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.
123
questions
1
vote
1
answer
67
views
Analysis of the Vigenere cipher
Im just starting out learning some cryptoanalysis techniques. I came across an idea which analyzes the vigenere cipher. Essentially the video explains that there is a standard english probability ...
- 11
3
votes
1
answer
111
views
How do I exactly use the Index of Coincidence in Cyphertext?
I came in contact with a ciphertext, which is:
...
- 161
0
votes
0
answers
50
views
Breaking vigenere cypher using the one-time pad flaw when used for a second time
I got an idea which may be wrong because I may have missed some important factor but for the moment I don't know if I really did. Let BM be the method used to break a reused one-time pad cipher (which ...
- 1
0
votes
1
answer
48
views
Does using ECB mode of Vigenère cipher on files (no plain text) with a key of 10,000 byte(char) is secure in today's standard?
Hi I'm fairly new to studying cryptography and I'm just curious about the security of Vigenère cipher.
Given today's powerful super computers, how secure/unsecure does Vigenère cipher can get?
let us ...
- 105
0
votes
0
answers
122
views
Vigenere Decryption with key length
I have a question. If I have 2 ciphertexts given and the same key has been used on both. They key lenght is the same as the plaintext and cipherrtext length. How do I decrypt them and find the key. So ...
1
vote
1
answer
83
views
What are the equations (Gen, Enc, Dec) for the vigenere cipher?
Long story short, trying to understand how I would write the vigenere cipher mathematically when using Gen, Enc, Dec and I can't figure it out. This is what I've come up with so far.
$$\mathrm{Gen}: k ...
- 11
1
vote
0
answers
51
views
Vigenère cipher with switching keys
I am looking for possible ways of attacking a modified Vigenère cipher. Let's say we have two keys e.g. 'stackoverflow' and 'Vigenère'. The V cipher starts with one of those keys but switches as ...
- 11
2
votes
1
answer
127
views
trying to identify the key of a vigenere cipher via brute force
I'm working on a bit of an ARG game type thing that uses the vigenere cipher. what im wondering is the chance a player could brute force said cipher by simply checking all possible key sequences of ...
- 133
1
vote
1
answer
68
views
how can identify which cryptanalysis is used ( Indistinguishability cryptanalysis against classical ciphers) [duplicate]
I have 10 ciphertexts and 10 plain texts I want to know which cipher is from which plain text
how can I know this
I know the name of substitution cipher, transposition cipher, Vigen`ere cipher and ...
- 13
1
vote
1
answer
126
views
Question about variations on Vigenere cipher
I'm new here and by no means an expert on cryptography. I like to dabble, and one of my favorite classical ciphers is the Vigenere. I understand that the normal method of Vigenere encrypting is to ...
1
vote
0
answers
103
views
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 ...
1
vote
1
answer
113
views
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 ...
- 11
0
votes
1
answer
51
views
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 ...
- 1
4
votes
1
answer
111
views
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 ...
- 141
0
votes
0
answers
41
views
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 ...
- 1
1
vote
0
answers
103
views
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 ...
- 11
1
vote
0
answers
55
views
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 ...
- 11
2
votes
1
answer
120
views
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: ...
- 199
0
votes
1
answer
384
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 ...
- 11
1
vote
1
answer
65
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)...
- 11
3
votes
0
answers
557
views
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 ...
- 33
1
vote
1
answer
107
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, ...
- 13
0
votes
1
answer
79
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 ...
- 1
1
vote
0
answers
165
views
Decryption of Vigenère cipher by hand using Kasiski method
My task is to decrypt the following message, which was encrypted with a Vigenère cipher of length 4:
...
- 11
2
votes
3
answers
1k
views
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.
- 31
0
votes
0
answers
343
views
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 ...
1
vote
0
answers
53
views
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 ...
- 111
1
vote
2
answers
174
views
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 a key be created that is indistinguishable from one generated in a truly random manner? Let's say the key is more than about ten ...
- 3,057
4
votes
2
answers
367
views
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 ...
- 481
1
vote
2
answers
425
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) ...
- 454
6
votes
2
answers
354
views
Is there an English translation of Vigenère's "Traicté des Chiffres"?
I Googled Vigenère'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 ...
- 200
2
votes
1
answer
3k
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 ...
- 305
0
votes
0
answers
45
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 ...
- 1
5
votes
2
answers
7k
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 ...
2
votes
1
answer
82
views
Repeated Vigenère Cipher
I was looking into the Vigenère cipher when I thought of something.
Would you improve the security of the cipher if you shifted each letter (from the text you want to encrypt) with each letter of the ...
- 23
0
votes
1
answer
83
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....
- 220
2
votes
1
answer
126
views
Mixing Autokey with Regular Vigenère
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 ...
- 21
1
vote
1
answer
1k
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 ...
- 45
0
votes
1
answer
511
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
...
3
votes
2
answers
686
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 ...
- 185
3
votes
1
answer
262
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 ...
- 33
2
votes
1
answer
568
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 ...
- 153
7
votes
2
answers
198
views
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 ...
2
votes
0
answers
316
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 ...
- 121
6
votes
2
answers
434
views
When does a multiple Vigenère cipher become intractable?
Multiple Vigenère 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 ...
- 171
1
vote
0
answers
293
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 ...
2
votes
1
answer
12k
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 ...
- 151
0
votes
1
answer
11k
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:
...
- 15
0
votes
1
answer
73
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 (...
- 103
2
votes
1
answer
52
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 ...
- 21