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t) Alice and Bob are using the ElGamal cipher with
the parameters p
173 and a = 2.
=
Alice makes the mistake of using the same ephemeral
key for two plaintexts, ₁ and 2. The eavesdropper
Eve suspects that x₁
169. She sees the two
ciphertexts y₁ = 153 and y2 = 135 in transit; these
are the encryptions of ₁ and 2, respectively.
a) What is the masking key k?
=
b) What is the plaintext ₂ ?

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