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20h
comment Why should I make my cipher public?
My suggestion was aimed at pointing it out more directly, that he didn't demand publication itself. But that in today's context that's the only (serious) way to substantiate a claim about security.
21h
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.
1d
comment Why should I make my cipher public?
I would suggest to add this to the answer: Kerckhoff did not require the publication of an algorithm. He said that it must be able to fall into the enemies hands and still remain secure. In the military context this means, that it's enough when your own cryptanalists can ensure this. But in today's practice this can't be proven without publication, because anyone in the world can claim his system is secure, or it all comes down to blind trust.
1d
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.
2d
comment need help for decrypting a cipher.. i am new to this so was wondering if someone could tell me how to go about it
Question: "what should an absolute beginner do to decode a code?" Answer: Take a course in cryptography.
2d
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.
2d
comment need help for decrypting a cipher.. i am new to this so was wondering if someone could tell me how to go about it
Welcome to crpto-SE. Unfortunately, your question is both off-topic and unsolvable. Please have a look at the Ask question section about what kind of questions are on-/off-topic. About your code fragment: Without knowledge what kind of cipher it is, this piece is way too short to make any reasonable argument. From the first glance, this looks just like a sequence of numbers and not really a code or cipher.
Jul
28
comment Has anyone heard of matrix-based “Roman 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
23
comment Are specially designed fonts sometimes used in cryptography?
Visual cryptography is not really an encryption method, but more like a secret sharing. Of course you can always consider this as a cipher if you consider one share to be the key and one share to be the ciphertext.
Jul
21
comment Are specially designed fonts sometimes used in cryptography?
Assuming the attacker knows nothing about the encoding algorithm is bad. That's like thinking "if I can't break the system, then no one else ever could". Both are assumptions that have proven to be wrong countless times.
Jul
20
comment RSA private key d knowing e,n
Just posting the solution to homework does not really help in understanding how to solve the problem, usually.
Jul
20
comment curious DHE implementation for key exchange
How do you know, that it is not a power of $4$? There is no other way for this to work, unless the server knows the logarithm of $g$ to base $4$. Essentially, this is just DH with the server's side always being static (similar to the public key in ElGamal). The generator used is actually $4$, and what is usually denoted $g^a$ in DH is called $g$ here.
Jul
16
comment What good is a hash accompanying a program?
Considering websites: It can also make a difference if the HTML is transmitted via HTTPS, and the file download is unencrypted.
Jul
16
comment What good is a hash accompanying a program?
The first two sentences indicate, you believe SHA-2 to be vulnerable to finding preimages to a certain hash value (e.g. with the length extension...). This is wrong. As others have already pointed out: SHA-2 is considered one of the stronger hashes (and pretty much state-of-the-art in practical applications). Even MD5 is still considered secure against preimage attacks (but not recommended any more). And that is still enough if you get the hash from a trusted source.
Jul
16
comment Is it a good practice to use plain text for derivation of Keys?
My guess is, that you are trying to re-invent key encapsulation like it is done in hybrid encryption, without defining if you are using symmetric or asymmetric crypto. Right now there is no reason to "hash" the plaintext to derive a key. Comparing to choosing a random one, this only can introduce possible weaknesses without granting any benefit. Especially, since your notation does not actually indicate the use of a hash function, or a PBKDF - which would be necessary, if the plaintext is somehow predictable or easy to guess.
Jul
14
comment Computational indistinguishability: are function parameters known?
I did not claim the Mersenne Twister is a good CSPRNG. It is a useful PRNG for simulations etc. where you need randomness with good statistical properties. It is kinda crucial to think of the "CS" part seperately: But I will point that out more explicitly