curious

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Apr 21	comment	Why would anyone use an elliptic curve with a cofactor > 1? then why we do care about even characteristic curves that imply even number of points since they are not secure?
Apr 19	comment	How does order-preserving encryption work? That approach is not secure if the same key is being used for all values. Suppose $c_1=OPE(a)=a+x$ and $c_2=OPE(b)=b+x$. Then the attacker obtains k=c2-c1 = a-b. So he knows that $a$ will in a range $[a-b,OPE(a)]$ . If $X$ is not big enough then the attacker with brute force can try all values in the range.
Apr 15	comment	Recovering SHA1 knowing 2/3 of the hash generated What is the today safe $n$ that make it impossible for an attacker to brute force in a "reasonable" time?Something greater than $80$ ?
Apr 11	comment	How to implement order preserving encryption or order preserving hashing I looked at the code and still it gets very complex when it comes in OPE. What they do is that they choose random numbers from a distribution and then they check for the order?Or this is the naive approach?
Apr 11	comment	Verify product without revealing multipliers @PulpSpy I mean that if you can observe whether or not two ciphertexts came from same plaintext encrypted with ELGamal then this leaks some info and cannot be treated as semantically secure. Or i am wrong?
Apr 11	comment	Verify product without revealing multipliers @PulpSpy "If they are the same, $d$ will be $1$ " , that implies a deterministic scheme with no randomness. Is that the case with the participants when choosing different keys?
Mar 22	comment	How to compute the dot product on encrypted values? It's stupid what i said. Of course itis because $(a + b) \cdot c = a \cdot c +b \cdot c$
Mar 22	comment	Can Elgamal be made additively homomorphic and how could it be used for E-voting? Can i use elgamal for both additions and multiplication of ciphertexts?I.e: Whenever i want to multiply i compute my message $x$ as $g^x$ and whenever i want to add i compute conventional Elgamal. My plaintext would be small integers in a range of $0 \ldots 2^{32} or 2^{64}$
Mar 22	comment	How to compute the dot product on encrypted values? That is is the other way around i think. Instead of $a_1 \cdot b_1 + a_2 \cdot b_2 +a_3 \cdot b_3 +\ldots+ a_n \cdot b_n$ i need $(a_1+b_1) \cdot c_1 + (a_2+b_2) \cdot c_2 + \ldots + (a_n+b_n) \cdot c_n$
Mar 22	comment	How to compute the dot product on encrypted values? Can i obtain the encryption of $E(x \cdot y)$ where $y=E(a)+E(b)=E(a+b)$ and x is $E(x)$ from the aforementioned scheme?
Mar 22	comment	How to compute the dot product on encrypted values? Thank now it's clear to me. I thought as i commented to @Ricky that you can only do one multiplication. Your clarification was very helpful. You can do as many multiplications you want and you only can add them.
Mar 22	comment	How to compute the dot product on encrypted values? @RickyDemer. I misunderstood the scheme. I thought that you were able to do just one multiplications but after D.W explanation it's clear that you can do more unless you want to multiply them together. Thank you
Mar 21	comment	How to compute the dot product on encrypted values? @RickyDemer in my case there is not secure multiparty computation. I have $m$ nodes. Each node is giving its $n$ integer values to another party who computes the dot product of all pairs of $m$ nodes.Also the cited reference at the link says for a public key construction with 1 multiplication but for dot product i need $n$
Mar 13	comment	Is there an efficient way to hide the encrypted plaintext length with a block cipher? @PaŭloEbermann i want to hide plaintext size
Mar 11	comment	Is there an efficient way to hide the encrypted plaintext length with a block cipher? The intuition of the question is to expand the ciphertext size such that when you encrypt only one block of plaintext and the message is one block to further produce more ciphertext blocks
Mar 11	comment	Is there an efficient way to hide the encrypted plaintext length with a block cipher? @fgrieu I.e: 16bytes of plaintext to 12816bytes of ciphertext or to k16bytes of ciphertext tuned by a parameter $k$ appropriately, given as input to the block cipher
Mar 3	comment	Why is elliptic curve cryptography not widely used, compared to RSA? @ThomasPornin Why then RSA outperfoms only in signature verification?and not in all other crypto-operations like encryption,decryption, signature.The operation is the same: Modular exponentiation vs multiplications on elliptic curve over much smaller modulo
Mar 3	comment	Why is elliptic curve cryptography not widely used, compared to RSA? @ThomasPornin Do you have a citation for the outperfomance of RSA on signatures verification ?
Feb 28	comment	Is SHA-1 still practical secure under specific scenarios? @CodesInChaos Yes the key is unknown
Feb 25	comment	Which one is fastest? Karatsuba or Montgomery multiplication? @HenrickHellström Thanks for your comment. But why on x64 is the other way around? You just have bigger registers on x64.At each clock pulse you can transfer 64bits. That means that you can save at once 64bits and your word size is 64 bits. So i guess it will further improve the running time of the scheme Karatsuba-then-Montgomery. Or i am missing sth?