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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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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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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66 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-...
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58 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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100 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(...
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1answer
106 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
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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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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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2answers
240 views
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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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
582 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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55 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
316 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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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
37 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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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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598 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.
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279 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
150 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
541 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
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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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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
383 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 ...
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1answer
295 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?
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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 ...
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3answers
215 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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356 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
122 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=...
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1answer
391 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 ...
4
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1answer
274 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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2answers
4k 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 ...
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177 views
Whch polygraphic cipher could this be?
I have a cipher with an odd number of letters. The thing is that there is no letter "j" in it, so first that comes in my mind is playfair cipher.
It can't be the playfair, because it has odd number ...
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What type of cipher or encryption method is this called?
Let's say I have a key value of 5.
The message I want to encrypt is "AAAA"
A = 1,
B = 2,
C = 3,
and so on...
the final message is "FLRX"
Each letter will be the value of itself + the value of the ...
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1answer
57 views
How does Fialka manage to have a letter encipher unto itself?
http://www.cryptomuseum.com/crypto/fialka/index.htm
Fialka was an electromechanical rotor machine.
How does it manage to have a letter encipher unto itself. I realize it does something clever by ...
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Is the Caesar cipher really a cipher?
In this lecture by Dan Boneh on Coursera it was stated at minute 03:37 that
The Caesar cipher, actually, is not a cipher at all. And the reason is that it doesn't have a key. What a Caesar cipher ...
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1answer
6k views
Finding a Caesar cipher key given encrypted message and part of decrypted message?
How can I find the Caesar cipher key if I have an encrypted message and part of the decrypted message? For example: I know that the message ends with a constant set of words, but the length of the key ...
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2answers
187 views
Does shift cipher with non-uniform plain text probability have perfect secrecy?
I am having a hard time grasping the perfect secrecy concept. (I have already tried solving a couple of similar problems, so please don't think I am trying to get you guys to do my work, I really am ...
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187 views
How to decrypt Vigenère ciphered text?
The method I am using: For example: we have to decrpyt one message
VVHQWVVRMHUSGJG
Step 1 Find the length
...
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1answer
687 views
How to decode a Playfair message with a partial key?
I've been given a Playfair ciphered message and a partial key, where a few key letters are missing:
Corrupted key (? stands for a missing letter): ...
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1answer
218 views
Is there a general way to crack this graph cipher? [closed]
Every coded message has a numerical key, it can be a number any digits long. Each decoded letter of the message is placed on separate points of a 10 by 10 coordinate graph. Each letter is represented ...
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How do you determine which classical technique was used?
For a class assignment we had to encrypt a message of at least 140 characters using only one of the classical cryptographic techniques. For extra credit we can decrypt someone else's message. I figure ...
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1answer
343 views
Why don't homophones hide multiple-letter patterns?
I am reading about mono-alphabetic ciphers, which are prone to letter frequency analysis. To counter this, we can provide multiple substitutions, known has homophones for a single letter e.g. e could ...
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1answer
350 views
M-94 disk cipher keyspace
If the M-94 had only 10 disks, what would be the keyspace of the resulting cipher and what is the useful keypspace of the 10 disk cipher?
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1answer
94 views
Has the Linear Congruent Generator ever been used in any of the early crypto algorithms?
The Linear Congruent random number generator is the simplest kind of pseudo random number generator. I know that its now long broken. But I am curious -- has it ever been used in any of the early ...
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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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363 views
Does adding more characters to the Enigma rotors improve crypto strength?
This seems like an obvious question but I haven't been able to find it, so here goes:
Enigma is based on an alphabet of A-Z (26 characters); obviously this directly affects message content (e.g. ...
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129 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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2answers
14k views
How to find the keyword of the Playfair cipher, given the plaintext and the ciphertext?
I know how the Playfair cipher works. I would like to know how to find the keyword of the Playfair cipher, given some ciphertext and the corresponding plaintext.
For example:
encrypted: ...
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Crack multiple One-Time-Pads with same key [duplicate]
I've got 12 pads, all with a length of 50 characters, except the last one. I also know, that the key has got a length of 50 and that the key has been re-used on all of the 12 pads.
What do I have to ...
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Concatenated Key Questions related to Poly-alphabetic Substitution and Columnar Transposition
I am working on a degree module, and have been tasked with designing an Encryption/Decryption algorithm. I hope to receive some help with a couple of questions, if possible.
Apologies if terminology ...
