# Questions tagged [substitution-cipher]

A substitution cipher is an encryption algorithm which works by replacing plaintext units with corresponding ciphertext units, following some rule depending on the key.

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### Can Index of Coincidence be used for ciphertext containing letters, numbers, and symbols? (All characters in cipher are from ASCII table)

I have been trying to figure out how to approach performing cryptanalysis on the following ciphertext, but am stumped on whether I can use classical techniques such as IoC to derive useful information ...
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### Can a Substitution Cipher achieve Confusion and Diffusion

Can a substitution cipher achieve confusion and diffusion? By a substitution cipher I mean one where each character is replaced by another. By confusion my definition is that to solve the question, ...
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### Is a Shift Cipher with Random Insertions Unbreakable?

Imagine an Encryption Algorithm which applies a classic Shift Cipher (also called Caesar or ROT-X) to a text (with only lowercase [a-z] and the space ...
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### How to break Random Subsitution Cipher that changes key every 16 characters?

Monoalphabhatic Random Subsitution Cipher is pretty hard to crack compared to Ceasar Cipher especially through brute force but using frequency analysis, provided enough cipher text is easy. But what ...
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### efficient way to break substitution cipher based on frequency attack

I wrote an attack based on frequency analysis to break the substitution cipher. The code is below by Python. ... ...
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### Substitution Cipher

For the Substitution Cipher, for functions such as $$f(x) = x^k \pmod{26}$$ or $$f(x) = x^k + k \pmod{26}$$ (functions that consist of x^k), why do the values of k=5 or k=7 or k > 10 have one-to-...
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### How do AES Substitution box's offer any additional security since it's 1 to 1?

If the Substitution box is 1 to 1 (a specific value can only ever be a specific box value), and the contents of Rijndael S-box is public, how does this offer any additional security? With AES the ...
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### All combinations to a substitution cipher [closed]

Is there any software that can output all possible solutions to a substitution cipher? I have a 34 character substitution cipher as follows: ABHIJCKDELMFNOEPQ RDSTUVWGFADBXCYGZ 15 of the characters in ...
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### AES with a different implementation of byte substitution step

I have tried to answer this question for quite some time now. But a complete intuitive understanding still eludes me: suggested a new implementation for AES: The byte substitution step will be ...
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### What is the difference between a substitution cipher and an oracle?

I was looking into the opaque authentication protocol and they discuss an oracle, which, if I understand it correctly is a projection $Z$ from $f$ to $g$ ($g$ at least the size of $f$), which maps ...
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### Finding a specific word in a substitution cipher

Rand48 is a pseudo-random generator which produces a sequence of any given integer using the following rule: $a_n=(25214903917 \cdot a_{n-1})\bmod 2^{48}$. If $b_n=\lfloor a_n/2^{16} \rfloor \bmod 52$,...
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### Decrypting Mono-Alphabetic Substitution Ciphertext

I am reading Introduction to Modern Cryptography 3rd Edition (Google Books Preview of Relevant section, pages 10-11) and am struggling to understand the description of an attack method on a ...
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### Efficient Obfuscation or Encryption method with low memory usage

We are manufacturing a sensor which transmits in 8 byte packets. This sensor will be used by several different receivers, some of which have very little spare RAM available (< 3 kb). On some of the ...
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### Connecting, joining or merging Substitution Permutation layer

I am trying to identify how the SP Network is constructed. I am looking for plausible solutions that help to connect these layers together and what are the ways that exist in literature other than Kam ...
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### Enigma machine rotor internal wiring question

I have a question regarding the internal wiring of the rotors of the Enigma machine. I'm trying to understand some details about the original Enigma machine. To the best of my understanding, each ...
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### How do I progress with cracking this monoalphabetic substitution cipher that ignores natural word divisions?

Having some trouble cracking this cipher (this is part of a homework assignment for a cryptology class) I've looked at letter frequencies but I'm not sure what else there is to help me. Given the ...
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### Key space of a substitution cipher

I was going through a cryptography course, and I found a question there that: What is the size of the key space of the substitution cipher with 26 letters? Its answer was 26! I am not sure what this ...
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### Need some help with decryption code for monoalphabetic substitution

I am working on decrypting ciphertext in monoalphabetic substitution algorithm. I tried to decrypt using frequency histogram of English alphabets individually. The percentage of these frequencies can ...
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### How to verify most appropriate cleartext?

So basically I was implementing a decryption tool (just for fun) and the first encryption logic I decided to implement was Caesar Cipher. So if I have the input as ...
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### symbol representation based cipher? [closed]

so i had an idea recently for a cipher. the idea is as follows: for every ascii character in the input, replace it with a corresponding sequence of 25 binary digits that, when arranged into a 5x5 grid,...
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### Enigma Machine rotors math

I have been doing a study about the enigma machine for the past weeks. I managed to get ahold of the formulae used in "Cryptography, Information theory and error-correction" book for the ...
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### How many different ciphertexts in repeated substitution cipher?

Consider an alphabet with 26 letters. Then a substitution cipher has $26!$ possible ciphertexts (with every letter substituted). What about repetive substitutions on a 5 letter word for example? How ...
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### Substitution ciphers amended with cipher block chaining: susceptible to frequency analysis?

I have been studying ways to amend a simple substitution cipher, and one of the toy suggestions was to use CBC in the following way: identify each letter with a number from $0\ldots 25$ start with a ...
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### Can anyone explain to me the difference between the OTP (one-time pad) and Vernam Cipher?

I heard they are very similar, although there are subtle differences between the two.
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### Are basic replacement ciphers always bad for structured data encryption?

