Question: Attacks against RSA (2 marks) To save time, Alice and Bob decide to find one good pair of primes p and q, and then publish

 Attacks against RSA (2 marks) To save time, Alice and Bob

Attacks against RSA (2 marks) To save time, Alice and Bob decide to find one good pair of primes p and q, and then publish the same modulus n = py. Alice and Bob then choose different public exponents e and e', and generate the corresponding secret exponents d and d', respectively. Show that in this system, it is possible to decrypt a message m sent to both of them if ged(e, e')1. That is givern CA mmod n -me" m od n An adversary Oscar can compute m without knowing the secret exponent d or d'. Note that Oscar does not know p or q. (Hint: Please study Euclidean Algorithm as it provides some important facts to find the solution. You may find reading material from http://mathworld. wolfram.com/EuclideanAlgorithm.html Note: You can consider how to solve the question by using the following fact: An important consequence of the Euclidean algorithm is finding integers z and y such that ax + by ged(a, b). That is, by given a and b, we can use Euclidean Algorithm to find z and y. Note that you can use this fact directly (explain how to use it), but no need to really find a or y Attacks against RSA (2 marks) To save time, Alice and Bob decide to find one good pair of primes p and q, and then publish the same modulus n = py. Alice and Bob then choose different public exponents e and e', and generate the corresponding secret exponents d and d', respectively. Show that in this system, it is possible to decrypt a message m sent to both of them if ged(e, e')1. That is givern CA mmod n -me" m od n An adversary Oscar can compute m without knowing the secret exponent d or d'. Note that Oscar does not know p or q. (Hint: Please study Euclidean Algorithm as it provides some important facts to find the solution. You may find reading material from http://mathworld. wolfram.com/EuclideanAlgorithm.html Note: You can consider how to solve the question by using the following fact: An important consequence of the Euclidean algorithm is finding integers z and y such that ax + by ged(a, b). That is, by given a and b, we can use Euclidean Algorithm to find z and y. Note that you can use this fact directly (explain how to use it), but no need to really find a or y

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