Sybex Book Review 2 Flashcards
Ryan is responsible for managing the cryptographic keys used by his organization. Which of the following statements are correct about how he should select and manage those keys? (Choose all that apply.)
A. Keys should be sufficiently long to protect against future attacks if the data is expected to remain sensitive.
B. Keys should be chosen using an approach that generates them from a predictable pattern.
C. Keys should be maintained indefinitely.
D. Longer keys provide greater levels of security.
A, D. Keys must be long enough to withstand attack for as long as the data is expected to remain sensitive. They should not be generated in a predictable way but, rather, should be randomly generated. Keys should be securely destroyed when they are no longer needed and not indefinitely retained. Longer keys do indeed provide greater security against brute-force attacks.
John recently received an email message from Bill. What cryptographic goal would need to be met to convince John that Bill was actually the sender of the message?
A. Nonrepudiation
B. Confidentiality
C. Availability
D. Integrity
A. Nonrepudiation prevents the sender of a message from later denying that they sent it. Confidentiality protects the contents of encrypted data from unauthorized disclosure. Integrity protects data from unauthorized modification. Availability is not a goal of cryptography.
You are implementing AES encryption for files that your organization plans to store in a cloud storage service and wish to have the strongest encryption possible. What key length should you choose?
A. 192 bits
B. 256 bits
C. 512 bits
D. 1,024 bits
B. The strongest keys supported by the Advanced Encryption Standard are 256 bits. The valid AES key lengths are 128, 192, and 256 bits.
You are creating a security product that must facilitate the exchange of symmetric encryption keys between two parties that have no way to securely exchange keys in person. What algorithm might you use to facilitate the exchange?
A. Rijndael
B. Blowfish
C. Vernam
D. Diffie–Hellman
D. The Diffie–Hellman algorithm allows the exchange of symmetric encryption keys between two parties over an insecure channel.
What occurs when the relationship between the plaintext and the key is complicated enough that an attacker can’t merely continue altering the plaintext and analyzing the resulting ciphertext to determine the key? (Choose all that apply.)
A. Confusion
B. Transposition
C. Polymorphism
D. Diffusion
A, D. Confusion and diffusion are two principles underlying most cryptosystems. Confusion occurs when the relationship between the plaintext and the key is so complicated that an attacker can’t merely continue altering the plaintext and analyzing the resulting ciphertext to determine the key. Diffusion occurs when a change in the plaintext results in multiple changes spread throughout the ciphertext.
Randy is implementing an AES-based cryptosystem for use within his organization. He would like to better understand how he might use this cryptosystem to achieve his goals. Which of the following goals are achievable with AES? (Choose all that apply.)
A. Nonrepudiation
B. Confidentiality
C. Authentication
D. Integrity
B, C, D. AES provides confidentiality, integrity, and authentication when implemented properly. Nonrepudiation requires the use of a public key cryptosystem to prevent users from falsely denying that they originated a message and cannot be achieved with a symmetric cryptosystem, such as AES.
Brian encountered encrypted data left on one of his systems by attackers who were communicating with one another. He has tried many cryptanalytic techniques and was unable to decrypt the data. He believes that the data may be protected with an unbreakable system. When correctly implemented, what is the only cryptosystem known to be unbreakable?
A. Transposition cipher
B. Substitution cipher
C. Advanced Encryption Standard
D. One-time pad
D. Assuming that it is used properly, the one-time pad is the only known cryptosystem that is not vulnerable to attacks. All other cryptosystems, including transposition ciphers, substitution ciphers, and even AES, are vulnerable to attack, even if no attack has yet been discovered.
Helen is planning to use a one-time pad to meet a unique cryptographic requirement in her organization. She is trying to identify the requirements for using this cryptosystem. Which of the following are requirements for the use of a one-time pad? (Choose all that apply.)
A. The encryption key must be at least one-half the length of the message to be encrypted.
B. The encryption key must be randomly generated.
C. Each one-time pad must be used only once.
D. The one-time pad must be physically protected against disclosure.
B, C, D. The encryption key must be at least as long as the message to be encrypted. This is because each key element is used to encode only one character of the message. The three other facts listed are all characteristics of one-time pad systems.
Brian administers a symmetric cryptosystem used by 20 users, each of whom has the ability to communicate privately with any other user. One of those users lost control of their account and Brian believes that user’s keys were compromised. How many keys must he change?
A. 1
B. 2
C. 19
D. 190
C. In a symmetric cryptosystem, a unique key exists for each pair of users. In this case, every key involving the compromised user must be changed, meaning that the key that the user shared with each of the other 19 users must be changed.
Which one of the following cipher types operates on large pieces of a message rather than individual characters or bits of a message?
