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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2answers
393 views

Vigenère cipher - sorted order

i'm new to cryptography so i feel sorry for this newbie question! Can anyone tell me how Vigenère work with sorted order? For example i have this in my book: LADY(KEY) 3124(SORTED ORDER) 312431243(...
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Plaintext with 'T' and 'E' alphabets missing and encrypted with Vigenere Cipher

I wrote the normal code to decrypt a Vigenere cipher encrypted text without knowing the key. But that won't work for this are two of the alphabets are missing and that would mess up the frequency ...
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1answer
138 views

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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1answer
389 views

Decrypting a vigenere cipher with a reused one-time pad

I understand that when a plaintext is encrypted with a key of the same length, it is referred to as a one-time pad. Now when this key is reused to encrypt another plaintext, there is potential for ...
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Using same key twice with Vigenere cipher

Could someone please give a walkthrough of how this works: Decrypting a vigenere cipher with a reused one-time pad. It was never fully answered with the example given in the comment. e.g Plaintext ...
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Are there official test vectors for historic ciphers? [closed]

In many cases when cryptographic algorithms are published the paper also provides a set of test vectors that can be used by developers to verify their implementations. For historic ciphers such as ...
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1answer
91 views

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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1answer
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How to solve cipher encrypted with Vigenère + Columnar Transposition?

Vigenère's weakness is Kasiski's test and index of coincidence. However, if you put columnar transposition on top of Vigenère, that weakness is gone. The text is now shuffled and you can't search for ...
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Are there ready-to-use software that can try many decryption techniques on a ciphertext, with no information?

Let's say I receive a 1 MB encrypted file, but I get no information about the encryption method, and no password. The only thing I can guess is that the person probably used a weak encryption method ...
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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 ...
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1answer
66 views

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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2answers
155 views

Modification of vigenere cipher cryptographically secure?

After looking for ages online for a python implementation of the Vigenere cipher, and finding few, I decided to implement it myself. After ironing out all of the flaws, it's now a working (and secure) ...
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1k views

What is the difference between a Vigenère cipher and a one time pad cipher?

I'm doing a decryption competition at a nearby college. We are allowed one cheat sheet so I'm trying to make one. I realized that the Vigenère cipher was very similar to the one time pad and wanted ...
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1answer
691 views

Mutual Index of Coincidence

I can't seem to find a simple explanation of Mutual Index of Coincidence. I am finding explanations of Mutual Index of Coincidence not Index of Coincidence. I don't understand what the formula below ...
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1answer
223 views

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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Vigenere with multiple encryption [duplicate]

I have a school project about cryptography. The question is the following (will only give a short phrase as example, just want to know the method). A text has been encoded with Vigenere 2 times. The ...
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1answer
1k views

How to break a Quagmire 3 cipher?

What would be a good way to go about attacking a Quagmire 3 cipher? I understand that it is polyalphabetic with a key and an indicator. I have started by taking the cipher text, taking every n-th ...
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2answers
303 views

When does a multiple Vignere cipher become intractable?

Multiple Vignere ciphers do not repeat the key until the message gets longer than the LCM of the cipher lengths. Are messages shorter than that safe? If not, what is the attack strategy? I believe ...
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1answer
108 views

Cracking short ciphertexts made by Vigenère cipher

I've encrypted a couple of 10 letters words from https://www.bestwordlist.com/10letterwords.htm using a key of 10 characters. This is done using Vigenere cipher. Decrypt the cipher and give the key ...
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4answers
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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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2answers
361 views

How to crack Vigenere ciphertext if multiple keys of coprime length are used?

I came across the idea of using multiple Vigenere keys of coprime lengths here. The idea is, what if you use multiple keys, whose lengths are all co-prime? Then your effective key length would be ...
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1answer
525 views

How would multiple uses of a vigenère cipher be decrypted on paper (classic)?

As far as I can tell (from reading the Wikipedia article about it) decrypting a message encrypted with the vigenère cipher is possible on paper. But what would happen if the message is encrypted ...
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Can I make a cipher (ex: Vigenère) harder to break?

The Vigenère cipher can relatively easy be broken when the key size is small compared to the size of the message. One first finds the length of the key, and then uses frequency analysis to actually ...
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1answer
173 views

Basic Vigenere Cipher

I'm taking my first cryptography course and having trouble deciphering some Vigenere encrypted text. I was able to crack the first one: I'm having difficulty with the other two. I think the ...
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1answer
247 views

Probability of Vigenere cipher

I am trying to figure out this quiz question on a course I am doing but keep getting it wrong. Consider the Vigenere cipher over the lowercase English alphabet, where the key can have length 1 or ...
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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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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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How do you go about breaking a Quagmire III Cipher? [duplicate]

For example, take K1, from the Kryptos sculpture, which has been long solved. It's text is as follows: EMUFPHZLRFAXYUSDJKZLDKRNSHGNFIVJ
YQTQUXQBQVYUVLLTREVJYQTMKYRDMFD Now, I already know they ...
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Kryptos : K1. What is the origin of the “palimpsest” keyword?

