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Jan
27
comment How can I find the prime numbers used in RSA?
The approach is just basic algebra. If the factors are close to the floor $x$ of the square root, the equation $r + (x-p)(q-x) - x(q+p-2x)$ will be dominated by the first and third term and the second factor of the third term will consequently be a function of the magnitude of $r$.
Jan
27
comment How cryptographically secure was the original WW2 Enigma machine, from a modern viewpoint?
AES is believed to be (IND-CPA) secure even if the plain text is chosen by the attacker, so why do you include the restriction of no operator errors?
Jan
14
comment Do I need to prepare plain text before encryption?
I see no obvious harm in anyone following your recommendation, but it is completely pointless as far as cryptographic security goes.
Jan
13
comment Do I need to prepare plain text before encryption?
Compression does not increase the total entropy of the plain text, but it does increase the average entropy per bit, by, well, compressing it. Theoretically, it might increase security in some sense, but only in so far that the compression algorithm effectively hides the length of the original plain text.
Jan
6
comment Shared secret: Generating Random Permutation
To avoid unnecessary confusion: I noted in my comment that a threshold scheme would introduce a risk of collusion and didn't "propose" such a scheme, but only stated a problem.
Jan
6
comment Shared secret: Generating Random Permutation
How are you going to enforce such a requirement? Suppose Alice, Bob and Carol are playing. Alice has already folded but remain online. Bob has gone all-in but realizes he is about to loose just before the last card is to be revealed. Bob privately asks Alice to pull the plug. Alice pulls the plug.
Jan
6
comment Shared secret: Generating Random Permutation
Please note that any mental poker protocol would leave you with a problem of how to fold, if there are more than two players. If all players have to be present to decrypt the next card, one player might simply go offline and make it impossible for the remaining players to complete the game. If you solve that by using threshold secret sharing, you introduce a possibility of collusion.
Dec
30
comment Random Number Generation with a Entropy pool versus Seed
Your first paragraph is a bit fuzzy. If you need a cryptographically secure pseudo random number generator, it is because you need cryptographically secure pseudo random numbers, and whatever that reason might be, it is cryptographic by definition. If not, you might need a PRNG, but not necessarily a CSPRNG, and should probably ask elsewhere.
Dec
28
comment Can an RSA public key be generated without ever knowing the factors?
crypto.stackexchange.com/questions/9191/…
Dec
23
comment Single Party Encryption, Multi Party Decryption
Benaloh's scheme seems to be exactly what I am asking for, yes. On the negative side, though, the scheme uses commitments that induce an overhead for the mixes by a factor greater than 100 (with the parameter values recommended in the paper). It is obvious that there would be a risk for integrity if only two commitments were used by each mix, but would it lead to a risk of compromised anonymity?
Dec
23
comment Single Party Encryption, Multi Party Decryption
I am missing your thoughts on how, exactly, this might be applied to a mixnet scheme.
Dec
22
comment Single Party Encryption, Multi Party Decryption
Clarification: My question concerns mixnets, so the requirement that decryption is done in sequence and deniably seems essential. If you thought of this and came to a different conclusion, please expand your answer.
Dec
22
comment Single Party Encryption, Multi Party Decryption
That paper seems to deal with a different scenario, where one user distributes a private RSA key to multiple devices. Hence, it violates the first requirement, in so far that there has to be a trusted dealer, and that dealer will (at least at some point in time) know the private key (share) of all of the other decryptors. Furthermore, the paper describes a method for the decryptors to work in parallel to decrypt a message, while the second and fourth requirements in my question entail that decryption must be done in sequence.
Dec
22
comment How does a backdoor in the RNG enable an attacker to break encryption protocols?
schneier.com/blog/archives/2007/11/the_strange_sto.html
Dec
21
comment Private Messaging
I think your answer summarizes the (publicly known) state of the art of traffic analysis counter measures, but I am holding my accept to see if there are any other takers.
Dec
19
comment Private Messaging
I wasn't clear. With such a solution Alice would of course have to send a message with layered encryption. When Sue has peeled off the first layer, all that it says is that the message is intended for Carol, etc. Obviously, if the first mixer sees the final recipient, Eve will just have to compromise the first mixer to get the actual traffic data.
Dec
19
comment Private Messaging
It is possible to let a third client Carol act as a mix. Sue is however the only entity that all parties are able reach directly (i.e. the only one with a static IP or registered DNS name). The routing could e.g. be: Alice->Sue->Carol->Sue->David->Sue->Bob.
Dec
18
comment Private Messaging
@DrLecter: Am I correct that those papers deal with the details of the "ideal" solution I outlined, and hence suffer from an overhead that is linear in either the number of users or the total number of messages?
Dec
17
comment Calculation of time to crack SHA-256 hash
Regardless, if you are only interested in a single password (for a specific user), brute force would be fast enough, to make actually programming the attack the most time consuming step, even if you attack by brute force.
Dec
17
comment Calculation of time to crack SHA-256 hash
Is this homework and you want an exact answer, or would "no more than two seconds" do?