CISSP (Chapter 7 - Cryptography) Flashcards
What is the goal of cryptanalysis?
A. To determine the strength of an algorithm
B. To increase the substitution functions in a cryptographic algorithm
C. To decrease the transposition functions in a cryptographic algorithm
D. To determine the permutations used
A. Cryptanalysis is the process of trying to reverse-engineer a cryptosystem, with the possible goal of uncovering the key used. Once this key is uncovered, all other messages encrypted with this key can be accessed. Cryptanalysis is carried out by the white hats to test the strength of the algorithm.
The frequency of successful brute force attacks has increased because
A. The use of permutations and transpositions in algorithms has increased.
B. As algorithms get stronger, they get less complex, and thus more susceptible to attacks.
C. Processor speed and power have increased.
D. Key length reduces over time
C. A brute force attack is resource-intensive. It tries all values until the correct one is obtained. As computers have more powerful processors added to them, attackers can carry out more powerful brute force attacks.
Which of the following is not a property or characteristic of a one-way hash function?
A. It converts a message of arbitrary length into a value of fixed length.
B. Given the digest value, it should be computationally infeasible to find the corresponding message.
C. It should be impossible or rare to derive the same digest from two different messages.
D. It converts a message of fixed length to an arbitrary length value.
D. A hashing algorithm will take a string of variable length, the message can be any size, and compute a fixed-length value. The fixed-length value is the message digest. The MD family creates the fixed-length value of 128 bits, and SHA creates one of 160 bits.
What would indicate that a message had been modified?
A. The public key has been altered.
B. The private key has been altered.
C. The message digest has been altered.
D. The message has been encrypted properly
C. Hashing algorithms generate message digests to detect whether modification has taken place. The sender and receiver independently generate their own digests, and the receiver compares these values. If they differ, the receiver knows the message has been altered.
Which of the following is a U.S. federal government algorithm developed for creating secure message digests? A. Data Encryption Algorithm B. Digital Signature Standard C. Secure Hash Algorithm D. Data Signature Algorithm
C. SHA was created to generate secure message digests. Digital Signature Standard (DSS) is the standard to create digital signatures, which dictates that SHA must be used. DSS also outlines the digital signature algorithms that can be used with SHA: RSA, DSA, and ECDSA
Which of the following best describes the difference between HMAC and CBC-MAC?
A. HMAC creates a message digest and is used for integrity; CBC-MAC is used to encrypt blocks of data for confidentiality.
B. HMAC uses a symmetric key and a hashing algorithm; CBC-MAC uses the first block for the checksum.
C. HMAC provides integrity and data origin authentication; CBC-MAC uses a block cipher for the process of creating a MAC.
D. HMAC encrypts a message with a symmetric key and then puts the result through a hashing algorithm; CBC-MAC encrypts the whole message
C. In an HMAC operation, a message is concatenated with a symmetric key and the result is put through a hashing algorithm. This provides integrity and system or data authentication. CBC-MAC uses a block cipher to create a MAC, which is the last block of ciphertext
What is an advantage of RSA over DSA?
A. It can provide digital signature and encryption functionality.
B. It uses fewer resources and encrypts faster because it uses symmetric keys.
C. It is a block cipher rather than a stream cipher.
D. It employs a one-time encryption pad
A. RSA can be used for data encryption, key exchange, and digital signatures. DSA can be used only for digital signatures
Many countries restrict the use or exportation of cryptographic systems. What is the reason given when these types of restrictions are put into place?
A. Without standards, there would be many interoperability issues when trying to employ different algorithms in different programs.
B. The systems can be used by some countries against their local people.
C. Criminals could use encryption to avoid detection and prosecution.
D. Laws are way behind, so adding different types of encryption would confuse the laws more.
C. The U.S. government has greatly reduced its restrictions on cryptography exportation, but there are still some restrictions in place. Products that use encryption cannot be sold to any country the United States has declared is supporting terrorism. The fear is that the enemies of the country would use encryption to hide their communication, and the government would be unable to break this encryption and spy on their data transfers.
What is used to create a digital signature? A. The receiver’s private key B. The sender’s public key C. The sender’s private key D. The receiver’s public key
C. A digital signature is a message digest that has been encrypted with the sender’s private key. A sender, or anyone else, should never have access to the receiver’s private key.
Which of the following best describes a digital signature?
A. A method of transferring a handwritten signature to an electronic document
B. A method to encrypt confidential information
C. A method to provide an electronic signature and encryption
D. A method to let the receiver of the message prove the source and integrity of a message
D. A digital signature provides authentication (knowing who really sent the message), integrity (because a hashing algorithm is involved), and nonrepudiation (the sender cannot deny sending the message).
How many bits make up the effective length of the DES key? A. 56 B. 64 C. 32 D. 16
A. DES has a key size of 64 bits, but 8 bits are used for parity, so the true key size is 56 bits. Remember that DEA is the algorithm used for the DES standard, so DEA also has a true key size of 56 bits, because we are actually talking about the same algorithm here. DES is really the standard, and DEA
is the algorithm. We just call it DES in the industry because it is easier
Why would a certificate authority revoke a certificate?
A. If the user’s public key has become compromised
B. If the user changed over to using the PEM model that uses a web
of trust
C. If the user’s private key has become compromised
D. If the user moved to a new location
C. The reason a certificate is revoked is to warn others who use that person’s public key that they should no longer trust the public key because, for some reason, that public key is no longer bound to that particular individual’s identity. This could be because an employee left the company, or changed his name and needed a new certificate, but most likely it is because the person’s private key was compromised.
What does DES stand for? A. Data Encryption System B. Data Encryption Standard C. Data Encoding Standard D. Data Encryption Signature
B. Data Encryption Standard was developed by NIST and the NSA to encrypt sensitive but unclassified government data.
Which of the following best describes a certificate authority?
A. An organization that issues private keys and the corresponding
algorithms
B. An organization that validates encryption processes
C. An organization that verifies encryption keys
D. An organization that issues certificates
D. A registration authority (RA) accepts a person’s request for a certificate and verifies that person’s identity. Then the RA sends this request to a certificate authority (CA), which generates and maintains the certificate.
What does DEA stand for? A. Data Encoding Algorithm B. Data Encoding Application C. Data Encryption Algorithm D. Digital Encryption Algorithm
C. DEA is the algorithm that fulfilled the DES standard. So DEA has all of the attributes of DES: a symmetric block cipher that uses 64-bit blocks, 16 rounds, and a 56-bit key.
