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C839 Introduction to Cryptography
Questions and Answers (Expert Solutions)
Q: Cryptography
ANS 🗹🗹: the science that studies encryption, which is the hiding of messages so
that only the sender and receiver can read them. Cybersecurity, computer science,
programming, and other IT career fields require a conceptual understanding of
cryptography and familiarity with its basic vocabulary.
Q: Caesar Cypher
ANS 🗹🗹: letter-by-letter method to make a cipher. For each letter, substitute
another letter 4 letters ahead. For "a", write "d".
Q: Employee B sends Employee A an encrypted message. What does employee A use to
decrypt the message from employee B
ANS 🗹🗹: Employee As private key
Q: Advanced encryption system (AES)
ANS 🗹🗹: is an example of a symmetric algorithm. RSA, SHA, and MD5 are not
symmetric algorithms.
Q: Employee A created a secret key and wants to send it to Employee B without any
coworkers being able to decrypt the message. Which key needs to encrypt the message?
ANS 🗹🗹: Employee B's public key
Q: Which type of cipher is ChaCha?
ANS 🗹🗹: stream
Q: What is the key size for RC4 with WEP?
ANS 🗹🗹: 40 bits
Q: What is the length (in bits) of an MD5 hash output?
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ANS 🗹🗹: 128 bits
Q: Which mode encrypts each group with the same key, leaving each group
independent of the others?
ANS 🗹🗹: ECB Electronic Code Book (ECB) is a simple mode of operation with a block
cipher that's mostly used with symmetric key encryption. It is a straightforward
way of processing a series of sequentially listed message blocks. The input plaintext
is broken into numerous blocks.
Q: ECB
ANS 🗹🗹: Electronic Code Book
Q: Which mode of block encryption results in the same outcome for matching blocks of
a plaintext message?
ANS 🗹🗹: Electronic Code Book (ECB)
Q: Which encryption mode always produces the same result for the same plaintext?
ANS 🗹🗹: Electronic Code Book (ECB)
Q: Skipjack
ANS 🗹🗹: Promoted by the NSA. Skipjack uses an 80-bit key, supports the same four
modes of operation as DES, and operates on 64-bit blocks of text. Skipjack provides
cryptographic routines in support of Clipper and Capstone. Skipjack faced public
opposition because it was developed so that the government could maintain
information enabling legal authorities (with a search warrant or approval of the
court) to reconstruct a Skipjack access key and decrypt private communications
between affected parties.
Q: How many transformation rounds does AES use with a 192-bit key?
ANS 🗹🗹: 12
Q: How many transformation rounds does AES use with a 128-bit key?
ANS 🗹🗹: 10
Q: Why is symmetric stream used to encrypt video when speed is a major concern?
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ANS 🗹🗹: It uses the same key to encrypt and decrypt large amounts of media. So, it
is faster.
Q: Why should an asymmetric public key be used to encrypt a symmetric key that is
being sent to one person?
ANS 🗹🗹: It encrypts a small amount of information, which is decrypted with the
corresponding private key.
Q: Which mechanism mitigates a copy-and-paste attack when using AES?
ANS 🗹🗹: Output feedback (OFB) loop
Q: Which mechanism can be used to ensure perfect forward secrecy during key
exchange when using symmetric encryption?
ANS 🗹🗹: Elliptical curve Diffie-Hellman (ECDH)
Q: Which encryption component ensures that the compromise of a long-term key
prevents the compromise of any previous session keys?
ANS 🗹🗹: Forward secrecy
Q: How does cipher block chaining (CBC) create randomness in a second block after
encrypting the first block with an initialization vector (IV)?
ANS 🗹🗹: Uses the results of the Initialization Vector (IV) to encrypt the next block
Q: How is information about Bitcoin transactions stored?
ANS 🗹🗹: Distributed peer-to-peer network
Q: What is one of the primary characteristics of a blockchain in the context of Bitcoin?
ANS 🗹🗹: Adding blocks to a blockchain is computationally expensive.
Q: What is the length (in bits) of the private key used to sign transactions and associated
with an individual wallet in the context of Bitcoin?
ANS 🗹🗹: 256 bits
Q: Which certificate management process involves key recovery?
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ANS 🗹🗹: Issued
Q: Which algorithm is used to generate the thumbprint of a certificate?
ANS 🗹🗹: Secure hash Algorithm 1 (SHA-1 )
Q: What is the maximum length (in bits) of encryption keys used by the WEP protocol?
ANS 🗹🗹: 40 bits
Q: How does TKIP improve WPA over WEP?
ANS 🗹🗹: Hashes the initialization vector and secret key
Q: An administrator has configured a virtual private network (VPN) connection
utilizing IPsec tunnel mode with Encapsulating Security Payload (ESP) between the
corporate office and a remote office.Where can the packets be inspected by intrusion
detection systems (IDSs) and virus scanners?
ANS 🗹🗹: At the headquarters and the offsite location
Q: Which default port must be open for the IPsec key exchange to be successful?
ANS 🗹🗹: UDP 500
Q: Which protocol indicates the virtual private network (VPN) is using Authentication
Header (AH)?
ANS 🗹🗹: 51
Q: Which cipher uses a grid to map letters into numeric values?
ANS 🗹🗹: Bifid The Bifid Cipher uses a Polybius Square to encipher a message in a
way that makes it fairly difficult to decipher without knowing the secret. This is
because each letter in the ciphertext message is dependent upon two letters from
the plaintext message. As a result, frequency analysis of letters becomes much more
difficult.
Q: Which cipher uses a five-by-five matrix with nonrepeating characters?
