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NEW QUESTION 53
When learning algorithms, such as RSA, it is important to understand the mathematics being used. In RSA, the number of positive integers less than or equal to some number is critical in key generation. The number of positive integers less than or equal to n that are coprime to n is called ______.
- A. Mersenne's number
- B. Fermat's number
- C. Fermat's prime
- D. Euler's totient
Answer: D
Explanation:
Euler's totient
https://en.wikipedia.org/wiki/Euler%27s_totient_function
In number theory, Euler's totient function counts the positive integers up to a given integer n that are relatively prime to n.
Incorrect answers:
Fibonacci number - commonly denoted Fn, form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1.
Fermat's number - named after Pierre de Fermat, who first studied them, is a positive integer of the form Fn = 2^2^n+1 where n is a non-negative integer. The first few Fermat numbers are:
3, 5, 17, 257, 65537, 4294967297, 18446744073709551617, ...
Mersenne prime - prime number that is one less than a power of two. That is, it is a prime number of the form Mn = 2^n - 1 for some integer n. They are named after Marin Mersenne, a French Minim friar, who studied them in the early 17th century.
NEW QUESTION 54
What must occur in order for a cipher to be considered 'broken'?
- A. Rendering the cipher no longer useable
- B. Decoding the key
- C. Uncovering the algorithm used
- D. Finding any method that is more efficient than brute force
Answer: D
Explanation:
Finding any method that is more efficient than brute force
https://en.wikipedia.org/wiki/Cryptanalysis
Bruce Schneier notes that even computationally impractical attacks can be considered breaks: "Breaking a cipher simply means finding a weakness in the cipher that can be exploited with a complexity less than brute force."
NEW QUESTION 55
A _____ is a function that takes a variable-size input m and returns a fixed-size string.
- A. Feistel
- B. Hash
- C. Symmetric cipher
- D. Asymmetric cipher
Answer: B
Explanation:
Hash
https://en.wikipedia.org/wiki/Hash_function
A hash function is any function that can be used to map data of arbitrary size to fixed-size values.
NEW QUESTION 56
Which one of the following uses three different keys, all of the same size?
- A. RSA
- B. DES
- C. 3DES
- D. AES
Answer: C
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 57
Which of the following is an asymmetric cipher?
- A. RSA
- B. DES
- C. AES
- D. RC4
Answer: A
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 58
What is the basis for the difficulty in breaking RSA?
- A. The birthday paradox
- B. Equations that describe an elliptic curve
- C. Hashing
- D. Factoring numbers
Answer: D
Explanation:
Factoring numbers
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.
NEW QUESTION 59
You are studying classic ciphers. You have been examining the difference between single substitution and multi-substitution. Which one of the following is an example of a multi-alphabet cipher?
- A. Rot13
- B. Caesar
- C. Vigenere
- D. Atbash
Answer: C
Explanation:
Vigenere
https://en.wikipedia.org/wiki/Vigen%C3%A8re_cipher
The 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.
First described by Giovan Battista Bellaso in 1553, the cipher is easy to understand and implement, but it resisted all attempts to break it until 1863, three centuries later. This earned it the description le chiffre indechiffrable (French for 'the indecipherable cipher'). Many people have tried to implement encryption schemes that are essentially Vigenere ciphers. In 1863, Friedrich Kasiski was the first to publish a general method of deciphering Vigenere ciphers.
NEW QUESTION 60
A disk you rotated to encrypt/decrypt. Created by Leon Alberti. Similar technologies were used in the Enigma machine. Considered the forefather of modern encryption.
- A. Enigma Machine
- B. Scytale Cipher
- C. Cipher Disks
- D. Chi Square
Answer: C
Explanation:
Cipher disks
https://en.wikipedia.org/wiki/Cipher_disk
A cipher disk is an enciphering and deciphering tool developed in 1470 by the Italian architect and author Leon Battista Alberti. He constructed a device, (eponymously called the Alberti cipher disk) consisting of two concentric circular plates mounted one on top of the other. The larger plate is called the "stationary" and the smaller one the "moveable" since the smaller one could move on top of the "stationary".
NEW QUESTION 61
Bruce Schneier is a well-known and highly respected cryptographer. He has developed several pseudo random number generators as well as worked on teams developing symmetric ciphers. Which one of the following is a symmetric block cipher designed in 1993 by Bruce Schneier team that is unpatented?
- A. Pegasus
- B. SHA1
- C. Blowfish
- D. AES
Answer: A
Explanation:
Blowfish
https://en.wikipedia.org/wiki/Blowfish_(cipher)
Blowfish is a symmetric-key block cipher, designed in 1993 by Bruce Schneier and included in many cipher suites and encryption products.
NEW QUESTION 62
You are explaining the details of the AES algorithm to cryptography students. You are discussing the derivation of the round keys from the shared symmetric key. The portion of AES where round keys are derived from the cipher key using Rijndael's key schedule is called what?
