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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How to break a vigenere cipher with a period of 2, and knowing a part of the plaintext

the encrypt code is "ARJHNRIUCGQHPFGQFHTXPDEHTLNOC", and the part that i ​know of the plaintext is "DERUNA". The key is period of 2, so the key are 2 letters. Each letter of the ...
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How does the frequency work with Vigenère Cipher?

So I have an unknown key but with the length of 6. I understand that I calculate my own English letter frequency of my letters. I then compare it with the standard English letter frequency and ...
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Pencil & paper encryption, some thoughts on polyalphabetic techniques [closed]

I have an idea for a simple cipher that builds on old techniques that I thought I would share with this group. It has probably been done but I have not been able to find a reference to it. Given two ...
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Does a one-time pad of digits 0-9 have any weaknesses?

I'm working on one of those unsolved puzzles, and one theory I have is that one or more sections of it are using digits of pi, e, or some other irrational number as a one-time pad. (The obvious ...
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decode Vigenere cipher that was encoded with Affine cipher

How do I decode some text that has been encoded like this: affine(vigenere(text, vigenere_key), *affine_key)? I don't know keys to either of them. At first I ...
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How can I break a Vigenère cipher with partial plain key? [closed]

I've got the cypher text: cöimamiçknsyznhaczstş and a partial plain key: ?ğre??i I've used "?" instead of unknown ...
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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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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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Need help finding keysize for Vigenere cipher

I am doing a crypto challenge for breaking a Vigenere style repeating XOR encryption (https://cryptopals.com/sets/1/challenges/6). I have looked at similar questions asked here, mainly this one: ...
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167 views

Can you break a Vigenere cipher with key length of 2 and message/cipher text length of 4?

I am currently working on a problem where an attacker knows that a user's password is either "pqrs" or "jmlo" and also knows that the encryption scheme is using the Vigenere cipher ...
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41 views

Attacking a variation of the Vigenere with very long key length

I am to decrypt the ciphertext YVBCXGJRYHHRCJIUL into its plaintext message. The information that I am given is that the key used in the cipher is very long (equivalent to the length of an entire book)...
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Identifying correct cipher

I am trying to decrypt a text(~900 characters) and I started with the assumption that its a Vigenère cipher as the one of the identifier tool identified it as Vigenère cipher and also the Index of ...
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84 views

How to decrypt a short ciphertext that is said to be immune to attacks?

I need to decrypt a ciphertext which is short, and I have the first word of the plaintext. I thought of doing a probable-word attack, but I already know the position of the known word. In addition, ...
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73 views

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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Need help cracking a Vigenère cypher with a period of 2

How do you crack a long Vigenère cypher when the key is unknown? I have tried frequency analysis, but I'm not making any progress.
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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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Concatenating “words,” is it possible to create a key that is indistinguishable from one made in a truly random manner?

By concatenating "words" and adding them Modulo 26, can we 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 ...
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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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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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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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2k 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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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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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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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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Mixing Autokey with Regular Vignere

It seems to me that cryptanalysis of the autokey cipher relies on patterns being found in key attempts, easy when it's English you're looking for, but how can you do this if you're just getting ...
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946 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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1answer
362 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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568 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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232 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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443 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 Vigenère Autokey self-synchronizing?

According to the Wikipedia, and to several of our school study materials, Vigenère 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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358 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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271 views

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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9k views

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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9k views

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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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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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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688 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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383 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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4k views

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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369 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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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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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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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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490 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(...