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NEW QUESTION 75
A cryptanalysis success where the attacker deduces the secret key.
- A. Shannon's Entropy
- B. Total Break
- C. Information Deduction
- D. Avalanche effect
Answer: B
Explanation:
Total Break
https://en.wikipedia.org/wiki/Cryptanalysis
The results of cryptanalysis can also vary in usefulness. For example, cryptographer Lars Knudsen (1998) classified various types of attack on block ciphers according to the amount and quality of secret information that was discovered:
Total break - the attacker deduces the secret key.
Global deduction - the attacker discovers a functionally equivalent algorithm for encryption and decryption, but without learning the key.
Instance (local) deduction - the attacker discovers additional plaintexts (or ciphertexts) not previously known.
Information deduction - the attacker gains some Shannon information about plaintexts (or ciphertexts) not previously known.
Distinguishing algorithm - the attacker can distinguish the cipher from a random permutation.
Incorrect answers:
Shannon's Entropy - average level of "information", "surprise", or "uncertainty" inherent in the variable's possible outcomes. The concept of information entropy was introduced by Claude Shannon in his 1948 paper "A Mathematical Theory of Communication".
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.
NEW QUESTION 76
A linear congruential generator is an example of what?
- A. A coprime generator
- B. A prime number generator
- C. A random number generator
- D. A pseudo random number generator
Answer: D
Explanation:
A pseudo random number generator
https://en.wikipedia.org/wiki/Linear_congruential_generator
A linear congruential generator (LCG) is an algorithm that yields a sequence of pseudo-randomized numbers calculated with a discontinuous piecewise linear equation. The method represents one of the oldest and best-known pseudorandom number generator algorithms. The theory behind them is relatively easy to understand, and they are easily implemented and fast, especially on computer hardware which can provide modular arithmetic by storage-bit truncation.
NEW QUESTION 77
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. A minimum key size of 256 bits is necessary for security
- D. Only the key needs to be secret, not the actual algorithm
Answer: D
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 78
This algorithm was published by the German engineering firm Seimans in 1993. It is a software based stream cipher using Lagged Fibonacci generator along with a concept borrowed from the shrinking generator ciphers.
- A. RC4
- B. FISH
- C. Blowfish
- D. Twofish
Answer: B
Explanation:
FISH
https://en.wikipedia.org/wiki/FISH_(cipher)
The FISH (FIbonacci SHrinking) stream cipher is a fast software based stream cipher using Lagged Fibonacci generators, plus a concept from the shrinking generator cipher. It was published by Siemens in 1993. FISH is quite fast in software and has a huge key length. However, in the same paper where he proposed Pike, Ross Anderson showed that FISH can be broken with just a few thousand bits of known plaintext.
NEW QUESTION 79
In steganography, ________ is the data to be covertly communicated (in other words, it is the message you wish to hide).
- A. Carrier
- B. Signal
- C. Channel
- D. Payload
Answer: D
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 80
The most widely used asymmetric encryption algorithm is what?
- A. DES
- B. Vigenere
- C. Caesar Cipher
- D. RSA
Answer: D
Explanation:
RSA
The RSA encryption algorithm is one of the most widely used public key encryption algorithms that have ever been invented. It was created by the three scientists Ronald Rivest, Adi Shamir, and Leonard Adleman in 1977, and today it is increasingly being used in the network area.
Incorrect answers:
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.
Vigenere - Multi alphabet cipher Invented by Giovan Battista Bellaso in middle 1553. Vigenere created a stronger version of the cipher. Combining/Weaving Caesar cipher. Not cracked until late 1800s. Widely used from 16th century to early 20th century. It is a cipher square with A to Z across all the columns and rows. You then use a keyword to encrypt the message DES - The Data Encryption Standard is a symmetric-key algorithm for the encryption of digital data.
NEW QUESTION 81
Hash. Created by Ronald Rivest. Replaced MD4. 128 bit output size, 512 bit block size, 32 bit word size, 64 rounds. Infamously compromised by Flame malware in 2012.
- A. SHA-1
- B. TIGER
- C. MD5
- D. Keccak
Answer: C
Explanation:
MD5
https://en.wikipedia.org/wiki/MD5
The MD5 message-digest algorithm is a widely used hash function producing a 128-bit hash value. Although MD5 was initially designed to be used as a cryptographic hash function, it has been found to suffer from extensive vulnerabilities. It can still be used as a checksum to verify data integrity, but only against unintentional corruption. It remains suitable for other non-cryptographic purposes, for example for determining the partition for a particular key in a partitioned database.
