Domain 3: Security Architecture and Engineering

Question 1

System architecture

Answer 1

System architecture is a formal tool used to design computer systems in a manner that ensures each of the stakeholders’ concerns is addressed.

Question 2

What makes up a system architecture?

Answer 2

A system’s architecture is made up of different views, which are representations of system components and their relationships.

Each view addresses a different aspect of the system (functionality, performance, interoperability, security).

Question 3

ISO/IEC/IEEE 42010

Answer 3

ISO/IEC/IEEE 42010 is an international standard that outlines how system architecture frameworks and their description languages are to be used.

Question 4

What are the components of a CPU?

Answer 4

A CPU contains a control unit, which controls the timing of the execution of instructions and data, and an ALU, which performs mathematical functions and logical operations.

Question 5

What do memory managers do?

Answer 5

Memory managers use various memory protection mechanisms:

• Base (beginning) and limit (ending) addressing
• Address space layout randomization
• Data execution prevention.

Question 6

What kind of addressing do operating systems use?

Answer 6

Operating systems use the following memory schemes:

• Absolute (hardware addresses)
• Logical (indexed addresses)
• Relative address (indexed addresses, including offsets)

Question 7

How do you address buffer overflow vulnerabilities?

Answer 7

Buffer overflow vulnerabilities are best addressed by implementing bounds checking.

Question 8

Garbage collector

Answer 8

A garbage collector is a software tool that releases unused memory segments to help prevent “memory starvation.”

Question 9

Why are there different processor families?

Answer 9

Different processor families work within different microarchitectures to execute specific instruction sets.

Question 10

Why were early operating systems considered “monolithic”?

Answer 10

Early operating systems were considered “monolithic” because all of the code worked within one layer and ran in kernel mode, and components communicated in an ad hoc manner.

Question 11

Operating system architectures

Answer 11

Operating systems can work within the following architectures:

• Monolithic kernel
• Layered
• Microkernel
• Hybrid kernel.

Question 12

Mode transition

Answer 12

Mode transition is when a CPU has to switch from executing one process’s instructions running in user mode to another process’s instructions running in kernel mode.

Question 13

Ringed architecture

Answer 13

CPUs provide a ringed architecture, which operating systems run within. The more trusted processes run in the lower-numbered rings and have access to all or most of the system resources. Nontrusted processes run in higher-numbered rings and have access to a smaller amount of resources.

Question 14

Processing modes for operating systems

Answer 14

Operating system processes are executed in privileged mode (also called kernel or supervisor mode), and applications are executed in user mode, also known as “problem state.”

Question 15

Virtual memory

Answer 15

Virtual memory combines RAM and secondary storage so the system seems to have a larger bank of memory.

Question 16

Security mechanism complexity

Answer 16

The more complex a security mechanism is, the less amount of assurance it can usually provide.

Question 17

Trusted Computing Base (TCB)

Answer 17

The trusted computing base (TCB) is a collection of system components that enforces the security policy directly and protects the system. These components are within the security perimeter.

Question 18

TCB components

Answer 18

Components that make up the TCB are

• Hardware
• Software
• Firmware

that provide some type of security protection.

Question 19

Security perimeter

Answer 19

A security perimeter is an imaginary boundary that has trusted components within it (those that make up the TCB) and untrusted components outside it.

Question 20

Reference Monitor

Answer 20

The reference monitor concept is an abstract machine that ensures all subjects have the necessary access rights before accessing objects. Therefore, it mediates all access to objects by subjects.

Question 21

Security kernel

Answer 21

The security kernel is the mechanism that actually enforces the rules of the reference monitor concept.

Question 22

Security kernel requirements

Answer 22

The security kernel must:

• Isolate processes carrying out the reference monitor concept
• Be tamperproof
• Be invoked for each access attempt
• Be small enough to be properly tested

Question 23

How are processes isolated?

Answer 23

Processes need to be isolated, which can be done through:

• Segmented memory addressing
• Encapsulation of objects
• Time multiplexing of shared resources
• Naming distinctions
• Virtual mapping.

Question 24

What determines a system’s level of security?

Answer 24

The level of security a system provides depends upon how well it enforces its security policy.

Question 25

Closed vs. open systems

Answer 25

A closed system is often proprietary to the manufacturer or vendor, whereas an open system allows for more interoperability.

Question 26

Common Criteria

Answer 26

The Common Criteria was developed to provide globally recognized evaluation criteria.

Question 27

How does the Common Criteria function?

Answer 27

The Common Criteria uses:

• Protection profiles
• Security targets
• Ratings (EAL1 to EAL7)

to provide assurance ratings for targets of evaluation (TOEs).

Question 28

Certification vs. Accreditation

Answer 28

Certification is the technical evaluation of a system or product and its security components.

Accreditation is management’s formal approval and acceptance of the security provided by a system.

Question 29

ISO/IEC 15408

Answer 29

ISO/IEC 15408 is the international standard that is used as the basis for the evaluation of security properties of products under the CC framework.

Question 30

Process isolation

Answer 30

Process isolation ensures that multiple processes can run concurrently and the processes will not interfere with each other or affect each other’s memory segments.

Question 31

TOC/TOU

Answer 31

TOC/TOU stands for time-of-check/time-of-use. This is a class of asynchronous attacks.

