Newest 'classical-cipher' Questions

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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 ...

classical-cipher vigenere

asked Sep 16 at 0:17

Kaldr

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vote

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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 ...

asked Aug 12 at 6:24

Akari_ATY

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3answers

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Common Classical Ciphers

When studying cryptography, the first thing every student learns is some historical ciphers. There are way too many of those ciphers to name them all. So my question is: What are the most important ...

classical-cipher history

asked Aug 6 at 9:51

Titanlord

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4answers

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Make a Strong, Easy-to-Remember Password Using Classical Cryptography?

Passwords can be tough to remember. For example: H7535637353959595*9608J614625C1313^398583I0397897j^ So Bob wants to make and use a good password for GPG that he ...

passwords classical-cipher

asked Jul 23 at 20:04

Patriot

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1answer

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What is a ciphertext only attack and how OTP is unbreakable using this attack

I was wondering that what actually is cipherText-only attack and how the One Time Pad Encryption cant be broken by this attack?

encryption one-time-pad classical-cipher

asked Jul 15 at 18:23

Chinmay Pant

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vote

1answer

39 views

Key space of a substitution cipher

I was going through a cryptography course, and I found a question there that: What is the size of the key space of the substitution cipher with 26 letters? Its answer was 26! I am not sure what this ...

encryption key-size classical-cipher substitution-cipher

asked Jul 11 at 17:08

Chinmay Pant

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0answers

41 views

Need some help with decryption code for monoalphabetic substitution

I am working on decrypting ciphertext in monoalphabetic substitution algorithm. I tried to decrypt using frequency histogram of English alphabets individually. The percentage of these frequencies can ...

encryption cryptanalysis classical-cipher substitution-cipher

asked Jun 3 at 12:39

devcode46

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vote

2answers

103 views

Can all affine cyphers be expressed with this formula

There are $26!$ permutations of the English alphabet. In Modern Cryptography textbook, William Easttom states that the basic formula for any affine cipher is $ax + b \equiv \pmod{26}$. I'm wondering ...

classical-cipher affine-cipher

asked May 15 at 21:18

mark mark

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How can I determine the number of times I have to reapply the Scytale until the original plaintext comes back?

Given "①②③④⑤⑥⑦⑧⑨⑩⑪⑫" as plain text and a 4 rows Scytale inscription with 3 as the length of the longest row, the original plaintext is back after 5 runs: ①④⑦⑩②⑤⑧⑪③⑥⑨⑫ ①⑩⑧⑥④②⑪⑨⑦⑤③⑫ ①⑥⑪⑤⑩④⑨③⑧②⑦...

classical-cipher permutation transposition-cipher

asked Feb 23 at 10:53

Rodrigo Panchiniak Fernandes

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4

votes

1answer

93 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 ...

stream-cipher one-time-pad classical-cipher vigenere

asked Jan 27 at 1:00

A. B.

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2answers

98 views

Does anyone have any hard ciphers to be cracked for fun?

The title says it all. Do you have any ciphers or encoded messages that you could post as a brainteaser? Thanks!

classical-cipher

asked Jan 21 at 22:30

Cole Henrich

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3

votes

2answers

360 views

How to determine which type of transposition cipher I have?

I have some ciphertext that I have determined using frequency analysis to be most likely encrypted using a transposition cipher, as the letter frequencies are similar to plain English language text. I ...

cryptanalysis classical-cipher transposition-cipher

asked Dec 27 '20 at 16:37

Lauren Hosking

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1answer

27 views

Can I use a Friedman test when decrypting a Playfair cipher?

I’d like to decrypt a Playfair ciphertext; however, I need to find the key word first. Is it possible to use the Friedman test here to find the length of the key word? My cipher has no J’s in it would ...

classical-cipher decryption playfair

asked Dec 18 '20 at 14:51

Lauren Hosking

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1answer

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Tranposition Ciphers

I am studying classical ciphers and have the following doubts: Is the row and columnar transposition cipher the same? It is similar since the process of encryption and decryption is the same for ...

classical-cipher transposition-cipher

asked Dec 14 '20 at 14:02

user10600161

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1answer

82 views

How to go about decrypting a cipher with known input and output? [closed]

I have a known input and a known output but how would I go about working out what the cipher was used. Below are a few examples of input and output. On the last one I noticed a repeating pattern. ...

encryption classical-cipher

asked Dec 11 '20 at 15:18

pee2pee

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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 ...

classical-cipher vigenere

asked Dec 6 '20 at 13:56

Just a human

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34 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 ...

classical-cipher vigenere frequency-analysis index-of-coincidence

asked Nov 17 '20 at 19:02

DarkFireGuy

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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 ...

cryptanalysis classical-cipher vigenere

asked Nov 12 '20 at 16:48

DarkFireGuy

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1answer

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Index of Coincidence Averages List

I am looking for a comprehensive list of the IOC values of any or all classical ciphers. I can't find a list, only pieces. Each cipher has an average IOC value, and I was wondering if there was a ...

classical-cipher index-of-coincidence

asked Oct 10 '20 at 22:11

Neo1009

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3

votes

1answer

77 views

LAT of an SBox, values are even

This is probably a silly question, but I could not find any reference. For the DDT of an SBox, it is easy to see why all the values are even. Is there any related result for LAT (i.e., all its values ...

classical-cipher linear-cryptanalysis s-boxes

asked Sep 13 '20 at 11:36

hola

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16

votes

7answers

3k views

Which is the simplest cryptographic algorithm which is close to commercial-level security?