I'm studying the Kryptos sculpture with its cryptographic puzzles K1 to K4. I understand that the keyword "palimpsest" was reverse-engineered using the tableau (and brute-force computer processing), ...
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1answer
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Breaking a XOR cipher of known key length?

For a challenge, I need to find the key that enciphered a text. I know that the key is of length N (invariable). There is no assurance that the key is only alphabetical or alphanumeric, but it could ...
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1answer
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How do I find the key of the Vigenere cipher is if I already know the key length?

Hi I am stuck in trying to crack the code of finding the key to decrypt a huge message. I have the frequencies of the letters: ...
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Vigenère cipher: Security when key length and plaintext length are the same

I have read the Vigenère cipher is secure as long as the key length is the same as the length of the data to be ciphered. Is this true when the same key is used multiple times? In such cases, after ...
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1answer
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How to decode a caesar that goes to transposed plaintext?

When decoding vigeneres, I am left with Caesars. Often when the key is longer, these are shorter so normal frequency analysis won't work. Is there another method I can implement without adding a load ...
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Creating your own encryption and decryption algorithm

I'm very uneducated when it comes to cryptography. I have tried to find an answer to my question, but what I've read doesn't quite cover what I'm asking. I have thought up my own encryption algorithm ...
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1answer
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Vigenere cipher with a shared resource [duplicate]

I'm pretty new to all of this and I apologize in advance if (as, I'm sure it has) this question has been asked and answered a million times previous, but I couldn't find anything through searching (...
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4answers
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Finding length of a key for a given vigenere cipher using Index of Coincidence

I'm developing an algorithm that takes in a vigenere cipher and produces the key length automatically. However, I'm having trouble understanding how to detect the key length when there are multiple ...
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2answers
571 views

Finding Vigenere's keys with part of decrypted text?

I have a text that was encrypted twice with two Vigenere keys. However, I know the seven first characters of the decrypted text. I have already implemented a function displaying for the five first ...
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1answer
272 views

Is the beaufort cipher just as secure as the Vigenere cipher?

Does the Beaufort cipher have the same strength as the vigenere cipher assuming you use the same complexity of key, or because of it's reciprocal nature make it less secure?
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How to find key given Vigenere Ciphertext? [duplicate]

I can't seem to find a tutorial online that helps me with this tasking. I have some Vigenere ciphertext (LVGPA...). It only says to assume that encrypting the key letter A results in no change, B ...
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1answer
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How to find key length of a Vigenere chiper?

I am trying to decrypt a Vigenere chiper, I saw a lot of youtube videos but I still can get a good value for the key length. In theory I have to get the repetions of letters shifting the text one ...
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268 views

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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Help me understand how to actually break an XOR/Vigenère cipher [closed]

My friend's server was recently hacked and I'm trying to decipher the malicious files I found in hopes of understanding the hack better. I can tell that they're using an XOR/Vigenère cipher and I've ...
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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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2answers
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Prove Vigenere cipher isn't perfectly secret

As part of a homework assignment I have to prove/disprove that a Vigenère Cipher with a key of length n, uniformly distributed in the alphabet, on a plain text of length 2n, also uniformly distributed ...
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1answer
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Vigenere cipher

I am attending cryptography course on Coursera. I am stuck at one question which I cannot answer right even after few tries. Which of the following are true about Vigenere cipher? (Check all that ...
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1answer
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Solving Vigenère Encryption

I'm trying to crack a cypher that I believe is Vigenère encrypted and I'm currently stuck. I calculated the key length by finding repeated sequences in the cypher and calculating the the common ...
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1answer
260 views

Probability for Vigenere cipher given distribution of key lengths

Given the exact same question and answer here: https://crypto.stackexchange.com/a/37212/40935. How does one derive/figure out (using equation, combination of equations, or "knowledge") the bold ...
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1answer
2k views

Using Chi-Square for Vigenère Cipher

I am writing a program which will use Chi-Square to determine which is the correct keyword for a ciphertext via Vigenère cipher. I came across a website that describes the Chi-Square statistics in a ...
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2answers
900 views

Vigenère cipher with sha512 and a little foresight turns to one-time pad. How safe can be?

I'm doing some exercises and of course I have read about the weaknesses of Vigenère cipher because it repeats the key. But what if I use a different hash every time? The hash of the "key + an ...
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1answer
966 views

Testing Kasiski Test and Mutual Index of Coincidence on Vigenere Encryption on Vigenere Encryption?

I was learning about Vigenere Ciphers and its various cryptanalytic attacks. One of them was, Kasiski test and Mutual Index of Coincidence. So, I was wondering can Kasiski test and Mutual Index of ...