Question 32

Distributed system

Answer 32

A distributed system is a system in which multiple computing nodes, interconnected by a network, exchange information for the accomplishment of collective tasks.

Question 33

Cloud computing

Answer 33

Cloud computing is the use of shared, remote computing devices for the purpose of providing improved efficiencies, performance, reliability, scalability, and security.

Question 34

Software as a Service (SaaS)

Answer 34

Software as a Service (SaaS) is a cloud computing model that provides users access to a specific application that executes on the service provider’s environment.

Question 35

Platform as a Service (PaaS)

Answer 35

Platform as a Service (PaaS) is a cloud computing model that provides users access to a computing platform that is typically built on a server operating system, but not the virtual machine on which it runs.

Question 36

Infrastructure as a Service (IaaS)

Answer 36

Infrastructure as a Service (IaaS) is a cloud computing model that provides users unfettered access to a cloud device, such as an instance of a server, which includes both the operating system and the virtual machine on which it runs.

Question 37

Parallel computing

Answer 37

Parallel computing is the simultaneous use of multiple computers to solve a specific task by dividing it among the available computers.

Question 38

Cyber-physical system

Answer 38

Any system in which computers and physical devices collaborate via the exchange of inputs and outputs to accomplish a task or objective is a cyber-physical system.

Question 39

Cryptography

Answer 39

Cryptography is the science of protecting information by encoding it into an unreadable format.

Question 40

Most famous rotor encryption machine

Answer 40

The most famous rotor encryption machine is the Enigma used by the Germans in World War II.

Question 41

Plaintext/Ciphertext

Answer 41

A readable message is in a form called plaintext, and once it is encrypted, it is in a form called ciphertext.

Question 42

Cryptographic algorithm

Answer 42

Cryptographic algorithms are the mathematical rules that dictate the functions of enciphering and deciphering.

Question 43

Cryptanalysis

Answer 43

Cryptanalysis is the study of breaking cryptosystems.

Question 44

Nonrepudiation

Answer 44

Nonrepudiation is a service that ensures the sender cannot later falsely deny sending a message.

Question 45

Key clustering

Answer 45

Key clustering is an instance in which two different keys generate the same ciphertext from the same plaintext.

Question 46

Keyspace

Answer 46

The range of possible keys is referred to as the keyspace. A larger keyspace and the full use of the keyspace allow for more random keys to be created. This provides more protection.

Question 47

Symmetric encryption mechanisms

Answer 47

The two basic types of encryption mechanisms used in symmetric ciphers are substitution and transposition.

Substitution ciphers change a character (or bit) out for another, while transposition ciphers scramble the characters (or bits).

Question 48

Polyalphabetic cipher

Answer 48

A polyalphabetic cipher uses more than one alphabet to defeat frequency analysis.

Question 49

Steganography

Answer 49

Steganography is a method of hiding data within another media type, such as a graphic, WAV file, or document. This method is used to hide the existence of the data.

Question 50

Key

Answer 50

A key is a random string of bits inserted into an encryption algorithm.

The result determines what encryption functions will be carried out on a message and in what order. Many algorithms are publicly known, so the secret part of the process is the key. The key provides the necessary randomization to encryption.

Question 51

Symmetric key algorithms

Answer 51

In symmetric key algorithms, the sender and receiver use the same key for encryption and decryption purposes.

Question 52

Asymmetric key algorithms

Answer 52

In asymmetric key algorithms, the sender and receiver use different keys for encryption and decryption purposes.

Question 53

Symmetric key advantages and disadvantages

Answer 53

Symmetric key processes provide barriers of secure key distribution and scalability.

However, symmetric key algorithms perform much faster than asymmetric key algorithms.

Symmetric key algorithms can provide confidentiality, but not authentication or nonrepudiation.

Question 54

Symmetric key algorithm examples

Answer 54

Examples of symmetric key algorithms include

• DES
• 3DES
• Blowfish
• IDEA
• RC4
• RC5
• RC6
• AES.

Question 55

Symmetric vs. Asymmetric

Answer 55

Asymmetric algorithms are used to encrypt keys, and symmetric algorithms are used to encrypt bulk data.

Question 56

Asymmetric key advantages and disadvantages

Answer 56

Asymmetric key algorithms are much slower than symmetric key algorithms, but can provide authentication and nonrepudiation services.

Question 57

Asymmetric key algorithm examples

Answer 57

Examples of asymmetric key algorithms include:

• RSA
• ECC
• Diffie-Hellman
• El Gamal
• Knapsack
• DSA.

Question 58

Symmetric key algorithm types

Answer 58

Two main types of symmetric algorithms are stream ciphers and block ciphers.

Stream ciphers use a keystream generator and encrypt a message one bit at a time.

A block cipher divides the message into groups of bits and encrypts them.

Question 59

Data Encryption Standard (DES)

Answer 59

Data Encryption Standard (DES) is a block cipher that divides a message into 64-bit blocks and employs S-box-type functions on them.

Question 60

Triple-DES (3DES)

Answer 60

Because technology has allowed the DES keyspace to be successfully broken, Triple-DES (3DES) was developed to be used instead. 3DES uses 48 rounds of computation and up to three different keys.

Question 61

International Data Encryption Algorithm (IDEA)

Answer 61

International Data Encryption Algorithm (IDEA) is a symmetric block cipher with a key of 128 bits.

