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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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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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2 answers
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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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2 answers
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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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3 answers
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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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2 votes
2 answers
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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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1 vote
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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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4 answers
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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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Is there a way to make a non-specific algorithm to decypher substitutions with "anti-frequency analysis" measures?

There's a code I'm trying to decipher. What I know is that it's a simple substitution, with just a few added rules intended to make frequency analysis and other very common methods a little less ...
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1 vote
1 answer
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Cryptoanalysis using Frequency Analysis

I have read some documents to decrypt ciphertext without a key using Frequency analysis. here are my questions: If the most occurring Char is not 'E' then how do we start? Let's say I have this ...
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4 votes
2 answers
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How does an S-box introduce confusion

I'm trying to find the logic for introducing the S-box, but having trouble understanding why. In a simple cipher, e.g. c = pt xor key I understand that I can ...
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2 votes
1 answer
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Repeated Vigenère Cipher

I was looking into the Vigenère cipher when I thought of something. Would you improve the security of the cipher if you shifted each letter (from the text you want to encrypt) with each letter of the ...
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7 votes
1 answer
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Does Format Preserving Encryption have significant advantages over a randomly generated lookup table?

I have a need to anonymise phone numbers so that I can carry out testing and analysis work on telecoms data sets and comply with GDPR. I typically receive a batch of a few hundred thousand events ...
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How to decrypt a simple substitution cipher where space is also encrypted by a character

I am trying to decrypt a text data encrypted with a simple substitution method with 2 steps. First, shift the alphabet of the source text by a few characters. For example, if we shift by 2 characters,...
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6 votes
1 answer
1k views

What is an accurate definition for a 'Monoalphabetic substitution cipher' and why does it provide a poor level of security

From my research online, I am confused about the difference between a 'monoalphabetic cipher' and 'monoalphabetic substitution cipher'. However, I have got my answer from the websites Kifanga and ...
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2 votes
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Non-exact substitution cyphers

Picture a simple substitution cypher of text with length $N$(spaces optional): Plain : ATTACK AT DAWN Encrypted: ELLETI EL HEPG Another way to represent the encrypted text is with an $N \times N$ ...
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What's the difference between confusion/diffusion and mode of operation?

I understand the concepts of confusion (substitution) and diffusion (permutation). My understanding of what a mode is that it's an algorithm that lets us encrypt arbitrary message size. i.e. AES is ...
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Can a message be encrypted with BOTH mono-alpha and poly-alpha ciphers?

For my class assignment, I was given this text; Qpuvu vo vv stazpuykzh Hhycmlmv asb. Ad dhyaqva wh uyo uzb jpwww Avlw. Tkpjllfdmbp zoatz vzjavfvna ZLHqh. Amva luy yyvlz yu bhk zua zlhvvalaz yow ...
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Common cyphers where the plaintext is the same length as the cyphertext

What are the common cyphers where the cyphertext is always the same length as the plaintext? I can think of XOR cyphers, and letter-substitution cyphers, what others are there?
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5 votes
1 answer
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Cryptanalysis in the middle ages -- publications

Are there any publications, articles or literature discussing cryptanalysis and crypt breaking techniques in the middle-ages? I have seen various manuals from the middle ages describing various types ...
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2 answers
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Decrypt Base64 Encoded Monoalphabetic Cipher

I'm attempting to decrypt a body of ciphertext which has been encrypted using a monoalphabetic cipher. The trouble I'm having is that the plaintext was base64 encoded before being encrypted. In this ...
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