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Aug
28
comment Proving an encrypted message contains (but does not 100% consist of) a plain-text message?
Can you edit in the info you posted? You should be able to now. Then just flag the answer below where you provided the info and I'll delete it.
Aug
28
comment Are there any cryptosystems that use multiple keys to perform encryption instead of one or two?
When you say "to perform encryption" you mean only encryption or encryption and decryption?
Aug
27
comment Hitting a counter example in homomorphic encryption over the integers
Maybe it is just a corner case that is so unlikely to happen with real parameters and proper use? Like in RSA if you try to encrypt a multiple of one of the prime factors, the encryption is the identity: crypto.stackexchange.com/questions/1004/…
Aug
27
comment Hitting a counter example in homomorphic encryption over the integers
Could it be order of operations? (1 xor 1) xor 1 = 0 xor 1 = 1 whereas an xor(1,1,1) = 0 for an xor operator that takes more than 2 inputs.
Aug
27
comment Privacy and Integrity in Public Cryptography
@Loris, a lot of the issues have been described on this site: RSA in ECB mode, attacks on textbook (no padding) RSA. Encrypting large files with RSA is very inefficient and this could lead to DoS attacks too.
Aug
27
comment CPA-security proof of “l-padded RSA” encryption scheme
That sounds like a reasonable way to do it.
Aug
27
comment CPA-security proof of “l-padded RSA” encryption scheme
I don't know this for a fact, but notice that the problem says "prove that if ... is hard ... then ... is CPA-secure". Could it be that your professor is saying that there is no formal proof that the if statement is true? In other words, the problem is saying, assume X, now prove Y, while your profesor is saying that we don't really know if X is true? Therefore, there is no conflict.
Aug
27
comment CPA-security proof of “l-padded RSA” encryption scheme
What is your question? There is no question mark in there. All I see are statements.
Aug
27
comment Privacy and Integrity in Public Cryptography
@Loris, unfortunately, without that type of information it is impossible to answer. There are ways it could be done and provide confidentiality and integrity (but be very, very slow) and there are ways it could be done that completely destroys confidentiality.
Aug
27
comment Privacy and Integrity in Public Cryptography
@Loris, but how are they encrypting large files with, I'm assuming, RSA? With RSA, if the modulus is only 2048 bits, you would have to break a large file into small chunks to encrypt. Are they using padding of any sort? All of these things will affect the security of the protocol, which is another reason to use a standard method (though it sounds like at the moment, this isn't up to you).
Aug
27
comment Encipher the following plaintext message using the Vignere method using the key K = [4,2,3]
I'm voting to close this question as off-topic because it does not give a clear description of the problem you are facing. Please edit to include those details.
Aug
27
comment Encipher the following plaintext message using the Vignere method using the key K = [4,2,3]
You can't find anything that matches this question online? Seriously? There is tons of material out there on Vigenere. You should start with the description of Vigenere on Wikipedia. Vigenere is a very simple cipher. If there are parts you don't understand, you should clearly describe what you don't understand about them to us. Then we can help you.
Aug
26
comment Shamir Secret Sharing: Why cannot we recover polynomial's root if we have $t-1$ shares?
@HenrickHellström I updated the answer to account for the case you mention. Thanks.
Aug
26
comment Shamir Secret Sharing: Why cannot we recover polynomial's root if we have $t-1$ shares?
@HenrickHellström I thought given the roots, you know the factorization of the polynomial, and hence, can reconstruct the polynomial. Take the example on Wolfram, roots are $2, 1, -1$. Therefore the factorization is $(x-2)(x-1)(x+1)$ and the polynomial is $x^3-2x^2-x+2$, so the secret would be $2$. Maybe this doesn't translate or is not always the case?
Aug
26
comment Shamir Secret Sharing: Why cannot we recover polynomial's root if we have $t-1$ shares?
I see you already had asked it :)
Aug
26
comment Shamir Secret Sharing: Why cannot we recover polynomial's root if we have $t-1$ shares?
My guess is that unless $(\beta, 0)$ is one of the shares, then the probability would be very small, something like $1/p$. But I'm not sure on that. That question in the comments would be a good question to ask on Math.SE.
Aug
26
comment Shamir Secret Sharing: Why cannot we recover polynomial's root if we have $t-1$ shares?
Definitely don't remove this. If that answers your question, let me know and we can mark this as a duplicate. I, however, don't think this is an exact duplicate and that we can leave it open.
Aug
26
comment Shamir Secret Sharing: Why cannot we recover polynomial's root if we have $t-1$ shares?
Related question: crypto.stackexchange.com/questions/19332/…
Aug
26
comment Shamir Secret Sharing: Why cannot we recover polynomial's root if we have $t-1$ shares?
@user13676 Which is what you meant? The former or the latter?
Aug
26
comment What is stopping someone from saving encrypted info, and decoding it later?
What is your definition of "a few years"? The common crypto in use today (128 bit AES, 2048 bit RSA, etc) should be secure for a few decades. Given, we don't know that for a fact.