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| bio | website | |
|---|---|---|
| location | ||
| age | 43 | |
| visits | member for | 1 year, 9 months |
| seen | May 12 at 12:36 | |
| stats | profile views | 9 |
programs in C and Perl, mostly
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Mar 12 |
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computing inverses in truncated polynomial rings manually for NTRU encryption Pretty sure, if I have more time, I'll try to compute it too, by hand, of course. |
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Mar 12 |
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computing inverses in truncated polynomial rings manually for NTRU encryption @SuniaRaharja yes, the polynomial $x$ (bad choice of notation) is indeed the inverse, and then you need to reduce mod 11. If all is well, you shouls get $a^{-1}$ or an equivalent (mod 11) polynomial. |
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Mar 11 |
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computing inverses in truncated polynomial rings manually for NTRU encryption Basically, using Extended Euclidean, do the inverse computation of $a$ in $\mathbb{Z}[X]$, doing the gcd with $X^7 - 1$, and reduce the coefficients modulo 11 afterwards. |
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Mar 11 |
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computing inverses in truncated polynomial rings manually for NTRU encryption @SuniaRaharja typo alert: $4^X$ should be $4X$; do you the result of the multiplication as correct, using $X^7 \equiv 1, X^8 \equiv X$, etc? This we do in $\mathbb{Z}[X]$ first, then reduce the coeffficients modulo $11$ (so $22 \equiv 0$, $-10 \equiv 1$). |
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Mar 11 |
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computing inverses in truncated polynomial rings manually for NTRU encryption @SuniaRaharja Take the coefficients (which are integers) modulo 11. |
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Mar 1 |
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Finding roots in $\mathbb{Z}_p$ Cantor-Zassenhaus or Berlekamp algorithms will factor polynomials, e.g. |
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Feb 20 |
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Why are RSA keys encoded with ASN.1 for TLS? @roger ASN.1 does not allow for arbitrary code execution, it's just a way (which is already used in many other standards!) to unambiguously code data, like a sequence of big integers (as we need to do, among other things). The parsing library can be bad and have bugs, but it's not the encoding that is the problem. Data is just data... And javascript has nothing to do with it. (I don't understand that remark at all) |
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Feb 19 |
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Why is Blum-Goldwasser not IND-CCA-2 secure? @Johannes We choose the same $y$. Read up on what the Ind-CCA2 game is: the adversary is allowed to ask for decryptions of all messages, except the ones that are totally identical to challenge messages. So we choose the message to be the same except the first bit, and this is allowed. You can see it is quite a strong notion of security! |
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Feb 19 |
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Why is Blum-Goldwasser not IND-CCA-2 secure? The argument is mentioned (briefly) under the point Security and Efficiency on that same page. |
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Feb 8 |
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RSA primes vs. largest known primes the problem with a Mersenne prime $p$ is that $p+1$ only has small factors, and this allows for faster factoring. Same holds when $p-1$ has lots of small factors as well. So in RSA keygeneration, such primes are not used, in the standard libraries.. |
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Oct 25 |
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Because the algorithm is known, it is no longer a trade secret @WilliamHird there were weaknesses in the system itself that were exploitable, e.g. the fact that no letter could encrypt to itself aided the placing of probable plaintext, and the specifics of the stepping (which was too regular) also implied the Stecker-settings could be separated from the wheel settings if probable plaintext was known. The allied rotor systems (Typex, SIGABA) did not suffer from such weaknesses. Human errors played a role (the weak indicator system in the beginning of WW II, stereotypical text) but were IMHO not even the most essential. |
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Oct 7 |
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RSA encryption input range - plaintexts that map to ciphertexts? Indeed. And that's why RSA is used with padding, to ensure that values like that cannot occur, and to ensure that the same message will have different encryptions at different times (which is another desirable property: the ciphertext leaks as little information as possible). |
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Oct 7 |
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When is each key used when encrypting an email using OpenPGP? @Xeoncross Indeed. |
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Oct 2 |
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Could the Enigma algorithm be classified as a Feistel network? Every position of the wheels (plus the Stecker-board) defines a unique mono-alphabetic substitution, that has no fixed points and is self-inverse. It's applied to one letter and then one wheel moves, sometimes triggering another wheel movement as well. We then get the next monoalphabetic etc. After all wheels have gone full circle, the cipher returns to the initial state (but this never happened in practice, as messages were shorter than the cycle length). Indeed a very different structure. |
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Oct 2 |
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When is each key used when encrypting an email using OpenPGP? You can sign your message using only your own (private) key (it could be a public message, say) but your public key should be known to someone that wants to verify your signature. You cannot encrypt for someone without knowing that person's public key, in a scheme like this. |
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Nov 7 |
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How to choose constants in a cryptographic function? it seems to be that this is hidden in the rka-advantage used in the bound of lemma 5.2 of that paper (the original Crypto 96 paper, to which I do not have access right now, might have more info, and could be my source of recollection); the homogeneity property that I mentioned might give a sharper security bound; and I cannot think the constants are irrelevant, I'd think that constants 0 and 0xff would give worse results, intuitively. |
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Nov 7 |
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How to choose constants in a cryptographic function? As to S-boxes: there was already a theorem proven that inversion in a field is almost optimally non-linear in a certain sense, and this was the reason the transform was used; the affine transform afterwards is to get rid of the fix point 0 --> 0. The precise form of the constants in the S-box then follows directly from the polynomial in the definition of the Galois field. |
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Nov 7 |
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How to choose constants in a cryptographic function? As to 0x36 and 0x5c: the requirement for these constants is that there are 4 types of bit positions in a byte: where both constants have 0-bits, both have 1-bits, constant1 has a 1 and constant2 a 0, and vice versa. This means that (when we xor this with a key byte) we toggle half the key bits every time. The security proof depends on the constants having these properties, IIRC. |
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Sep 27 |
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What is the difference between a stream cipher and a one-time-pad? Also note that a computationally unbounded adversary could break a stream cipher (having enough known plaintext) but not a one-time pad. |