Question 62

RSA

Answer 62

RSA is an asymmetric algorithm developed by Rivest, Shamir, and Adleman and is the de facto standard for digital signatures.

Question 63

Elliptic curve cryptosystems (ECCs)

Answer 63

Elliptic curve cryptosystems (ECCs) are used as asymmetric algorithms and can provide:

• Digital signature
• Secure key distribution
• Encryption functionality

They use fewer resources, which makes them better for wireless device and cell phone encryption use.

Question 64

Hybrid system

Answer 64

When symmetric and asymmetric key algorithms are used together, this is called a hybrid system. The asymmetric algorithm encrypts the symmetric key, and the symmetric key encrypts the data.

Question 65

Session key

Answer 65

A session key is a symmetric key used by the sender and receiver of messages for encryption and decryption purposes.

The session key is only good while that communication session is active and then it is destroyed.

Question 66

Public key infrastructure (PKI)

Answer 66

A public key infrastructure (PKI) is a framework of programs, procedures, communication protocols, and public key cryptography that enables a diverse group of individuals to communicate securely.

Question 67

Certificate authority (CA)

Answer 67

A certificate authority (CA) is a trusted third party that generates and maintains user certificates, which hold their public keys.

Question 68

How does a CA handle revoked certificates?

Answer 68

The CA uses a certification revocation list (CRL) to keep track of revoked certificates.

Question 69

Certificate

Answer 69

A certificate is the mechanism the CA uses to associate a public key to a person’s identity.

Question 70

Registration authority (RA)

Answer 70

A registration authority (RA) validates the user’s identity and then sends the request for a certificate to the CA. The RA cannot generate certificates.

Question 71

One-way function

Answer 71

A one-way function is a mathematical function that is easier to compute in one direction than in the opposite direction.

Question 72

What is RSA based upon?

Answer 72

RSA is based on a one-way function that factors large numbers into prime numbers.

Only the private key knows how to use the trapdoor and how to decrypt messages that were encrypted with the corresponding public key.

Question 73

What does hashing provide?

Answer 73

Hashing algorithms provide data integrity only.

Question 74

Hashing algorithm process

Answer 74

When a hash algorithm is applied to a message, it produces a message digest, and this value is signed with a private key to produce a digital signature.

Question 75

Hashing algorithm examples

Answer 75

Some examples of hashing algorithms include:

• SHA-1
• SHA-2
• SHA-3
• MD4
• MD5

Question 76

SHA

Answer 76

SHA produces a 160-bit hash value and is used in DSS.

Question 77

Birthday attack

Answer 77

A birthday attack is an attack on hashing functions through brute force. The attacker tries to create two messages with the same hashing value.

Question 78

One-time pad

Answer 78

A one-time pad uses a pad with random values that are XORed against the message to produce ciphertext.

The pad is at least as long as the message itself and is used once and then discarded.

Question 79

Digital signature

Answer 79

A digital signature is the result of a user signing a hash value with a private key. It provides authentication, data integrity, and nonrepudiation.

The act of signing is the actual encryption of the value with the private key.

Question 80

Digital signature algorithm examples

Answer 80

Examples of algorithms used for digital signatures include:

• RSA
• El Gamal
• ECDSA
• DSA

Question 81

Key management

Answer 81

Key management is one of the most challenging pieces of cryptography. It pertains to:

• Creating
• Maintaining
• Distributing
• Destroying cryptographic keys

Question 82

Crime Prevention Through Environmental Design (CPTED)

Answer 82

Crime Prevention Through Environmental Design (CPTED) combines the physical environment and sociology issues that surround it to reduce crime rates and the fear of crime.

CPTED provides three main strategies, which are:

• Natural access control
• Natural surveillance
• Natural territorial reinforcement

Question 83

How do you determine the physical security budget?

Answer 83

The value of property within the facility and the value of the facility itself need to be ascertained to determine the proper budget for physical security so that security controls are cost effective.

Question 84

Site selection criteria

Answer 84

When looking at locations for a facility, consider:

• Local crime
• Natural disaster possibilities
• Distance to hospitals, police and fire stations, airports, and railroads.

Question 85

Exterior fencing

Answer 85

Exterior fencing can be costly and unsightly, but can provide crowd control and help control access to the facility.

Question 86

Interior partitions

Answer 86

If interior partitions do not go all the way up to the true ceiling, an intruder can remove a ceiling tile and climb over the partition into a critical portion of the facility.

Question 87

Power sources

Answer 87

The primary power source is what is used in day-to-day operations, and the alternative power source is a backup in case the primary source fails.

Question 88

Smoke detector regulation

Answer 88

Smoke detectors should be located on and above suspended ceilings, below raised floors, and in air ducts to provide maximum fire detection.

Question 89

How do you suppress fire?

Answer 89

A fire needs:

• High temperatures
• Oxygen
• Fuel

To suppress it, one or more of those items needs to be reduced or eliminated.

Question 90

Gas fire suppression

Answer 90

Gases like FM-200 and other halon substitutes interfere with the chemical reaction of a fire.

Question 91

Fire extinguisher regulation

Answer 91

Portable fire extinguishers should be located within 50 feet of electrical equipment and should be inspected quarterly.

