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NEW QUESTION 114
A _____ is a function is not reversible.
- A. Block Cipher
- B. Asymmetric cipher
- C. Stream cipher
- D. Hash
Answer: D
Explanation:
Hash
https://en.wikipedia.org/wiki/Hash_function
Hash functions are irreversible. This is actually required for them to fulfill their function of determining whether someone possesses an uncorrupted copy of the hashed data. This brings susceptibility to brute force attacks, which are quite powerful these days, particularly against MD5.
NEW QUESTION 115
With Electronic codebook (ECB) what happens:
- A. The block cipher is turned into a stream cipher
- B. The cipher text from the current round is XORed with the plaintext from the previous round
- C. The cipher text from the current round is XORed with the plaintext for the next round
- D. The message is divided into blocks and each block is encrypted separately. This is the most basic mode for symmetric encryption
Answer: D
Explanation:
The message is divided into blocks and each block is encrypted separately. This is the most basic mode for symmetric encryption
https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Electronic_codebook_(ECB) The simplest of the encryption modes is the electronic codebook (ECB) mode (named after conventional physical codebooks). The message is divided into blocks, and each block is encrypted separately.
NEW QUESTION 116
If you use substitution alone, what weakness is present in the resulting cipher text?
- A. It is too simple
- B. It is easily broken with modern computers
- C. It maintains letter and word frequency
- D. It is the same length as the original text
Answer: C
Explanation:
It maintains letter and word frequency
https://en.wikipedia.org/wiki/Frequency_analysis
Frequency analysis (also known as counting letters) is the study of the frequency of letters or groups of letters in a ciphertext. The method is used as an aid to breaking classical ciphers.
Frequency analysis is based on the fact that, in any given stretch of written language, certain letters and combinations of letters occur with varying frequencies. Moreover, there is a characteristic distribution of letters that is roughly the same for almost all samples of that language. For instance, given a section of English language, E, T, A and O are the most common, while Z, Q, X and J are rare. Likewise, TH, ER, ON, and AN are the most common pairs of letters (termed bigrams or digraphs), and SS, EE, TT, and FF are the most common repeats. The nonsense phrase "ETAOIN SHRDLU" represents the 12 most frequent letters in typical English language text.
In some ciphers, such properties of the natural language plaintext are preserved in the ciphertext, and these patterns have the potential to be exploited in a ciphertext-only attack.
NEW QUESTION 117
Which of the following is an asymmetric cipher?
- A. DES
- B. RSA
- C. AES
- D. RC4
Answer: B
Explanation:
RSA
https://en.wikipedia.org/wiki/RSA_(cryptosystem)
RSA (Rivest-Shamir-Adleman) is a public-key cryptosystem that is widely used for secure data transmission. It is also one of the oldest. The acronym RSA comes from the surnames of Ron Rivest, Adi Shamir, and Leonard Adleman, who publicly described the algorithm in 1977. An equivalent system was developed secretly, in 1973 at GCHQ (the British signals intelligence agency), by the English mathematician Clifford Cocks. That system was declassified in 1997.
In a public-key cryptosystem, the encryption key is public and distinct from the decryption key, which is kept secret (private). An RSA user creates and publishes a public key based on two large prime numbers, along with an auxiliary value. The prime numbers are kept secret. Messages can be encrypted by anyone, via the public key, but can only be decoded by someone who knows the prime numbers.
Incorrect answers:
DES - is a symmetric-key algorithm for the encryption of digital data. Although its short key length of 56 bits makes it too insecure for applications, it has been highly influential in the advancement of cryptography.
RC4 - RSA (Rivest-Shamir-Adleman) is one of the first public-key cryptosystems and is widely used for secure data transmission (stream cipher).
AES - is a subset of the Rijndael block cipher developed by two Belgian cryptographers, Vincent Rijmen and Joan Daemen, who submitted a proposal to NIST during the AES selection process. Rijndael is a family of ciphers with different key and block sizes. For AES, NIST selected three members of the Rijndael family, each with a block size of 128 bits, but three different key lengths: 128, 192 and 256 bits.
