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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How to attack polyalphabetic affine cipher with only ciphertext?

How to attack polyalphabetic affine cipher with only the ciphertext? A polyalphabetic affine cipher can be seen as the composition of an affine cipher ($p \mapsto c \equiv a \times p + b \pmod{26})$ ...
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Deriving Minimum Description Length of Substitution Key

Given a plaintext: Now is the time for all good men to come to the aid of their country because the quick brown fox jumped over the lazy dog. and a substitution ciphertext: Mpe od yjr yo,r ...
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Does composing multiple substitution ciphers improve security?

Will using two substitution ciphers one after the another be more secure than using single substitution cipher?
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How would multiple uses of a vigenère cipher be decrypted on paper (classic)?

As far as I can tell (from reading the Wikipedia article about it) decrypting a message encrypted with the vigenère cipher is possible on paper. But what would happen if the message is encrypted ...
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Breaking Homophonic Cipher [project]

This is basically my project. I would be much appreciated if anyone could help me figure out how to do this in an efficient way. This cryptanalysis project consists of a software implementation of ...
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39 views

Perfect secrecy of affine cipher

Given any probability distribution P r on the set $\{k ∈ \mathbb{Z}_{26} : \gcd(k, 26) = 1\}$. Show that the Affine Cipher achieves perfect secrecy if the key (k, a) is used with probability $Pr(k) ...
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What is the difference between substitution cipher and block cipher?

I'm studying(and clearing my head) about block cipher. I started from Caesar Cipher which can be considered as a kind of substitution cipher (if my understanding is right). And an ideal substitution ...
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2answers
163 views

How to decode a (Vigenère?) substitution cipher? [closed]

I am trying to decode a message that I suspect has been encrypted with a Vigenère cipher: Utl zluuocp zsc rvzu hbcp ztvibfz vrabzz utl ilry. Utlal flal cb fbaiz, qszu zbsciz. Utvu cllihl vhzb dvil ...
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Research for video game: Novice cryptography concepts [closed]

I'm making a video game which has some basic cryptography as a main base for puzzle design. I'm hoping players will get great puzzle challenge and learn a few cryptography concepts through playing the ...
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55 views

How do substution-permutation networks work? [duplicate]

I understand what is going on in higher level. But I don't understand what's really going on in page 3 and 4 of this slide. Specifically, How $S_0$ and $S_1$ is used? What goes in what goes out? ...
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Determining Involutary Keys in Substitution Ciphers

How would I be able to show that a key $K=(a,b)$ is involutary for an Affine Cipher over the integers modulo n? Similarly, is there a way to generalize the conditions for a key to be involutary for a ...
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1answer
145 views

Can a book cipher be cracked without key?

Book cipher works this way : Choose a reference book. For each word find its position in the book. replace each word by its coordinates (ie: 2,3,4 = page 2, 3rd line, 4th word). How would ...
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33 views

Creating a custom 2 way encryption class [closed]

I am trying to make a simple 2 way encryption function that currently uses a substitute cipher for the encryption and an inverse substitution for the decryption. I want to move away from this ...
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85 views

Comparison Vigènere vs. Monoalphabetic cipher

I have a question for a class of secure communication, but I have no idea about how to proceed in order to answer it. I'll be very grateful to whom replies to me. Assuming that brute force attack ...
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1answer
64 views

What is the difference between LCG and Affine cipher?

What is the difference between LCG and Affine cipher? More specific: What are they used for, and what are the structural differences between them?
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1answer
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Is frequency analysis a viable attack on non-text data encoded by substitution?

Is frequency analysis a viable attack on non-text data encoded by substitution (eg image and audio formats encoded with a substitution cipher)?
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72 views

How to overcome issues with big ciphers? E.g. with small vs. big Vigenére Ciphers

I understand that bigger ciphers show more recurring patterns and therefore should be easier (or at least faster) to decrypt as you'll have a better statistical analysis, being However if we use a ...
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107 views

Solving Vigenére with unknown alphabet

I'm trying to decrypt a cipher that I suppose has been encrypted with Vigenére. However I came about the following thought: The cipher consists of characters from ...
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1answer
324 views

Deciphering “easy” ciphers without hints

I've been keen on IT Security for a long time now and I've learned a lot about networking & security. However trying a "decryption challenge" I'm lacking what I think is basic ...
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1answer
50 views

How exactly is an enigma simulation software supposed to encrypt alphabets?

EDIT: The model I'm trying to make is "Enigma 1". I learned initially about it from a book called "Code Book" and then looked at it in detail from its wikipedia page. The rotor wiring and other ...
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1answer
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How does the ring settings of enigma change wiring tables?

EDIT: The model I'm trying to make is "Enigma 1". I learned initially about it from a book called "Code Book" and then looked at it in detail from its wikipedia page. The site wont allow me too add ...
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2answers
65 views

One time pad- XORing or substitution

I have come across 2 versions of otp while reading it and want to confirm it. they have taken a plain text consisting of alphabets where they are shifted and replaced by alphabets itself. XORing of ...
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4answers
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Are specially designed fonts sometimes used in cryptography?

As a font designer, I was thinking that it would be very easy to design a special font that could either jumble characters of a language (or of a code) or simply (with the features offered by the OTF ...
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1answer
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Compacting a substitution cipher key

In a substitution cipher, I recieve 3 bits and than I return another 3 bits. The key of this cipher could be a matrix represented as: ...
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1answer
300 views

Vigenère, auto-correlation vs Kasiski examination

What are the differences between 'Kasiski examination' and 'auto-correlation' ? In Cryptool site, they state that autocorrelation analysis is more efficient and clearer than the Friedman or Kasiski ...
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1answer
124 views

Why is a Feistel network not a type of substitution-permutation network?

