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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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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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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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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Using ML to detect what classical cipher the ciphertext is encrypted with

I was considering creating an ML project where it is fed some ciphertext by any classical cipher and would return possible ciphers that encrypted the text. I would have to create a sizeable dataset ...
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Need some help with decryption code for monoalphabetic substitution

I am working on decrypting ciphertext in monoalphabetic substitution algorithm. I tried to decrypt using frequency histogram of English alphabets individually. The percentage of these frequencies can ...
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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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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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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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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 ...
abcdefghijklmnop151's user avatar
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How to Calculate Digraphic/Trigraphic Index of Coincidence?

How do you calculate the digraphic and trigraphic IOCs and the same expected IOCs? I'm aware of the formula for calculating the single letter IOC which is given at this formula but I can't find the ...
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How do the notch and window positions on an Enigma machine correlate?

I am having difficulty visualizing the stepping process. The permutation of Wheel I of Enigma I is as follows: ...
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Is there any known/standard encoding or cipher method that uses a 64-character alphabet from byte 30 (ASCII `0`) to byte 6F (ASCII `o`)?

Is there any known/standard encoding or cipher method that uses a 64-character alphabet from byte 30 (ASCII 0) to byte 6F (ASCII ...
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Vigenère cipher with switching keys

I am looking for possible ways of attacking a modified Vigenère cipher. Let's say we have two keys e.g. 'stackoverflow' and 'Vigenère'. The V cipher starts with one of those keys but switches as ...
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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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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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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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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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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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How to cryptanalyze Bifid cipher?

this is my first question. I've been into classical cryptography for about a year or so, but I am getting started with cryptanalysis of these ciphers. I am trying to figure out how to reconstruct the ...
Bentley H.'s user avatar
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How to encrypt affine cipher in block?

Assuming the alphabet of capital letters, if an affine linear cipher $v\to Av+b \bmod 26$ with block length $3$ maps plaintext ENCRYPTAGAIN to ciphertext ...
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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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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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