- A. The round key phase
- B. The bit shifting phase
- C. The initial round
- D. The key expansion phase
Answer: D
Explanation:
The key expansion phase
https://en.wikipedia.org/wiki/Advanced_Encryption_Standard
KeyExpansion - round keys are derived from the cipher key using the AES key schedule. AES requires a separate 128-bit round key block for each round plus one more.
NEW QUESTION 63
Denis is looking at an older system that uses DES encryption. A colleague has told him that DES is insecure due to a small key size. What is the key length used for DES?
- A. 0
- B. 1
- C. 2
- D. 3
Answer: B
Explanation:
56
https://en.wikipedia.org/wiki/DES
The Data Encryption Standard 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.
NEW QUESTION 64
Which of the following is not a key size used by AES?
- A. 256 bits
- B. 192 bits
- C. 128 bits
- D. 512 b
Answer: D
Explanation:
512 bits
https://en.wikipedia.org/wiki/Advanced_Encryption_Standard
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 65
This is a proprietary version of PAP. Encrypts username and password as it is sent across network.
- A. S-PAP
- B. Kerberos
- C. WPA2
- D. PPTP VPN
Answer: A
Explanation:
S-PAP
Shiva Password Authentication Protocol (S-PAP) - PAP with encryption for the usernames/passwords that are transmitted.
Incorrect answers:
Kerberos - a computer-network authentication protocol that works on the basis of tickets to allow nodes communicating over a non-secure network to prove their identity to one another in a secure manner. Its designers aimed it primarily at a client-server model and it provides mutual authentication-both the user and the server verify each other's identity. Kerberos protocol messages are protected against eavesdropping and replay attacks.
WPA2 - (Wi-Fi Protected Access II) security certification program developed by the Wi-Fi Alliance to secure wireless computer networks. It includes mandatory support for CCMP, an AES-based encryption mode.
PPTP VPN - works at layer 2 (data link) layer of OSI model. Provides both authentication and encryption. EAP or CHAP is used to provide the authentication for PPTP. MPPE (Microsoft Point to Point Encryption) is used to encrypt the traffic. MPPE - a specific Microsoft implementation of DES. Can only use over a traditional Ethernet network.
NEW QUESTION 66
If you use substitution alone, what weakness is present in the resulting cipher text?
- A. It is the same length as the original text
- B. It maintains letter and word frequency
- C. It is too simple
- D. It is easily broken with modern computers
Answer: B
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 67
RFC 1321 describes what hash?
- A. GOST
- B. MD5
- C. SHA1
- D. RIPEMD
Answer: B
Explanation:
MD5
https://en.wikipedia.org/wiki/MD5
MD5 was designed by Ronald Rivest in 1991 to replace an earlier hash function MD4, and was specified in 1992 as RFC 1321.
NEW QUESTION 68
Which of the following statements is most true regarding binary operations and encryption?
- A. They are completely useless
- B. They can provide secure encryption
- C. They can form a part of viable encryption methods
- D. They are only useful as a teaching method
Answer: C
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 69
What is the basis for the FISH algorithm?
- A. Equations that describe an ellipse
- B. Prime number theory
- C. The difficulty in factoring numbers
- D. The Lagged Fibonacci generator
Answer: D
Explanation:
The Lagged Fibonacci generator
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 70
You are explaining basic mathematics to beginning cryptography students. You are covering the basic math used in RSA. A prime number is defined as
- A. Any number only divisible by one and itself
- B. Odd numbers with no divisors
- C. Odd numbers
- D. Any number only divisible by odd numbers
Answer: D
Explanation:
Any number only divisible by one and itself
https://en.wikipedia.org/wiki/Prime_number
A prime number (or a prime) is a natural number greater than 1 that is not a product of two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number. For example, 5 is prime because the only ways of writing it as a product, 1 × 5 or 5 × 1, involve 5 itself. However, 4 is composite because it is a product (2 × 2) in which both numbers are smaller than 4. Primes are central in number theory because of the fundamental theorem of arithmetic: every natural number greater than 1 is either a prime itself or can be factorized as a product of primes that is unique up to their order.
NEW QUESTION 71
Cryptographic hashes are often used for message integrity and password storage. It is important to understand the common properties of all cryptographic hashes. What is not true about a hash?
- A. Fixed length output
- B. Reversible
- C. Few collisions
- D. Variable length input
Answer: B
Explanation:
Reversible
https://en.wikipedia.org/wiki/Hash_function
Hash functions are not reversible.
Incorrect answers:
Fixed length output and Variable length input. Hash function receive variable length input and produce fixed length output Few collisions. Every hash function with more inputs than outputs will necessarily have collisions
NEW QUESTION 72
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. Block cipher
- B. Asymmetric
- C. Symmetric
- D. Stream 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 73
Modern symmetric ciphers all make use of one or more s-boxes. Both Feistel and non-Feistel ciphers use these s-boxes. What is an s-box?