MD5 was designed by Ronald Rivest in 1991 to replace an earlier hash function MD4, and was specified in 1992 as RFC 1321 Incorrect answers:
TIGER - hash. Created by Ross Anderson and Eli Baham. 192/160/128 bit output size, 512 bit block size, 53 bit word size, 24 rounds.
SHA-1 - Secure Hashing Algorithm. Designed by NSA. 160 bit output size, 512 bit block size, 40 bit word size, 80 rounds.
Keccak - SHA-3 (Secure Hash Algorithm 3) is the latest member of the Secure Hash Algorithm family of standards, released by NIST on August 5, 2015. SHA-3 is a subset of the broader cryptographic primitive family Keccak, designed by Guido Bertoni, Joan Daemen, Michael Peeters, and Gilles Van Assche, building upon RadioGatun.
NEW QUESTION 82
The reverse process from encoding - converting the encoded message back into its plaintext format.
- A. Decoding
- B. Whitening
- C. Encoding
- D. Substitution
Answer: A
Explanation:
Decoding
Decoding - reverse process from encoding,converting the encoded message back into its plaintext format.
NEW QUESTION 83
A _________ is a digital representation of information that identifies you as a relevant entity by a trusted third party.
- A. Digest
- B. Digital Signature
- C. Hash
- D. Ownership stamp
Answer: B
Explanation:
Digital Signature
https://en.wikipedia.org/wiki/Digital_signature
A digital signature is a mathematical scheme for verifying the authenticity of digital messages or documents. A valid digital signature, where the prerequisites are satisfied, gives a recipient very strong reason to believe that the message was created by a known sender (authentication), and that the message was not altered in transit (integrity).
NEW QUESTION 84
The mode makes a block cipher into a synchronous stream cipher. It generates keystream blocks, which are then XORed with the plaintext blocks to get the ciphertext.
- A. Output feedback (OFB)
- B. Cipher-block chaining (CBC)
- C. Cipher feedback (CFB)
- D. Electronic codebook (ECB)
Answer: A
Explanation:
Output feedback (OFB)
https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Output_feedback_(OFB) The output feedback (OFB) mode makes a block cipher into a synchronous stream cipher. It generates keystream blocks, which are then XORed with the plaintext blocks to get the ciphertext. Just as with other stream ciphers, flipping a bit in the ciphertext produces a flipped bit in the plaintext at the same location. This property allows many error-correcting codes to function normally even when applied before encryption.
Incorrect answers:
Cipher feedback (CFB) - mode, a close relative of CBC, makes a block cipher into a self-synchronizing stream cipher.
Electronic codebook (ECB) - the simplest of the encryption modes (named after conventional physical codebooks). The message is divided into blocks, and each block is encrypted separately.
Cipher-block chaining (CBC) - Ehrsam, Meyer, Smith and Tuchman invented the cipher block chaining (CBC) mode of operation in 1976. In CBC mode, each block of plaintext is XORed with the previous ciphertext block before being encrypted. This way, each ciphertext block depends on all plaintext blocks processed up to that point. To make each message unique, an initialization vector must be used in the first block.
NEW QUESTION 85
Which one of the following best describes a process that splits the block of plaintext into two separate blocks, then applies the round function to one half, and finally swaps the two halves?
- A. Symmetric cryptography
- B. Feistel cipher
- C. Block ciphers
- D. Substitution cipher
Answer: B
Explanation:
Correct answer:
https://en.wikipedia.org/wiki/Feistel_cipher
Feistel cipher (also known as Luby-Rackoff block cipher) is a symmetric structure used in the construction of block ciphers, named after the German-born physicist and cryptographer Horst Feistel who did pioneering research while working for IBM (USA); it is also commonly known as a Feistel network. A large proportion of block ciphers use the scheme, including the US Data Encryption Standard, the Soviet-developed GOST and the more recent Blowfish and Twofish ciphers. In a Feistel cipher, encryption and decryption are very similar operations, and both consist of iteratively running a function called a "round function" a fixed number of times.
Incorrect answers:
Symmetric cryptography - Symmetric-key algorithms are algorithms for cryptography that use the same cryptographic keys for both encryption of plaintext and decryption of ciphertext. The keys may be identical or there may be a simple transformation to go between the two keys.
