Explanation
Correlation attacks are possible when there is a significant correlation between the output state of one individual LFSR in the keystream generator and the output of the Boolean function that combines the output state of all of the LFSRs. Combined with partial knowledge of the keystream (which is easily derived from partial knowledge of the plaintext, as the two are simply XORed together), this allows an attacker to brute-force the key for that individual LFSR and the rest of the system separately. For instance, if, in a keystream generator in which four 8-bit LFSRs are combined to produce the keystream, and one of the registers is correlated to the Boolean function output, we may brute force it first and then the remaining three, for a total attack complexity of 28 + 224. Compared to the cost of launching a brute force attack on the entire system, with complexity 232, this represents an attack effort saving factor of 255, which is substantial. If a second register is correlated with the function, we may repeat this process and drop the attack complexity to 28 + 28 + 216 for an effort saving factor of 65027. In this sense, correlation attacks can be considered divide and conquer algorithms.
Read more about this topic: Correlation Attack
Famous quotes containing the word explanation:
“Herein is the explanation of the analogies, which exist in all the arts. They are the re-appearance of one mind, working in many materials to many temporary ends. Raphael paints wisdom, Handel sings it, Phidias carves it, Shakspeare writes it, Wren builds it, Columbus sails it, Luther preaches it, Washington arms it, Watt mechanizes it. Painting was called “silent poetry,” and poetry “speaking painting.” The laws of each art are convertible into the laws of every other.”
—Ralph Waldo Emerson (1803–1882)
“To develop an empiricist account of science is to depict it as involving a search for truth only about the empirical world, about what is actual and observable.... It must involve throughout a resolute rejection of the demand for an explanation of the regularities in the observable course of nature, by means of truths concerning a reality beyond what is actual and observable, as a demand which plays no role in the scientific enterprise.”
—Bas Van Fraassen (b. 1941)
“Young children constantly invent new explanations to account for complex processes. And since their inventions change from week to week, furnishing the “correct” explanation is not quite so important as conveying a willingness to discuss the subject. Become an “askable parent.””
—Ruth Formanek (20th century)