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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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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How to break a columnar transposition cipher?

I'm currently studying for a cryptography exam. I've been given ciphertext that has been encrypted by a columnar transposition cipher. I've been given no shift key length or key word, the only thing I ...
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Would the encryption of bigrams and trigrams weaken the code?

Supposing a rotor machine of the 1940s or 50s, with 36 characters instead of 26. Would the encryption of the ten additional characters as the most frequent bigrams or trigrams weaken the code? What ...
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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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How would you name and/or describe this algorithm?

First up: this is not a decoding request or anything. This is about terminology. Twice per year, we email another department to ask for a new licence file for their software. They are always slow to ...
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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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Concatenated Key Question - Poly-alphabetic Substitution and Columnar Transposition

I am working on a degree module, and have been tasked with designing an Encryption/Decryption algorithm. I hope to receive some help with a couple of questions, if possible. Apologies if terminology ...
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autocorrelation and entropy of historical ciphers

I'm learning cryptography and come across historical ciphers such as vigenere cipher,hill cipher,random substitution and etc.I'm using cryptool for learning purposes and I have a question in mind.I've ...
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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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Solving ADFGVX decoding with only ciphertext

Hi I'm new to the world of crypto and I'm trying to decode a message. I know it is encrypted using the ADFGVX cipher. I also have a ciphertext, but I have no other information given to me. My question ...
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How to calculate unicity distance of Fleissner grille?

I need to calculate unicity distance of Fleissners grille of $M \times M$ size. All I know is that plaint text redundancy equals $2$. The alphabet is not specified. Is it possible to calculate its ...