Chapter 1: Q28E (page 49)
In an RSA cryptosystem, p = 7and q = 11(as in Figure 1.9). Find appropriate exponents and .
Short Answer
The correct exponent of d is 37 and e is 13.
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Chapter 1: Q28E (page 49)
In an RSA cryptosystem, p = 7and q = 11(as in Figure 1.9). Find appropriate exponents and .
The correct exponent of d is 37 and e is 13.
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Show that if a has a multiplicative inverse modulo N, then this inverse is unique (modulo N).
A positive integer is a power if it is of the form , where ,role="math" localid="1658399000008" are positive integers and .
(a) Give an efficient algorithm that takes as input a number and determines whether it is a square, that is, whether it can be written as for some positive integer . What is the running time of your algorithm?
(b) Show that if (with role="math" localid="1658399171717" , , and all positive integers), then either role="math" localid="1658399158890" .
(c) Give an efficient algorithm for determining whether a positive integer is a power. Analyze its running time.
Find the inverse of:.
1.36. Square roots. In this problem, we'll see that it is easy to compute square roots modulo a prime pwith .
(a) Suppose . Show that is an integer.
(b) We say x is a square root of a modulo p if . Show that if and if a has a square root modulo p, then is such a square root.
Digital signatures, continued.Consider the signature scheme of Exercise .
(a) Signing involves decryption, and is therefore risky. Show that if Bob agrees to sign anything he is asked to, Eve can take advantage of this and decrypt any message sent by Alice to Bob.
(b) Suppose that Bob is more careful, and refuses to sign messages if their signatures look suspiciously like text. (We assume that a randomly chosen messagethat is, a random number in the range is very unlikely to look like text.) Describe a way in which Eve can nevertheless still decrypt messages from Alice to Bob, by getting Bob to sign messages whose signatures look random.
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