# Questions tagged [cryptography]

Questions about the construction and analysis of protocols and algorithms for secure computation and communication (including authentication, integrity, and privacy aspects).

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### Does a random phenomenon have a pre defined probability distribution? what does it mean for something to be random?

While studying Shannon's notion of perfect secrecy I came upon the idea that a bit is perfectly random if it happens to be 0 or 1 with an equal probability. What does this mean? Also, what can we say ...
1 vote
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### LWE with a low rank matrix

Consider the decision LWE setting, where we have to distinguish between $(A, As + e)$ and $(A, u)$, for a randomly chosen $m \times n$ matrix $A$, an $n \times 1$ secret vector $s$, an $m \times 1$ ...
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### Reference for the formal definition of sigma protocol

I'm looking for a book that contains the formal definition of sigma protocol (something like: A sigma protocol for a relation $R$ and a challenge space $C$ is... that satisfies the properties of ...
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1 vote
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### How can I prove the file on DVD is the original?

I have an old file written to a DVD-R several decades ago, and it turned out this file can potentially has some value as NFT (non-fungible token). The file was published online and have been copied ...
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1 vote
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### Where does 2^32 come from with bitcoin?

Several months ago I was doing research into calculating mining revenue for several crypto currencies. When trying to calculate BTC revenue I found this value 1/2^32 which was described somewhere ...
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### How do these Crypto terms relate to each other and what do they all mean?

Alright this is another day of my pursuit to learn about how crypto works. I have several terms that I have found linked together. I was trying to do research on how the Target Hash is determined and ...
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### What happens in the event of a collision in a crypto hash function?

I was reading about hash functions in crypto and a website had mentioned that they were collision free, which obviously isn't possible if there are infinite input values that are mapped to outputs of ...
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1 vote
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### How MAC (Mandatory Access Control) model prevents trojan horse attacks?

I've heard that the MAC Model prevents Trojans to charm files on the system. How is it possible? Can somebody show any example that MAC model protects us against it?
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### What is the use or how can we implement zero-knowledge proof system in Elections?

I recently heard about the concept of zero-knowledge proof. However, I still do not get how it is possible to make it a solution to some real-world problems. One thing I heard is that zero-knowledge ...
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### Why is M^e mod N the ciphertext and not just M^e

I watched a video on why the RSA algorithm works and it said that $(M^e \bmod N)^d \mod N = M^{ed} \bmod N$ which makes sense if $M^e$ is smaller than $N$. Would $M^e$ not be smaller than $N$, the ...
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### If someone has an encrypted message and it's original plaintext, could he guess the private key if it's the one used to encrypt the message?

In digital signatures, the private key is used to encrypt a (hashed) message and the public key is used to decrypt it. This made me wonder since the receiver has the cipher text (digital signature) ...
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### Cryptosystems whose hardness depends on solving the halting problem?

There has been a lot of work on building cryptosystems whose general security guarantees are attached to famous complexity classes. This post Gives a list of some famous cryptosystems whose underlying ...
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### Permutation with stable partitions

I am searching a fast pseudo-random permutation function with the following requirements. Given a predefined set of values $V$ and an integer $k$. Split $V$ to $k$ subset, and iterate over any subset ...
1 vote
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### Non-Interactive Zero Knowledge Proofs: zk-snarks and zk-stark

I read up on an abstract example of ZKPs (the cave and the door), but I'm trying to understand NIZKs (specifically zk-snarks and zk-stark). All the examples I can find online seem to have some ...
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### Is there any neutral element for the cryptographic hash function SHA256? (or its variants)

My question is the following: Is it possible to compute a string given that after applying a SHA256 function the result is the same string? Edit for clarification: If my string A is a neutral element ...
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### Books for learning Cryptocurrency

Please suggest a good for mathematical section of studying cryptocurrency.
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### Manually Performing ECB & CBC

I am learning about block ciphers and while I understand the concept of Electronic Codeblock mode and cipher block chaining, I could not find any relevant practical examples online. Can someone ...
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### Undetectable error correcting codes

I have a 256 bit string (indistinguishable from random) which I wish to encode into a greater length string using an error correction code. The result must also be indistinguishable from random. It ...
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I am a software developer new to the site. I am currently learning about LFSR (linear feedback shift register). Every day I solve a question which is given to me, but today I am lost. I can not solve ...
1 vote
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### One-way function is not injective when it is in NP

Let us $\Sigma = \{0,1\}$ and $f: \Sigma^* \rightarrow \Sigma^* \in FP$ for which is valid that \$\exists k: \forall x \in \Sigma^* : \lvert x \rvert ^ {1/k} \leq \lvert f(x) \rvert \leq \lvert x \...
1 vote
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### Accessible CS Math Job [closed]

I am a CS undergrad and a huge enthusiast of pure math. I have been doing competitive programming and proofs for a while. My ambition is to become an academic in theoretical computer science. The ...
1 vote
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### Decryption of RSA

How can we decrypt an RSA message if we only have the public key? For example, Message: 21556870,12228498 Public Key: ...
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### How to perform matrix multiplication in Mixing Columns step of AES?

I am studying AES and trying to implement it. But I am having difficulty understanding the Mixing Column step. In that step we have to perform matrix multiplication between the state matrix and ...
1 vote
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### Converting Smart Contracts into Arithmetic Circuits [closed]

Are there any existing programs available to convert smart contracts into Arithmetic Circuits with which I can implement and experiment with Secure Multiparty Computation (MPC) protocols?
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### Absolute limit in Huffman encoding

I have computed the average code length using the Huffman encoding. Now, I am asked to compare the average code length with Absolute limit but I ain't sure about the absolute limit here is :( Could ...
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### Extracting text from a hidden image

Say i have cropped an image and have hidden some part of it, like shown below Is it possible for anyone to download this image and able to decipher what the hidden text is?
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