Chapter 1: Q12E (page 48)
What is ?
Short Answer
The solution is .
Chapter 1: Q12E (page 48)
What is ?
The solution is .
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Get started for freeConsider the problem of computing x y for given integers x and y: we want the whole answer, not modulo a third integer. We know two algorithms for doing this: the iterative algorithm which performs y − 1 multiplications by x; and the recursive algorithm based on the binary expansion of y. Compare the time requirements of these two algorithms, assuming that the time to multiply an n-bit number by an m-bit number is O(mn).
Determine necessary and sufficient conditions on so that the following holds: for any if , then .
In an RSA cryptosystem, p = 7and q = 11(as in Figure 1.9). Find appropriate exponents and .
Consider the problem of computing .
(a) If is an role="math" localid="1658397956489" -bit number, how many bits long is , approximately ( form)?
(b) Give an algorithm to compute and analyze its running time.
1.38. To see if a number, say , is divisible by , you just add up the digits of its decimalrepresentation, and see if the result is divisible by role="math" localid="1658402816137" .
( , so it is not divisible by ).
To see if the same number is divisible by , you can do this: subdivide the number into pairs ofdigits, from the right-hand end , add these numbers and see if the sum is divisible by (if it's too big, repeat).
How about ? To see if the number is divisible by , subdivide it into triples from the end add these up, and see if the sum is divisible by .
This is true for any prime other than and . That is, for any prime , there is an integer such that in order to see if divides a decimal number , we break into -tuples of decimal digits (starting from the right-hand end), add up these -tuples, and check if the sum is divisible by .
(a) What is the smallest such for ? For ?
(b) Show that is a divisor of .
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