origin authentication, data integrity and signatory non-repudiation.” Thus, a digital signature is a data-dependent bit pattern, generated by an agent as a function of a file, message, or other form of data block FIPS 186-4 specifies the use of one of three digital signature algorithms: – Digital Signature Algorithm (DSA) – RSA Digital Signature Algorithm – Elliptic Curve Digital Signature Algorithm (ECDSA) Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 2.7 Simplified Depiction of Essential Elements of Digital Signature Process Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 2.8 Public-Key Certificate Use Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 2.9 Digital Envelopes Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Random Numbers Uses include generation of: Keys for public-key algorithms Stream key for symmetric stream cipher Symmetric key for use as a temporary session key or in creating a digital envelope Handshaking to prevent replay attacks Session key Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Random Number Requirements Randomness Unpredictability Criteria: Each number is statistically – Uniform distribution independent of other numbers in the sequence ▪ Frequency of occurrence of each of the numbers Opponent should not be should be approximately able to predict future the same elements of the sequence – Independence on the basis of earlier ▪ No one value in the elements sequence can be inferred from the others Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Random Versus Pseudorandom Cryptographic applications typically make use of algorithmic techniques for random number generation – Algorithms are deterministic and therefore produce sequences of numbers that are not statistically random Pseudorandom numbers are: – Sequences produced that satisfy statistical randomness tests – Likely to be predictable True random number generator (TRNG): – Uses a nondeterministic source to produce randomness – Most operate by measuring unpredictable natural processes ▪ e.g. radiation, gas discharge, leaky capacitors – Increasingly provided on modern processors Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Practical Application: Encryption of Stored Data Common to encrypt transmitted data Much less common for stored data – There is often little protection beyond domain authentication and operating system access controls – Data are archived for indefinite periods – Even though erased, until disk sectors are reused data are recoverable Approaches to encrypt stored data: – Use a commercially available encryption package – Back-end appliance – Library based tape encryption – Background laptop/PC data encryption Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Summary (1 of 2) Confidentiality with symmetric encryption – Symmetric encryption – Symmetric block encryption algorithms – Stream ciphers Message authentication and hash functions – Authentication using symmetric encryption – Message authentication without message encryption – Secure hash functions – Other applications of hash functions Random and pseudorandom numbers – The use of random numbers – Random versus pseudorandom Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Summary (2 of 2) Public-key encryption – Structure – Applications for public-key cryptosystems – Requirements for public-key cryptography – Asymmetric encryption algorithms Digital signatures and key management – Digital signature – Public-key certificates – Symmetric key exchange using public-key encryption – Digital envelopes Practical Application: Encryption of Stored Data Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Copyright This work is protected by United States copyright laws and is provided solely for the use of instructors in teaching their courses and assessing student learning. Dissemination or sale of any part of this work (including on the World Wide Web) will destroy the integrity of the work and is not permitted. The work and materials from it should never be made available to students except by instructors using the accompanying text in their classes. All recipients of this work are expected to abide by these restrictions and to honor the intended pedagogical purposes and the needs of other instructors who rely on these materials. Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Computer Security: Principles and Practice Fourth Edition Chapter 3 User Authentication Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved NIST SP 800-63-3 (Digital Authentication Guideline, October 2016) Defines Digital User Authentication As: “The process of establishing confidence in user identities that are presented electronically to an information system.” Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 3.1 Identification and Authentication Security Requirements (NIST SP 800-171) (1 of 2) Basic Security Requirements: 1. Identify information system users, processes acting on behalf of users, or devices. 2. Authenticate (or verify) the identities of those users, processes, or devices, as a prerequisite to allowing access to organizational information systems. Derived Security Requirements: 3. Use multifactor authentication for local and network access to privileged accounts and for network access to non-privileged accounts. 4. Employ replay-resistant authentication mechanisms for network access to privileged and non-privileged accounts. Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 3.1 Identification and Authentication Security Requirements (NIST SP 800-171) (2 of 2) 5. Prevent reuse of identifiers for a defined period. 6. Disable identifiers after a defined period of inactivity. 7. Enforce a minimum password complexity and change of characters when new passwords are created. 8. Prohibit password reuse for a specified number of generations. 9. Allow temporary password use for system logons with an immediate change to a permanent password. 10. Store and transmit only cryptographically-protected passwords. 11. Obscure feedback of authentication information. Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 3.1 The NIST SP 800-63-3 E- Authentication Architectural Model Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved The Four Means of Authenticating User Identity Are Based On: Something the individual knows – Password, PIN, answers to prearranged questions Something the individual possesses (token) – Smartcard, electronic keycard, physical key Something the individual is (static biometrics) – Fingerprint, retina, face Something the individual does (dynamic biometrics) – Voice pattern, handwriting, typing rhythm Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 3.2 Multifactor Authentication Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Risk Assessment for User Authentication There are three separate concepts: – Assurance Level – Potential impact – Areas of risk Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Assurance Level (1 of 2) Describes an organization’s degree of certainty that a user has presented a credential that refers to his or her identity More specifically is defined as: – The degree of confidence in the vetting process used to establish the identity of the individual to whom the credential was issued – The degree of confidence that the individual who uses the credential is the individual to whom the credential was issued Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Assurance Level (2 of 2) Four levels of assurance – Level 1 ▪ Little or no confidence in the asserted identity's validity – Level 2 ▪ Some confidence in the asserted identity’s validity – Level 3 ▪ High confidence in the asserted identity's validity – Level 4 ▪ Very high confidence in the asserted identity’s validity Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Potential Impact FIPS 199 defines three levels of potential impact on organizations or individuals should there be a breach of security: – Low ▪ An authentication error could be expected to have a limited adverse effect on organizational operations, organizational assets, or individuals – Moderate ▪ An authentication error could be expected to have a serious adverse effect – High ▪ An authentication error could be expected to have a severe or catastrophic adverse effect Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 3.2 Maximum Potential Impacts for Each Assurance Level Assurance Assurance Assurance Assurance Potential Impact Categories for Level Impact Level Impact Level Impact Level Impact Authentication Errors Profiles 1 Profiles 2 Profiles 3 Profiles 4 Inconvenience, distress, or damage Low Mod Mod High to standing or reputation Financial loss or organization Low Mod Mod High liability Harm to organization programs or None Low Mod High interests Unauthorized release of sensitive None Low Mod High information Personal safety None None Low Mod/High Civil or criminal violations None Low Mod High Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Password-Based Authentication Widely used line of defense against intruders – User provides name/login and password – System compares password with the one stored for that specified login The user ID: – Determines that the user is authorized to access the system – Determines the user’s privileges – Is used in discretionary access control Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Password Vulnerabilities Offline dictionary attack Specific account attack Popular password attack Password guessing against single user Workstation hijacking Exploiting user mistakes Exploiting multiple password use Electronic monitoring Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 3.3 UNIX Password Scheme Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved UNIX Implementation Original scheme – Up to eight printable characters in length – 12-bit salt used to modify DES encryption into a one-way hash function – Zero value repeatedly encrypted 25 times – Output translated to 11 character sequence Now regarded as inadequate – Still often required for compatibility with existing account management software or multivendor environments Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Improved Implementations Much stronger hash/salt schemes available for Unix Recommended hash function is based on MD5 – Salt of up to 48-bits – Password length is unlimited – Produces 128-bit hash – Uses an inner loop with 1000 iterations to achieve slowdown OpenBSD uses Blowfish block cipher based hash algorithm called Bcrypt – Most secure version of Unix hash/salt scheme – Uses 128-bit salt to create 192-bit hash value Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Password Cracking Dictionary attacks – Develop a large dictionary of possible passwords and try each against the password file – Each password must be hashed using each salt value and then compared to stored hash values Rainbow table attacks – Pre-compute tables of hash values for all salts – A mammoth table of hash values – Can be countered by using a sufficiently large salt value and a sufficiently large hash length Password crackers exploit the fact that people choose easily guessable passwords – Shorter password lengths are also easier to crack John the Ripper – Open-source password cracker first developed in in 1996 – Uses a combination of brute-force and dictionary techniques Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Modern Approaches Complex password policy – Forcing users to pick stronger passwords However password-cracking techniques have also improved – The processing capacity available for password cracking has increased dramatically – The use of sophisticated algorithms to generate potential passwords – Studying examples and structures of actual passwords in use Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 3.4 The Percentage of Passwords Guessed After a Given Number of Guesses Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Password File Access Control Can block offline guessing attacks by denying access to encrypted passwords – Make available only to privileged users – Shadow password file Vulnerabilities – Weakness in the OS that allows access to the file – Accident with permissions making it readable – Users with same password on other systems – Access from backup media – Sniff passwords in network traffic Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Password Selection Strategies User education – Users can be told the importance of using hard to guess passwords and can be provided with guidelines for selecting strong passwords Computer generated passwords – Users have trouble remembering them Reactive password checking – System periodically runs its own password cracker to find guessable passwords Complex password policy – User is allowed to select their own password, however the system checks