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I try to learn ElGamal re-encrypts scheme and I have a question about the example: How is a re-encryption done with elGamal?.

  • The $g$ value of Alice must be the same as $g$ value of Bob or not?
  • And what about of Prime $p$ value for Alice and Bob? Alice.$p$ must be the same as Bob.$p$ or not?

Thanks!

kelalaka
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Eugene
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    Yes, and Yes.${}$ – kelalaka Mar 28 '19 at 10:50
  • Ok, thank you!
    I try test it:
    2. Bob reencrypts (x,w) as (x′,w′) with x′=xg^u, w′=wy^u(x′)^b.
    I use BigInteger. I look that x1>0, ok but w1=0, becourse x1 > p:
    var x1 = g.modPow(u, p).multiply(x);
    var tmpB = y.modPow(u, p).multiply(w);
    var w1 = x1.modPow(b,p).multiply(tmpB);
    this w1 = 0
    Where I mistake? –     – Eugene Mar 29 '19 at 13:40
  • Eugene, CryptoSO is not programming site. You can ask your programming question with your programming codes in Stackoverflow. – kelalaka Apr 04 '19 at 15:34

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