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Dec
11
revised In RSA, why is it important choosing e so that it is coprime to φ(n)?
Grumble typo...
Dec
11
revised In RSA, why is it important choosing e so that it is coprime to φ(n)?
Expanded explination
Dec
11
revised In RSA, why is it important choosing e so that it is coprime to φ(n)?
typo
Dec
11
revised In RSA, why is it important choosing e so that it is coprime to φ(n)?
English fixup; added final note
Dec
11
answered In RSA, why is it important choosing e so that it is coprime to φ(n)?
Dec
10
comment Diffie-Hellman: Does the size of the prime modulus depend on the potential size of the secret?
@user10800: well, I'm not sure what you should call it (stream cipher really doesn't apply either, come to think of it; it uses inputs from both sides; it appears to be closest to El Gammal, but it's not that either). The term OTP doesn't apply, because the one point that you're missing is a very important point about OTPs. As for exhaustive search, well, you're secure computationally, and so the correct protection against exhaustive search is to make it computationally to difficult to consider. As for each character getting its own random shift, we have better ways to protect plaintext.
Dec
10
answered What are the pros/cons of using symmetric crypto vs. hash in a commitment scheme?
Dec
10
comment Diffie-Hellman: Does the size of the prime modulus depend on the potential size of the secret?
@RickyDemer: thanks; if you go through my answers, you'll find that I often think one word, but type something else...
Dec
10
revised Diffie-Hellman: Does the size of the prime modulus depend on the potential size of the secret?
Rewording
Dec
10
answered Diffie-Hellman: Does the size of the prime modulus depend on the potential size of the secret?
Dec
10
comment How should I manage Diffie-Hellman parameters on a Web Server?
@noloader: if you're worried about the NSA having back doors in the selection of the groups, that is unlikely; those groups are of open design, and the majority of the bits come from the binary expansion of $\pi$.
Dec
9
comment How should I manage Diffie-Hellman parameters on a Web Server?
@noloader: $g^{(p-1)/2} \bmod p = 1$ iff $g$ is a quadratic residue modulo $p$ (and, in this specific case, $g$ isn't; $p = 3 \bmod 8$ is enough to determine that with $g=2$). That has nothing to do with whether $q$ is prime or not.
Dec
9
revised How should I manage Diffie-Hellman parameters on a Web Server?
Added update
Dec
9
revised How should I manage Diffie-Hellman parameters on a Web Server?
added 17 characters in body
Dec
9
revised How should I manage Diffie-Hellman parameters on a Web Server?
added 107 characters in body
Dec
9
answered How should I manage Diffie-Hellman parameters on a Web Server?
Dec
6
comment How can I tell how many bits of security a secure hash function has?
@rath: I believe that this is what is confusing you: if we generate images in such a way so that we'll never generate the same hash value twice, then yes, after $2^{160}$ hashes, we'd be guarranteed to generate the hash we're looking for (and the expected, or average time to find it would be $2^{160}/2 = 2^{159}$). However, with a strong hashing function, we have no such generate to never repeat hashes, and so it turns out the expected (average) time to be $2^{160}$, with no strong bound on how many hashes we'd need if we get unlucky
Dec
6
comment How can I tell how many bits of security a secure hash function has?
@rath: no. Actually, hashing $2^{160}$ images doesn't guarrantee us to find a preimage; it's just that if we hash that many, we have a good chance to find one. Another way to look at it; if we hash a random image, we have a probability $2^{-160}$ of the hash being the value we're looking for; if we hash $2^{80}$ random images, then the probability that one of the resulting hashes is the one we're looking for is about $2^{80} \times 2^{-160} = 2^{-80}$; rather unlikely.
Dec
6
comment How can I tell how many bits of security a secure hash function has?
@rath: no, a second preimage doesn't work that way. For a hash function without any cryptographical weaknesses, the knowledge of one preimage doesn't really help; we've no better strategy than hashing that one image, and then doing a preimage search on that hash value, looking for a second image.
Dec
6
answered How can I tell how many bits of security a secure hash function has?