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Mar
25
answered Does perfect secrecy imply uniform ciphertext distribution?
Mar
25
comment Bit commitment, two blobs with same bit, without revealing it?
@tylo: Actually, this is subtly different from Goldwasser-Micali; in GM, the holder of the private key knew the factorization of $n$; here, the committer need not know that -- they can reveal the secret by revealing $x$. And, they can generate a ZKP that $y_1y_2$ is a QR (if $b_1=b_2$) because they know the squareroot (either $x_1x_2$ or $x_1x_2t$)
Mar
25
comment Authentication using a one-time pad
@thirtythreeforty: Davies-Meyer is intended to turn the cipher into a hash. Thinking about it more, perhaps CBC-MAC (you don't need to worry about the attacker extending the message, do you?) would work out better. If you need to worry about replays, putting in a counter (which would be included in the integrity check) is the obvious solution.
Mar
24
answered Authentication using a one-time pad
Mar
24
comment Authentication using a one-time pad
What level of integrity protection are you looking for? That is, if someone modified a packet, what is an acceptable level of probability that the modification be undetected? $2^{-16}$? $2^{-64}$?
Mar
24
comment Bit commitment, two blobs with same bit, without revealing it?
@RobertNACIRI: actually, that is not true; the Jacobi symbol will be 1 regardless of whether $b$ is 0 or 1. Remember, $t$ is chosen with a Jacobi symbol 1, $x^2$ also has Jacobi symbol 1, and so both $x^2t^0$ and $x^2t^1$ will have Jacobi symbol one. You might be thinking of a prime modulus (where the Jacobi symbol does indicate whether the number is a QR); this is done over a composite modulus, where there are nonQRs with Jacobi symbol 1.
Mar
24
comment Twofish encryption in Python
I'm voting to close this question as off-topic because it is a question about a specific cryptographical library, and not cryptography in general.
Mar
24
revised Bit commitment, two blobs with same bit, without revealing it?
edited body
Mar
24
revised Bit commitment, two blobs with same bit, without revealing it?
added 487 characters in body
Mar
24
answered Bit commitment, two blobs with same bit, without revealing it?
Mar
24
reviewed Reviewed feistel structure? why decryption is so easy with reverse order of subkey
Mar
24
comment feistel structure? why decryption is so easy with reverse order of subkey
As a suggestion, perform a simple Feistel network on paper (using an Oracle as the round function -- make a list of inputs and outputs to the round function, when you get an input you haven't seen before, pick the output randomly, and put them on the list); try both encrypting and then decryption, and see exactly what's happening.
Mar
24
reviewed Close Credit card number encryption using AES counter mode
Mar
23
reviewed Leave Open cryptographic hash function
Mar
23
comment Is Encryption without knowing the input directly possible at all?
Not unless the $n$ parties sit down and compare results afterwards -- that wasn't mentioned within the problem statement.
Mar
23
comment Is Encryption without knowing the input directly possible at all?
One of the things that both Alice and Bob need to prove is that what they generate is some permutation of the inputs; for example, Bob didn't discard $t_1$, and gave two encryptions of $t_2$.
Mar
23
reviewed Reviewed Is Encryption without knowing the input directly possible at all?
Mar
23
reviewed Reviewed What is this cryptosystem called?
Mar
23
reviewed Reviewed cryptographic hash function
Mar
23
revised cryptographic hash function
The question was not about universal hashes (which are a completely different primitive)