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I am working on my project that uses elgamal elliptic curve. I know when the elgamal ec encrypt by following steps

  1. Represent the message m as a point M in E(Fp).
  2. Select k ∈R [1,n−1].
  3. Compute C1 = kP.
  4. Compute C2 = M +kQ.
  5. Return(C1,C2).
    Where Q is the intended recipient’s public key, P is base point. My qusetion at number one. how represent m as a point. Is point represent one character or represent group of characters.
MHS
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There's no obvious way to attach m to points in E(Fp). However, you can use variant algorithm of ElGamal such as Menezes-Vanstone Elliptic curve cryptosystem to encode a message in a point, a good reference here(P.31).

As for java code, I suggest you do some work, and post another question on SO when you encounter a problem you really can't solve by yourself.

Chiara Hsieh
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  • Mr ChiaraHsieh Thank you for your answer – MHS May 20 '14 at 19:47
  • I've got just wondered algorithm Menezes-Vanstone Elliptic Curve Cryptosystem What is the intent of this phrase The ciphertext of a message m = (m1, m2) ∈ Zp * × Zp * What is meant by Zp*×Zp* Is that the message is within the domain finite field Zp must be a message within the period from 1 to 10. – MHS May 21 '14 at 22:41
  • It means m1 and m2 are both elements of Zp*, which could be from 1 to p-1 – Chiara Hsieh May 22 '14 at 02:09
  • Just I ask about Menezes-Vanstone Elliptic curve cryptosystem. Howcan encode a message while C1= M1 * k1, C2= K2 * M2. I now M1 and M2 here is message. Is M1, M2 represent on one character or more that. Or represent many characters binay size less than P. – MHS Nov 02 '14 at 19:01