C839 Introduction to Cryptography
Questions and Answers (Expert Solutions)
Q: Cryptography
ANS 🗹🗹: the science that studies encryption, which is the hiding of messages so
that only the sender and receiver can read them. Cybersecurity, computer science,
programming, and other IT career fields require a conceptual understanding of
cryptography and familiarity with its basic vocabulary.
Q: Caesar Cypher
ANS 🗹🗹: letter-by-letter method to make a cipher. For each letter, substitute
another letter 4 letters ahead. For "a", write "d".
Q: Employee B sends Employee A an encrypted message. What does employee A use to
decrypt the message from employee B
ANS 🗹🗹: Employee As private key
Q: Advanced encryption system (AES)
ANS 🗹🗹: is an example of a symmetric algorithm. RSA, SHA, and MD5 are not
symmetric algorithms.
Q: Employee A created a secret key and wants to send it to Employee B without any
coworkers being able to decrypt the message. Which key needs to encrypt the message?
ANS 🗹🗹: Employee B's public key
Q: Which type of cipher is ChaCha?
ANS 🗹🗹: stream
Q: What is the key size for RC4 with WEP?
ANS 🗹🗹: 40 bits
Q: What is the length (in bits) of an MD5 hash output?
, Page | 2
ANS 🗹🗹: 128 bits
Q: Which mode encrypts each group with the same key, leaving each group
independent of the others?
ANS 🗹🗹: ECB Electronic Code Book (ECB) is a simple mode of operation with a block
cipher that's mostly used with symmetric key encryption. It is a straightforward
way of processing a series of sequentially listed message blocks. The input plaintext
is broken into numerous blocks.
Q: ECB
ANS 🗹🗹: Electronic Code Book
Q: Which mode of block encryption results in the same outcome for matching blocks of
a plaintext message?
ANS 🗹🗹: Electronic Code Book (ECB)
Q: Which encryption mode always produces the same result for the same plaintext?
ANS 🗹🗹: Electronic Code Book (ECB)
Q: Skipjack
ANS 🗹🗹: Promoted by the NSA. Skipjack uses an 80-bit key, supports the same four
modes of operation as DES, and operates on 64-bit blocks of text. Skipjack provides
cryptographic routines in support of Clipper and Capstone. Skipjack faced public
opposition because it was developed so that the government could maintain
information enabling legal authorities (with a search warrant or approval of the
court) to reconstruct a Skipjack access key and decrypt private communications
between affected parties.
Q: How many transformation rounds does AES use with a 192-bit key?
ANS 🗹🗹: 12
Q: How many transformation rounds does AES use with a 128-bit key?
ANS 🗹🗹: 10
Q: Why is symmetric stream used to encrypt video when speed is a major concern?
, Page | 3
ANS 🗹🗹: It uses the same key to encrypt and decrypt large amounts of media. So, it
is faster.
Q: Why should an asymmetric public key be used to encrypt a symmetric key that is
being sent to one person?
ANS 🗹🗹: It encrypts a small amount of information, which is decrypted with the
corresponding private key.
Q: Which mechanism mitigates a copy-and-paste attack when using AES?
ANS 🗹🗹: Output feedback (OFB) loop
Q: Which mechanism can be used to ensure perfect forward secrecy during key
exchange when using symmetric encryption?
ANS 🗹🗹: Elliptical curve Diffie-Hellman (ECDH)
Q: Which encryption component ensures that the compromise of a long-term key
prevents the compromise of any previous session keys?
ANS 🗹🗹: Forward secrecy
Q: How does cipher block chaining (CBC) create randomness in a second block after
encrypting the first block with an initialization vector (IV)?
ANS 🗹🗹: Uses the results of the Initialization Vector (IV) to encrypt the next block
Q: How is information about Bitcoin transactions stored?
ANS 🗹🗹: Distributed peer-to-peer network
Q: What is one of the primary characteristics of a blockchain in the context of Bitcoin?
ANS 🗹🗹: Adding blocks to a blockchain is computationally expensive.
Q: What is the length (in bits) of the private key used to sign transactions and associated
with an individual wallet in the context of Bitcoin?
ANS 🗹🗹: 256 bits
Q: Which certificate management process involves key recovery?
, Page | 4
ANS 🗹🗹: Issued
Q: Which algorithm is used to generate the thumbprint of a certificate?
ANS 🗹🗹: Secure hash Algorithm 1 (SHA-1 )
Q: What is the maximum length (in bits) of encryption keys used by the WEP protocol?
ANS 🗹🗹: 40 bits
Q: How does TKIP improve WPA over WEP?
ANS 🗹🗹: Hashes the initialization vector and secret key
Q: An administrator has configured a virtual private network (VPN) connection
utilizing IPsec tunnel mode with Encapsulating Security Payload (ESP) between the
corporate office and a remote office.Where can the packets be inspected by intrusion
detection systems (IDSs) and virus scanners?
ANS 🗹🗹: At the headquarters and the offsite location
Q: Which default port must be open for the IPsec key exchange to be successful?
ANS 🗹🗹: UDP 500
Q: Which protocol indicates the virtual private network (VPN) is using Authentication
Header (AH)?
ANS 🗹🗹: 51
Q: Which cipher uses a grid to map letters into numeric values?
ANS 🗹🗹: Bifid The Bifid Cipher uses a Polybius Square to encipher a message in a
way that makes it fairly difficult to decipher without knowing the secret. This is
because each letter in the ciphertext message is dependent upon two letters from
the plaintext message. As a result, frequency analysis of letters becomes much more
difficult.
Q: Which cipher uses a five-by-five matrix with nonrepeating characters?