- A. A black box for the algorithm implementation
- B. Another name for the round function
- C. A shifting box where input bits are shifted
- D. A substitution box where input bits are replaced
Answer: D
Explanation:
Substitution box where input bits are replaced
https://en.wikipedia.org/wiki/S-box
In cryptography, an S-box (substitution-box) is a basic component of symmetric key algorithms which performs substitution. In block ciphers, they are typically used to obscure the relationship between the key and the ciphertext - Shannon's property of confusion.
NEW QUESTION 74
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. Null Cipher
- B. ROT-13
- C. Vigenere Cipher
- D. Rail Fence Cipher
Answer: D
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 75
Encryption of the same plain text with the same key results in the same cipher text. Use of an IV that is XORed with the first block of plain text solves this problem.
- A. GOST
- B. CFB
- C. ECB
- D. RC4
Answer: C
Explanation:
ECB
https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation
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.
The disadvantage of this method is a lack of diffusion. Because ECB encrypts identical plaintext blocks into identical ciphertext blocks, it does not hide data patterns well. ECB is not recommended for use in cryptographic protocols.
ECB mode can also make protocols without integrity protection even more susceptible to replay attacks, since each block gets decrypted in exactly the same way.
Incorrect answers:
RC4 - stream symmetric cipher that was created by Ron Rivest of RSA. Used in SSL and WEP.
GOST - the GOST block cipher (Magma), defined in the standard GOST 28147-89 (RFC 5830), is a Soviet and Russian government standard symmetric key block cipher with a block size of 64 bits. The original standard, published in 1989, did not give the cipher any name, but the most recent revision of the standard, GOST R 34.12-2015, specifies that it may be referred to as Magma. The GOST hash function is based on this cipher. The new standard also specifies a new 128-bit block cipher called Kuznyechik.
CFB - the process wherein the ciphertext block is encrypted then the ciphertext produced is XOR'd back with the plaintext to produce the current ciphertext block.
NEW QUESTION 76
Which of the following acts as a verifier for the certificate authority?
- A. Certificate Management system
- B. Certificate authority
- C. Directory management system
- D. Registration authority
Answer: D
Explanation:
Registration authority
https://en.wikipedia.org/wiki/Registration_authority
Registration authorities exist for many standards organizations, such as ANNA (Association of National Numbering Agencies for ISIN), the Object Management Group, W3C, IEEE and others. In general, registration authorities all perform a similar function, in promoting the use of a particular standard through facilitating its use. This may be by applying the standard, where appropriate, or by verifying that a particular application satisfies the standard's tenants. Maintenance agencies, in contrast, may change an element in a standard based on set rules - such as the creation or change of a currency code when a currency is created or revalued (i.e. TRL to TRY for Turkish lira). The Object Management Group has an additional concept of certified provider, which is deemed an entity permitted to perform some functions on behalf of the registration authority, under specific processes and procedures documented within the standard for such a role.
NEW QUESTION 77
Developed by Netscape and has been replaced by TLS. It was the preferred method used with secure websites.
- A. CRL
- B. SSL
- C. VPN
- D. OCSP
Answer: B
Explanation:
SSL
https://en.wikipedia.org/wiki/Transport_Layer_Security
Transport Layer Security (TLS), and its now-deprecated predecessor, Secure Sockets Layer (SSL), are cryptographic protocols designed to provide communications security over a computer network. Several versions of the protocols find widespread use in applications such as web browsing, email, instant messaging, and voice over IP (VoIP). Websites can use TLS to secure all communications between their servers and web browsers.
Netscape developed the original SSL protocols, and Taher Elgamal, chief scientist at Netscape Communications from 1995 to 1998, has been described as the "father of SSL". SSL version 1.0 was never publicly released because of serious security flaws in the protocol. Version 2.0, released in February 1995, contained a number of security flaws which necessitated the design of version 3.0. Released in 1996, SSL version 3.0 represented a complete redesign of the protocol produced by Paul Kocher working with Netscape engineers Phil Karlton and Alan Freier, with a reference implementation by Christopher Allen and Tim Dierks of Consensus Development.
Incorrect answers:
CRL - a list of every certificate that has been revoked.
VPN - A virtual private network (VPN) extends a private network across a public network and enables users to send and receive data across shared or public networks as if their computing devices were directly connected to the private network. Applications running across a VPN may therefore benefit from the functionality, security, and management of the private network. Encryption is a common, although not an inherent, part of a VPN connection OCSP - The Online Certificate Status Protocol (OCSP) is an Internet protocol used for obtaining the revocation status of an X.509 digital certificate. It is described in RFC 6960 and is on the Internet standards track. It was created as an alternative to certificate revocation lists (CRL), specifically addressing certain problems associated with using CRLs in a public key infrastructure (PKI).
NEW QUESTION 78
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