NEW QUESTION 118
Which of the following is a key exchange protocol?
- A. DES
- B. RSA
- C. AES
- D. MQV
Answer: D
Explanation:
MQV
https://en.wikipedia.org/wiki/MQV
MQV (Menezes-Qu-Vanstone) is an authenticated protocol for key agreement based on the Diffie-Hellman scheme. Like other authenticated Diffie-Hellman schemes, MQV provides protection against an active attacker. The protocol can be modified to work in an arbitrary finite group, and, in particular, elliptic curve groups, where it is known as elliptic curve MQV (ECMQV).
Incorrect answers:
RSA - (Rivest-Shamir-Adleman) is a public-key cryptosystem that is widely used for secure data transmission. It is also one of the oldest. The acronym RSA comes from the surnames of Ron Rivest, Adi Shamir, and Leonard Adleman, who publicly described the algorithm in 1977.
AES - Advanced Encryption Standard (AES), also known by its original name Rijndael, is a specification for the encryption of electronic data established by the U.S. National Institute of Standards and Technology (NIST) in 2001.
DES - Data Encryption Standard is a symmetric-key algorithm for the encryption of digital data.
NEW QUESTION 119
What is Kerchoff's principle?
- A. A minimum of 15 rounds is needed for a Feistel cipher to be secure
- B. Both algorithm and key should be kept secret
- C. Only the key needs to be secret, not the actual algorithm
- D. A minimum key size of 256 bits is necessary for security
Answer: C
Explanation:
Only the key needs to be secret, not the actual algorithm
https://en.wikipedia.org/wiki/Kerckhoffs%27s_principle
Kerckhoffs's principle of cryptography was stated by Netherlands born cryptographer Auguste Kerckhoffs in the 19th century: A cryptosystem should be secure even if everything about the system, except the key, is public knowledge.
NEW QUESTION 120
Which of the following is generally true about key sizes?
- A. Key size is irrelevant to security
- B. Larger key sizes increase security
- C. Smaller key sizes increase security
- D. Key sizes must be more than 256 bits to be secure
Answer: B
Explanation:
Larger key sizes increase security
https://en.wikipedia.org/wiki/Key_size
Key length defines the upper-bound on an algorithm's security (i.e. a logarithmic measure of the fastest known attack against an algorithm), since the security of all algorithms can be violated by brute-force attacks. Ideally, the lower-bound on an algorithm's security is by design equal to the key length (that is, the security is determined entirely by the keylength, or in other words, the algorithm's design doesn't detract from the degree of security inherent in the key length). Indeed, most symmetric-key algorithms are designed to have security equal to their key length. However, after design, a new attack might be discovered. For instance, Triple DES was designed to have a 168 bit key, but an attack of complexity 2112 is now known (i.e. Triple DES now only has 112 bits of security, and of the 168 bits in the key the attack has rendered 56 'ineffective' towards security). Nevertheless, as long as the security (understood as 'the amount of effort it would take to gain access') is sufficient for a particular application, then it doesn't matter if key length and security coincide. This is important for asymmetric-key algorithms, because no such algorithm is known to satisfy this property; elliptic curve cryptography comes the closest with an effective security of roughly half its key length.
NEW QUESTION 121
Bob's password is hashed, and so is John's. Even though they used different passwords, the hash is the same. What is this called?
- A. A mistake
- B. A collision
- C. Convergence
- D. Transposition
Answer: B
Explanation:
A collision
https://en.wikipedia.org/wiki/Collision_(computer_science)
A collision or clash is a situation that occurs when two distinct pieces of data have the same hash value, checksum, fingerprint, or cryptographic digest.
NEW QUESTION 122
Which one of the following attempts to hide data in plain view?
