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Aug
26
answered What is matrix branching program?
Aug
17
comment Hardness of finding mutual discrete logarithms of small generators in $\mathbb{Z}_p$
The entire argument of "what if $p=2^n-3^m$" is pointless. A random prime has a negligible chance to fulfill this requirement. Similar arguments can be made for RSA numbers having a specific format: E.g. if $p$ and $q$ are close together, Fermat factoring works. The knowledge of a fixed element to a fixed base does not help solving arbitrary logarithms. For example: $\log_2(8)=3$ is known to be true in any $\mathbb{Z}_p$ with $p>8$.
Aug
13
comment Is SHA-1 safe for signing ECDHE parameters?
Why would you deliberately use SHA1 today? This is like building a new car with a 20 year old engine design. It still works, but it simply isn't up-to-date any more.
Aug
13
comment Can one construct OTPs without using XOR?
The first sentence is a little confusing: "each of the construction is (not) perfectly secure" It was not clear to me before reading the rest of the answer, what the brackets around not actually mean in this case. Is it secure or not? I would suggest changing it into "each of the constructions is perfectly secure or not..."
Aug
7
comment How can recovered 5-letters plain text help me to recover reused OTP key
I suggest to ignore this so-called "Crib Drag" method, because it is actually just a fancy name for the least efficient methods to analyze multi-time-pad. Please don't call it OTP, when it clearly isn't. This site should offer a lot of questions and answers to this topic.
Aug
4
comment LUKS multiple key slots - what's the intuition?
@SauceCode How about wikipedia: related-key attacks and related-key attacks on AES.
Aug
3
comment What are the practical implications of ciphertext distinguishability?
The question was about practical implications, and this answer remains entirely within the theoretical scenario of a CPA attack.
Aug
3
comment Can string lookups be vulnerable to timing attacks like array lookups are?
If you consider C, then strings actually are arrays, so anything there can just be applied to both. But in general: It depends on the context and the actual usage in the algorithm. As a rule of thumb: If you have a algorithm where no one took explicitly care of sidechannels, it is very likely that there is one. This is especially true for any deterministic part.
Jul
31
comment ElGamal signatures systems
Start by writing $g^s$ on one side of the equation. And then try to get the same term on the other side by using $g,k,h(m),a$ only. Keep in mind that the term $r$ is defined by the exercise, and $a$ is only known in the form $y=g^a$. There's not much more we can help you with, without giving you the solution directly. And that surely isn't the goal of this exercise.
Jul
30
comment ElGamal signatures systems
SEJPM already gave you one solution. For the others: Just think about what could cancel each other out with the according $s$. Since the computation of $s$ is done mod $q$, you can be sure that the parts of $s$ are only used in the exponent.
Jul
30
answered For $p=23$, $g=2$, $q=11$ you are given the signature $(18,3)$ in the message $m=2$. Construct a signature in the message $m'=3$
Jul
30
revised What if the p and q used in keys generation of Pailler cryptosystem are composite?
Corrected a mistake
Jul
29
answered What if the p and q used in keys generation of Pailler cryptosystem are composite?
Jul
29
comment Is there any such thing as “proof of location”?
The tricky part in your question is "without a trusted third party". Does that mean you want a proof of location without infrastructure at all (e.g. senders and receivers of radio transmissions, etc.)? Maybe you should clarify your setting some more, but without some trusted infrastructure for localization, you won't find a solution.
Jul
28
comment Has anyone heard of matrix-based “Russian Doll” encryption techniques?
I've never heard of this, but a statement like "security closer to a one-time-pad" means (most likely) the author either doesn't understand perfect secrecy or doesn't have a proof. A reference would help, but right now this looks like snake oil.
Jul
28
comment Playfair Cipher + Vigenere Cipher?
The "looking for repetitions" is just one way to find out of the length of the key in the Vigenere cipher (Kasiski test). Then you have the Friedman test, which gives you an approximation of the length. And then there is the possibility to check the auto-correlation (shift the positions by $i$, starting with 1, and then count the number of equal characters, this will spike when shifting by the correct keylength).
Jul
28
comment Why calculate pi to estimate randomness?
I don't think that's relevant. But a 64 bit approximation is not nearly enough to estimate the quality of a RNG. If you think of applications which require a lot of random numbers (e.g. simulations), the required entropy might be higher.
Jul
28
comment Why calculate pi to estimate randomness?
So basically you just detected what was in fgrieu's answer all along implicitly. Anyway, the pi-test is quite irrelevant for cryptographic purposes, as explained in the other answer in detail.
Jul
27
comment Factorize RSA knowing several N and E
in a solvable math challenge, there has to be some trick for all the numbers you are given. And since you already figured out that two numbers share one prime, the rest should be straight forward. No need for some fancy library or program, your common math library for large integers should have the $gcd$ functionality built in and you don't need to test a lot of numbers. Worst case should be 25 gcd, 10 divisions and 15 primality tests. (Asumming they are in fact RSA numbers)
Jul
27
answered Can a 1 byte difference in AES 128 bit keys make huge difference in output?