to see if the password is allowable, and if not, rejects it – Goal is to eliminate guessable passwords while allowing the user to select a password that is memorable Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Proactive Password Checking Rule enforcement – Specific rules that passwords must adhere to Password checker – Compile a large dictionary of passwords not to use Bloom filter – Used to build a table based on hash values – Check desired password against this table Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 3.5 Performance of Bloom Filter Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 3.3 Types of Cards Used as Tokens Card Type Defining Feature Example Embossed Raised characters only, on front Old credit card Magnetic stripe Magnetic bar on back, characters Bank card on front Memory Electronic memory inside Prepaid phone card Smart Electronic memory and processor Biometric ID card Contact inside Contactless Electrical contacts exposed on surface Radio antenna embedded inside Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Memory Cards Can store but do not process data The most common is the magnetic stripe card Can include an internal electronic memory Can be used alone for physical access – Hotel room – ATM Provides significantly greater security when combined with a password or PIN Drawbacks of memory cards include: – Requires a special reader – Loss of token – User dissatisfaction Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Smart Tokens Physical characteristics: – Include an embedded microprocessor – A smart token that looks like a bank card – Can look like calculators, keys, small portable objects User interface: – Manual interfaces include a keypad and display for human/token interaction Electronic interface – A smart card or other token requires an electronic interface to communicate with a compatible reader/writer – Contact and contactless interfaces Authentication protocol: – Classified into three categories: ▪ Static ▪ Dynamic password generator ▪ Challenge-response Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Smart Cards (1 of 2) Most important category of smart token – Has the appearance of a credit card – Has an electronic interface – May use any of the smart token protocols Contain: – An entire microprocessor ▪ Processor ▪ Memory ▪ I/O ports Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Smart Cards (2 of 2) Typically include three types of memory: – Read-only memory (ROM) ▪ Stores data that does not change during the card’s life – Electrically erasable programmable ROM (EEPROM) ▪ Holds application data and programs – Random access memory (RAM) ▪ Holds temporary data generated when applications are executed Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 3.6 Smart Card/Reader Exchange Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Electronic Identity Cards (eID) (1 of 2) Use of a smart card as a national identity card for citizens – Can serve the same purposes as other national ID cards, and similar cards such as a driver’s license, for access to government and commercial services – Can provide stronger proof of identity and can be used in a wider variety of applications – In effect, is a smart card that has been verified by the national government as valid and authentic Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Electronic Identity Cards (eID) (2 of 2) Most advanced deployment is the German card neuer Personalausweis – Has human-readable data printed on its surface ▪ Personal data ▪ Document number ▪ Card access number (CAN) ▪ Machine readable zone (MRZ) Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 3.4 Electronic Functions and Data for eID Cards (1 of 2) PACE Function Purpose Password Data Uses ePass Authorized offline CAN or MRZ Face image; two Offline biometric (mandatory) inspection systems fingerprint images identity verification read the data. (optional); MRZ data reserved for government access eID Online applications eID PIN Family and given Identification; age (activation read the data or names; artistic name verification; optional) access functions as and doctoral degree: community ID authorized. date and place of verification; restricted birth; address and identification community ID; (pseudonym); expiration date revocation query eID( a cti vati o noptiona l) Offline inspection CAN or MRZ Family and given Identification; age systems read the names; artistic name verification; data and update the and doctoral degree: community ID address and date and place of verification; restricted community ID. birth; address and identification community ID; (pseudonym); expiration date revocation query Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 3.4 Electronic Functions and Data for eID Cards (2 of 2) PACE Function Purpose Password Data Uses eSign A certification eID PIN Signature key; X.509 Electronic signature (certificate authority installs the certificate creation optional) signature certificate online. eSign( cert if cateoptiona l) Citizens make CAN Signature key; X.509 Electronic signature signature creation certificate creation electronic signature with eSign PIN. CAN = card access number MRZ = machine-readable zone PACE = password authenticated connection establishment PIN = personal identification number Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 3.7 User Authentication with eID Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Password Authenticated Connection Establishment (PACE) Ensures that the contactless RF chip in the eID card cannot be read without explicit access control For online applications, access is established by the user entering the 6-digit PIN (which should only be known to the holder of the card) For offline applications, either the MRZ printed on the back of the card or the six-digit card access number (CAN) printed on the front is used Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Biometric Authentication Attempts to authenticate an individual based on unique physical characteristics Based on pattern recognition Is technically complex and expensive when compared to passwords and tokens Physical characteristics used include: – Facial characteristics – Fingerprints – Hand geometry – Retinal pattern – Iris – Signature – Voice Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 3.8 Cost Versus Accuracy of Various Biometric Characteristics in User Authentication Schemes Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 3.9 A Generic Biometric System Enrollment creates an association between a user and the user’s biometric characteristics. Depending on the application, user authentication either involves verifying that a claimed user is the actual user or identifying an unknown user. Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 3.10 Profiles of a Biometric Characteristic of an Imposter and an Authorized Users In this depiction, the comparison between the presented feature and a reference feature is reduced to a single numeric value. If the input value (s) is greater than a preassigned threshold (t), a match is declared. Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 3.11 Idealized Biometric Measurement Operating Characteristic Curves (Log-Log Scale) Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 3.12 Actual Biometric Measurement Operating Characteristic Curves Reported in [MANS 01] To clarify differences among systems, a log-log scale is used. Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Remote User Authentication Authentication over a network, the Internet, or a communications link is more complex Additional security threats such as: – Eavesdropping, capturing a password, replaying an authentication sequence that has been observed Generally rely on some form of a challenge-response protocol to counter threats Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 3.13 Basic Challenge-Response Protocols for Remote User Authentication Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 3.5 Some Potential Attacks, Susceptible Authenticators, and Typical Defenses (1 of 2) Attacks Authenticators Examples Typical Defenses Client attack Password Guessing, exhaustive search Large entropy; limited attempts Cli e nt att a ck Token Exhaustive search Large entropy; limited attempts; theft of object requires presence Cli e nt att a ck Biometric False match Large entropy; limited attempts Host attack Password Plaintext theft, Hashing; large entropy; protection of dictionary/exhaustive search password database Hostat tac k Token Passcode theft Same as password; 1-time passcode Hostat tac k Biometric Template theft Capture device authentication; challenge response Eavesdroppi Password “Shoulder surfing” User diligence to keep secret; ng, theft, and administrator diligence to quickly copying revoke compromised passwords; multifactor authentication Eav esd r opp i ng , th ef t, a ndcopy i ng Token Theft, counterfeiting hardware Multifactor authentication; tamper resistant/evident token Eav esd r opp i ng , th ef t, a ndcopy i ng Biometric Copying (spoofing) biometric Copy detection at capture device and capture device authentication Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 3.5 Some Potential Attacks, Susceptible Authenticators, and Typical Defenses (2 of 2) Attacks Authenticators Examples Typical Defenses Replay Password Replay stolen password Challenge-response protocol response Replay Token Replay stolen passcode Challenge-response protocol; 1-time response passcode Replay Biometric Replay stolen biometric Copy detection at capture device and template response capture device authentication via challenge-response protocol Trojan horse Password, token, Installation of rogue client or Authentication of client or capture biometric capture device device within trusted security perimeter Denial of Password, token, Lockout by multiple failed Multifactor with token service biometric authentications Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Authentication Security Issues Eavesdropping: Adversary attempts to learn the password by some sort of attack that involves the physical proximity of user and adversary Host Attacks: Directed at the user file at the host where passwords, token passcodes, or biometric templates are stored Replay: Adversary repeats a previously captured user response Client Attacks: Adversary attempts to achieve user authentication without access to the remote host or the intervening communications path Trojan Horse: An application or physical device masquerades as an authentic application or device for the purpose of capturing a user password, passcode, or biometric Denial-of-Service: Attempts to disable a user authentication service by flooding the service with numerous authentication attempts Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 3.14 General Iris Scan Site Architecture for UAE System Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 3.15 ATM Architectures Most small to mid-sized issuers of debit cards contract processors to provide core data processing and electronic funds transfer (EFT) services. The bank’s ATM machine may link directly to the processor or to the bank. Case Study: ATM Security Problems Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Summary (1 of 2) Digital user authentication principles – A model for digital user authentication – Means of authentication – Risk assessment for user authentication Password-based authentication – The vulnerability of passwords – The use of hashed passwords – Password cracking of user-chosen passwords – Password file access control – Password selection strategies Token-based authentication – Memory cards – Smart cards – Electronic identity cards Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Summary (2 of 2) Biometric authentication – Physical characteristics used in biometric applications – Operation of a biometric authentication system – Biometric accuracy Remote user authentication – Password protocol – Token protocol – Static biometric protocol – Dynamic biometric protocol Security issues for user authentication Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Copyright This work is protected by United States copyright laws and is provided solely for the use of instructors in teaching their courses and assessing student learning. Dissemination or sale of any part of this work (including on the World Wide Web) will destroy the integrity of the work and is not permitted. The work and materials from it should never be made available to students except by instructors using the accompanying text in their classes. All recipients of this work are expected to abide by these restrictions and to honor the intended pedagogical purposes and the needs of other instructors who rely on these materials. Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Computer Security: Principles and Practice Fourth Edition Chapter 4 Access Control Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Access Control Definitions (1 of 2) NISTIR 7298 defines access control as: “the process of granting or denying specific requests to: (1) obtain and use information and related information processing services; and (2) enter specific physical facilities” Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Access Control Definitions (2 of 2) RFC 4949 defines access control as: “a process by which use of system resources is regulated according to a security policy and is permitted only by authorized entities (users, programs, processes, or other systems) according to that policy” Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 4.1 Access Control Security Requirements (SP 800-171) (1 of 4) Basic Security Requirements 1. Limit information system access to authorized users, processes acting on behalf of authorized users, or devices (including other information systems). 2. Limit information system access to the types of transactions and functions that authorized users are permitted to execute. Derived Security Requirements 3. Control the flow of CUI in accordance with approved authorizations. 4. Separate the duties of individuals to reduce the risk of malevolent activity without collusion. Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 4.1 Access Control Security Requirements (SP 800-171) (2 of 4) 5. Employ the principle of least privilege, including for specific security functions and privileged accounts. 6. Use non-privileged accounts or roles when accessing nonsecurity functions. 7. Prevent non-privileged users from executing privileged functions and audit the execution of such functions. 8. Limit unsuccessful logon attempts. 9. Provide privacy and security notices consistent with applicable C UI rules. Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 4.1 Access Control Security Requirements (SP 800-171) (3 of 4) 10. Use session lock with pattern-hiding displays to prevent access and viewing of data after period of inactivity. 11. Terminate (automatically) a user session after a defined condition. 12. Monitor and control remote access sessions. 13. Employ cryptographic mechanisms to protect the confidentiality of remote access sessions. 14. Route remote access via managed access control points. 15. Authorize remote execution of privileged commands and remote access to security-relevant information. 16. Authorize wireless access prior to allowing such connections. Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 4.1 Access Control Security Requirements (SP 800-171) (4 of 4) 17. Protect wireless access using authentication and encryption. 18. Control connection of mobile devices. 19. Encrypt CUI on mobile devices. 20. Verify and control/limit connections to and use of external information systems. 21. Limit use of organizational portable storage devices on external information systems. 22. Control CUI posted or processed on publicly accessible information systems. CUI = controlled unclassified information Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Access Control Principles In a broad sense, all of computer security is concerned with access control RFC 4949 defines computer security as: “measures that implement and assure security services in a computer system, particularly those that assure access control service” Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 4.1 Relationship Among Access Control and Other Security Functions Source: Based on [SAND94]. Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved  Access Control Policies Discretionary access control (DAC) Role-based access control (RBAC) – Controls access based on the – Controls access based on the identity of the requestor and roles that users have within the on access rules system and on rules stating what (authorizations) stating what accesses are allowed to users in requestors are (or are not) given roles allowed to do Attribute-based access control (ABAC) Mandatory access control (MAC) – Controls access based on – Controls access based on attributes of the user, the comparing security labels with resource to be accessed, and security clearances current environmental conditions Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Subjects, Objects, and Access Rights Subject Object Access right – An entity – A resource – Describes the capable of to which way in which a accessing access is subject may objects controlled access an object – Three classes – Entity used – Could include: ▪ Owner to contain ▪ Read and/or ▪ Group ▪ Write receive ▪ World information ▪ Execute ▪ Delete ▪ Create ▪ Search Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Discretionary Access Control (DAC) Scheme in which an entity may be granted access rights that permit the entity, by its own violation, to enable another entity to access some resource Often provided using an access matrix – One dimension consists of identified subjects that may attempt data access to the resources – The other dimension lists the objects that may be accessed Each entry in the matrix indicates the access rights of a particular subject for a particular object Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 4.2 Example of Access Control Structures (1 of 2) Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 4.2 Example of Access Control Structures (2 of 2) Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 4.2 Authorization Table for Files in Figure 4.2 Subject Access Mode Object Subject Access Mode Object A Own File 1 C Read File 1 A Read File 1 C Write File 1 A Write File 1 C Read File 2 A Own File 3 C Own File 4 A Read File 3 C Read File 4 A Write File 3 C Write File 4 B Read File 1 B Own File 2 B Read File 2 B Write File 2 B Write File 3 B Read File 4 Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 4.3 Extended Access Control Matrix Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Figure 4.4 An Organization of the Access Control Function Copyright © 2018, 2015, 2012 Pearson Education, Inc. All Rights Reserved Table 4.3 Access Control System Commands (1 of 2) Rule Command (by S0 ) left par enthesis by S sub 0 r ight par enthesis Authorization Operation  *  “ *” in A[S0 , X ]  * Transfer, a 2 by 1 matrix with column entries as follows. Column 1. alpha aster