A. Stream cipher
B. Caesar cipher
C. Block cipher
D. ROT3 cipher
C. Block ciphers operate on message “chunks” rather than on individual characters or bits. The other ciphers mentioned are all types of stream ciphers that operate on individual bits or characters of a message.
James is the administrator for his organization’s symmetric key cryptographic system. He issues keys to users when the need arises. Mary and Beth recently approached him and presented a need to be able to exchange encrypted files securely. How many keys must James generate?
A. One
B. Two
C. Three
D. Four
A. Symmetric key cryptography uses a shared secret key. All communicating parties utilize the same key for communication in any direction. Therefore, James only needs to create a single symmetric key to facilitate this communication.
Dave is developing a key escrow system that requires multiple people to retrieve a key but does not depend on every participant being present. What type of technique is he using?
A. Split knowledge
B. M of N Control
C. Work function
D. Zero-knowledge proof
B. M of N Control requires that a minimum number of agents (M) out of the total number of agents (N) work together to perform high-security tasks. M of N Control is an example of a split knowledge technique, but not all split knowledge techniques are used for key escrow.
What is used to increase the strength of cryptography by creating a unique ciphertext every time the same message is encrypted with the same key?
A. Initialization vector
B. Vigenère cipher
C. Steganography
D. Stream cipher
A. An initialization vector (IV) is a random bit string (a nonce) that is the same length as the block size that is XORed with the message. IVs are used to create a unique ciphertext every time the same message is encrypted with the same key. Vigenère ciphers are an example of a substitution cipher technique. Steganography is a technique used to embed hidden messages within a binary file. Stream ciphers are used to encrypt continuous streams of data.
Tammy is choosing a mode of operation for a symmetric cryptosystem that she will be using in her organization. She wants to choose a mode that is capable of providing both confidentiality and data authenticity. What mode would best meet her needs?
A. ECB
B. GCM
C. OFB
D. CTR
B. Galois/Counter Mode (GCM) and Counter with Cipher Block Chaining Message Authentication Code mode (CCM) are the only two modes that provide both confidentiality and data authenticity. Other modes, including Electronic Code Book (ECB), Output Feedback (OFB), and Counter (CTR) modes, only provide confidentiality.
Julie is designing a highly secure system and is concerned about the storage of unencrypted data in RAM. What use case is she considering?
A. Data in motion
B. Data at rest
C. Data in destruction
D. Data in use
D. Data that is stored in memory is being actively used by a system and is considered data in use. Data at rest is data that is stored on nonvolatile media, such as a disk. Data in motion is being actively transferred over a network.
Renee conducted an inventory of encryption algorithms used in her organization and found that they are using all of the algorithms below. Which of these algorithms should be discontinued? (Choose all that apply.)
A. AES
B. DES
C. 3DES
D. RC5
B, C. The Advanced Encryption Standard (AES) and Rivest Cipher 6 (RC6) are modern, secure algorithms. The Data Encryption Standard (DES) and Triple DES (3DES) are outdated and no longer considered secure.
Which one of the following encryption algorithm modes suffers from the undesirable characteristic of errors propagating between blocks?
A. Electronic Code Book
B. Cipher Block Chaining
C. Output Feedback
D. Counter
B. One important consideration when using CBC mode is that errors propagate—if one block is corrupted during transmission, it becomes impossible to decrypt that block and the next block as well. The other modes listed here do not suffer from this flaw.
Which one of the following key distribution methods is most cumbersome when users are located in different geographic locations?
A. Diffie–Hellman
B. Public key encryption
C. Offline
D. Escrow
C. Offline key distribution requires a side channel of trusted communication, such as in-person contact. This can be difficult to arrange when users are geographically separated. Alternatively, the individuals could use the Diffie–Hellman algorithm or other asymmetric/public key encryption technique to exchange a secret key. Key escrow is a method for managing the recovery of lost keys and is not used for key distribution.
Victoria is choosing an encryption algorithm for use within her organization and would like to choose the most secure symmetric algorithm from a list of those supported by the software package she intends to use. If the package supports the following algorithms, which would be the best option?
A. AES-256
B. 3DES
C. RC4
D. Skipjack
A. The AES-256 algorithm is a modern, secure cryptographic algorithm. 3DES, RC4, and Skipjack are all outdated algorithms that suffer from significant security issues.
The Jones Institute has six employees and uses a symmetric key encryption system to ensure confidentiality of communications. If each employee needs to communicate privately with every other employee, how many keys are necessary?
A. 1
B. 6
C. 15
D. 30
C. A separate key is required for each pair of users who want to communicate privately. In a group of six users, this would require a total of 15 secret keys. You can calculate this value by using the formula (n * (n – 1) / 2). In this case, n = 6, resulting in (6 * 5) / 2 = 15 keys.