Question 92

CO2 fire suppression

Answer 92

CO2 is a colorless, odorless, and potentially lethal substance because it removes the oxygen from the air in order to suppress fires.

Question 93

Window types

Answer 93

Window types that should be understood are:

• Standard
• Tempered
• Acrylic
• Wired
• Laminated

Question 94

Describe process isolation.

Answer 94

Process isolation is a technique designed to control the interaction between different executing processes within a computer.

Process isolation is a critical component of the security model of a computer operating system. It ensures that processes do not conflict with one another, communicate in an insecure manner, or negatively affect each other.

Question 95

What is a reference monitor within an operating system model?

Answer 95

A reference monitor is an abstract machine that mediates all access subjects have to objects.

This both ensures that the subjects have the necessary access rights, and to protect the objects from unauthorized access and destructive modification.

Question 96

Cryptosystems provide various services within the information security world. Name these five services.

Answer 96

• Confidentiality
• Integrity
• Authentication
• Authorization
• Nonrepudiation

Cryptoservices can provide the following services:

• Confidentiality to render the information unintelligible except to authorized entities.
• Integrity to ensure that data has not been altered in an unauthorized manner, because it was created, transmitted, and stored properly.
• Authentication to verify the identity of the user or system that created and/or sent the information.
• Authorization, which, upon proving someone’s identity, provides an individual with the key or password that enables access to some resource.
• Nonrepudiation, which ensures that the sender cannot deny sending the message

Question 97

What is the difference between public key cryptography and public key infrastructure?

Answer 97

Public key cryptography is the use of an asymmetric algorithm.

Public Key Infrastructure (PKI) is not an algorithm, a protocol, or an application; it is the implementation of the requirements for creating and distributing digital certificates, a common application of public key cryptography.

Public key cryptography is another name for asymmetric cryptography. Examples of asymmetric algorithms are:

• RSA
• Elliptic curve cryptosystem (ECC)
• Diffie-Hellman
• El Gamal
• LUC
• Knapsack

These algorithms create public/private key pairs, perform key exchange or agreement, and generate and verify digital signatures. Public key infrastructure (PKI) is an arrangement that simplifies the use of public key cryptography.

Question 98

Describe the ring architecture in operating systems and computer processors.

Answer 98

A ring architecture is a hierarchical model in which concentric rings provide strict boundaries for what processes will work and which operations can be executed within them.

Operating systems vary in the number of protection rings they use, but for all, the numbers increase and trust decreases as you move toward the outer bounds of the model.

Processes in the innermost rings are the most privileged or trusted and allow the most direct access with the central processor or hardware. These exist in a privileged or supervisor mode.

Processes in the outermost rings are the least privileged and allow the least direct access to the central processor or hardware. These processes execute in user mode.

Question 99

In a client-server SSL connection, which party creates the session key?

Answer 99

The client.

After a server authenticates to a client, when setting up an SSL connection, the client creates a session key that will be used by both the client and the server for bulk encryption. The client encrypts the session key with the server’s public key and sends it. Only the server can decrypt it, because only the server is supposed to have the corresponding private key.

Question 100

What asymmetric algorithm would be ideal to employ within cell phones or PDAs?

Answer 100

ECC (Elliptic Curve Cryptosystem)

ECC provides services similar to the RSA algorithm, but requires much less processing power. Thus, it is an ideal choice for cell phone and small wireless electronic devices.

ECC’s mathematics are much more simple compared to other asymmetric algorithms, thus it uses less resources. It is being used more and more in devices with a smaller amount of processing resources.

Question 101

Describe the scalar and superscalar architecture processor models.

Answer 101

• Scalar processor: A single processor that executes one instruction at a time. Typically operates on one or two data items at a time.
• Superscalar processor: A single processor that enables concurrent execution of multiple instructions. Typically operates on more data items simultaneously.

Question 102

Describe the Brewer-Nash model.

Answer 102

The Brewer-Nash model allows for dynamically changing access controls that protect against conflicts of interest. The Brewer-Nash model is also known as the Chinese wall model.

The Brewer-Nash model is another information flow model. No information can flow between subjects and objects in a way that would result in a conflict of interest. The model states that a subject can write to an object if, and only if, the subject cannot read another object that is in a different dataset.

Question 103

What is the common use of the Diffie-Hellman asymmetric algorithm?

Answer 103

The distribution of symmetric keys

The Diffie-Hellman algorithm enables two systems to receive a symmetric key securely without requiring a previous relationship or prior arrangements.

The algorithm enables for key distribution, but does not provide encryption or digital signature functionality. The algorithm is based on the difficulty of calculating discrete logarithms in a finite field. The Diffie-Hellman algorithm is vulnerable to a man-in-the-middle attack because no authentication occurs before public keys are exchanged.

Question 104

List at least five symmetric algorithms.

Answer 104

• Data Encryption Standard (DES)
• 3DES (Triple DES)
• Blowfish
• Twofish
• IDEA (International Data Encryption Algorithm)
• RC4
• RC5
• RC6
• AES
• SAFER
• Serpent

Question 105

What is secondary storage?

Answer 105

Secondary storage consists of various nonvolatile memory storage media, such as:

• Hard drives
• Jump drives
• CD-ROMs

When RAM utilizes secondary storage to extend memory capacity beyond what the volatile memory can hold, it is called virtual memory.

