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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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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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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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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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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Levels of strength: The Caesar Cipher
SITREP: I am deciding what form of "Random" Number generation would fit best for a Caesar Cipher that encrypts each letter with a different integer as a shift. This encryption is being handled via C# ...
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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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What is the keyspace of ROT-13?
Today I was having a discussion with my cryptography lecturer about the keyspace of a ROT-13 cipher. He argues that the keyspace is 0 because it doesn't have a key.
Could anyone explain to me why the ...
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Correct way to read a given permutation cipher?
In some literature I am reading – where they are explaining the permutation cipher – they have two examples, which encrypt a small block of text. But they seem to contradict each other:
First ...
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What are requirements for this grille?
I'm trying to program a Cardan grille, but I can't find requirements for grille. In my case, grille is square matrix A with $N$ x $N$ size, and elements are $0$ or $1$ (where $1$ means that it is hole)...
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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 ...
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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)...
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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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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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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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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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Number of different substitution alphabet ciphers possible with given conditions?
If you consider a 26 letter alphabet, and a cipher where 24 of the letters are sent to themselves, and only 2 letters switch, how many different substitution alphabet ciphers are there, and what ...
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How to solve custom made ciphers? [closed]
How would you go about solving basic custom made ciphers - e.g. one generated from this website http://www.wikihow.com/Write-a-Custom-Cipher-Carefully?
This is solving it without knowing the method ...
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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 ...
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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 ...
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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!
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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, ...
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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 ...
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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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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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Analysis of the Vigenere cipher
Im just starting out learning some cryptoanalysis techniques. I came across an idea which analyzes the vigenere cipher. Essentially the video explains that there is a standard english probability ...
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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 ...
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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 ...
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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. ...
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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: ...
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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 ...
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About LFSR based M209 Cipher Machine
Can some one please express M209 Cipher Machine in terms of LFSR with Diagram or any simple method?
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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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Using Alberti Disks to Create a Strong Cipher
Could one use three different disks set at different positions and encrypt a strong message?
For example:
Wheel 1: A = J
Wheel 2: A = E
Wheel 3: A = B
The first letter is encrypted using 1, and then ...
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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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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 ...
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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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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 ...
user8339
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Best non-digital cipher?
Is there a cipher that was considered the undisputed best before the computer age? (This is not supposed to be a discussion; it's either a yes or no.)
Please give a brief description why it is yes ...
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How would you name and/or describe this algorithm?
First up: this is not a decoding request or anything. This is about terminology.
Twice per year, we email another department to ask for a new licence file for their software. They are always slow to ...
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Help defining a shift cipher mathematically
For an assignment question, I am trying to prove formally that double encryption with two keys by the shift-cipher encryption function results in a shift cipher as well.
If the Shift-cipher encryption ...
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For calculating the index of coincidence for each sequence
I was learning about the finding the key length reading the following web site...
http://practicalcryptography.com/cryptanalysis/stochastic-searching/cryptanalysis-vigenere-cipher/
and I really don't ...
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Different patterns of different paterns, wildcard
I'm not realy experienced with programming and such but I am wondering if the following could be implemented in, lets say, python
we have the following ciphertext sequence
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What are some approaches to attack an triple key polyalphabetic cipher when the IV key and PT key are known?
The cipher is an triple key polyalphabetic cipher also known as an Quagmire IV by the ACA. An example would be here: Quagmire IV example and info (pardon the ads)
I posses the IV key and the PT key. ...
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Cryptanalysing Affine cipher
I am trying to cryptanalyse a cipher–text encrypted by Affine cipher.
The encryption formula is: $c = f(x) = (ax+b)\bmod m$, where $a$ and $b$ are unknown constants; $x$ is a plain-text symbol, and $...
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Could this be a cipher or not? [closed]
I am trying to solve a puzzle, and I think have to solve a cipher. But I'm not actually sure what I have to do ... Example :
...
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How to Calculate Digraphic/Trigraphic Index of Coincidence?
How do you calculate the digraphic and trigraphic IOCs and the same expected IOCs? I'm aware of the formula for calculating the single letter IOC which is given at this formula but I can't find the ...
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How do the notch and window positions on an Enigma machine correlate?
I am having difficulty visualizing the stepping process.
The permutation of Wheel I of Enigma I is as follows:
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Is there any known/standard encoding or cipher method that uses a 64-character alphabet from byte 30 (ASCII `0`) to byte 6F (ASCII `o`)?
Is there any known/standard encoding or cipher method that uses a 64-character alphabet from byte 30 (ASCII 0) to byte 6F (ASCII ...
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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 ...
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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...
