212-81 Online Practice Questions and Answers

Correct Answer: C

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.

Correct Answer: A

IDEA https://en.wikipedia.org/wiki/International_Data_Encryption_Algorithm In cryptography, the International Data Encryption Algorithm (IDEA), originally called Improved Proposed Encryption Standard (IPES), is a symmetric-key block cipher designed by James Massey of ETH Zurich and Xuejia Lai and was first described in 1991. The algorithm was intended as a replacement for the Data Encryption Standard (DES). IDEA is a minor revision of an earlier cipher Proposed Encryption Standard (PES). The cipher was designed under a research contract with the Hasler Foundation, which became part of Ascom-Tech AG. The cipher was patented in a number of countries but was freely available for noncommercial use. The name "IDEA" is also a trademark. The last patents expired in 2012, and IDEA is now patent-free and thus completely free for all uses. IDEA was used in Pretty Good Privacy (PGP) v2.0 and was incorporated after the original cipher used in v1.0, BassOmatic, was found to be insecure. IDEA is an optional algorithm in the OpenPGP standard.

Correct Answer: A

Single substitution https://en.wikipedia.org/wiki/Substitution_cipher#Simple_substitution Substitution of single letters separately--simple substitution--can be demonstrated by writing out the alphabet in some order to represent the substitution. This is termed a substitution alphabet. The cipher alphabet may be shifted or reversed (creating the Caesar and Atbash ciphers, respectively) or scrambled in a more complex fashion, in which case it is called a mixed alphabet or deranged alphabet.

Correct Answer: C

Instance Deduction

https://en.wikipedia.org/wiki/Cryptanalysis

The results of cryptanalysis can also vary in usefulness. For example, cryptographer Lars Knudsen (1998) classified various types of attack on block ciphers according to the amount and quality of secret information that was discovered:

Total break -- the attacker deduces the secret key. Global deduction -- the attacker discovers a functionally equivalent algorithm for encryption and decryption, but without learning the key. Instance (local) deduction -- the attacker discovers

additional plaintexts (or ciphertexts) not previously known.

Information deduction -- the attacker gains some Shannon information about plaintexts (or ciphertexts) not previously known.

Distinguishing algorithm -- the attacker can distinguish the cipher from a random permutation.

Correct Answer: D

Steganography https://en.wikipedia.org/wiki/Steganography

Correct Answer: C

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:

Correct Answer: A

A collision

https://en.wikipedia.org/wiki/Collision_(computer_science) A collision or clash is a situation that occurs when two distinct pieces of data have the same hash value, checksum, fingerprint, or cryptographic digest.

Correct Answer: D

Encrypting with RSA

https://en.wikipedia.org/wiki/RSA_(cryptosystem)

RSA Encrypting a message m (number) with the public key (n, e) is calculated:

M' := m^e %n

Correct Answer: D

The server that grants Kerberos tickets https://en.wikipedia.org/wiki/Kerberos_(protocol) The client authenticates itself to the Authentication Server (AS) which forwards the username to a key distribution center (KDC). The KDC issues a ticket-granting ticket (TGT), which is time stamped and encrypts it using the ticket-granting service's (TGS) secret key and returns the encrypted result to the user's workstation. This is done infrequently, typically at user logon; the TGT expires at some point although it may be transparently renewed by the user's session manager while they are logged in.

Correct Answer: D

https://en.wikipedia.org/wiki/Modulo_operation The modulo operation returns the remainder or signed remainder of a division, after one number is divided by another (called the modulus of the operation). Given two positive numbers a and n, a modulo n (abbreviated as a mod n) is the remainder of the Euclidean division of a by n, where a is the dividend and n is the divisor. The modulo operation is to be distinguished from the symbol mod, which refers to the modulus (or divisor) one is operating from. For example, the expression "5 mod 2" would evaluate to 1, because 5 divided by 2 has a quotient of 2 and a remainder of 1, while "9 mod 3" would evaluate to 0, because the division of 9 by 3 has a quotient of 3 and a remainder of 0; there is nothing to subtract from 9 after multiplying 3 times 3.