Substitution cipher - is a method of encrypting by which units of plaintext are replaced with ciphertext, according to a fixed system; the "units" may be single letters (the most common), pairs of letters, triplets of letters, mixtures of the above, and so forth. The receiver deciphers the text by performing the inverse substitution.
Block ciphers - block cipher is a deterministic algorithm operating on fixed-length groups of bits, called blocks. It uses an unvarying transformation, that is, it uses a symmetric key. They are specified elementary components in the design of many cryptographic protocols and are widely used to implement the encryption of large amounts of data, including data exchange protocols.
NEW QUESTION 86
Ciphers that write message letters out diagonally over a number of rows then read off cipher row by row. Also called zig-zag cipher.
- A. Vigenere Cipher
- B. Rail Fence Cipher
- C. ROT-13
- D. Null Cipher
Answer: B
Explanation:
Rail Fence Cipher
https://en.wikipedia.org/wiki/Rail_fence_cipher
The rail fence cipher (also called a zigzag cipher) is a form of transposition cipher. It derives its name from the way in which it is encoded.
Incorrect answers:
Null cipher - also known as concealment cipher, is an ancient form of encryption where the plaintext is mixed with a large amount of non-cipher material. Today it is regarded as a simple form of steganography, which can be used to hide ciphertext.
Vigenere cipher - is a 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.
ROT13 - ("rotate by 13 places", sometimes hyphenated ROT-13) is a simple letter substitution cipher that replaces a letter with the 13th letter after it, in the alphabet. ROT13 is a special case of the Caesar cipher which was developed in ancient Rome.
NEW QUESTION 87
Which one of the following uses three different keys, all of the same size?
- A. RSA
- B. DES
- C. AES
- D. 3DES
Answer: D
Explanation:
3DES
https://en.wikipedia.org/wiki/Triple_DES
Triple DES (3DES or TDES), officially the Triple Data Encryption Algorithm (TDEA or Triple DEA), is a symmetric-key block cipher, which applies the DES cipher algorithm three times to each data block.
NEW QUESTION 88
Which of the following is generally true about key sizes?
- A. Key sizes must be more than 256 bits to be secure
- B. Smaller key sizes increase security
- C. Key size is irrelevant to security
- D. Larger key sizes increase security
Answer: D
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 89
Which of the following statements is most true regarding binary operations and encryption?
- A. They can form a part of viable encryption methods
- B. They are only useful as a teaching method
- C. They can provide secure encryption
- D. They are completely useless
Answer: A
Explanation:
They can form a part of viable encryption methods
for example - https://en.wikipedia.org/wiki/XOR_cipher
The XOR operator is extremely common as a component in more complex ciphers. By itself, using a constant repeating key, a simple XOR cipher can trivially be broken using frequency analysis. If the content of any message can be guessed or otherwise known then the key can be revealed. Its primary merit is that it is simple to implement, and that the XOR operation is computationally inexpensive. A simple repeating XOR (i.e. using the same key for xor operation on the whole data) cipher is therefore sometimes used for hiding information in cases where no particular security is required. The XOR cipher is often used in computer malware to make reverse engineering more difficult.
NEW QUESTION 90
Which of the following is a type of encryption that has two different keys. One key can encrypt the message and the other key can only decrypt it?
- A. Symmetric
- B. Asymmetric
- C. Stream cipher
- D. Block cipher
Answer: B
Explanation:
Asymmetric
Public-key cryptography, or asymmetric cryptography, is a cryptographic system that uses pairs of keys: public keys, which may be disseminated widely, and private keys, which are known only to the owner. The generation of such keys depends on cryptographic algorithms based on mathematical problems to produce one-way functions. Effective security only requires keeping the private key private; the public key can be openly distributed without compromising security.
Incorrect answers:
Symmetric - Symmetric-key algorithms are algorithms for cryptography that use the same cryptographic keys for both encryption of plaintext and decryption of ciphertext.
Block cipher - A block cipher is a deterministic algorithm operating on fixed-length groups of bits, called blocks. It uses an unvarying transformation, that is, it uses a symmetric key.
Stream cipher - A stream cipher is a symmetric key cipher where plaintext digits are combined with a pseudorandom cipher digit stream (keystream). In a stream cipher, each plaintext digit is encrypted one at a time with the corresponding digit of the keystream, to give a digit of the ciphertext stream.
NEW QUESTION 91
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