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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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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0answers
35 views
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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2answers
225 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
106 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
67 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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243 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
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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
139 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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165 views
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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240 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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227 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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1answer
3k 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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1answer
3k 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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1answer
55 views
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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1answer
38 views
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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383 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
199 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
1k 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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180 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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267 views
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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5answers
16k views
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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722 views
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
323 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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1answer
230 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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2answers
876 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
814 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 ...
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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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1answer
809 views
Can a Vigenère cipher be solved if the alphabet is modified (custom)?
Let's say I have about a statistically good sample of characters of text that appear to be uniformly distributed, but the composition of the text is [A-Z], [a-z], [0-9], +, and / — constituting ...
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0answers
101 views
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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139 views
Does Kasisky test for Vigenère cyphers assumption always hold?
In the notes from which I'm studying I read about Kasisky test:
"Key observation: Two identical segments of $l ≤ L$ plaintext letters,
will be encrypted to the same $l ≤ L$ ciphertext letters."
...
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1answer
834 views
Conditional probability with Vigenere Cipher given specific plaintexts and key sizes
Apologies if this should be in the Mathematics stack exchange, I just ask it here because the context is cryptography. Here is the question that I seemingly cannot get correct:
Consider the ...
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2answers
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Conditions for Perfect Secrecy with the Vigenere Cipher
Please forgive my ignorance here as I'm far from a math major and I've never looked into cryptography before so if this seems stupid - it probably is. There is a question in a quiz I'm attempting that ...
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1answer
2k views
Reversing a known encryption algorithm (4-byte repeating key XOR)
I've been practicing for an upcoming CTF competition, and I've finally reached the cryptography stage. I'm a complete newbie in this field (my knowledge is essentially that bcrypt is awesome and md5 ...
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1answer
160 views
Cracking vigenere of non-text cleartext
I've begun a course in crypto on coursera and the first homework was writing a vigenere(xor) cracker. It works, which was a rush :) but it makes one core assumption, one has encrypted a natural ...
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1answer
4k views
Cryptanalysis of XOR cipher with repeated key phrase
My assignment is to cryptanalyze cipher text that we know was encrypted with a stream cipher (bitwise XOR of plain text and key stream), and decrypt to plain text. We know the key stream is a repeated ...
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1answer
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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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1answer
215 views
Product of Vigenère ciphers is not a Vigenère cipher with length of LCM
I have always thought that using two Vigenère ciphers leads to another Vigenère cipher with key length of LCM (least common multiple) of the two previous Vigenère ciphers. But I have stumbled upon ...
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1answer
418 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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2answers
727 views
Levels of strength: The Caesar Cipher
SITREP: I am deciding what form of "Random" Number generation would fit best for a Caesar Cipher that encrypts each letter with a different integer as a shift. This encryption is being handled via C# ...
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235 views
Is there any difference between a one-time pad and a Vigenère cipher with a long key? [duplicate]
I've been browsing Wikipedia and stumbled on the article for the Vigenère cipher. I realized after seeing the example that it's quite similar to the one time pad, except with a short key repeated as ...
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2answers
1k views
How to decode a (Vigenère?) substitution cipher? [closed]
I am trying to decode a message that I suspect has been encrypted with a Vigenère cipher:
Utl zluuocp zsc rvzu hbcp ztvibfz vrabzz utl ilry. Utlal flal cb fbaiz, qszu zbsciz. Utvu cllihl vhzb dvil ...
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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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1answer
207 views
K Friedman - two texts explanation
I read the $K$-Friedman test to determine the period of a Vigenère ciphertext, and I understand something like this:
$K$-Friedman test tries to find out what period of the cipher by calculating some ...
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1answer
196 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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1answer
576 views
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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0answers
74 views
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 ...
