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May
6
revised Is G is a secure PRG?
added 26 characters in body; edited tags
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
reviewed Leave Closed Is it true, that non-military cryptography appeared in 50's and 60's only thanks to leaks from the NSA?
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.
May
2
reviewed Leave Open PRF and hash functions
May
1
answered PRF and hash functions
Apr
22
reviewed Close Is less security required for a short stream cipher than for the AES enciphering of very long messages?
Apr
22
reviewed Reject How secure is AES-256?
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.