Question 106

What type of ancient encryption method utilized paper wrapped around a wooden rod?

Answer 106

The Scytale cipher

The Scytale cipher was employed by the Spartans in 400 B.C. and consisted of a type of paper wrapped around a wooden rod. The message to be encrypted was written lengthwise down the paper. The rod was then discarded and the paper was delivered to the intended recipient who would need to get a rod of the same diameter, rewind the paper around the new rod, and read the message.

For people intercepting the paper and attempting to read the message without the proper rod, the letters would not match up; thus, it was not an understandable message.

Question 107

What is the most common attack against simple substitution and transposition ciphers?

Answer 107

Frequency analysis

In every language, some letters are used more often than others. For instance, in the English language, the most commonly used letter is E. An attacker would look for the most frequently repeated pattern of the bits that make up E. It is the frequency in a specific vocabulary that allows attackers to identify frequencies in ciphertext.

Question 108

What is the most popular asymmetric or public key algorithm?

Answer 108

RSA

RSA is a worldwide de facto standard and can be used for digital signatures, key exchange, and encryption.

The security of this algorithm comes from the difficulty of factoring large numbers into their original prime numbers. The public and private keys are functions of a pair of large prime numbers, and the necessary activity required to decrypt a message from ciphertext to plaintext using a private key is comparable to factoring a product into two prime numbers.

Question 109

What are the three main rules of the Biba model of security?

Answer 109

• Integrity axiom (“no write up”)
• Simple integrity axiom (“no read down”)
• Invocation property

The Biba model is a state machine model that enforces levels of integrity that are outlined in the software’s security policy. The Biba model uses a lattice of integrity levels.

If implemented and enforced properly, the Biba model prevents data from any integrity level from flowing to a higher integrity level. Biba has three main rules to provide this type of protection:

• Integrity axiom: A subject cannot write data to an object at a higher integrity level.
• Simple integrity axiom: A subject cannot read data from a lower integrity level.
• Invocation property: A subject cannot request service (invoke) from subjects of higher integrity.

Question 110

In the context of cryptography, what is an asymmetric algorithm?

Answer 110

In an asymmetric key cryptographic operation, the sender and receiver use two different but mathematically related keys.

The sender and receiver in an asymmetric key cryptographic operation use a public/private key combination. In this scheme, the message is encrypted using the public key of the key pair. The message can be decrypted using only the private key in the key pair. The public and private keys are related mathematically, and the private key cannot be derived from the public key.

Question 111

Provide examples of each level in the Generation Language (GL) scheme?

Answer 111

• 1 GL: A computer’s machine language
• 2 GL: An assembly language
• 3 GL: FORTRAN, BASIC, PL/1, and C languages
• 4 GL: Database query languages
• 5 GL: Artificial intelligence languages (Prolog, LISP) that process symbols or implement predicate logic

Question 112

Describe a cryptographic hybrid system.

Answer 112

In the hybrid approach, symmetric and asymmetric algorithms are used in a complementary manner, with each performing a different function.

A symmetric algorithm creates keys used for encrypting bulk data, and an asymmetric algorithm creates keys used for automated key distribution. In a hybrid system, the asymmetric key is used to encrypt the symmetric key, and the symmetric key is used to encrypt the message.

Question 113

In the context of cryptography, what is a symmetric algorithm?

Answer 113

A symmetric algorithm is one in which the same key is used to both encrypt and decrypt data.

In a cryptosystem that uses symmetric cryptography, the sender and receiver use two instances of the same key for encryption and decryption. So the key has dual functionality; it can carry out both encryption and decryption processes.

Symmetric keys are also called secret keys because this type of encryption relies on each user to keep the key a secret and properly protected. If an intruder were to get this key, she could decrypt any intercepted message encrypted with it.

Question 114

In the context of cryptography, what is a cryptovariable?

Answer 114

A cryptovariable is another name for a key.

A cryptovariable (or key) is the data used by a cryptographic algorithm to encipher plaintext or decipher encrypted data. It should remain secret between the parties exchanging the encrypted communication.

Question 115

What is the difference between volatile and nonvolatile memory?

Answer 115

Data stored in volatile memory is wiped out, or lost, when the system loses power. Random access memory (RAM) is a type of volatile memory.

Nonvolatile memory can persist even while the power is off and enables the storage of data in a more long-term fashion. A PC hard disk drive is an example of nonvolatile storage.

Question 116

What encryption scheme requires an amount of random data the same size as the data to be encrypted?

Answer 116

A one-time pad, also known as a Vernam cipher.

The one-time pad is a key sequence based on random numbers used only one time and then destroyed. It has to be the same length as the data to be encrypted (typically in an exclusive OR [XOR] process) to encrypt each bit.

The key values are distributed following an independent and uniform distribution over the key span. A one-time pad is a perfect encryption scheme because it is considered unbreakable if implemented properly. It was invented by Gilbert Vernam in 1917, so sometimes it is referred to as the Vernam cipher.

Question 117

What four factors are necessary to provide strong cryptography?

Answer 117

• A strong algorithm
• A secret key
• A lengthy key
• Sound key management practices

Many people think that strong cryptography only requires a strong algorithm. There are several pieces involved with cryptography—a strong algorithm is just one of the requirements.