- A. Steganography
- B. Asymmetric cryptography
- C. Substitution
- D. Cryptography
Answer: A
Explanation:
Steganography
https://en.wikipedia.org/wiki/Steganography
Steganography is the practice of concealing a file, message, image, or video within another file, message, image, or video. The word steganography comes from Greek steganographia, which combines the words steganos , meaning "covered or concealed", and -graphia meaning "writing".
NEW QUESTION 123
In steganography, ________ is the data to be covertly communicated (in other words, it is the message you wish to hide).
- A. Payload
- B. Carrier
- C. Signal
- D. Channel
Answer: A
Explanation:
Payload
https://en.wikipedia.org/wiki/Steganography
The payload is the data covertly communicated. The carrier is the signal, stream, or data file that hides the payload, which differs from the channel, which typically means the type of input, such as a JPEG image. The resulting signal, stream, or data file with the encoded payload is sometimes called the package, stego file, or covert message. The proportion of bytes, samples, or other signal elements modified to encode the payload is called the encoding density and is typically expressed as a number between 0 and 1.
NEW QUESTION 124
Which analysis type is based on the statistics of the numbers of unique colors and close-color pairs in a 24-bit image, a method that analyzes the pairs of colors created by LSB embedding?
- A. Raw Quick Pair
- B. Differential Analysis
- C. Discrete Cosine Transform
- D. Chi squared analysis
Answer: A
Explanation:
Raw Quick Pair
https://www.cs.auckland.ac.nz/courses/compsci725s2c/archive/termpapers/yy.pdf Du and Long2 (2000) introduced Raw Quick Pairs detecting method of Stego-images (the images that contain the steganographic message). The underlying principle of the method is that the number of close color pairs of Stego-images will be larger compare with the number of close color pairs of normal images. In contrast, Fridrich and Goljan (2001) pointed out that RQP method only works if the number of unique colors is relatively low; and the method can not be applied to grayscale images. However, this paper will outline the core principle of RQP method; and evaluate such critical comments in details. In addition, this paper suggests potential improvement of RQP method and provides one possible alternative.
Incorrect answers:
Chi squared analysis - https://en.wikipedia.org/wiki/Chi-squared_test
Differential Analysis - https://en.wikipedia.org/wiki/Differential_cryptanalysis Discrete Cosine Transform - https://en.wikipedia.org/wiki/Discrete_cosine_transform
NEW QUESTION 125
All of the following are key exchange protocols except for____
- A. ECDH
- B. MQV
- C. AES
- D. DH
Answer: C
NEW QUESTION 126
What is a TGS?
- A. A protocol for encryption
- B. The server that escrows keys
- C. A protocol for key exchange
- D. The server that grants Kerberos tickets
Answer: D
Explanation:
The server that grants Kerberos tickets
https://en.wikipedia.org/wiki/Kerberos_(protocol)
The client authenticates itself to the Authentication Server (AS) which forwards the username to a key distribution center (KDC). The KDC issues a ticket-granting ticket (TGT), which is time stamped and encrypts it using the ticket-granting service's (TGS) secret key and returns the encrypted result to the user's workstation. This is done infrequently, typically at user logon; the TGT expires at some point although it may be transparently renewed by the user's session manager while they are logged in.
NEW QUESTION 127
A number that is used only one time, then discarded is called what?
- A. Chain
- B. Nonce
- C. Salt
- D. IV
Answer: B
Explanation:
Nonce
https://en.wikipedia.org/wiki/Cryptographic_nonce
A nonce is an arbitrary number that can be used just once in a cryptographic communication. It is similar in spirit to a nonce word, hence the name. It is often a random or pseudo-random number issued in an authentication protocol to ensure that old communications cannot be reused in replay attacks.
NEW QUESTION 128
Which of the following is a substitution cipher used by ancient Hebrew scholars?
