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 Dec 22 comment ElGamal in a different group Yehuda the link you provided does not work. Can you tell me the title? Thanks Dec 21 comment What libraries do people use to implement and evaluate cryptography protocols? The paper you mentioned has implementation results here homepage.rub.de/andy.rupp/papers/p4r_full.pdf Dec 21 comment What libraries do people use to implement and evaluate cryptography protocols? You can check PBC library for pairings and the for math operations the GMP library. Then Charm crypto abstracts a lot of useful basic crypto operations Dec 21 comment Is that simple additive homomorphic scheme secure? that is very weak. The attacker always can ask for encryptions. In its weakest form a security game for confidentiality provides ciphers to the attacker at its will Dec 19 comment Homomorphic OR operations Can you elaborate? i have 0,1 and the or equals 1 and not 0 as it would be if i multiplied Dec 19 comment Homomorphic OR operations I don't get it very clearly. It the truth table of or 3/4 entries are 1 and 1 is zero. If you multiply the elements then 3/4 entries become zero and 1/4 is one. From the cases it becomes 0 when multiplying only one is correct (0*0) and the others (0*1),(1*0) they do give the wrong result, because the OR gives 1. Dec 19 comment Homomorphic OR operations So i just need an additive homomorphic scheme?Then pailier will work?No because the ciphertext space has many elements. So how E(1)+E(1) will result in E(1) at the ciphertext space?By quadratic residuosity you mean the GM scheme?I thought that was only XOR homoorphic Dec 19 comment Homomorphic OR operations I can't get your formula. why you do not just write x+y-xy. And if this circuit is translated to an OR than you do not need just an additively homomorphic scheme but a multiplicative at the same time... Dec 3 comment Sorting over encrypted data with different symmetric keys it seems that you need to put a bit of trust to some third party in order the latter to transform ciphertexts coming from different users to ciphers seem to be encrypted by a single user. Look at proxy re-encryption techniques Nov 28 comment Bilinear map assumpion Ok, i said DL is the strongest in the sense that breaking DL you break CDH and then DDH Nov 26 comment Bilinear map assumpion You were right about the other type of forgery by exponentiation. What about now? Assiming k is secret Nov 26 comment Bilinear map assumpion I thought DL is the strongest assumption. XDH assumes DDH is hard in G1 for asymmetric pairings Nov 15 comment what problem happen if we always use IV Zero in CBC Mode? Do not forget to mark the post as a valid answer Nov 15 comment what problem happen if we always use IV Zero in CBC Mode? If $0$ comes as a result of a random generation then it is fine, but every time it should change Nov 15 comment what problem happen if we always use IV Zero in CBC Mode? The property that we need for the IV is to be a random number , that changes per encryption Nov 10 comment Difference between collision resistance and target collision resistance @archie. In 2PIR the adversary is also trying to find a collision for a fixed message. I do not understand the difference with TCR. You are explaining it as TCR is 2PIR and 2PIR ("compared to the more general notion of Second Preimage Resistance, where the adversary to find a second preimage for a randomly chosen message") is collision resistance Sep 25 comment What are the differences between proofs based on simulation and proofs based on games? Thank you. But, in sb proofs there is a pre-agreed leakage in the ideal evironment. From my point of view and maybe i am wrong the question is and what is missing from sb proofs: How this leakage does not affect the security definition. And i am saying that because in the sb proofs that i have seen the point of interest is to show that the two worlds behave equivalently and not how the leakage affects the scheme. So it seems on me that this is the negative part with sb proofs. And as you correctly pointed out with game based there is no connection from IND-CPA to semantic security Sep 1 comment What are the roles of the simulator in simulation based proofs Does not seem as cheating in the proof when the simulator is interacting with the real world adversary in order to output indistinguishable outputs?Since in the proof it is desirable to show that the two parties (real world adversary-ideal simulator) learn equal information. Jul 30 comment What consequences do the plaintext space size has on the performances in the BGV scheme? I think it is not clear in your mind. Ciphertext size depends on the size on the group and its bitstring representation which depends on $p$ obviously. What is your question about?size of p=1024bit which is the ciphertext space then |ciphertext|=1024 bits. Since you want additions why you need BGV, and not Paillier? Jul 30 comment What consequences do the plaintext space size has on the performances in the BGV scheme? You have to be more precise with respect to what operations you need to perform. For instance for multiplication there are various techniques:Karatsuba, Montgomery. Here you can find an idea : en.wikipedia.org/wiki/…