The strength of different cryptographic methods comes from the algorithm, secrecy of the key, length of the key, and the key management practices. The larger the keyspace, the more random the actual bits that make up the key can be.

Question 118

What is the function of the central processing unit (CPU) in a computer?

Answer 118

The CPU is basically the brain of a computer.

The CPU is composed of an arithmetic logic unit (ALU) that is responsible for executing arithmetic and logical instructions, an instruction register, a program counter, and other general-purpose registers. The CPU is connected to other components of the computer by buses.

Question 119

Describe RISC and CISC.

Answer 119

The reduced instruction set computer (RISC) is a CPU that executes only a limited collection of instructions and usually requires fewer clock cycles to execute.

The complex instruction set computer (CISC) is a more robust collection of instructions that require additional processing time.

Question 120

Describe the three goals of integrity when assessing the assurance levels of operating systems.

Answer 120

• The data is protected from modification by unauthorized users.
• The data is protected from unauthorized modification by authorized users.
• The data is internally and externally consistent

For example, the data held in a database must balance internally and must correspond to the external, real-world situation. The integrity levels are implemented by different controls depending upon the access control model being used (Biba, Clark-Wilson, etc.). The controls enforce the necessary integrity outlined by the operating system or application security policy.

Question 121

What type of encryption would be considered the most secure method across a single MAN or WAN link?

Answer 121

Link encryption

Link encryption will encrypt all data along a physical path between two endpoints and provides higher security and performance for the encryption services. Headers, trailers, data payload, and routing data would all be encrypted.

Link encryption requires a physical link encryptor and decryptor at both ends of the physical link.

Question 122

What is the security perimeter when discussing an operating system and its protection mechanisms?

Answer 122

The security perimeter is a boundary that divides the trusted from the untrusted processes within an operating system.

Processes and resources inside the security perimeter fall within the Trusted Computing Base (TCB), and anything beyond the security perimeter is inherently untrusted. For example, a resource that is within the boundary of the TCB, or security perimeter, must not allow less trusted components access to critical system resources. The processes within the TCB must also be careful about the commands and information they accept from less trusted resources. These limitations and restrictions are built into the interfaces that permit this type of communication to take place and are the mechanisms that enforce the security perimeter.

Question 123

What security services are provided by an HMAC?

Answer 123

HMAC provides data origin authentication and data integrity.

A hashed message authentication code (HMAC) is created when a symmetric key is combined with the message, and then that result is put through a hashing algorithm. The result is an HMAC value.

Question 124

3DES is a widely used encryption algorithm. What are the four variants of 3DES?

Answer 124

• DES-EEE3
• DES-EDE3
• DES-EEE2
• DES-EDE2

3DES uses 48 rounds in its computation, which makes it highly resistant to differential cryptanalysis; however, because of the extra work 3DES performs, there is a heavy performance hit. It can take up to three times longer than DES to perform encryption and decryption.

3DES can work in different modes, and the mode chosen dictates the number of keys used and what functions are carried out:

• DES-EEE3: Uses three different keys for encryption, and the data is encrypted, encrypted, encrypted.
• DES-EDE3: Uses three different keys for encryption, and the data is encrypted, decrypted, and encrypted.
• DES-EEE2: The same as DES-EEE3, but uses only two keys, and the first and third encryption processes use the same key.
• DES-EDE2: The same as DES-EDE3, but uses only two keys, and the first and third encryption processes use the same key.

Question 125

What two operations make up an execution cycle?

Answer 125

Fetch and execute

Each instruction execution cycle consists of a fetch and an execute operation. In the fetch phase, the CPU retrieves the instruction from memory. An instruction typically consists of an operation and operands. In the execute phase, the retrieved instruction is executed and the result is stored in the accumulator.

Question 126

What is a trusted system?

Answer 126

A trusted computer system is one that employs the necessary hardware and software assurance mechanisms to enable processing of multiple levels of classified or sensitive information and meeting specified requirements for reliability and security.

This includes all protection mechanisms within a system that enforce the security policy and provide an environment that will behave in a manner expected of it.

Question 127

In terms of cryptography, what is an algorithm?

Answer 127

An algorithm is a set of mathematical and logical rules that dictates how enciphering and deciphering take place.

Many of the mathematical algorithms used in computer systems today are publicly known. Therefore, these algorithms require some private data, known as a key, to encipher and decipher information.

Question 128

What is steganography?

Answer 128

Steganography is a method of hiding data in another media type so the very existence of the data is concealed.

Steganography is mainly accomplished by hiding messages in graphic images. This practice does not affect the graphic enough to be detected. Steganography does not use algorithms or keys to encrypt information. This is a process to hide data within another object so that no one can detect its presence.

Question 129

What are the three security rules of the Bell-LaPadula model?

Answer 129

• Simple security (“no read up”)
• *-property rule (“no write down”)
• Strong star property rule

The Bell-LaPadula model is a confidentiality model that describes the allowable information flow and formalizes the military security policy. It is the first mathematical model of a multilevel security policy that defines the concept of a secure state and necessary modes of access.

Bell-LaPadula three security rules are:

• The simple security rule: A subject cannot read data at a higher security level (no read up).
• The *-property rule: A subject cannot write data to an object at a lower security level (no write down).
• The strong star property rule: A subject can perform read and write functions only to the objects at its same security level.

