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Mar
21
comment Entropy when iterating cryptographic hash functions
Thanks, Stephen! I've edited the question further to ask about the general situation, as @fgrieu suggests.
Mar
21
revised Entropy when iterating cryptographic hash functions
Generalization the question to be generally useful, per comment thread.
Mar
20
answered Distinguishing Attack on CBC-MACs
Mar
20
comment What is the idea behind hashing the QueryString in OAuth?
I'd speculate that they want to protect the querystring parameters from tampering/modification. If they weren't included in the hash/MAC input, an attacker could change them freely and the modification would go undetected.
Mar
19
answered Zero Knowledge Proof for Correctness of the product of additive ElGamal Ciphers
Mar
19
comment Zero Knowledge Proof for Correctness of the product of additive ElGamal Ciphers
I encourage you to put in a bit more effort on formatting the question to be easily readable. Did you know you can use Latex (Mathjax) on this site? See the help center for more.
Mar
19
reviewed Approve Zero Knowledge Proof for Correctness of the product of additive ElGamal Ciphers
Mar
19
revised Entropy when iterating cryptographic hash functions
incorporate comments from fgrieu
Mar
19
comment Entropy when iterating cryptographic hash functions
@fgrieu, great point! For large enough $i$, this formula certainly becomes inaccurate. For instance, when $i \ge 2^{n/2}$, it is likely that the entropy will be about $n/2$ bits, and after a certain point it won't get any smaller no matter how much you increase $i$ (because typically when iterating a large random function, there is a single large cycle of length about $2^{n/2}$ that most inputs feed into). Thank you!
Mar
18
comment Subexponential algorithms for DLP in $\mathbb{Z}_s \times \mathbb{Z}_t$
JasonJones, yup! It does suggest that the DLP is easier to solve than in the corresponding elliptic curve. It does suggest that the DLP can be solved faster than exponential time. The faulty premise is in assuming this means it is claiming that the DLP can be solved in sub-exponential time, e.g., in $L_n[\alpha,c]$ time.
Mar
18
comment Meet in the middle attack - message and key
Read about known-plaintext attacks.
Mar
18
answered Entropy when iterating cryptographic hash functions
Mar
18
comment Subexponential algorithms for DLP in $\mathbb{Z}_s \times \mathbb{Z}_t$
This question starts from a faulty premise. The accepted answer you link to does not suggest that there are subexponential algorithms for solving DLP in $\mathbb{Z}_s \times \mathbb{Z}_t$. (In fact I don't even see the word subexponential in that answer.)
Mar
18
revised Subexponential algorithms for DLP in $\mathbb{Z}_s \times \mathbb{Z}_t$
Add elaboration from my comment.
Mar
18
comment Are there hash algorithms with variable length output?
@curious, again, ask a new, separate question -- and make sure to follow best practices before doing so (e.g., searching to make sure it hasn't been answered before). This is not a discussion forum. One question per question. I'm not going to answer any new questions posed in the comment threads.
Mar
18
comment Are there hash algorithms with variable length output?
@curious, that's a different question, which is probably best answered separatately, but the concise answer is: treat the output of SHA256(m) as a 256-bit integer, reduce it modulo 360, and use the remainder a syour random number.
Mar
17
answered counter to indicate hotp count
Mar
17
answered Why do we apply the concept of circuit in homomorphic encryption schemes?
Mar
16
comment What functions allow for practical indistinguishability obfuscation?
Thanks, @xagawa! On log-size circuits: What is the log of? i.e., log of which parameter? (presumably not the size of the input to the circuit) For normal forms: are there known classes of circuits that have a normal form? I know that BDDs can be put into normal form. That's all I know but I'm guessing probably more is known....
Mar
16
comment How can I create an RSA modulus for which no one knows the factors?
Yes, but the algorithms are not practical for reasonable-sized RSA modulus. I'm pretty sure this has been asked before on this site but I can't seem to find where...