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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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 ...
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1answer
68 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
116 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
58 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
47 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 ...
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1answer
77 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
62 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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41 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
141 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
29 views
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 decypher. What I know is that it's a simple substitution, with just a few added rules intended to make frequency analysis and other super classic method a little less ...
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48 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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2answers
41 views
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 ...
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2answers
100 views
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
52 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
162 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
47 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
81 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
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1answer
40 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
76 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
106 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
146 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
85 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
132 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(...
3
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1answer
214 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
51 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 ...
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2answers
154 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
345 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
800 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
61 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 $E′$...
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2answers
392 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
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 ...
4
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0answers
66 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
830 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.
3
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1answer
372 views
Affine Cipher Keys that map plaintext to a given ciphertext
We first need to show that for each pair of plaintext-ciphertext
letters ( x,y ), there are exactly 12 keys that encrypt x to y . For
each choice of a , the key ( a,y − ax ) encrypts the ...
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3answers
227 views
How to “score” partially decoded ciphertext?
I am attempting to write a basic codebreaking program to break simple ciphers (think caesar cipher & railfence) such as these here https://en.wikipedia.org/wiki/Classical_cipher.
The program ...
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3answers
694 views
An unbreakable book cipher?
In a recent press interview, a former terrorist of the 1970s described the cipher his group used to communicate. He claimed that method was unbreakable and I wonder if cryptographers today would agree....
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2answers
478 views
Is there any quantum resistant pen-and-paper or mind cipher?
I know about VIC and Solitare but as I understand they are not quantum resistant ciphers. Is there any quantum resistant pen-and-paper or mind cipher?
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5answers
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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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1answer
552 views
What kind of classical ciphers are there? [closed]
I want a list of classical ciphers that can be used, I'm trying to find more classical ciphers online, but there isn't too much information, so, can someone list some more classical ciphers, and not ...
3
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1answer
361 views
How can I decode a substitution cipher in the form of pictures?
I'm very new to cryptography (and cryptanalysis), and I'm wondering how to decode a substitution cipher, where all of the letters are replaced with symbols, that is, pictogram cipher?
5
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1answer
248 views
What are Alternatives to basic ROT-n Ciphers which Don't Lose 'Context'?
I've got this neural network running like a champ on my machine. The data is concatenated works of shakespeare in a plaintext file. RNN trains on the data, then gives you a 'sample', aka it tries to ...
3
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3answers
284 views
How is the affine cipher a permutation?
It seems there would be some collisions in what the different symbols map to, resulting in loss of information.
For example, say we use the English alphabet, multiply by 2 and take the congruence ...
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0answers
441 views
Shannon cipher with fewer keys than messages
Alice and Bob have a set $\mathcal{M}$ of $|\mathcal{M}|$ messages and a set $\mathcal{K}$ of $|\mathcal{K}|$ keys. Alice wants to send a message $m \in \mathcal{M}$ to Bob. She uniformly picks a key $...
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1answer
130 views
Mathematical structure for Sbox
Recently, when I studied the permutation cipher, I saw a matrices structure which is same as permutation cipher. This method was so simple and interesting for me.
Let $m$ be $n$-bit plain text and $P=...
3
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1answer
480 views
monoalphabetic substitution perfect secrecy
I have this question that I'm trying to answer:
Consider a monoalphabetic substitution cipher applied to plaintexts
consisting of just a single letter. That is, $$M = \{0, 1, . . . ,
25\}$$ The ...
3
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1answer
334 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(...
3
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2answers
6k views
To decrypt a cipher text encrypted using keyed substitution
I'm looking for decryption of this cipher text which was encrypted using simple substitution using secret key. I have already spend a lot of time on this. However it should not be that tough. So I ...