Question 130

Define cryptography and explain why it is useful in information security.

Answer 130

Cryptography is a method of storing and transmitting data in a form that only those it is intended for can read and process.

The goals of cryptography and its attendant mechanism are to hide information unauthorized individuals. With enough time, resources, and motivation, hackers can break most algorithms and reveal the encoded information. So a more realistic goal of cryptography is to make obtaining the information too work-intensive or time-consuming to be worthwhile to the attacker.

Question 131

What is the Trusted Computing Base (TCB)?

Answer 131

The TCB is defined as the total combination of protection mechanisms within a computer system.

The TCB includes:

• hardware
• software
• firmware

Hardware, software, and firmware are part of the TCB because the system is sure these components will enforce the security policy and not violate it.

Question 132

In the context of encryption, define the term work factor as it relates to a given cryptographic algorithm.

Answer 132

Work factor is an estimate of the effort and resources it would take for an attacker to penetrate a cryptosystem.

When designing an encryption method, the goal is to make compromising it prohibitively expensive or time-consuming. Work factor is another name for cryptography strength.

In asymmetric algorithms, the work factor relates to the difference in time and effort that carrying out a one-way function in the easy direction takes compared to carrying out a one-way function in the hard direction.

Question 133

What type of key is dynamically generated and destroyed after each use?

Answer 133

A session key

Most data encryption takes place through the use of symmetric keys.

A static key is used over and over again because it is usually computed from a password derived by a user.

Because a session key is dynamic and destroyed after it is used, it provides more protection than a static key because there is a smaller window for the bad guy to identify it.

Question 134

Describe virtual memory.

Answer 134

Virtual memory is when a portion of secondary memory is used to emulate and extend RAM.

The operating system memory manager operates by loading process data into main memory (RAM). When there is not enough space in memory to load a new process, operating systems that support virtual memory addressing can extend the addressable memory space by referencing program data that is stored in secondary memory.

When a reference is made to data in the virtual address space, the memory manager removes a portion of a running process from main memory to load the portion of the requested process into main memory.

Question 135

Describe the Clark-Wilson integrity model.

Answer 135

Clark-Wilson model enforces the three goals of integrity by using:

• Access triples (subject, software, object)
• Separation of duties
• Auditing

This model enforces integrity by using well-formed transactions (through access triples) and separation of user duties.

The Clark-Wilson model dictates that subjects can only access objects through applications.

This model also illustrates how to provide functionality for separation of duties and requires auditing tasks within software.

Question 136

In the context of encryption, describe the term plaintext.

Answer 136

Plaintext is data that is readable in its current form and can be understood without further processing.

Plaintext is in a form that can be understood either by a person (a document) or by a computer (executable code). When it is transformed into ciphertext, neither human nor machine can properly process it until it is decrypted.

Question 137

Define the following terms: cipher, cryptanalysis, cryptographic algorithm, and cryptology.

Answer 137

• Cipher: A cryptographic transformation that operates on bytes or bits. It is another name for algorithm.
• Cryptanalysis: The science of studying and breaking the secrecy of encryption process, compromising authentication schemes, and reverse-engineering algorithms and keys.
• Cryptographic algorithm: A procedure that enciphers plaintext and deciphers ciphertext.
• Cryptology: The study of cryptology and cryptanalysis. -A cipher is another word for an algorithm.
• Cryptanalysis is an important piece of cryptography and cryptology.
• Cryptographic algorithms provide the underlying tools to most security protocols used in today’s infrastructures. The algorithms work off of mathematical functions and provide various types of functionality and levels of security.
• Cryptology is the practice and study of hiding information.

Question 138

Which service in a PKI will vouch for the identity of an individual or company?

Answer 138

The certificate authority

A certificate authority (CA) generates a digital certificate, which binds the public key to the individual or company’s identity. The CA vouches for the identification of the owner of the certificate. The digital certificate is used to authenticate individuals or companies to each other.

Question 139

What is meant when a system is described as a multiprogramming system?

Answer 139

In a multiprogramming system, more than one program (or process) can be loaded into memory at the same time.

Multiprogramming enables you to run your antivirus software, word processor, personal firewall, and email client application simultaneously.

Question 140

List the three different components of a memory architecture in modern computing systems.

Answer 140

• Cache memory
• Random access memory (RAM)
• Secondary memory

Memory architecture is organized in layers differentiated by size, speed, and cost.

Closer to the CPU, cache memory stores data and instructions used by the CPU.

Random access memory (RAM) stores user and process data managed by the computer.

Secondary memory stores user data, applications, and (in special circumstances) virtual address space for the memory manager.

Question 141

What is the difference between programmed I/O and direct memory access (DMA)?

Answer 141

In programmed I/O, the CPU manages the execution of I/O operations (secondary stage access, network access, printer access, and so on). Direct memory access (DMA) allows other subsystems to access memory independent of the CPU.

The drawback of programmed I/O is that while the I/O operation is executing, the CPU cannot service another process. Direct memory access (DMA) reduces strain on the CPU.

Question 142

Describe the information flow model.

Answer 142

The information flow model is a model in which information is restricted in its flow to only go to and from entities in a way that does not negate the security policy.

In the information flow model, data is thought of as being held in individual and discrete compartments.

