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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How did the cryptographers of Bletchley Park figure out the chi stream of the Lorenz cipher?

How did the Bletchley Park code breakers figure out the chi stream of the Lorenz cipher, that was obscured in the ciphertext, which British code breakers eventually decoded? It's written in The ...
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488 views

Shannon cipher with fewer keys than messages

Alice and Bob have a set $\mathcal{M}$ of $|\mathcal{M}|$ messages and a set $\mathcal{K}$ of $|\mathcal{K}|$ keys. Alice wants to send a message $m \in \mathcal{M}$ to Bob. She uniformly picks a key $...
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Сryptanalysis of Hill's method

The brutal ciphertext is given. The text volume is more than 6000 characters. It is known that the text is encrypted with a 7x7 matrix. Unknown key and plaintext. Is it possible to crack this code? ...
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1answer
112 views

VIC cipher author known?

Does anybody know if the design of VIC cipher is attributed to anybody? I've tried Google and found nothing. There are quite a few sites describing the method in detail, a few implementing it ...
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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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138 views

Fastest / easiest way to find rotor wiring without physical inspection on Enigma Machine emulator

We have an Enigma machine emulator we are trying to replicate. Machine has 3 rotor positions and 6 rotors that can be selected. The input goes through 3 rotors then is reflected back to start as is ...
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44 views

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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414 views

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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113 views

Avoiding doubled letters in encrypted text

I have an encrypted string based on an "alphabet" of 29 runes and access to successfully decrypted (runes->English) plaintext. Testing for a Vigenere cipher, I tried a Friedman attack (aka Kappa test, ...
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225 views

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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How can I determine the number of times I have to reapply the Scytale until the original plaintext comes back?

Given "①②③④⑤⑥⑦⑧⑨⑩⑪⑫" as plain text and a 4 rows Scytale inscription with 3 as the length of the longest row, the original plaintext is back after 5 runs: ①④⑦⑩②⑤⑧⑪③⑥⑨⑫ ①⑩⑧⑥④②⑪⑨⑦⑤③⑫ ①⑥⑪⑤⑩④⑨③⑧②⑦...
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What does the normalizing coefficient do in the Index of Coincidence?

In school we only learned the formula without the normalizing coefficient: But Wikipedia has one that says: I am using IC in a cryptography class to find the key length and am checking various key ...
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Is there a name for strong human-computable encryption schemes? Are there definitions for “human-computable”?

Background: There is some interest in encryption schemes meant for humans to perform without computational aid. (Relevant questions here, here, and here.) People often cite the VIC pen-and-paper ...
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How to find/determine the Polybius Square Key and Additive Key, if only the Cipher Text is known, in Nihilist Cipher?

I was solving a Crypto Challenge in a CTF, and I got a Nihilist Cipher Encoded String. Luckily the additive key was given as a hint, and for the polybius Square key, I kinda bruteforced or I just got ...
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90 views

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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50 views

How do you determine which classical technique was used?

For a class assignment we had to encrypt a message of at least 140 characters using only one of the classical cryptographic techniques. For extra credit we can decrypt someone else's message. I figure ...
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123 views

Are there any historic examples of breaking the one-time pad because of a careless key re-use? i.e simple attack on a multiple-time pad?

It doesn't have be using a truly random key, (it could be the Enigma) but the attack must be based on XORing two parts of ciphertext.
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Hill cipher key space

Key space is the set of all possible keys that can be used to generate a key. We using the number of valid key to describe it. I've given a hill cipher of block size $k$ over alphabet of size $p$, ...
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1answer
79 views

How does Fialka manage to have a letter encipher unto itself?

http://www.cryptomuseum.com/crypto/fialka/index.htm Fialka was an electromechanical rotor machine. How does it manage to have a letter encipher unto itself. I realize it does something clever by ...
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What is the formal name for determining the key to a Vigenere cipher using frequency analysis once the key length has been found?

In short, I am writing a paper about cracking the Vigenere cipher. There are supposed to be three parts to it and each is supposed to be related to an academic article (or anything formal). I chose ...
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Index of Coincidence Averages List

I am looking for a comprehensive list of the IOC values of any or all classical ciphers. I can't find a list, only pieces. Each cipher has an average IOC value, and I was wondering if there was a ...
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46 views

How do you determine the recorded value of a cipher when using the shift key?

I am taking a cryptography class and having a hard time understanding how to utilize Ceasar Cipher and how to determine the shift key values. Is it based on many characters are in the cipher or is it ...
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Packing technique for large data storage

Packing multiple plaintext messages into a single ciphertext block is known to increase the effeciency of homomorphic encryption. Can someone let me know if this technique can support large data ? For ...
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286 views

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 ...