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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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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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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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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Is a book cipher provably secure?

I've seen ciphers (usually in spy drama shows) that involve taking a book and writing down an index to individual characters. Essentially it's a keyed substitution cipher, where the key is the name ...
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1answer
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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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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
161 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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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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1answer
104 views

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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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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2answers
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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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What are the main weaknesses of a Playfair cipher, if any?

What are the main weaknesses of a Playfair cipher, if any? I know that they depend on none of the letters missing, but that is an easy fix if a letter gets dropped. Besides that, are there any other ...
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1answer
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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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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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4answers
548 views

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
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
63 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
322 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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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
47 views

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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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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Possible ways to crack simple substitution ciphers

We had a quiz in class today where we had to break the ciphertext with the key given, but not the algorithm. Suffice to say that I wasn't able to decrypt it within the allotted time of 12 mins and ...
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1answer
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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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Relative security of a Vigenère cipher

Within a closed computer network, I am ciphering some plaintext data as an added security measure. This is below several other layers of protection. For various technical reasons, I am restricted to ...
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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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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
298 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
123 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
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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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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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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1answer
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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1answer
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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544 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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1answer
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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335 views

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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1answer
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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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1answer
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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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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Cracking the Beaufort cipher

Is there any easy way to crack a Beaufort cipher? We have a Vigenère table, and are trying to guess the keyword. Any easier way?
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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 ...