Examples of information flow models are Bell-LaPadula and Biba.

• The Bell-LaPadula model focuses on preventing information from flowing from a high security level to a low security level.
• The Biba model focuses on preventing information from flowing from a low integrity level to a high integrity level.

Question 143

What binary mathematical function is used in the one-time pad encryption scheme?

Answer 143

The exclusive OR (XOR) process.

The exclusive OR process is a Boolean operation that essentially performs binary addition without carrying on the input bits.

• For two inputs that are equal, a 0 (false) is the result.
• For two inputs where the values are not equal, the result is a 1 (true).

Exclusive OR is usually abbreviated as XOR. It is an operation that is applied to two bits and is a function commonly used in binary mathematics and encryption methods. When combining the bits, if both values are the same, the result is 0 (1 XOR 1 = 0; 0 XOR 0 = 0). If the bits are different from each other, the result is 1 (1 XOR 0 = 1; 0 XOR 1 = 1).

Question 144

What are the two basic types of symmetric encryption ciphers?

Answer 144

• Substitution
• Transposition (or permutation)

The substitution cipher replaces bits, characters, or blocks of characters with different bits, characters, or blocks. A substitution cipher uses a key to dictate how the substitution should be carried out.

The transposition cipher does not replace the original text with different text, but rather moves the original values around. It rearranges the bits, characters, or blocks of characters to hide the original meaning. The key determines the positions the values are moved to.

Question 145

Describe the difference between S-HTTP and HTTPS.

Answer 145

S-HTTP provides protection for each message sent between two computers, but not the actual link.

HTTPS protects the communication channel.

HTTPS is HTTP that uses SSL for security purposes. HTTP is a protocol that works at the application layer within the OSI model. SSL is a protocol that works at the transport layer. HTTPS is a very common combination; it is the most used protection mechanism when moving data over transmission lines for ecommerce. S-HTTP was an early attempt to secure HTTP that was never widely adopted.

Question 146

Describe sequential memory.

Answer 146

Sequential memory gets its name because the contents are stored sequentially and must be read or retrieved sequentially, or in a linear fashion.

An example of sequential memory is the use of magnetic tapes for data storage. Retrieving information requires searching from the beginning until the target data is located.

Question 147

What is the difference between RAM and ROM?

Answer 147

Random access memory (RAM) is a volatile and fast type of memory that is used closest to the processor in the computer system.

Read-only memory (ROM) is nonvolatile memory that retains information even if power is removed.

RAM takes the same amount of time to retrieve information from any address. ROM is typically used to load and store firmware. An example of ROM is erasable programmable read-only memory (EPROM).

Question 148

What is meant by pipelining?

Answer 148

Pipelining is the interweaving of various fetch and execute instruction cycles to allow for faster response times.

Question 149

What is the equation to calculate the number of symmetric keys needed among N parties?

Answer 149

N(N – 1)/2

For example, if 10 people need to communicate via symmetric encryption processes, then 10(10-1)/2 or 45 keys are needed. Each pair of users who want to exchange data using symmetric key encryption must have two instances of the same key.

Question 150

What is the difference between a closed and an open system?

Answer 150

A closed system is proprietary to a specific vendor or group, and the specific operations are not disclosed.

An open system has published functions and code that is verifiable by the public.

Question 151

What is a trusted path?

Answer 151

A trusted path is a communication channel between the user, or program, and the kernel.

The Trusted Computing Base TCB provides protection resources to ensure this channel cannot be compromised in any way.

Question 152

What is meant when a system is described as a multiprocessing system?

Answer 152

A multiprocessing system has more than one CPU.

Multiprocessing requires an operating system capable of addressing more than one processor. Multiprocessing can be done either symmetrically, where CPU processing is doled out in a load-balancing fashion between the processors, or asymmetrically, where individual processors can be dedicated to a specific application or process.

Question 153

In the context of encryption, what is ciphertext and how does it differ from plaintext?

Answer 153

Plaintext is in a form that can be understood either by a person (a document) or by a computer (executable code). After it is transformed into ciphertext, neither human nor machine can properly process it until it is decrypted.

Ciphertext is a product of encryption that enables the transmission of confidential information over insecure channels without unauthorized disclosure.

Plaintext is the readable version of a message. After an encryption process, the resulting text is referred to as ciphertext.

Question 154

What is an operating system and its different common components?

Answer 154

An operating system is the collection of applications that control the resources and operations of a computer.

Operating systems perform:

• Process management
• Memory management
• System file management
• I/O management
• Operation of the user interface

Question 155

What is meant when a system is described as a multitasking system?

Answer 155

Multitasking is the capability of a computer system to carry out several different functions simultaneously.

In reality, the CPU executes instructions one at a time, but it executes instructions from different processes and applications in such rapid succession that the net effect is that all the processes or applications are operating simultaneously.

Question 156

What are two basic methods (ciphers) for transforming plaintext into ciphertext?

Answer 156

• Block ciphers
• Stream ciphers

When a block cipher is used for encryption and decryption purposes, the message is divided into blocks of bits. These blocks are then put through mathematical functions, one block at a time.

A stream cipher, on the other hand, does not divide a message into blocks. Instead, a stream cipher treats the message as a stream of bits and performs mathematical functions on each bit individually.