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So textbook ElGamal is known to be vulnerable to CPA, and although there are several proposals (DHAES/EIES) for modifications none of those are formally accepted or standardized.

My question is whether if I simply "preprocess" the plaintext with the good-old hybrid asymmetric method won't that solve the chiphertext modification problem? (yes I know a DoS-like error is still present if the AES key is altered midway)

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  • $\begingroup$ Textbook ElGamal is not vulnerable to CPA. It is vulnerable to CCA(2) attacks. $\endgroup$
    – SEJPM
    Commented Jun 5, 2017 at 14:54
  • $\begingroup$ Can you quickly line out (using pseudo-code or $\LaTeX$) what precisely you mean with "pre-processing" or are you asking for a more general "secure authenticated encryption of the plaintext"? $\endgroup$
    – SEJPM
    Commented Jun 5, 2017 at 14:55
  • $\begingroup$ Why would you use ElGamal over IES style algorithms if you don't need the homomorphic properties of ElGamal? $\endgroup$
    – CodesInChaos
    Commented Jun 5, 2017 at 17:41

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