An algorithm is simpler than another if It is easier to explain to a noob with basic high-school math knowledge. It is easier to securely self-implement by an intermediate programmer (Yes I know one ...

encryption public-key symmetric classical-cipher

asked Aug 7 '20 at 12:20

An Ant

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Is there a name for strong human-computable encryption schemes? Are there definitions for "human-computable"?

Background: There is some interest in encryption schemes meant for humans to perform without computational aid. (Relevant questions here, here, and here.) People often cite the VIC pen-and-paper ...

encryption classical-cipher pen-and-paper

asked Jul 11 '20 at 16:46

lynn

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1answer

110 views

Can someone help me understand this?

In the book Serious Cryptography It says for a cipher's permutation to be secure "Different keys should result in different permutations. Otherwise it becomes easier to decrypt without the key: ...

encryption cryptanalysis classical-cipher

asked Jun 19 '20 at 5:53

user80873

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vote

1answer

93 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, ...

classical-cipher vigenere

asked May 6 '20 at 9:33

Jeff

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0answers

55 views

Packing technique for large data storage

Packing multiple plaintext messages into a single ciphertext block is known to increase the effeciency of homomorphic encryption. Can someone let me know if this technique can support large data ? For ...

classical-cipher secure-storage

asked Mar 26 '20 at 0:05

sof

613 bronze badges

1

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2answers

1k views

How to decipher an ADFGVX cipher?

I got introduced to the ADFGVX cipher, and it seems very tedious to decipher such ciphertexts. If I do not have access to the key square and the keyword, and I am just given the ciphertext and a ...

classical-cipher decryption

asked Mar 13 '20 at 20:00

tomtomtom

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2

votes

1answer

101 views

Why was it easier to decode messages that you had several copies of?

During WW1 the German ambassador in Washington, von Bernstorff, blamed their numerous transmissions of the same messages as the cause for the successful decoding done by the British. I don't see the ...

classical-cipher history

asked Mar 13 '20 at 11:31

Kristian Francisco Milla Niels

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2answers

377 views

How were codes in WW1 reciphered (to enhance security levels) without them turning meaningless?

In WW1, the Germans made their communications secret by encoding their messages. This meant that the message's sender would have a codebook with all possible words and phrases he might use listed in ...

classical-cipher substitution-cipher history military-encryption

asked Mar 2 '20 at 12:25

Kristian Francisco Milla Niels

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36 views

Hill cipher. Any way around the not invertible matrices [duplicate]

Question: The plaintext JULY is encrypted using Hill Cipher with m = 2, to give the ciphertext DELW, then determine the encryption and decryption matrix My approach: We will form a 2x2 matrix of ...

classical-cipher hill-cipher

asked Feb 29 '20 at 18:50

kkheelan

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2answers

255 views

Prove monoalphabetic cipher is a valid symmetric cipher

I should prove mathematically that: $D_k(E_k(p))=p$ I know $E_k(p)=c=(p+k)\bmod26$ and $D_k(c)=p=(c-k)\bmod26$ Substituting the two formulas to the initial assertion I have $((p+k)\bmod26-k)\...

classical-cipher

asked Feb 28 '20 at 14:36

kappa

512 bronze badges

1

vote

0answers

305 views

How to find/determine the Polybius Square Key and Additive Key, if only the Cipher Text is known, in Nihilist Cipher?

I was solving a Crypto Challenge in a CTF, and I got a Nihilist Cipher Encoded String. Luckily the additive key was given as a hint, and for the polybius Square key, I kinda bruteforced or I just got ...

attack classical-cipher

asked Feb 21 '20 at 6:49

Razor Sharp

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1answer

87 views

How to make this cipher strong?

Suppose I have an arbitrary 256 bit number $m$ another secret number $k$ of the same bit length, and then I multiply them both modulo a 256 bit prime number $p$ to get $c$ as follows: $$ c = (m\cdot k)...

one-time-pad finite-field classical-cipher

asked Jan 29 '20 at 8:57

Vivekanand V

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27 views

Classic cipher method [closed]

I am struggling with these two cipher texts, I cannot identify which king of cipher was used. First: otnpeetrnneepeufofutisrtrllohcdmetoeheeatyngonrmrm And second: ...

classical-cipher

asked Dec 18 '19 at 15:39

Bálint Ružinský

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2

votes

1answer

74 views

Running Key Gibbs Sampling

I am trying to implement the algorithm described in this paper. It uses blocked Gibbs sampling to perform a ciphertext-only attack on text encrypted with a running key cipher. However, I am confused ...

one-time-pad classical-cipher ciphertext-only-attack

asked Nov 6 '19 at 14:44

Woafer

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330 views

Is it possible to crack the trifid cipher without the keyword?

