# All Questions

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### Perfect secrecy of a crypto system

Suppose we have the following crypto system: $P = C = K = \{0, 1, . . . , n − 1\}$, $E_k(x) = (x + k) \bmod n$ and $D_k(y) = (y − k) \bmod n$. Prove that the crytosystem has perfect secrecy. Perfect ...
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### Possible hashing scheme

Plaintext(binary) : 10101100 //very short for easy understanding Suppose we have 4 predefined schemes/functions, rotate (101 -> 011) flip (1101 -> 1011) exchange (11011 -> 10111) stretch (1100 -> ...
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### What would be the best plain text Cryptography method without the use of a computer? [closed]

What would be the best Cryptography method without the use of a computer? This could be a list of the current options available, that could be used without the use of a computer ...
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### Dancing confusion with Daniel J. Bernstein's stream ciphers

I know of Salsa20 which won the ESTREAM competition. This is dated of 25 Dec 2007. There is also the ChaCha20 stream cipher (cr.yp.to/chacha.html). This claims to increase the amount of diffusion ...
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### fully homomorphic encryption (FHE)

Please, I would like to find some hints or solution to my following problem, I would appreciate your assistance to walk with me throughout the solution Given fully homomorphic encryption (FHE) ...
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### Why is authenticated CFB mode insecure?

I read that the following adaptation of the CFB block cipher mode into an authenticated mode is prone to chosen plaintext attacks, yet Im still unsure how to prove it: Let $P_1,P_2,\ldots P_n$ be the ...
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### How represent message in Menezes–Vanstone elliptic curve cryptography

I ask about represent message in Menezes–Vanstone elliptic curve cryptography I now encrypt function as follow $C_1 = (M_1 * K_1) mod\ P$ $C_2=(M2 * k_2) mod\ P$ My question is about how much the ...
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### Block cipher to encrypt 8 bytes/64 bits - Use 64 or 128 bit cipher?

Here's the problem: I have a transport stream that I have been requested to encrypt between the transmitter and receiver. The data size is at most 8 bytes so it seems I can only use ECB as I only have ...
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### “Kernel attack” on MinRank — why do we guess $\left\lceil \frac k n \right\rceil$ vectors?

The kernel attack on MinRank is described here (page 5). My question refers to this line: Note that if $m = \left\lceil \frac k n \right\rceil$, the system essentially has only one solution ...
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### Encryption key input by a user [on hold]

I was looking for some research papers where the security scheme is using 'user input' key method (but could not find). I mean, some approaches where user will be the one who will put keys for ...
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### Extending pseudorandom generator by one bit using exclusive-or of previous bits

Is it possible to have a pseudorandom generator that extends its output by 1 bit by simply appending the exclusive-or of all the previous bits? I know the output of a pseudorandom generator is ...
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### How to replicate GPA's Sign and Compress option on command line in Windows [migrated]

As the title says, I need to replicate GPA's "Sign and Compress" option on the command line. I'm trying to automate some encryption of files for submission to a bank and the instructions they gave me ...
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### Shannon confusion and diffusion concept

I read the document(not the whole document) from Shannon where he speaks about the concepts of confusion and diffusion. I read in many places(not in the document but around the internet) that ...
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### What is the difference between uniformly and at random in crypto definitions?

Very often in the description and analysis of a cryptographic protocol there is a need for a an element $k$ that is sampled uniformly AND at random. Is there a redundancy in the definition with ...
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### Why does the recommended key size between symmetric and assymetric encryption differ greatly?

In various articles it is mentioned that for secure communications, the recommended key sizes are 128-bit key size for symmetric encryption (which makes it $2^{128}$ possible keys?) and 2048-bit key ...
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### Is cm signed signature verification considered “slow”

I put slow in double quotes because I'm no expert in encryption (I heard that "cryptography in general is inherently slow"). Just trying to gauge and see how and where I can increase performance of my ...
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### request for data to test deterministic ecdsa signature algorithm for secp256k1

I’m implementing the RFC 6979 procedure to compute a message signature. I want to test my program on the secp256k1 elliptic curve. Note the “k” in secp256k1, i.e. the Koblitz curve. If you have the ...
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### How to customize a standard encryption algorithm?

I want to modify and customize AES encryption algorithm and develop a variant of it. What factors should I consider so that it does not become weaker? What skill sets would be required to undertake ...
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### Why is AES resistant to known-plaintext attacks?

At least it's my understanding that AES isn't affected by known-plaintext. Is it immune to such an attack, or just resistant? Does this vary for chosen-plaintext?
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### At what point does passphrase strength match the strength of the cipher?

Let's say that I have an ordinary hard drive encrypted with VeraCrypt 1.0e full disk encryption and implementing: -AES -RIPEMD-160 Hash Algorithm Now let's say that for an arbitrary machine, the ...
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### Malleability of homomorphic encryption

El Gamal is a malleable homomorphic encryption system, so is Rabin. Are all homomorphic encryption systems malleable? Or are there any that are not malleable? Thanks!
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### electronic voting system [migrated]

Was looking at cryptocurrency and how, as a non techy, to get involved when I began thinking about the security of it being developed to undermine the stranglehold bankers have on economy and the ...