Questions tagged [vigenere]

The Vigenère cipher is a classical cipher that shifts each plaintext character by the value of the key at the same position modulo the key-length.

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Is there an English translation of Vigeneré's “Traicté des Chiffres”?

I Googled Vigeneré's "Traicté des Chiffres": no English translations, not even a reference to one. Perhaps someone's Google-wu is better than mine; I can't find it. I'm slogging my way through a PDF ...
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Why is Vigenére Autokey self-synchronizing?

According to the Wikipedia, and to several of our school study materials, Vigenére autokey ciphers are considered to be self-synchronizing stream ciphers. If I understand it correctly, the main idea ...
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Breaking an addition-based cipher with two ciphertexts but no known plaintext

I'm attempting to break a system which uses decryption code functionally equivalent to the following: ...
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Are some combinations of Substitution + Transposition more vulnerable than others?

Iterating multiple substitution ciphers is not mathematically different from using a single substitution cipher (3 Vigenere iterations with a 31-, a 32-, and a 33-letter key would essentially be a ...
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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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Index of coincidence for completely random text over k alphabets

I'm confused about /Friedman's method 2 (using a table with column of k size of key, and n/k rows, n is the total size for cipher text) \begin{equation} m = \Bigl(\varphi(l)-\varphi(o)\Bigr)/\Bigl(\...
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Base 64 Vigenere

I'm working on breaking a base64 Vigenere cipher. My guess is that the plaintext has been first base64-encoded, and then a variation of Vigenere with a 64*64 alphabet table used, the alphabet being ...
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785 views

Breaking Vigenere via Kasiski/Babbage method? (non-programmatic)

I'm really hoping someone can explain to me what is going on in the second major component of this form of analysis. If you wish, for convenience, here's a page that already has some ciphered text ...
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Applying Vigenere on small strings with sorting capability

I am new to cryptography and have a question about a use of Vigenere cipher in the case of small strings. I'd like to encrypt keywords that are smaller than 10 characters. If I use Vigenere ...
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393 views

Solving Vigenére with unknown alphabet

I'm trying to decrypt a cipher that I suppose has been encrypted with Vigenére. However I came about the following thought: The cipher consists of characters from [...
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507 views

Vigenère cipher frequency analysis not working

I'm writing a C++ program to use the Kasiski method to crack the Vigenère cipher. I'm testing it with a bit of Shakespeare encrypted with the key ABCDEFGHIJKL. It ...
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Correlation attack on Lagged Fibonacci Generator

Say that one uses a known LFG (2 known lags $a$ & $b$, known inner state length $N$, known modulo $m$) to hide some text with a basic à la Vigenère cipher: $C_i=(P_i + {PRNG}_i) \bmod 26$. Say ...