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.
2
votes
0answers
51 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
<...
0
votes
0answers
35 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 ...
0
votes
1answer
136 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 ...
0
votes
0answers
24 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 ...
1
vote
0answers
41 views
Does the Richard Sorge cipher still provide good security?
Is the cipher used by soviet spy Richard Sorge still sufficiently secure nowadays?
1
vote
2answers
40 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 ...
2
votes
1answer
81 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?
1
vote
1answer
49 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
votes
0answers
140 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:
...
0
votes
1answer
46 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....
1
vote
1answer
79 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
38 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 ...
1
vote
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 ...
1
vote
0answers
100 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 ...
0
votes
1answer
109 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-...
2
votes
0answers
81 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 ...
1
vote
1answer
129 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
votes
1answer
201 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 ...
0
votes
1answer
49 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 ...
2
votes
2answers
136 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 ...
0
votes
4answers
882 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 ...
0
votes
1answer
322 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 ...
0
votes
1answer
741 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 ...
...
1
vote
2answers
60 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 $E′$...
11
votes
2answers
363 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 ...
5
votes
0answers
199 views
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 ...
2
votes
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
votes
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? ...
1
vote
1answer
799 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
votes
1answer
365 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 ...
0
votes
3answers
200 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 ...
2
votes
3answers
637 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....
7
votes
2answers
463 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?
15
votes
5answers
16k views
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 ...
-1
votes
1answer
506 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
votes
1answer
350 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
votes
1answer
235 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
votes
3answers
274 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 ...
4
votes
0answers
426 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 $...
3
votes
1answer
127 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=...
2
votes
1answer
476 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
votes
1answer
323 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(...
2
votes
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 ...
1
vote
2answers
216 views
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 ...
1
vote
1answer
62 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 ...
14
votes
1answer
4k views
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 ...
1
vote
1answer
7k 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 ...
0
votes
2answers
228 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 ...
1
vote
1answer
829 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): ...
1
vote
1answer
243 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 ...
