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Feb
14
comment How much computing resource is required to brute-force RSA?
@dave_thompson_085 "Slightly" by two orders of magnitude. :D Fixed it. (though it's 5.95495, so 5.95)
Feb
9
comment Hash function as secure as one-time pad?
This does not seem to attempt to answer the question.
Feb
8
comment Is $f(x)\oplus x$ a one-way function?
If one-way functions do not exist, then the statement is trivially true, because it is an all quantified statement about the empty set.
Feb
8
comment Is $f(x)\oplus x$ a one-way function?
Thanks, fixed the $x_1$ mixup. About the generality, yes that is true, as long as the length of $x_1$ is superlogarithmic, everything should be fine. But as this is a counter example, I think it's fine to be more specific.
Feb
2
comment Definition of ciphertext security
Where does it state in the screenshot that such a scheme is secure?
Feb
2
comment Definition of ciphertext security
Where do you get the idea from that such a scheme would be CCA secure?
Jan
22
comment Is it an example of bilinear pairing?
The second one is not bilinear: $e(x,y^z) =x^{(y^z)} \neq (x^{yz})} = e(x,y)^z$. For the first one I don't see the problem with bilinearity at the moment, but the group is pretty useless for crypto since discrete log is trivial.
Jan
2
comment Why is proof-by-reduction needed (for Elgamal proof of security, for example)?
@curious I'm only showing that the distribution is not uniform, not that it can be efficiently distinguished from a uniform distribution.
Nov
16
comment plaintext distribution ,perfect secrecy cryptosystem
I'm not sure that the claim actually holds. Are you sure that there are no additional constraints on the "specific plaintext distribution"? Unless I'm confused, any encryption scheme (or even the identityfunction) offers perfect secrecy for the distribution that has probability 0 for all but one plaintext. But obviously this does not imply perfect secrecy for other distributions.
Jul
13
comment pairing-based schemes
Well scalar multiplication does not have bilinearity, a pairing does.
Jun
24
comment Is there a way to compress multiple signatures of the same data?
Aggregate Signatures are more general than that, but might offer you what you want.
May
22
comment One-time pad, zero key and Shannon
By "using Shannon" you mean applying Shannon's theorem? Sure, you can define your key-generation algorithm to pick the all zero key with probability 0 and all others with probability $1/(|\mathcal{M}|-1)$. That's exactly your encryption scheme. Then apply the theorem which states that the scheme is perfectly secret if and only if two condition hold. One of those conditions is that every key is chosen with the same probability, which obviously does not hold.
May
22
comment One-time pad, zero key and Shannon
@CGFoX Well, we are talking about the OTP here (except that the all zero key is not allowed), so by definition, $\mathcal{M}=\mathcal{C}=\{0,1\}^n$. But even if they are some other sets. If the set of keys has an element less that the messages, then for any ciphertext $c$, there exists at least one message $m$ that cannot possibly result in $c$ no matter which key is chosen.
May
21
comment Which concrete applications benefit from Oblivious RAM constructions?
@e-sushi I don't quite get what your comment is trying to convey. He is NOT asking about attacks on ORAM (this is indeed a much used abbreviation). He is asking about the attacks on non oblivious encrypted data-structures that are the motivation to develop ORAM construction (be that Hash based or whatever)
May
21
comment Prefix property for variable length pseudo-random generators
$m_0$ and $m_1$ certainly still have to have the same length. Check Definition 3.8. With messages of different length, the security definition becomes meaningless.
May
11
comment The advantages of Merkle Signature and One time Signature
Of course it does: Only a single message can ever be securely signed under the public key of an OTS. In contrast, many messages can be signed under the public key of the Merkle scheme without compromising security.
May
6
comment Is G is a secure PRG?
You should specify what F is (I assume a pseudorandom function) and where k comes from.
May
4
comment Block cipher encryption of decryption with the same key
It depends on what you mean by "encrypt with a blockcipher". If you mean using a blockcipher in a secure mode of operation, then no, the probability of this happening will be negligible.
May
3
comment PRF and hash functions
No, hash functions are only modeled as random oracles for proofs in the random oracle model. If we work in the standard model, a hash function is only assumed to be collision resistant. The key of a hash function stems from a technicality of defining collision resistance. The problem is that it is (almost) impossible to define collision resistance for a single function. Therefore collision resistance is defined for a function family, and the key is required to select a member of that family.
Apr
15
comment What is a 'secret key factory'? What precisely is it doing?
This question appears to be off-topic because it is about the inner workings of a particular java library. But to answer your question: What you are seeing is the Object ID being printed because you tried to print an object to the standard output. Check the documentation docs.oracle.com/javase/7/docs/api/javax/crypto/spec/… what you are looking for is probably the output of the getEncoded() method.