Questions tagged [classical-cipher]
Ciphers invented before the era of computers and modern cryptographic theory. Classical ciphers typically operate on letters instead of bits and are usually designed to be implemented by hand or using simple mechanical devices.
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How to do cryptography without knowing computer science or AI?
I'm interested in ciphers, codes, patterns, and mathematics, but do not have extensive computer programming acumen (VERY basic Java skills). I know nothing about machine learning, AI or anything in ...
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Are there any web puzzles I can solve without programming knowledge?
I don't know much about computer programming (taking an Intro to Computer Programming course at school), but discovered Cicada 3301 and was hoping there is something similar I might pursue for my own ...
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1answer
54 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 ...
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48 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 ...
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1answer
86 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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3answers
229 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 ...
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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 ...
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2answers
59 views
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 ...
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1answer
110 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 ...
3
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2answers
150 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 ...
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1answer
54 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 ...
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1answer
125 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 ...
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235 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?
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1answer
49 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?
4
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1answer
132 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 ...
3
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1answer
109 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
...
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2answers
154 views
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?
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1answer
115 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.
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1answer
59 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.
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Strong and Practical Hand Ciphers [duplicate]
I know monoalphabetic ciphers are weak, but my message recipient doesn't like taking the time for the decryption process. I've tried Vigenere, Gronsfeld, Beaufort and Digraphic Ciphers, but he doesn't ...
2
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1answer
220 views
Shuffling alphabet cipher [closed]
Disclaimer: this is actually a coding challenge therefore I am expressly not looking for complete solutions.
The way the cipher works is as follows:
Start with ...
3
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0answers
99 views
Crack a polyalphabetic cipher given a pair of (plaintext, ciphertext) encrypted by it
The original question only states that a classical cipher is used, and I am going to articulate 1) why I think a polyalphabetic substitution cipher is used AND 2) my attempts so far.
The Question
<...
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55 views
Method for Cryptanalysis of a keyword-keyletter cipher?
I am a CS student who is in an introductory Cryptography course. I am not looking for the complete plaintext of this message, as I am not looking to cheat. I am simply stuck, and have no idea what to ...
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1answer
151 views
Codes of “SAS und Chiffrierdienst”
The german site "SAS und Chiffrierdienst der DDR"
http://scz.bplaced.net
has some interesting content under point 11.3 in the category "manuelle Verfahren" I found ciphers named from A to D. But I ...
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0answers
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Is there a way to make a non-specific algorithm to decypher substitutions with “anti-frequency analysis” measures?
There's a code I'm trying to decipher. What I know is that it's a simple substitution, with just a few added rules intended to make frequency analysis and other very common methods a little less ...
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0answers
67 views
Does the Richard Sorge cipher still provide good security?
Is the cipher used by soviet spy Richard Sorge still sufficiently secure nowadays?
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How secure is a book derived key and what can be done to strenghten it? [duplicate]
If you have a manual encryption system where the keying is done by extracting a key from a book, a major weakness is that an adversary can search trough all existing books to find a perfect Match and ...
4
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2answers
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How was the 5 digit random number in the VIC cipher generated?
Knowing that VIC was a "spy cipher" it is unlikely that the agents used a cryptographic device to genreate the 5 digit number but how did they do it?
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1answer
56 views
Repeated Vignère Cipher
I was looking into the Vignère 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 ...
2
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0answers
246 views
How can I determine the Hill cipher key in this case?
I have been struggling with a Hill cipher problem for many days, without any luck.
I have the following ciphertext, which I know is an encrypted excerpt from an Edgar Allan Poe story:
...
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1answer
62 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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1answer
99 views
flaw in perfect secrecy of shift cipher?
Why do we say shift cipher is perfectly secure when it is easy to break it (source)?
Let's say I have a plaintext.
"Australia is a big country";
I encrypt it using a shift of 2;
That ciphertext can be ...
2
votes
1answer
46 views
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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1answer
90 views
Can a message be encrypted with BOTH mono-alpha and poly-alpha ciphers?
