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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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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Can an Enigma-style cipher of sufficient complexity be considered secure today?

Regarding the German Enigma machines, if I recall correctly, the reason they were defeated was because the Allies were able to generate a massive database of possible rotor settings, and because the ...
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About Cryptography in a Character Language

Suppose I had a message in Chinese (or another non-phonetic language) and I wanted to encipher it. Some of the simplest encryptions in English are substitution ciphers, but such ciphers don't seem ...
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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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Possible ways to crack simple hand 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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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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Toy cipher — does it have a name?

When I was perhaps nine years, I borrowed a book from the library on various maths and CS topics. It outlined various simple ciphers, including one that I used a lot, just for fun. I can't remember ...
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Encryption/ciphers/codes in Chinese

I am quite curious as to how you can perform simple encryption for the Chinese language. Saw a similar question related to encryption/Chinese here: About cryptography in a character language, ...
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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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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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687 views

Using a mono-alphabetic substitution cipher with a different language per word

How much harder is it to determine the secret key for a mono-alphabetic substitution cipher, if each word is translated into a different language before the cipher is applied? If somehow computers ...
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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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140 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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622 views

Can you break a multi language code using Frequency analysis?

Let say that I wrote a 26 letter alphabet, each letter of my alphabet represent a letter from the latin alphabet. I'm writing in 3 languages, only I know which languages. Grammar is the one from my ...
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1answer
734 views

What is the best method to determine the language used in a monoalphabetic substitution cipher?

Working on a cipher (which I assume to be a mono-alphabetic substitution cipher due to the letter frequency) I struggle with the fact that I don't know which language the plain text is written in. ...
5
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1answer
102 views

Does adding more characters to the Enigma rotors improve crypto strength?

This seems like an obvious question but I haven't been able to find it, so here goes: Enigma is based on an alphabet of A-Z (26 characters); obviously this directly affects message content (e.g. ...
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113 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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868 views

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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Alphabetic Substitution with Symbols

I was reading on a site about the Zodiac Killer and how he used a basic substitution cipher, but instead of substituting english letters and characters he substituted symbols. I was wondering, if you ...
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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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Is this hand cipher any more secure than the Vigenère cipher?

I know that inventing one's one crypto always sucks, but the problem is that hand ciphers are usually very insecure very slow. This is an attempt to make a relatively secure, keyable, and ...
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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 can one break a monoalphbetic substitution chipher at pseudorandom text?

Does anybody know how to break monoalphbetic substitution cipher, if it is applied to some pseudorandom text (for example to some surrogate key filed in a database)? Let us assume that we have only ...
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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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Not-So-Simple Substitution Cipher?

The first go-to weakness when talking about substitution ciphers is frequency analysis. It assumes that there's a simple 1 to 1 character mapping between the plain text and the cipher text. Could a ...
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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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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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1answer
350 views

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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356 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 encryption/...
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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
161 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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1answer
69 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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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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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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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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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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How to get the keyword from a keyword cipher?

I was given a ciphertext and now I am trying to break it via looking for the keyword. This is a keyword cipher. So: PlainEnglish: ABCDEFGHIJKLMNOPQRSTUVWXYZ If ...
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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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Can I make a cipher (ex: Vigenère) harder to break?

The Vigenère cipher can relatively easy be broken when the key size is small compared to the size of the message. One first finds the length of the key, and then uses frequency analysis to actually ...
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1answer
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What is the diffrence between Feistel networks and SPN?

I recently read about the concept of Feistel Networks and Substitution Permutation Networks but what is exactly the difference between the two ?
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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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plaintext and its encrypted version known [duplicate]

I have a (long) text in two versions, encrypted and plaintext. I think it was encrypted using a substitution cipher method (I'm pretty sure, indeed). I'm not good in this matter, I know little about ...
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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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Chi-Squared Step of Vigenere Cipher Decryption [duplicate]

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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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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1answer
60 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 ...
1
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1answer
278 views

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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601 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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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 alphabets ...
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Existing dictionaries of popular words to help solve a random substitution cipher?

I'm trying to find faster ways to solve this: http://cryptogram.org/solve_cipher.html Actually lists of common words are good, but they are often limited to 1000 words. I found this, but I'm not ...