I understand what substitution-permutation networks look like. I understand what Feistel networks and Feistel-like networks look like. A Feistel network or a Feistel-like network features substitution ...
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common ways / methods to try to break a SP network

I have a very little cryptography background (but a relatively solid maths background) so my below question is very general. Basically I have been given a SP network with an output to reverse. I ...
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1answer
85 views

One-one correspondance complete function

I am reading the paper by John B. Kam and Georges I. Davida (1979) titled Structured Design of Substitution-Permutation Encryption Networks. On page 749 it reads ...
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Affine transformation in finite field SubBytes

Can anyone please explain how this computation was done? I picked it up from How are the AES S-Boxes calculated? The affine transformation is as follows. The input bits are multiplied against the ...
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164 views

Deriving a decryption equation

Consider a very simple symmetric block encryption algorithm, in which 32-bits blocks of plaintext are encrypted using a 64-bit key. Encryption is defined as C = (P⊕KL)⊗KR where C = ciphertext; K = ...
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202 views

Base64 with shuffled alphabet

I have a base64 'cipher' text, I know that in clear text is a hidden xml document (I do not know nothing about its structure), but the base64 aplhabet was somehow shuffled. Is there any smart way, how ...
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How to perform frequency analysis of a substitution cipher using a Base64 alphabet

Let's imagine a cipher that works like the following: Plaintext is encoded to Base64. The characters in the encoded plaintext are substituted with a randomly shuffled character set(A-z, 0-9, -, _, ...
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1answer
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Available programs that can verify the working of a simple substitution cipher

Is there any tool available that can test whether a simple substitution cipher is working. I will put my scenario in detail. Lets say I built a simple substitution cipher that maps 8 bit data to 16 ...
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405 views

What is meaning of “Decipher the rest of the message by deducing additional words”?

I have an assignment in cryptography. I am not asking here answer, but meaning of question. This is a question : 2.4 The following ciphertext was generated using a simple substitution algorithm. ...
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546 views

What benefits do substitution boxes and permutation boxes offer in DES?

I understand that with more encryption rounds the more complex the ciphertext becomes due to multiple substitutions and permutations. What I don't understand is the purpose of these features. I am ...
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125 views

Known-plaintext attack on two-dimensional affine cipher

Problem: We have a two-dimensional affine cipher with $n = 2,\,\,\,\mathcal{P} = \mathcal{C} = {\mathbb{F}_{16}^2}$, where $\mathcal{K} = \{ A,\,\,b\} $ and $b = (0,0)$. The encryption and decryption ...
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Strategy to crack a presumed substitution cipher

The ciphertext given is: ejitp spawa qleji taiul rtwll rflrl laoat wsqqj atgac kthls iraoa twlpl qjatw jufrh lhuts qataq itats aittk stqfj cae I've done ...
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Chi-Squared Step of Vigenere Cipher Decryption

So, I have been assigned an assignment where I had to solve a Vigenere cipher. Following along with this webpage I managed to get all the way to the chi-squared step. But, that is the problem. Upon ...
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493 views

Vigenère cipher: Security when key length and plaintext length are the same

I have read the Vigenère cipher is secure as long as the key length is the same as the length of the data to be ciphered. Is this true in cases where the same key is used multiple times. In that case ...
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Number of different substitution alphabet ciphers possible with given conditions?

If you consider a 26 letter alphabet, and a cipher where 24 of the letters are sent to themselves, and only 2 letters switch, how many different substitution alphabet ciphers are there, and what ...
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How to solve cipher encrypted with Vigenère + Columnar Transposition?

Vigenère's weakness is Kasiski's test and index of coincidence. However, if you put columnar transposition on top of Vigenère, that weakness is gone. The text is now shuffled and you can't search for ...
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How to retrieve the plaintext of a substitution ciphertext?

So the other day, I was piqued by a ciphertext that was trivially encoded through substitution. Solvable only because we can use our eyes to determine word boundary word detection, etc. Trawling the ...
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1answer
169 views

Encryption of numeric value using playfair

I am studying in CSE and in my recent exam paper, A question was asked as: Construct a playfair cipher for Plaintext: semester5 and key:technology. Generally as we are taught yet, there is no ...
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592 views

Can a monoalphabetic substitution cipher attain perfect secrecy?

Can a monoalphabetic substitution cipher attain perfect secrecy? Definition of perfect secrecy: $${\rm Pr}[\,{\rm Enc}_k(m_1) = c\,] = {\rm Pr}[\,{\rm Enc}_k(m_2) = c\,]$$
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Can anyone tell me the name of this cipher please?

Can anyone tell me the name of this cipher please? I know it's a simple substitution cipher, I just don't know the name of it. Cipher Key: help Cipher alphabet: ...
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2answers
379 views

Regex searchable word list for space-less monoalphabetic substitution [closed]

I am working on teaching myself basic cryptography, in the process I created a simple substitution cipher based on a single alphabet, and a statically defined offset (no key for now). Now that ...
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How do I test my encryption? (absolute amateur)

I am a hobby programmer with a background in biology and have developed an encryption program based on DNA. I tried to make it hard to crack, but it's essentially a substitution cipher and uses the ...
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Why was the winner of the AES competition not a Feistel cipher?

The winner of the AES competition has a structure that does not qualify as a Feistel cipher, as explained in answers to this recent question. However, most many of the AES candidates, and all 3 out ...
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How would I make a secret notation alphabet more secure?

Disclaimer: I was looking for a place to ask this question on SE and this site seems to be the most fitting. If this question doesn't belong here, feel free to redirect me. Just out of boredom and ...
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Question on monoalphabetic substitution

Question: A stream of cipher operates on a data stream of 6-bit characters using a simple mono-alphabetic substitution technique. Estimate and explain the number of different substitution ...