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May
22
reviewed Reviewed Can a TLS client perform any DH regeneration?
May
22
answered Why is Bcrypt called a Key Derivation Function?
May
21
revised P10 to P8 in S-DES
edited tags
May
21
revised Cryptanalysis of S-DES - Equations
edited tags
May
21
wiki created s-des description
May
21
wiki created s-des excerpt
May
21
revised Ciphertext-only attack on Simplified DES
edited tags
May
21
answered one-way deterministic hash for low entropy input?
May
21
comment Elliptic Curve Cryptography Encryption and text representation implementation
This does not appear to answer the question in any meaningful sense.
May
20
awarded  Good Answer
May
19
comment Do hand-based hash functions / MACs exist?
Similar, maybe duplicate question: crypto.stackexchange.com/questions/765/… (although it doesn't mention MACs).
May
19
comment Why cant Public Key Encryption be perfectly secure?
@RickyDemer: Right, that's more or less what I had in mind. Sorry for the fuzzy language. (Also, if the message length is bounded, you can just check all possible messages. You might still want to weigh the messages by plausibility, though, if reasonable messages only make up a small fraction of the full message space.)
May
19
comment Why cant Public Key Encryption be perfectly secure?
@RickyDemer: Iterate over possible private keys, check whether the private key can correctly decrypt most messages encrypted with the known public key. (We can reasonably assume that nobody would use a private key that doesn't work most of the time, at least unless there's an additional error checking and redundancy layer involved, in which case it really should be considered part of the cryptosystem.)
May
19
awarded  Popular Question
May
19
comment Is One Time Pad considered Chosen-Plaintext Attack Secure?
... We should be able fix the first issue by making the keyspace $\{0,1\}^*$ and restricting the total length of messages that can be encrypted with each key to a polynomial function of $n$. This seems reasonable enough, since the adversary can only make a polynomial number of queries anyway. But the statefulness issue remains, although I guess we could just make the keys long enough compared to the maximum total message length to make the probability of overlap negligible. Lots of handwaving here, I admit, but it seems like it should work.
May
19
comment Is One Time Pad considered Chosen-Plaintext Attack Secure?
I guess we could define the "keyspace" for a one-time pad as $\{0,1\}^{\Bbb N}$, regardless of the security parameter $n$, and prefix each ciphertext with a starting offset in the key sequence that is guaranteed not to overlap any previously used key segment. That should be enough to (almost) make the one-time pad an IND-CPA secure encryption system, if I'm not mistaken. The only problems being that 1) $\rm Gen$ will not actually be an algorithm in the strict sense, and will surely not be polynomial-time, and 2) $\rm Enc$ would have to be stateful to guarantee the non-overlap property.
May
19
revised Can you make a hash out of a stream cipher?
add provable-security tag; remove the footnote about Carter-Wegman MACs, since none of the answers really address it (and it probably should be a separate question anyway)
May
19
comment Can you make a hash out of a stream cipher?
I don't really see how this adds anything to B-Con's second answer. In particular, as noted in the comments to that answer, it's not quite obvious how to obtain a block cipher that actually satisfies the (rather strict) security properties needed to prove the security of the resulting hash function.
May
19
comment Why cant Public Key Encryption be perfectly secure?
@RickyDemer: I don't really see any way to have sender-deniable public key encryption against a computationally unbounded adversary; in particular, the adversary can always recover the private key by enumerating the keyspace, and then decrypt the message. With overwhelming probability, the plaintext they get is what was originally encrypted, or at least what the intended recipient would have received.
May
19
comment How can a block cipher in counter mode be a reasonable PRNG when it's a PRP?
The answer is basically the PRF/PRP switching lemma, which essentially says that a pseudorandom permutation is indistinguishable from a pseudorandom function unless we observe a collision for one of them. See also this question on cstheory.SE.