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comment How is SSL secure from rogue Certificate Authorities?
In basic HTTPS, there is no protection against this attack. And it has been conducted in real life. However, there are a number of proposals to address this attack that have reached various stages of deployment but generally require either the client or the server to opt-in. For a history of these attacks and a list and evaluation of solutions, see this paper: people.scs.carleton.ca/~clark/papers/2013_sp.pdf (In particular, the first 8 rows in Table 1)
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comment Can Elgamal be made additively homomorphic and how could it be used for E-voting?
Reading between the lines of what you are asking, the answer is no. Elgamal can handle both multiplication and addition, but you cannot mix the two operations on any given ciphertexts. You must decide when you encrypt to lock the ciphertext into only doing addition or only doing multiplication. The ability to do both is a "fully homomorphic" cryptosystem, of which there are some, but they are mainly theoretical and too slow to be practical. One efficient scheme, BGN, allows a single multiplication and as many additions as you want.
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revised Encrypting a key with the same key using AES
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answered Encrypting a key with the same key using AES
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comment Why is proof-by-reduction needed (for Elgamal proof of security, for example)?
@Maeher is correct. What is amiss is that you are not considering all the values (that are functionally dependent on x,r,m) that you have available. As for a step-by-step proof, see: shoup.net/papers/games.pdf (Section 3). And read the whole paper if you want more intuition into how to structure proofs.