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Apr
16
reviewed Leave Open How can I convert numbers into prime numbers?
Apr
16
reviewed Leave Open Exchanging Keyspace and Message space in PRF
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.
Apr
7
reviewed Looks OK Should we MAC-then-encrypt or encrypt-then-MAC?
Apr
7
reviewed Looks OK Should we MAC-then-encrypt or encrypt-then-MAC?
Apr
7
reviewed Leave Open Compression step of PGP
Apr
7
reviewed Leave Open What is h in this RSA variant?
Mar
18
revised Why concatenate the key a second time in HMAC?
added 9 characters in body; edited tags
Mar
17
reviewed Reject Randomness test question from FIPS 140-1 and comparison with 140-2
Mar
14
comment Is this a pseudo random function (PRF)? F(k,x) = f(k,x) - f(k,x-1)
@fgrieu This is getting way too long for the comments. But you have some basic misunderstanding about the proof technique here. IF the construction from the proof WOULD work against $f$, THEN the proof would lead to the conclusion that F'' is a PRF. But it does not.
Mar
14
comment Is this a pseudo random function (PRF)? F(k,x) = f(k,x) - f(k,x-1)
@fgrieu The reasoning (which while correct is missing a crucial argument about the distribution of sums of uniformly and independently distributed values) simply does not apply to your example. The reasoning goes as follows: To simulate the oracle for a dist. against $F$ we simply follow the construction of $F$, but use the oracle (containing either $f$ or a random function) instead of $f$. Now the following holds: (1) If the oracle is $f$, then we perfectly simulate $F$. (2) If the oracle is a random function then we perfectly simulate a random function. The second part fails for $F''$.
Mar
14
comment Is this a pseudo random function (PRF)? F(k,x) = f(k,x) - f(k,x-1)
@fgrieu Yes, the proof sketch is missing the argument, why it is that the reduction perfectly simulates a random function in the case that it itself is given access to a random function. But my point is that the proof does NOT need " profound change" besides that. The reduction trivially fails for the examples you give, because the distribution of outputs is incorrect for the random case. In particular your distinguisher would always output the same bit when run as a subroutine of the reduction, because the condition you check would hold in both cases.
Mar
13
comment Is this a pseudo random function (PRF)? F(k,x) = f(k,x) - f(k,x-1)
@fgrieu I don't see how the same argument would work for your examples. If we assume an analogous simulation of the oracle for $F'$, it is easy to see that the simulation of the random case simply fails. That is, in both cases (PRF and random function) the simulated oracle exhibits the bias you mention. The hard part in proving such PRF constructions secure is always to argue why the simulation does not fail in the random case. Here, such an argument can be made for the original function, but not for your examples.
Mar
3
reviewed Approve What RC4 key value will completely invert $S$ after initial permutation?
Feb
28
reviewed Approve Cryptographic Protocol using NaCl
Feb
21
revised Prove that two MACs with incremendal PRF application are not secure
fixed index of key
Feb
21
comment Prove that two MACs with incremendal PRF application are not secure
Well, to show that they are not secure, you have to present an adversary that is able to forge them. For the first one, think about how, given a message and a tag, you can find another message for which the same tag will verify. For the second one, think about how you might be able to compute a tag for a longer message without knowing the key.
Feb
20
reviewed Leave Closed Complexity class of an idealised version of Bitcoin's proof-of-work (hashcash)?
Feb
20
reviewed Reopen RSA vs El Gamal digital signature. Which is more secure?
Feb
20
reviewed Leave Closed Why does a one-time-pad key have to be at least as long as a message?