For my class assignment, I was given this text;
Qpuvu vo vv stazpuykzh Hhycmlmv asb. Ad dhyaqva wh uyo uzb jpwww Avlw.
Tkpjllfdmbp zoatz vzjavfvna ZLHqh. Amva luy yyvlz yu bhk zua zlhvvalaz
yow ...
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0answers
119 views
Cryptanalyze strategy for cipher text [closed]
I have the following ciphertext that I want to decipher:
bnmkogt vgyhni uioopkm xswercvdf yuiogvbnm ghjy cftyhng tgeyjn
xdrtygvc zsefx xdrgbhu tgbnmko tgbnmhyui yhnmko vbnmgyuiok
So far, what I ...
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1answer
299 views
Does there exist a Cipher / Hash identification tool?
Let's suppose I have two strings
One string is plaintext
The other is the result of running the plaintext through an unknown cipher.
Does there exist a tool where I can enter the pre and post-...
3
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0answers
94 views
Fastest / easiest way to find rotor wiring without physical inspection on Enigma Machine emulator
We have an Enigma machine emulator we are trying to replicate. Machine has 3 rotor positions and 6 rotors that can be selected. The input goes through 3 rotors then is reflected back to start as is ...
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1answer
158 views
Please prove distinguishability given a non-perfectly secure cipher
I'm trying to prove that a perfectly secure cipher yields indistinguishability. I already know and can prove that a perfect cipher => indistinguishability by the following proof:
\begin{align}
\Pr(...
4
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1answer
302 views
Keys-space for a restricted substitution cipher
How can one calculate the key-space for a restricted substitution cipher? A restricted substitution cipher is one where no letter is assigned to itself. For an alphabet with 26 letters how many keys ...
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1answer
55 views
How would I go about solving this cipher? [closed]
I am not sure this is the right place to post this... recently I was given the following image by my friend in the context of a game we play together. Please note the characters at the bottom.
I ...
3
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2answers
210 views
rotor machines: secrecy of wiring
During the heydays of rotor machines, the internal rotor wiring was always a closely guarded secret. Even fully cleared repair staff was not allowed to do anything that could reveal it.
As the ...
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4answers
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In English, are there any words which encrypt to other words under the Caesar Cipher?
Are there any words in the English language which, when encrypted using the Caesar Cipher with any key, result in another English word? How may one go about determining which Caesar shifts are weakest ...
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1answer
449 views
Clarification on Hill Cipher crib dragging technique
--- this has been edited as I realised the question was silly. replaced with helpful information ---
I want to confirm the following:
Given ciphertext "AGHTDIX... [cont.]" (C)
and crib (a word ...
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1answer
946 views
Cracking transposition cipher
I have a task to decrypt custom made transposition cipher, as I'm not the cryptography expert, I would appreciate any help.
I've been given the table of characters ...
...
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2answers
65 views
What is the difference between a dual cipher and a tweak?
I have looked at the idea of dual ciphers but I cannot convince myself I really understand them. I think I just need a very simple worked example.
I was given the definition:
Two ciphers $E$ and $E′$...
13
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2answers
534 views
How were one-time pads and keys historically generated?
In the 20th century, it was common for various intelligence agencies and military organizations to use ciphering machines and one-time pads.
However, no source I've seen ever mentions the process of ...
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0answers
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How did the cryptographers of Bletchley Park figured out the chi stream of the Lorenz cipher?
How did the Bletchy Park code breakers figured out the chi stream of the Lorenz cipher, that was obscured in the cipher text, which Britain code breakers eventually decoded. It's written in The ...
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1answer
40 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 ...
4
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0answers
69 views
Сryptanalysis of Hill's method
The brutal ciphertext is given. The text volume is more than 6000 characters. It is known that the text is encrypted with a 7x7 matrix. Unknown key and plaintext. Is it possible to crack this code? ...
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1answer
1k views
How large is the Playfair cipher keyspace? [duplicate]
In the Playfair cipher, is the key space 5 x 5 = 25 or 25 x 25 = 625? I'm trying to work out the size of the key space if each set of equivalent keys is counted as one key.
