Questions tagged [classical-cipher]

Ciphers invented before the era of computers and modern cryptographic theory. Classical ciphers typically operate on letters instead of bits and are usually designed to be implemented by hand or using simple mechanical devices.

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Does the transposition cipher have a network application?

So I'm reading a chapter in my networking book, and it talks about substitution and transposition ciphers. I know that most network security uses public key or symmetric encryption, but I wonder ...
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Classic cipher method [closed]

I am struggling with these two cipher texts, I cannot identify which king of cipher was used. First: otnpeetrnneepeufofutisrtrllohcdmetoeheeatyngonrmrm And second: ...
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How can frequency analysis be applied to modern ciphers?

I am building a computer program that deciphers Caesar, Vigenere and monoalphabetic substitution ciphers. All of those are susceptible to frequency analysis. However, it does not seem to be real-world ...
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Is it possible to crack the trifid cipher without the keyword?

I was learning about the classical ciphers and was looking up the methods to break them without the keywords and when I searched up "cryptanalysis of the trifid cipher" I couldn't find anything. I ...
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Running Key Gibbs Sampling

I am trying to implement the algorithm described in this paper. It uses blocked Gibbs sampling to perform a ciphertext-only attack on text encrypted with a running key cipher. However, I am confused ...
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Using a classical method, is it possible to create a key that is indistinguishable from one made in a truly random manner?

Is there a classical method that will allow us to create a key that cannot be distinguished from one that was generated in a truly random manner? For example, let's say we use three "words" to create ...
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Applications of machine learning in classical ciphers?

Machine learning is definitely applicable in analyzing simple shift ciphers like Caesar and affine ciphers, as well as substitution ciphers like Vigenère, but is it possible for machine learning to ...
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What is the strength of this machine? [closed]

This machine has the stator, with one half of the alphabet, and three rotors with replications of the other half in different order and repeated twice. There can have two rotors in use or the full ...
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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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Strong and Practical Hand Ciphers [duplicate]

I know monoalphabetic ciphers are weak, but my message recipient doesn't like taking the time for the decryption process. I've tried Vigenere, Gronsfeld, Beaufort and Digraphic Ciphers, but he doesn't ...
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How to “score” partially decoded ciphertext?

I am attempting to write a basic codebreaking program to break simple ciphers (think caesar cipher & railfence) such as these here https://en.wikipedia.org/wiki/Classical_cipher. The program ...
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Pen and Paper Authentication

What is the best way to prove that you wrote the encrypted message on a piece of paper? As most of us know, many conspirators have died because of false message implants, Mary Queen of Scots, for ...
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Is there a way to easily encode a message without a computer on either end?

I enjoy making notes and passing them to my friends, and I also like making them encrypted for no reason. My friends enjoy it too, but it's a bit annoying to use the Caesar cipher for everything ...
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In cryptography, what is “fractionation”?

I understand how fractionation is used in the straddling keyboard, which is an important feature of the VIC Cipher, and in the Polybius Square of the ADFGVX cipher, but I am not sure how to describe ...
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How to attack a general polyalphabetic cipher?

I am able to decrypt Vigenere ciphertext using the index of coincidence and chi-squared test. However, out of interest, how do you go about attacking ciphertext that was encrypted using a mixed ...
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Vigenere Cipher Methods

Is there already a cipher which uses a method like vigenere yet the shifted encrypting alphabets are mixed? i.e. ASDFGHJKLZXCVBNMQWERTYUIOP BNMQWERTYUIOPASDFGHJKLZXCV CVBNMQWERTYUIOPASDFGHJKLZX etc....
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About LFSR based M209 Cipher Machine

Can some one please express M209 Cipher Machine in terms of LFSR with Diagram or any simple method?
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Can frequency attack be successful on Vigenère cipher?

Here is my question when learning Vigenère cipher, can we perform frequency analysis attack toward this cipher? My first impression is no, because each column of its matrix has exactly 26 English ...
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Is there a cipher that avoids double bigrams?

Are there any known ciphers that whose ciphertext (given any plaintext) avoids bigrams of the form "aa, bb, cc, etc."? What about known ciphers that make bigrams of form "aa, bb, cc, etc." rare ...
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Most secure but feasible encryption running on WWII technology

Imagine you are transported back to ~1940. What is the best (i.e. most secure, but technologically feasible) encryption you can think of for widespread (i.e. military) use? How would you implement it?
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Keys-space for a restricted substitution cipher

How can one calculate the key-space for a restricted substitution cipher? A restricted substitution cipher is one where no letter is assigned to itself. For an alphabet with 26 letters how many keys ...
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286 views

Playfair cipher or ADFGX? [closed]

As part of an assignment, I have been given a cipher text of FFFXXXFGXAGFAFDAFXADDAGAD with the following description, ...
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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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How was the 5 digit random number in the VIC cipher generated?

