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Free 212-81 Exam Braindumps (page: 14)

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PDF with 206 Questions

Collision resistance is an important property for any hashing algorithm. Joan wants to find a cryptographic hash that has strong collision resistance. Which one of the following is the most collision resistant?

  1. SHA2
  2. MD5
  3. MD4
  4. PIKE

Answer(s): A

Explanation:

SHA2
https://en.wikipedia.org/wiki/Collision_resistance
Collision resistance is a property of cryptographic hash functions: a hash function H is collision- resistant if it is hard to find two inputs that hash to the same output; that is, two inputs a and b where a ≠ b but H(a) = H(b). The pigeonhole principle means that any hash function with more inputs than outputs will necessarily have such collisions; the harder they are to find, the more cryptographically secure the hash function is.
Due to the Birthday Problem, for a hash function that produces an output of length n bits, the probability of getting a collision is 1/2^n/2.
So, just looking for a hash function with larger "n".
The SHA-2 family consists of six hash functions with digests (hash values) that are 224, 256, 384 or 512 bits: SHA-224, SHA-256, SHA-384, SHA-512, SHA-512/224, SHA-512/256.



How did the ATBASH cipher work?

  1. By substituting each letter for the letter from the opposite end of the alphabet (i.e. A becomes Z, B becomes Y, etc.)
  2. By rotating text a given number of spaces
  3. By Multi alphabet substitution
  4. By shifting each letter a certain number of spaces

Answer(s): A

Explanation:

By substituting each letter for the letter from the opposite end of the alphabet (i.e. A becomes Z, B becomes Y, etc.) https://en.wikipedia.org/wiki/Atbash The Atbash cipher is a particular type of monoalphabetic cipher formed by taking the alphabet (or abjad, syllabary, etc.) and mapping it to its reverse, so that the first letter becomes the last letter, the second letter becomes the second to last letter, and so on.



Calculates the average LSB and builds a table of frequencies and Pair of Values. Performs a test on the two tables. It measures the theoretical vs. calculated population difference.

  1. Certificate Authority
  2. Raw Quick Pair
  3. Chi-Square Analysis
  4. SP network

Answer(s): C

Explanation:

Chi-Square Analysis
https://en.wikipedia.org/wiki/Chi-squared_test
A chi-squared test, is a statistical hypothesis test that is valid to perform when the test statistic is chi- squared distributed under the null hypothesis, specifically Pearson's chi-squared test and variants thereof. Pearson's chi-squared test is used to determine whether there is a statistically significant difference between the expected frequencies and the observed frequencies in one or more categories of a contingency table.
In cryptanalysis, the chi-squared test is used to compare the distribution of plaintext and (possibly) decrypted ciphertext. The lowest value of the test means that the decryption was successful with high probability. This method can be generalized for solving modern cryptographic problems.
Incorrect answers:
Raw Quick Pair - statistical analysis on number of unique colors and color number pairs in the picture and you look for least significant bits and manipulation of data in those bits, typically inside of whitespace.
SP network - substitution–permutation network is a series of linked mathematical operations used in block cipher algorithms such as AES (Rijndael), 3-Way, Kalyna, Kuznyechik, PRESENT, SAFER, SHARK, and Square.
Certificate Authority - component of a PKI that creates and maintains digital certificates throughout their life cycles.



Encryption of the same plain text with the same key results in the same cipher text. Use of an IV that is XORed with the first block of plain text solves this problem.

  1. CFB
  2. GOST
  3. ECB
  4. RC4

Answer(s): C

Explanation:

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.

Incorrect answers:
RC4 - stream symmetric cipher that was created by Ron Rivest of RSA. Used in SSL and WEP.
GOST - the GOST block cipher (Magma), defined in the standard GOST 28147-89 (RFC 5830), is a Soviet and Russian government standard symmetric key block cipher with a block size of 64 bits. The original standard, published in 1989, did not give the cipher any name, but the most recent revision of the standard, GOST R 34.12-2015, specifies that it may be referred to as Magma. The GOST hash function is based on this cipher. The new standard also specifies a new 128-bit block cipher called Kuznyechik.
CFB - the process wherein the ciphertext block is encrypted then the ciphertext produced is XOR'd back with the plaintext to produce the current ciphertext block.






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