Brian computes the digest of a single sentence of text using a SHA-2 hash function. He then changes a single character of the sentence and computes the hash value again. Which one of the following statements is true about the new hash value?
A. The new hash value will be one character different from the old hash value.
B. The new hash value will share at least 50 percent of the characters of the old hash value.
C. The new hash value will be unchanged.
D. The new hash value will be completely different from the old hash value.
D. Any change, no matter how minor, to a message will result in a completely different hash value. There is no relationship between the significance of the change in the message and the significance of the change in the hash value.
Alan believes that an attacker is collecting information about the electricity consumption of a sensitive cryptographic device and using that information to compromise encrypted data. What type of attack does he suspect is taking place?
A. Brute force
B. Side channel
C. Known plaintext
D. Frequency analysis
B. Side-channel attacks use information gathered about a system’s use of resources, timing, or other characteristics to contribute to breaking the security of encryption. Brute-force attacks seek to exhaust all possible encryption keys. Known plaintext attacks require access to both plaintext and its corresponding ciphertext. Frequency analysis attacks require access to ciphertext.
If Richard wants to send a confidential encrypted message to Sue using a public key cryptosystem, which key does he use to encrypt the message?
A. Richard’s public key
B. Richard’s private key
C. Sue’s public key
D. Sue’s private key
C. Richard must encrypt the message using Sue’s public key so that Sue can decrypt it using her private key. If he encrypted the message with his own public key, the recipient would need to know Richard’s private key to decrypt the message. If he encrypted it with his own private key, any user could decrypt the message using Richard’s freely available public key. Richard could not encrypt the message using Sue’s private key because he does not have access to it. If he did, any user could decrypt it using Sue’s freely available public key.
If a 2,048-bit plaintext message were encrypted with the ElGamal public key cryptosystem, how long would the resulting ciphertext message be?
A. 1,024 bits
B. 2,048 bits
C. 4,096 bits
D. 8,192 bits
C. The major disadvantage of the ElGamal cryptosystem is that it doubles the length of any message it encrypts. Therefore, a 2,048-bit plaintext message would yield a 4,096-bit ciphertext message when ElGamal is used for the encryption process.
Acme Widgets currently uses a 3,072-bit RSA encryption standard companywide. The company plans to convert from RSA to an elliptic curve cryptosystem. If the company wants to maintain the same cryptographic strength, what ECC key length should it use?
A. 256 bits
B. 512 bits
C. 1,024 bits
D. 2,048 bits
A. The elliptic curve cryptosystem requires significantly shorter keys to achieve encryption that would be the same strength as encryption achieved with the RSA encryption algorithm. A 3,072-bit RSA key is cryptographically equivalent to a 256-bit elliptic curve cryptosystem key.
John wants to produce a message digest of a 2,048-byte message he plans to send to Mary. If he uses the SHA-2 hashing algorithm, what is a possible size for the message digest generated?
A. 160 bits
B. 512 bits
C. 1,024 bits
D. 2,048 bits
B. The SHA-2 hashing algorithm comes in four variants. SHA-224 produces 224-bit digests. SHA-256 produces 256-bit digests. SHA-384 produces 384-bit digests, and SHA-512 produces 512-bit digests. Of the options presented here, only 512 bits is a valid SHA-2 hash length.
After conducting a survey of encryption technologies used in her organization, Melissa suspects that some may be out of date and pose security risks. Which one of the following technologies is considered flawed and should no longer be used?
A. SHA-3
B. TLS 1.2
C. IPsec
D. SSL 3.0
D. The Secure Sockets Layer (SSL) protocol is deprecated and no longer considered secure. It should never be used. The Secure Hash Algorithm 3 (SHA-3), Transport Layer Security (TLS) 1.2, and IPsec are all modern, secure protocols and standards.
You are developing an application that compares passwords to those stored in a Unix password file. The hash values you compute are not correctly matching those in the file. What might have been added to the stored password hashes?
A. Salt
B. Double hash
C. Added encryption
D. One-time pad
A. Cryptographic salt values are added to the passwords in password files before hashing to defeat rainbow table and dictionary attacks. Double hashing does not provide any added security. Adding encryption to the passwords is challenging, because then the operating system must possess the decryption key. A one-time pad is only appropriate for use in human-to-human communications and would not be practical here.
Richard received an encrypted message sent to him from Sue. Sue encrypted the message using the RSA encryption algorithm. Which key should Richard use to decrypt the message?
A. Richard’s public key
B. Richard’s private key
C. Sue’s public key
D. Sue’s private key
B. Sue would have encrypted the message using Richard’s public key. Therefore, Richard needs to use the complementary key in the key pair, his private key, to decrypt the message.
