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I know how to solve this question manually, but I don't know how to solve it using the program gp/pari. It is based on randomised Elgamal

Let p = 739. Given the following ciphertext of some message m1 encrypted using randomized Elgamal, what is the ciphertext of m1 · m2, where m2 ≡ 2 (mod p)? (c1,c2) = (246,609)

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    $\begingroup$ specify how you would solve it by hand, and the exact details of what you are referring to as randomised el-gamal. what's its relation to hashed el-gamal $\endgroup$
    – kodlu
    Commented Oct 29, 2021 at 0:53
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    $\begingroup$ The problem statement's second phrase is wrong. Read: “Given the following ciphertext of some message $m_1$ encrypted using randomized ElGamal, what is a ciphertext for $m_1·m_2\bmod p$, where $m_2=2$?” Hint: write the equations for ciphertext under randomized ElGamal. Assume the same random is used to encrypt $m_1$ and $m_3=m_1\cdot m_2\bmod p$. How can you deduce the later ciphertext from the former? GP/Pari is overkill: all computations can be done mentally, or pen and paper, or any calculator, depending on fluency with numbers. $\endgroup$
    – fgrieu ♦
    Commented Oct 29, 2021 at 7:53

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