212-81 Exam Brain Dumps - Study Notes and Theory [Sep-2022]
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NEW QUESTION 52
The most common way steganography is accomplished is via which one of the following?
- A. rsb
- B. asb
- C. msb
- D. Isb
Answer: D
Explanation:
lbs
https://en.wikipedia.org/wiki/Bit_numbering#:~:text=In%20computing%2C%20the%20least%20significant,number%20is%20even%20or%20odd.
The least significant bit (LSB) is the bit position in a binary integer giving the units value, that is, determining whether the number is even or odd. The LSB is sometimes referred to as the low-order bit or right-most bit, due to the convention in positional notation of writing less significant digits further to the right. It is analogous to the least significant digit of a decimal integer, which is the digit in the ones (right-most) position.
NEW QUESTION 53
Which of the following is an asymmetric algorithm that was first publically described in 1977?
- A. Twofish
- B. RSA
- C. DESX
- D. Elliptic Curve
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.
Incorrect answers:
Elliptic Curve - Elliptic-curve cryptography (ECC) is an approach to public-key cryptography based on the algebraic structure of elliptic curves over finite fields. ECC allows smaller keys compared to non-EC cryptography (based on plain Galois fields) to provide equivalent security.
Twofish - is a symmetric key block cipher with a block size of 128 bits and key sizes up to 256 bits. It was one of the five finalists of the Advanced Encryption Standard contest, but it was not selected for standardization. Twofish is related to the earlier block cipher Blowfish.
DESX - is a variant on the DES (Data Encryption Standard) symmetric-key block cipher intended to increase the complexity of a brute-force attack using a technique called key whitening.
NEW QUESTION 54
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. Asymmetric
- B. Symmetric
- C. Block cipher
- D. Stream cipher
Answer: A
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 55
Which of the following is a substitution cipher used by ancient Hebrew scholars?
- A. Atbash
- B. Vigenere
- C. Scytale
- D. Caesar
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 56
The concept that if one bit of data changes, the cipher text will all completely change as well.
- A. Substitution
- B. Collision
- C. Confusion
- D. Avalanche
Answer: D
Explanation:
Avalanche
https://en.wikipedia.org/wiki/Avalanche_effect
In cryptography, the avalanche effect is 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. The actual term was first used by Horst Feistel, although the concept dates back to at least Shannon's diffusion.
Incorrect answers:
Confusion - Confusion means that each binary digit (bit) of the ciphertext should depend on several parts of the key, obscuring the connections between the two.
The property of confusion hides the relationship between the ciphertext and the key.
This property makes it difficult to find the key from the ciphertext and if a single bit in a key is changed, the calculation of the values of most or all of the bits in the ciphertext will be affected.
Confusion increases the ambiguity of ciphertext and it is used by both block and stream ciphers.
Substitution - 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.
Collision - occurs when a hash function generates the same output for different inputs.
NEW QUESTION 57
John is trying to explain the basics of cryptography to a group of young, novice, security students. Which one of the following most accurately defines encryption?
- A. Changing a message so it can only be easily read by the intended recipient
- B. Complex mathematics to conceal a message
- C. Applying keys to a message to conceal it
- D. Changing a message using complex mathematics
Answer: A
Explanation:
Changing a message so it can only be easily read by the intended recipient
https://en.wikipedia.org/wiki/Encryption
Encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can decipher a ciphertext back to plaintext and access the original information. Encryption does not itself prevent interference but denies the intelligible content to a would-be interceptor.
NEW QUESTION 58
Which of the following is the successor of SSL?
- A. GRE
- B. RSA
- C. IPSec
- D. TLS
Answer: D
Explanation:
TLS
https://en.wikipedia.org/wiki/Transport_Layer_Security#History_and_development TLS 1.0 was first defined in RFC 2246 in January 1999 as an upgrade of SSL Version 3.0, and written by Christopher Allen and Tim Dierks of Consensus Development. As stated in the RFC, "the differences between this protocol and SSL 3.0 are not dramatic, but they are significant enough to preclude interoperability between TLS 1.0 and SSL 3.0". Tim Dierks later wrote that these changes, and the renaming from "SSL" to "TLS", were a face-saving gesture to Microsoft, "so it wouldn't look [like] the IETF was just rubberstamping Netscape's protocol".
NEW QUESTION 59
Which of the following equations is related to EC?
- A. P = Cd%n
- B. y^2 = x^3 + Ax + B
- C. Let m = (p-1)(q-1)
- D. Me%n
Answer: B
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 60
Widely used, particularly with Microsoft operating systems. Created by MIT and derives its name from the mythical three headed dog. The is a great deal of verification for the tickets and the tickets expire quickly. Client authenticates to the Authentication Server once using a long term shared secret and receives back a Ticket-Granting Server. Client can reuse this ticket to get additional tickets without reusing the shared secret. These tickets are used to prove authentication to the Service Server.