Richard wants to digitally sign a message he’s sending to Sue so that Sue can be sure the message came from him without modification while in transit. Which key should he use to encrypt the message digest?
A. Richard’s public key
B. Richard’s private key
C. Sue’s public key
D. Sue’s private key
B. Richard should encrypt the message digest with his own private key. When Sue receives the message, she will decrypt the digest with Richard’s public key and then compute the digest herself. If the two digests match, she can be assured that the message truly originated from Richard.
Which one of the following algorithms is not supported by the Digital Signature Standard under FIPS 186-4?
A. Digital Signature Algorithm
B. RSA
C. ElGamal DSA
D. Elliptic Curve DSA
C. The Digital Signature Standard allows federal government use of the Digital Signature Algorithm, RSA, or the Elliptic Curve DSA in conjunction with the SHA-1 hashing function to produce secure digital signatures.
Which International Telecommunications Union (ITU) standard governs the creation and endorsement of digital certificates for secure electronic communication?
A. X.500
B. X.509
C. X.900
D. X.905
B. X.509 governs digital certificates and the public key infrastructure (PKI). It defines the appropriate content for a digital certificate and the processes used by certificate authorities to generate and revoke certificates.
Ron believes that an attacker accessed a highly secure system in his data center and applied high-voltage electricity to it in an effort to compromise the cryptographic keys that it uses. What type of attack does he suspect?
A. Implementation attack
B. Fault injection
C. Timing
D. Chosen ciphertext
B. Fault injection attacks compromise the integrity of a cryptographic device by causing some type of external fault, such as the application of high-voltage electricity. Implementation attacks rely on flaws in the cryptographic algorithm. Timing attacks measure the length of time consumed by encryption operations. Chosen ciphertext attacks require access to the algorithm and work by having the attacker perform encryption that results in an expected ciphertext.
Brandon is analyzing network traffic and is searching for user attempts to access websites over secure TLS connections. What TCP port should Brandon add to his search filter because it would normally be used by this traffic?
A. 22
B. 80
C. 443
D. 1443
C. HTTPS uses TCP port 443 for encrypted client/server communications over TLS. Port 22 is used by the secure shell (SSH) protocol. Port 80 is used by the unencrypted HTTP protocol. Port 1433 is used for Microsoft SQL Server database connections.
Beth is assessing the vulnerability of a cryptographic system to attack. She believes that the cryptographic keys are properly secured and that the system is using a modern, secure algorithm. Which one of the following attacks would most likely still be possible against the system by an external attacker who did not participate in the system and did not have physical access to the facility?
A. Ciphertext only
B. Known plaintext
C. Chosen plaintext
D. Fault injection
A. An attacker without any special access to the system would only be able to perform ciphertext-only attacks. Known plaintext and chosen plaintext attacks require the ability to encrypt data. Fault injection attacks require physical access to the facility.
Which of the following tools can be used to improve the effectiveness of a brute-force password cracking attack?
A. Rainbow tables
B. Hierarchical screening
C. TKIP
D. Random enhancement
A. Rainbow tables contain precomputed hash values for commonly used passwords and may be used to increase the efficiency of password-cracking attacks.
Chris is searching a Windows system for binary key files and wishes to narrow his search using file extensions. Which one of the following certificate formats is closely associated with Windows binary certificate files?
A. CCM
B. PEM
C. PFX
D. P7B
C. The PFX format is most closely associated with Windows systems that store certificates in binary format, whereas the P7B format is used for Windows systems storing files in text format. The PEM format is another text format, and the CCM format does not exist.
What is the major disadvantage of using certificate revocation lists?
A. Key management
B. Latency
C. Record keeping
D. Vulnerability to brute-force attacks
B. Certificate revocation lists (CRLs) introduce an inherent latency to the certificate expiration process due to the time lag between CRL distributions.
Which one of the following encryption algorithms is now considered insecure?
A. ElGamal
B. RSA
C. Elliptic Curve Cryptography
D. Merkle–Hellman Knapsack
D. The Merkle–Hellman Knapsack algorithm, which relies on the difficulty of factoring super-increasing sets, has been broken by cryptanalysts.
Brian is upgrading a system to support SSH2 rather than SSH1. Which one of the following advantages will he achieve?
A. Support for multifactor authentication
B. Support for simultaneous sessions
C. Support for 3DES encryption
D. Support for IDEA encryption
B. SSH2 adds support for simultaneous shell sessions over a single SSH connection. Both SSH1 and SSH2 are capable of supporting multifactor authentication. SSH2 actually drops support for the IDEA algorithm, whereas both SSH1 and SSH2 support 3DES.