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Free 212-81 Exam Braindumps (page: 17)

Page 16 of 50
PDF with 206 Questions

What is the basis for the difficulty in breaking RSA?

  1. Hashing
  2. The birthday paradox
  3. Equations that describe an elliptic curve
  4. Factoring numbers

Answer(s): D

Explanation:

Factoring numbers
https://en.wikipedia.org/wiki/RSA_(cryptosystem)
RSA (Rivest–Shamir–Adleman) is a public-key cryptosystem that is widely used for secure data transmission. It is also one of the oldest. The acronym RSA comes from the surnames of Ron Rivest, Adi Shamir, and Leonard Adleman, who publicly described the algorithm in 1977. An equivalent system was developed secretly, in 1973 at GCHQ (the British signals intelligence agency), by the English mathematician Clifford Cocks. That system was declassified in 1997. In a public-key cryptosystem, the encryption key is public and distinct from the decryption key, which is kept secret (private). An RSA user creates and publishes a public key based on two large prime numbers, along with an auxiliary value. The prime numbers are kept secret. Messages can be encrypted by anyone, via the public key, but can only be decoded by someone who knows the prime numbers.



What best describes the shifting of each letter a fixed number of spaces to the left or right?

  1. Single substitution
  2. Multi substitution
  3. XOR
  4. Bit shifting

Answer(s): A

Explanation:

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.



Which analysis type is based on the statistics of the numbers of unique colors and close-color pairs in a 24-bit image, a method that analyzes the pairs of colors created by LSB embedding?

  1. Differential Analysis
  2. Discrete Cosine Transform
  3. Raw Quick Pair
  4. Chi squared analysis

Answer(s): C

Explanation:

Raw Quick Pair https://www.cs.auckland.ac.nz/courses/compsci725s2c/archive/termpapers/yy.pdf
Du and Long2 (2000) introduced Raw Quick Pairs detecting method of Stego-images (the images that contain the steganographic message). The underlying principle of the method is that the number of close color pairs of Stego-images will be larger compare with the number of close color pairs of normal images. In contrast, Fridrich and Goljan (2001) pointed out that RQP method only works if the number of unique colors is relatively low; and the method can not be applied to grayscale images. However, this paper will outline the core principle of RQP method; and evaluate such critical comments in details. In addition, this paper suggests potential improvement of RQP method and provides one possible alternative.

Incorrect answers:
Chi squared analysis - https://en.wikipedia.org/wiki/Chi-squared_test Differential Analysis - https://en.wikipedia.org/wiki/Differential_cryptanalysis
Discrete Cosine Transform - https://en.wikipedia.org/wiki/Discrete_cosine_transform



Electromechanical rotor-based cipher used in World War II

  1. ROT13 Cipher
  2. Cipher Disk
  3. Enigma Machine
  4. Rail Fence Cipher

Answer(s): C

Explanation:

Enigma Machine https://en.wikipedia.org/wiki/Enigma_machine
The Enigma machine is an encryption device developed and used in the early- to mid-20th century to protect commercial, diplomatic and military communication. It was employed extensively by Nazi Germany during World War II, in all branches of the German military.
Enigma has an electromechanical rotor mechanism that scrambles the 26 letters of the alphabet.
Incorrect answers:
Rail Fence Cipher - a form of transposition cipher. In the rail fence cipher, the plain text is written downwards and diagonally on successive "rails" of an imaginary fence, then moving up when the bottom rail is reached. When the top rail is reached, the message is written downwards again until the whole plaintext is written out. The message is then read off in rows.
Cipher Disk - an enciphering and deciphering tool developed in 1470 by the Italian architect and author Leon Battista Alberti. He constructed a device, (eponymously called the Alberti cipher disk) consisting of two concentric circular plates mounted one on top of the other. The larger plate is called the "stationary" and the smaller one the "moveable" since the smaller one could move on top of the "stationary". The first incarnation of the disk had plates made of copper and featured the alphabet, in order, inscribed on the outer edge of each disk in cells split evenly along the circumference of the circle. This enabled the two alphabets to move relative to each other creating an easy to use key. Rather than using an impractical and complicated table indicating the encryption method, one could use the much simpler cipher disk. This made both encryption and decryption faster, simpler and less prone to error.
ROT13 Cipher - ("rotate by 13 places", sometimes hyphenated ROT-13) is a simple letter substitution cipher that replaces a letter with the 13th letter after it, in the alphabet. ROT13 is a special case of the Caesar cipher which was developed in ancient Rome.






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