- A. Diffie-Hellman
- B. Yarrow
- C. Kerberos
- D. ElGamal
Answer: C
Explanation:
Kerberos
https://en.wikipedia.org/wiki/Kerberos_(protocol)
Kerberos is 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. The protocol was named after the character Kerberos (or Cerberus) from Greek mythology, the ferocious three-headed guard dog of Hades. 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.
Kerberos builds on symmetric key cryptography and requires a trusted third party, and optionally may use public-key cryptography during certain phases of authentication. Kerberos uses UDP port 88 by default.
Incorrect answers:
ElGamal - ElGamal encryption system is an asymmetric key encryption algorithm for public-key cryptography which is based on the Diffie-Hellman key exchange. It was described by Taher Elgamal in 1985. ElGamal encryption is used in the free GNU Privacy Guard software, recent versions of PGP, and other cryptosystems. The Digital Signature Algorithm (DSA) is a variant of the ElGamal signature scheme, which should not be confused with ElGamal encryption.
Diffie-Hellman - Diffie-Hellman key exchange is a method of securely exchanging cryptographic keys over a public channel and was one of the first public-key protocols as conceived by Ralph Merkle and named after Whitfield Diffie and Martin Hellman.[1][2] DH is one of the earliest practical examples of public key exchange implemented within the field of cryptography. Published in 1976 by Diffie and Hellman, this is the earliest publicly known work that proposed the idea of a private key and a corresponding public key.
Yarrow - algorithm is a family of cryptographic pseudorandom number generators (CPRNG) devised by John Kelsey, Bruce Schneier, and Niels Ferguson and published in 1999. The Yarrow algorithm is explicitly unpatented, royalty-free, and open source; no license is required to use it. Yarrow is incorporated in iOS and macOS for their /dev/random devices, and was in FreeBSD (where it is superseded by Fortuna).
NEW QUESTION 61
Which of the following is an asymmetric cipher?
- A. AES
- B. RSA
- C. RC4
- D. DES
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 62
What is the name of the attack where the attacker obtains the ciphertexts corresponding to a set of plaintexts of his own choosing?
- A. Kasiski examination
- B. Differential cryptanalysis
- C. Chosen plaintext
- D. Known-plaintext attack
Answer: C
Explanation:
Chosen plaintext
https://en.wikipedia.org/wiki/Chosen-plaintext_attack
A chosen-plaintext attack (CPA) is an attack model for cryptanalysis which presumes that the attacker can obtain the ciphertexts for arbitrary plaintexts. The goal of the attack is to gain information that reduces the security of the encryption scheme.
Incorrect answers:
Differential cryptanalysis - is a general form of cryptanalysis applicable primarily to block ciphers, but also to stream ciphers and cryptographic hash functions. In the broadest sense, it is the study of how differences in information input can affect the resultant difference at the output. In the case of a block cipher, it refers to a set of techniques for tracing differences through the network of transformation, discovering where the cipher exhibits non-random behavior, and exploiting such properties to recover the secret key (cryptography key).
Known-plaintext attack - (KPA) is an attack model for cryptanalysis where the attacker has access to both the plaintext (called a crib), and its encrypted version (ciphertext). These can be used to reveal further secret information such as secret keys and code books.
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. In polyalphabetic substitution ciphers where the substitution alphabets are chosen by the use of a keyword, the Kasiski examination allows a cryptanalyst to deduce the length of the keyword. Once the length of the keyword is discovered, the cryptanalyst lines up the ciphertext in n columns, where n is the length of the keyword. Then each column can be treated as the ciphertext of a monoalphabetic substitution cipher. As such, each column can be attacked with frequency analysis.
NEW QUESTION 63
Which of the following techniques is used (other than brute force) to attempt to derive a key?
- A. Cryptoanalysis
- B. Password cracking
- C. Cryptography
- D. Hacking
Answer: A
Explanation:
Cryptoanalysis
https://en.wikipedia.org/wiki/Cryptanalysis
Cryptanalysis is the study of analyzing information systems in order to study the hidden aspects of the systems. Cryptanalysis is used to breach cryptographic security systems and gain access to the contents of encrypted messages, even if the cryptographic key is unknown.
NEW QUESTION 64
A real time protocol for verifying certificates (and a newer method than CRL).
- A. Public Key Infrastructure (PKI)
- B. Server-based Certificate Validation Protocol (SCVP)
- C. Online Certificate Status Protocol (OCSP)
- D. Registration Authority (RA)
Answer: C
Explanation:
Online Certificate Status Protocol (OCSP)
https://en.wikipedia.org/wiki/Online_Certificate_Status_Protocol
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).