I have read that basic replacement ciphers, such as replacing one byte with another specific byte at each location, are far less effective with non-randomized data. My question is, can this problem be ...
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### Which sub operation is more expensive in the AES encryption process?

In the AES encryption process, there are various sub-operations, like SubByte, MixColumns, ARK etc. My question is which of these operations is more expensive? In a video lecture by Dan Boneh, it is ...
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### Enigma ring settings - is the relative location of the turnover all that matters?

I understand that the ring setting of an Enigma rotor changes the alignment between the internal wiring and the letters on the ring. For example, in the diagram below, rotor I has ring setting 2 (B), ...
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### Hill cipher concepts

I have some questions about the Hill cipher. There is a rule for key K: Determinant of matrix and number of characters of the alphabet must be coprime. What does ...
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### Rotor that divides binary number by mod 3

Let's say we have transformer(?) A = $\{0;1 \}$, B = $\{0;1\}$, $Q = \{q_0,q_1,q_2\}$, where A - plaintext alphabet, B - encryption alphabet, Q - the set of states. The functions of the rotor are ...
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### Identifying correct cipher

I am trying to decrypt a text(~900 characters) and I started with the assumption that its a Vigenère cipher as the one of the identifier tool identified it as Vigenère cipher and also the Index of ...
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### Deciphering a substitution cipher if frequency analysis doesn't work (hypothetically)

If a text ciphered by substitution is in a artificial language with equal frequency distribution of characters, and perhaps 2 or 3-grams too, what would be the next, easy to understand, ways to ...
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### Personal ledgible quick cipher

The problem: When I'm writing or reading information (be it on a screen or a physical medium) the information is vulnerable. So long as I'm not alone, anyone can simply glance at my screen or journal ...
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### How does pairing letters increase the security of a substitution cipher?

Hello can someone help me to understand this : One way to reduce this problem is to increase the size of the cipher alphabet. Rather than considering our cipher alphabet to be just the 26 letters, ...
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### How were codes in WW1 reciphered (to enhance security levels) without them turning meaningless?

In WW1, the Germans made their communications secret by encoding their messages. This meant that the message's sender would have a codebook with all possible words and phrases he might use listed in ...
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### Cracking a Shift Cipher that uses an Unknown Deterministic Scheduling Algorithm

Consider a shift cipher that has the following encryption scheme: The plaintext contains lowercase characters and spaces, is composed of English text, and is length 500. Thus, the message (and ...
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### Simple Cipher Cryptography on Hex File [closed]

I have been assigned this hex file : https://drive.google.com/file/d/1EeidY67VuIddIC-e-xiiKhth1ucMhM_r/view?usp=sharing The goal is to decrypt it to something meaningful. The only hint given is that ...
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### How do I calculate the conditional probability of a Caesar cipher?

I have a frequency distribution of letters for the plaintext and the ciphertext. I'm trying to determine the conditional probabilities to identify the plaintext/ciphertext pairings. If I encrypt ...
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### Why is the Keyspace of a Substitution Cipher not 2^26 but 2^88

It is known that a cipher has a keyspace of cryptographic algorithm whose key length is $n$ is given by $2^n$, but the keyspace of the substitution cipher is $2^{88}$ which is an approximation of $26!$...
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### How to decrypt a combination of transposition and substitution cipher text

I'm having problems decrypting a cipher text that has an transposition cipher applied to it but also a substitution cipher. I don't know in which order they were applied. Does anyone know what steps I ...
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### Decrypting a substitution cipher, but with symbols instead of letters

I'm trying to decipher a message encrypted by a substitution cipher (probably a monosubstitution). But the problem is, that we have symbols instead of letters (letters were substituted for random ...
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### How to distinguish a transposition cipher from a simple substitution cipher only given a ciphertext?

I am working on one interesting question. There is a ciphertext that has 10,000 letters. We need to distingish whether this ciphertext was encrypted by a transposition cipher or a simple subsitution ...
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### Most efficient way to crack a monoalphabetic substitution cipher with spacing intact

I've got a cipher I've been challenged to crack by hand. It's a monoalphabetic substitution cipher, and the English spacing is intact, so all of the words are the right size. Is there a more ...
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### What kind of decryption is used in this example? [closed]

I stumbled upon an encrypted text on a website, to which Google had brought me, showing me the plain text also. So does anyone know what kind of encryption was used here and how to decrypt it, so I ...
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### Was the Enigma's double stepping mechanism intentional?

It's sometimes refered to as the double stepping anomaly, so was it just a design flaw or was it put in place deliberately?
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### Enigma rotation example

According to wikipedia: BDZGO is the expected outcome when doing the enigma chipher on the letters AAAAA with rotors I,II,III and reflector B. ...
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### modified substitution permutation networks

I have a model of substitution permutation networks, modified as follows: instead of iterating $n$ times a round(each of which is composed of the key mixing phase, substitution S-BOX) and ...
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### Crack a polyalphabetic cipher given a pair of (plaintext, ciphertext) encrypted by it

The original question only states that a classical cipher is used, and I am going to articulate 1) why I think a polyalphabetic substitution cipher is used AND 2) my attempts so far. The Question <...
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### Proving at most one affine permutation mapping $x$ to $u$ and $y$ to $v$ with $x,y \in \mathbb{Z}_n$ and $\gcd(x−y,n) = 1$

Suppose that $x,y \in \mathbb{Z}_n$ with $\gcd(x−y,n) = 1$. Prove that for any $u,v \in \mathbb{Z}_n$ there is at most one affine permutation mapping $x$ to $u$ and $y$ to $v$.
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