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Free 212-81 Exam Braindumps (page: 20)

Page 19 of 50
PDF with 206 Questions

A ___________is a function is not reversible.

  1. Stream cipher
  2. Asymmetric cipher
  3. Hash
  4. Block Cipher

Answer(s): C

Explanation:

Hash https://en.wikipedia.org/wiki/Hash_function
Hash functions are irreversible. This is actually required for them to fulfill their function of determining whether someone possesses an uncorrupted copy of the hashed data. This brings susceptibility to brute force attacks, which are quite powerful these days, particularly against MD5.



A cryptanalysis success where the attacker discovers additional plain texts (or cipher texts) not previously known.

  1. Total Break
  2. Distinguishing Algorithm
  3. Instance Deduction
  4. Information Deduction

Answer(s): C

Explanation:

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.



What size block does AES work on?

  1. 64
  2. 128
  3. 192
  4. 256

Answer(s): B

Explanation:

128
https://en.wikipedia.org/wiki/Advanced_Encryption_Standard
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.



Which of the following would be the fastest.

  1. EC
  2. DH
  3. RSA
  4. AES

Answer(s): D

Explanation:

AES
https://en.wikipedia.org/wiki/Symmetric-key_algorithm
AES - symmetric cipher. Symmetric keys use the same key for both encryption and decryption. Both the sender and receiver of the data must know and share the secret key. For standard encrypt/decrypt functions, symmetric algorithms generally perform much faster than their asymmetrical counterparts. This is due to the fact that asymmetric cryptography is massively inefficient. Symmetric cryptography is designed precisely for the efficient processing of large volumes of data. In other words, symmetric encryption is generally used for speed and performance, e.g. when there's a large amount of data that needs to be encrypted/protected.

Incorrect answers:
RSA - asymmetric 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.
EC - Elliptic-curve cryptography (ECC) is an approach to public-key cryptography based on the algebraic structure of elliptic curves over finite fields.






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