Incorrect answers:
Public Key Infrastructure (PKI) - set of roles, policies, hardware, software and procedures needed to create, manage, distribute, use, store and revoke digital certificates and manage public-key encryption. The purpose of a PKI is to facilitate the secure electronic transfer of information for a range of network activities such as e-commerce, internet banking and confidential email. It is required for activities where simple passwords are an inadequate authentication method and more rigorous proof is required to confirm the identity of the parties involved in the communication and to validate the information being transferred.
Registration Authority (RA) - component of PKI that validates the identity of an entity requesting a digital certificate.
Server-based Certificate Validation Protocol (SCVP) - Internet protocol for determining the path between an X.509 digital certificate and a trusted root (Delegated Path Discovery) and the validation of that path (Delegated Path Validation) according to a particular validation policy.
NEW QUESTION 65
Which of the following is a block cipher?
- A. RSA
- B. RC4
- C. AES
- D. DH
Answer: C
Explanation:
AES
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 Incorrect answers:
RC4. RC4 (Rivest Cipher 4 also known as ARC4 or ARCFOUR meaning Alleged RC4, see below) is a stream cipher.
DH. Diffie-Hellman key exchange is a method of securely exchanging cryptographic keys over a public channel and was one of the first public-key protocols as conceived by Ralph Merkle and named after Whitfield Diffie and Martin Hellman.
RSA. RSA (Rivest-Shamir-Adleman) is one of the first public-key cryptosystems and is widely used for secure data transmission.
NEW QUESTION 66
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 substitution box where input bits are replaced
- B. Another name for the round function
- C. A shifting box where input bits are shifted
- D. A black box for the algorithm implementation
Answer: A
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 67
In which of the following password protection technique, random strings of characters are added to the password before calculating their hashes?
- A. Key Stretching
- B. Double Hashing
- C. Salting
- D. Keyed Hashing
Answer: C
Explanation:
Salting
https://en.wikipedia.org/wiki/Salt_(cryptography)
A salt is random data that is used as an additional input to a one-way function that hashes data, a password or passphrase. Salts are used to safeguard passwords in storage. Historically a password was stored in plaintext on a system, but over time additional safeguards were developed to protect a user's password against being read from the system.
A new salt is randomly generated for each password. In a typical setting, the salt and the password (or its version after key stretching) are concatenated and processed with a cryptographic hash function, and the output hash value (but not the original password) is stored with the salt in a database. Hashing allows for later authentication without keeping and therefore risking exposure of the plaintext password in the event that the authentication data store is compromised.
Salts defend against a pre-computed hash attack, e.g. rainbow tables.Since salts do not have to be memorized by humans they can make the size of the hash table required for a successful attack prohibitively large without placing a burden on the users. Since salts are different in each case, they also protect commonly used passwords, or those users who use the same password on several sites, by making all salted hash instances for the same password different from each other.
NEW QUESTION 68
Message hidden in unrelated text. Sender and receiver have pre-arranged to use a pattern to remove certain letters from the message which leaves only the true message behind.
- A. Null Ciphers
- B. Vigenere Cipher
- C. Playfair Cipher
- D. Caesar Cipher
Answer: A
Explanation:
Null Ciphers
https://en.wikipedia.org/wiki/Null_cipher
A 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.
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 - 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.
Playfair Cipher - manual symmetric encryption technique and was the first literal digram substitution cipher. The scheme was invented in 1854 by Charles Wheatstone, but bears the name of Lord Playfair for promoting its use.
NEW QUESTION 69
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. Electronic codebook (ECB)
- C. Cipher-block chaining (CBC)
- D. Cipher feedback (CFB)
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 70
A linear congruential generator is an example of what?
- A. A random number generator
- B. A prime number generator
- C. A pseudo random number generator
- D. A coprime generator
Answer: C
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 71
Frank is trying to break into an encrypted file... He is attempting all the possible keys that could be used for this algorithm. Attempting to crack encryption by simply trying as many randomly generated keys as possible is referred to as what?
- A. Frequency analysis
- B. Kasiski
- C. Brute force
- D. Rainbow table
Answer: C
Explanation:
Brute force
https://en.wikipedia.org/wiki/Brute-force_attack
Brute-force attack consists of an attacker submitting many passwords or passphrases with the hope of eventually guessing correctly. The attacker systematically checks all possible passwords and passphrases until the correct one is found. Alternatively, the attacker can attempt to guess the key which is typically created from the password using a key derivation function. This is known as an exhaustive key search.
Incorrect answers:
Kasiski - 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.
Rainbow table - is a precomputed table for caching the output of cryptographic hash functions, usually for cracking password hashes. Tables are usually used in recovering a key derivation function (or credit card numbers, etc.) up to a certain length consisting of a limited set of characters. It is a practical example of a space-time tradeoff, using less computer processing time and more storage than a brute-force attack which calculates a hash on every attempt, but more processing time and less storage than a simple key derivation function with one entry per hash. Use of a key derivation that employs a salt makes this attack infeasible.
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.
NEW QUESTION 72
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