Test on Fundamentals of Cryptography

Question 1: CBC mode allows for parallel processing of encryption and decryption.

A. Ano

B. Ne

Explanation: The study materials state that CTR mode allows for parallel processing. For CBC mode, it is noted that 'Each ciphertext block is dependent on all message blocks before it', which implies a sequential process rather than parallel.

Question 2: Based on the provided study materials, which of the following statements about the speed of cryptographic algorithms is accurate?

A. RC4 (stream) encryption is significantly slower than AES-128 cbc encryption.

B. SHA1 is the fastest among the listed hash algorithms.

C. RSA decryption at 1024 key size is faster than 3DES cbc encryption.

D. DSA signing at 1024 key size is faster than RSA decryption at 1024 key size.

Explanation: According to the 'Speed of algorithms' table, SHA1 operates at 447 MB/s, which is faster than md5 (377 MB/s), hmac(md5) (359 MB/s), sha256 (195 MB/s), and sha512 (265 MB/s). Therefore, SHA1 is indeed the fastest among the listed hash algorithms. RC4 (stream) encryption is 436 MB/s, which is much faster than AES-128 cbc at 76 MB/s, making option 0 incorrect. RSA decryption (1024) is 3.4 MB/s, which is slower than 3DES cbc at 15 MB/s, making option 2 incorrect. DSA sign (1024) is 3.1 MB/s, which is slower than RSA dec (1024) at 3.4 MB/s, making option 3 incorrect.

Question 3: In the Bob and Alice scenario, the phone call channel undermines the data integrity verification process for the file.

A. Ano

B. Ne

Explanation: The study materials state that the phone call is a 'separate channel' used by Bob to communicate with Alice to compare hash values (h1 = h1), explicitly linking this process to 'Very important data with respect to their INTEGRITY!'. Therefore, the phone call channel is part of, and does not undermine, the integrity verification process.

Question 4: According to the study materials, which method is used to achieve data authentication with symmetric cryptography?

A. Verifying the identity of a principal involved in a transaction.

B. Adding a small tag to protected data, computed using a shared key with either a block cipher or a hash function.

C. Making sure non-public information is accessible only to authorized parties.

D. Generating strong evidence of unique data origination.

Explanation: The study materials state that for data authentication with symmetric crypto, a 'small tag added to protected data' is used. This tag is 'computed using block cipher or hash function (both use two inputs: key and message)'. The other options describe entity authentication, confidentiality, or non-repudiation of origin, respectively, not data authentication by this method.

Question 5: The primary motivation for governments to research public-key cryptography, particularly concerning key distribution, was to ensure that public keys remain confidential.

A. Ano

B. Ne

Explanation: The study materials explicitly state that the primary desire that led governments to research public-key cryptography was that 'Public keys don’t have to be confidential!!!', indicating that confidentiality of public keys was not a requirement or motivation, but rather their non-confidential nature was a key aspect.