I was learning about the classical ciphers and was looking up the methods to break them without the keywords and when I searched up "cryptanalysis of the trifid cipher" I couldn't find anything. I ...

cryptanalysis classical-cipher

asked Oct 25 '19 at 17:19

Manav

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2answers

163 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 ...

classical-cipher vigenere key-generation

asked Oct 4 '19 at 15:56

Patriot

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6

votes

3answers

1k views

How can frequency analysis be applied to modern ciphers?

I am building a computer program that deciphers Caesar, Vigenere and monoalphabetic substitution ciphers. All of those are susceptible to frequency analysis. However, it does not seem to be real-world ...

encryption block-cipher classical-cipher ecb frequency-analysis

asked Oct 3 '19 at 1:03

Marvin

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What is the strength of this machine? [closed]

This machine has the stator, with one half of the alphabet, and three rotors with replications of the other half in different order and repeated twice. There can have two rotors in use or the full ...

encryption classical-cipher pen-and-paper

asked Sep 30 '19 at 15:49

Neo1009

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Is there a way to easily encode a message without a computer on either end?

I enjoy making notes and passing them to my friends, and I also like making them encrypted for no reason. My friends enjoy it too, but it's a bit annoying to use the Caesar cipher for everything ...

algorithm-design classical-cipher pen-and-paper

asked Sep 23 '19 at 3:51

Moregano Coran

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5

votes

1answer

208 views

In cryptography, what is "fractionation"?

I understand how fractionation is used in the straddling keyboard, which is an important feature of the VIC Cipher, and in the Polybius Square of the ADFGVX cipher, but I am not sure how to describe ...

terminology classical-cipher

asked Sep 21 '19 at 12:19

Patriot

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4

votes

2answers

2k views

Can frequency attack be successful on Vigenère cipher?

Here is my question when learning Vigenère cipher, can we perform frequency analysis attack toward this cipher? My first impression is no, because each column of its matrix has exactly 26 English ...

symmetric classical-cipher

asked Sep 4 '19 at 14:46

lllllllllllll

1436 bronze badges

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1answer

165 views

Is there a cipher that avoids double bigrams?

Are there any known ciphers that whose ciphertext (given any plaintext) avoids bigrams of the form "aa, bb, cc, etc."? What about known ciphers that make bigrams of form "aa, bb, cc, etc." rare ...

encryption classical-cipher

asked Aug 26 '19 at 21:48

mtheorylord

1011 bronze badge

2

votes

1answer

249 views

Applications of machine learning in classical ciphers?

Machine learning is definitely applicable in analyzing simple shift ciphers like Caesar and affine ciphers, as well as substitution ciphers like Vigenère, but is it possible for machine learning to ...

cryptanalysis classical-cipher machine-learning

asked Aug 22 '19 at 21:42

abcdefghijklmnop151

211 bronze badge

3

votes

3answers

334 views

Most secure but feasible encryption running on WWII technology

Imagine you are transported back to ~1940. What is the best (i.e. most secure, but technologically feasible) encryption you can think of for widespread (i.e. military) use? How would you implement it?

classical-cipher cryptographic-hardware history

asked Aug 2 '19 at 12:28

3244611user

1333 bronze badges

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vote

1answer

74 views

About LFSR based M209 Cipher Machine

Can some one please express M209 Cipher Machine in terms of LFSR with Diagram or any simple method?

encryption classical-cipher lfsr

asked Jul 11 '19 at 19:53

SK Niazi

111 bronze badge

6

votes

1answer

229 views

Pen and Paper Authentication

What is the best way to prove that you wrote the encrypted message on a piece of paper? As most of us know, many conspirators have died because of false message implants, Mary Queen of Scots, for ...

authentication classical-cipher pen-and-paper

asked Jun 27 '19 at 21:18

Neo1009

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3

votes

1answer

570 views

How can the Enigma's plugboard settings be found with partially known plaintext?

I don't quite understand the procedure described on wikipedia, is there a generalized procedure you can follow to rule out a pairing on the plugboard? For example, let's say the cipher text is ...

encryption cryptanalysis classical-cipher enigma

asked Jun 22 '19 at 15:52

b3nj4m1n

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2

votes

2answers

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Was the Enigma's double stepping mechanism intentional?

It's sometimes refered to as the double stepping anomaly, so was it just a design flaw or was it put in place deliberately?

encryption classical-cipher substitution-cipher enigma

asked Jun 17 '19 at 12:59

b3nj4m1n

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1

vote

1answer

440 views

Enigma rotation example

According to wikipedia: BDZGO is the expected outcome when doing the enigma chipher on the letters AAAAA with rotors I,II,III and reflector B. ...

classical-cipher substitution-cipher enigma

asked Jun 11 '19 at 18:55

b3nj4m1n

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vote

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715 views

Ciphers based on Keywords

I am looking for different ciphers that use a key word (like "hello" or "awesome") to encrypt a given text. I know about the Keyword Cipher already; I'm looking for others.

encryption stream-cipher classical-cipher

asked May 31 '19 at 19:59

DUO Labs

1135 bronze badges

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