Knowing that VIC was a "spy cipher" it is unlikely that the agents used a cryptographic device to genreate the 5 digit number but how did they do it?
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Best non-digital cipher?

Is there a cipher that was considered the undisputed best before the computer age? (This is not supposed to be a discussion; it's either a yes or no.) Please give a brief description why it is yes ...
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How can the Enigma's plugboard settings be found with partially known plaintext?

I don't quite understand the procedure described on wikipedia, is there a generalized procedure you can follow to rule out a pairing on the plugboard? For example, let's say the cipher text is ...
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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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Ciphers based on Keywords

I am looking for different ciphers that use a key word (like "hello" or "awesome") to encrypt a given text. I know about the Keyword Cipher already; I'm looking for others.
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Is the Caesar cipher really a cipher?

In this lecture by Dan Boneh on Coursera it was stated at minute 03:37 that The Caesar cipher, actually, is not a cipher at all. And the reason is that it doesn't have a key. What a Caesar cipher ...
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Shuffling alphabet cipher [closed]

Disclaimer: this is actually a coding challenge therefore I am expressly not looking for complete solutions. The way the cipher works is as follows: Start with ...
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Codes of “SAS und Chiffrierdienst”

The german site "SAS und Chiffrierdienst der DDR" http://scz.bplaced.net has some interesting content under point 11.3 in the category "manuelle Verfahren" I found ciphers named from A to D. But I ...
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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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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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In English, are there any words which encrypt to other words under the Caesar Cipher?

Are there any words in the English language which, when encrypted using the Caesar Cipher with any key, result in another English word? How may one go about determining which Caesar shifts are weakest ...
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Method for Cryptanalysis of a keyword-keyletter cipher?

I am a CS student who is in an introductory Cryptography course. I am not looking for the complete plaintext of this message, as I am not looking to cheat. I am simply stuck, and have no idea what to ...
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What is the viability of a hybrid vigenere cipher?

So a vigenere cipher's main weakness is that you can use frequency analysis on each alternated alphabet, and thus crack the cipher with relative ease... But that implies that you know what the ...
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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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What is the most secure hand cipher?

By "hand cipher", I mean a symmetric cipher for which encryption and decryption can can both be performed with a pencil on graph paper, consuming about 10-20 seconds per character by a proficient user....
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Does the Richard Sorge cipher still provide good security?

Is the cipher used by soviet spy Richard Sorge still sufficiently secure nowadays?
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How secure is a book derived key and what can be done to strenghten it? [duplicate]

If you have a manual encryption system where the keying is done by extracting a key from a book, a major weakness is that an adversary can search trough all existing books to find a perfect Match and ...
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Repeated Vignère Cipher

I was looking into the Vignère 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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How can I determine the Hill cipher key in this case?

I have been struggling with a Hill cipher problem for many days, without any luck. I have the following ciphertext, which I know is an encrypted excerpt from an Edgar Allan Poe story: ...
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flaw in perfect secrecy of shift cipher?

Why do we say shift cipher is perfectly secure when it is easy to break it (source)? Let's say I have a plaintext. "Australia is a big country"; I encrypt it using a shift of 2; That ciphertext can be ...
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Mixing Autokey with Regular Vignere

It seems to me that cryptanalysis of the autokey cipher relies on patterns being found in key attempts, easy when it's English you're looking for, but how can you do this if you're just getting ...
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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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161 views

Please prove distinguishability given a non-perfectly secure cipher

I'm trying to prove that a perfectly secure cipher yields indistinguishability. I already know and can prove that a perfect cipher => indistinguishability by the following proof: \begin{align} \Pr(...
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Cryptanalyze strategy for cipher text [closed]

I have the following ciphertext that I want to decipher: bnmkogt vgyhni uioopkm xswercvdf yuiogvbnm ghjy cftyhng tgeyjn xdrtygvc zsefx xdrgbhu tgbnmko tgbnmhyui yhnmko vbnmgyuiok So far, what I ...
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Assistance Cracking Classical Cipher

Below is the cipher text I am trying to break and as you can see its rather short which is why I am having so much trouble. ...
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Breaking a Modified Caesar Cipher

Does anyone know of an efficient way of breaking a modified Caesar cipher (where the key is a set of numbers (the amount of shift) that is repeated throughout the plaintext, e.g. {1,2,3,4,5}) via ...