- A. Atbash
- B. Vigenere
- C. Caesar
- D. Scytale
Answer: A
Explanation:
Atbash
https://en.wikipedia.org/wiki/Atbash
Atbash is a monoalphabetic substitution cipher originally used to encrypt the Hebrew alphabet. It can be modified for use with any known writing system with a standard collating order.
Incorrect answers:
Scytale - Transposition cipher. A staff with papyrus or letter wrapped around it so edges would line up. There would be a stream of characters which would show you your message. When unwound it would be a random string of characters. Would need an identical size staff on other end for other individuals to decode message.
Vigenere - method of encrypting alphabetic text by using a series of interwoven Caesar ciphers, based on the letters of a keyword. It employs a form of polyalphabetic substitution.
Caesar Cipher - Monoalphabetic cipher where letters are shifted one or more letters in either direction. The method is named after Julius Caesar, who used it in his private correspondence.
NEW QUESTION 129
A type of frequency analysis used to attack polyalphabetic substitution ciphers. It's used to try to discover patterns and use that information to decrypt the cipher.
- A. Integral Cryptanalysis
- B. Kasiski Method
- C. Birthday Attack
- D. Information Deduction
Answer: B
Explanation:
Kasiski Method
https://en.wikipedia.org/wiki/Kasiski_examination
In cryptanalysis, Kasiski examination (also referred to as Kasiski's test or Kasiski's method) is a method of attacking polyalphabetic substitution ciphers, such as the Vigenere cipher. It was first published by Friedrich Kasiski in 1863, but seems to have been independently discovered by Charles Babbage as early as 1846.
Incorrect answers:
Integral Cryptanalysis - uses lots of sets of plaintext that are similar with slight modifications. These are encrypted and then the variations are analyzed to determine if there's anything that can be zeroed in on.
Information Deduction - the attacker gains some Shannon information about plaintexts (or ciphertexts) not previously known.
Birthday Attack - cryptographic attack that exploits the mathematics behind the birthday problem in the probability theory forces collisions within hashing functions.
NEW QUESTION 130
Which of the following equations is related to EC?
- A. Let m = (p-1)(q-1)
- B. Me%n
- C. y^2 = x^3 + Ax + B
- D. P = Cd%n
Answer: C
Explanation:
y^2 = x^3 + Ax + B
https://en.wikipedia.org/wiki/Elliptic-curve_cryptography
For current cryptographic purposes, an elliptic curve is a plane curve over a finite field (rather than the real numbers) which consists of the points satisfying the equation:
NEW QUESTION 131
The art and science of writing hidden messages so that no one suspects the existence of the message, a type of security through obscurity. Message can be hidden in picture or audio file for example. Uses least significant bits in a file to store data.
- A. Avalanche effect
- B. Steganography
- C. Key Schedule
- D. Cryptosystem
Answer: B
Explanation:
Steganography
https://en.wikipedia.org/wiki/Steganography
Steganography is the practice of concealing a file, message, image, or video within another file, message, image, or video.
The first recorded use of the term was in 1499 by Johannes Trithemius in his Steganographia, a treatise on cryptography and steganography, disguised as a book on magic. Generally, the hidden messages appear to be (or to be part of) something else: images, articles, shopping lists, or some other cover text. For example, the hidden message may be in invisible ink between the visible lines of a private letter. Some implementations of steganography that lack a shared secret are forms of security through obscurity, and key-dependent steganographic schemes adhere to Kerckhoffs's principle.
Incorrect answers:
Avalanche effect - the desirable property of cryptographic algorithms, typically block ciphers and cryptographic hash functions, wherein if an input is changed slightly (for example, flipping a single bit), the output changes significantly (e.g., half the output bits flip). In the case of high-quality block ciphers, such a small change in either the key or the plaintext should cause a drastic change in the ciphertext.
Cryptosystem - a suite of cryptographic algorithms needed to implement a particular security service, most commonly for achieving confidentiality (encryption) Key Schedule - an algorithm for the key that calculates the subkeys for each round that the encryption goes through.
NEW QUESTION 132
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