# Tagged Questions

Coding theory studies the properties of codes and their fitness for specific applications, and typically involves the removal of redundancy and the detection and/or correction of errors in transmitted data.

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### How do Raptor (Fountain codes) encoding and decoding work? [on hold]

As described in this article, a Raptor code is a fountain code that encodes a message of $k$ symbols into a limitless sequence of encoding symbols, such that knowledge of any $k$ or more encoding ...
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### What does this notation stand for when describing a code?

This code has appeared in some online course material. I understand the $(5, 4, 3)$ refers to (length, num codewords, distance) but no explanation of the $Z_2^5$ notation is given: One $(5,4,3)$ ...
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### Filling in MD5 input variables

I have a majority of an input string(as well as the total length) and the output for an MD5 hash. Is there a way to calculate the remaining input bytes that I am missing?
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### How to hash similar strings to the same hash value?

Suppose that $s_1$ and $s_2$ are two stings that have a small hamming distance. Is there a preimage resistant "hash" function ($H$) that can map them to the same value i.e., $H(s_1) = H(s_2)$?
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### Words having weight near to minimum distance

I am studying the NP-Problem of the codes Syndrome Decoding. The formulation is show below. Input: a binary matrix $H$ of dimension $r \times n$ and a bit string $S$ of length $r$. Property: there ...
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### Convolution and catastrophic codes

i'm reading the article of Massey and Sain (here) and i cannot unserstand - what is "foreforward inversion"? I mean There is a description of circles in convolutional codes and a little bit ...
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### Implementing the Mceliece Encryption - making the Generator Matrix

I am working on an implementation of the Mceliece Encryption system (MCE) and the Niederreiter encryption system. I have been through the basics of finite fields, polynomial arithmetic and some coding ...
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### RS Erasure Coding and Shamir's Secret Sharing

So I was trying to understand the basic difference between erasure coding and secret sharing, and I found this paper (that you can find here or here). For what I understand, it states that Shamir's ...