Questions tagged [substitution-cipher]

A substitution cipher is an encryption algorithm which works by replacing plaintext units with corresponding ciphertext units, following some rule depending on the key.

Filter by
Sorted by
Tagged with
5
votes
2answers
3k views

How to break homophonic substitutions and nomenclators with too many symbols?

Early attempts to thwart frequency analysis attacks on ciphers involved using homophonic substitutions, ie. some letters map to more than one ciphertext symbol. The earliest known example of this, ...
3
votes
1answer
507 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?
7
votes
2answers
2k views

Can you help me find a cryptanalytic way to attack a simple monoalphabetic substitution cipher algorithm?

I have decided to make a project at uni that requires me to crack a monoalphabetic substitution cipher. The text is an english text with spaces. The key is a permutation of the alphabet. This isn’t ...
1
vote
0answers
426 views

Substitution Cipher Help: Can't figure out keyword [closed]

Given a keyword, you can encrypt a message using alphabetical substitution like this: ...
5
votes
1answer
160 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
votes
1answer
3k views

How to decrypt a substitution cipher using a Base64 alphabet [duplicate]

Let us consider a cipher that works like the following: Plaintext is encoded to Base64. The characters in the encoded plaintext are substituted with a randomly shuffled character set (a-z, 0-9, A-Z, /...
3
votes
2answers
8k 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 ...
15
votes
2answers
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 ...
4
votes
2answers
487 views

Will compression help defeat single letter frequency attack against a mono alphabetic substitution cipher?

Alice has a long message to send. She is using mono alphabetic substitution cipher. She thinks that if she compresses the message it may protect the text from single letter frequency attack by Eve. ...
1
vote
1answer
10k 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 ...
1
vote
1answer
581 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 ...
1
vote
1answer
469 views

Frequency analysis [closed]

In a way or another, a text is encoded based on a alphabet layout; What if the layout is scrambled (based on a key) for every plain char (scramble layout, encode D, scramble, encode A etc) ? The ...
-1
votes
1answer
227 views

Same-length plaintext results in predictable ciphertext. Can a substitution cipher avoid this issue?

I started with a basic mixed-monoalphabetic substitution cipher. To work against predictable ciphertext generation, I introduced a modulo in my cipher whose purpose is to scramble the substitution in ...
6
votes
1answer
525 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. ...
1
vote
0answers
171 views

I Have An Encrypted Message [closed]

I am a newbie to cryptography and am stuck on decrypting a message. This message was received from a friend and I would like to crack it in order to respond. I have decrypted part of it but am unable ...
6
votes
1answer
1k views

Not-So-Simple Substitution Cipher?

The first go-to weakness when talking about substitution ciphers is frequency analysis. It assumes that there's a simple 1 to 1 character mapping between the plain text and the cipher text. Could a ...
5
votes
2answers
3k views

What is the diffrence between Feistel networks and SPN?

I recently read about the concept of Feistel Networks and Substitution Permutation Networks but what is exactly the difference between the two ?
4
votes
1answer
2k views

How to break a Quagmire 3 cipher?

What would be a good way to go about attacking a Quagmire 3 cipher? I understand that it is polyalphabetic with a key and an indicator. I have started by taking the cipher text, taking every n-th ...
4
votes
1answer
2k views

How to attack polyalphabetic affine cipher with only ciphertext?

How to attack polyalphabetic affine cipher with only the ciphertext? A polyalphabetic affine cipher can be seen as the composition of an affine cipher ($p \mapsto c \equiv a \times p + b \pmod{26})$ ...
1
vote
0answers
60 views

Deriving Minimum Description Length of Substitution Key

Given a plaintext: Now is the time for all good men to come to the aid of their country because the quick brown fox jumped over the lazy dog. and a substitution ciphertext: Mpe od yjr yo,r ...
14
votes
3answers
4k views

Does composing multiple substitution ciphers improve security?

Will using two substitution ciphers one after the another be more secure than using single substitution cipher?
3
votes
1answer
608 views

How would multiple uses of a vigenère cipher be decrypted on paper (classic)?

As far as I can tell (from reading the Wikipedia article about it) decrypting a message encrypted with the vigenère cipher is possible on paper. But what would happen if the message is encrypted ...
-1
votes
1answer
977 views

Perfect secrecy of affine cipher

Given any probability distribution P r on the set $\{k ∈ \mathbb{Z}_{26} : \gcd(k, 26) = 1\}$. Show that the Affine Cipher achieves perfect secrecy if the key (k, a) is used with probability $Pr(k) ·(...
2
votes
3answers
4k views

What is the difference between substitution cipher and block cipher?

I'm studying(and clearing my head) about block cipher. I started from Caesar Cipher which can be considered as a kind of substitution cipher (if my understanding is right). And an ideal substitution ...
2
votes
2answers
2k views

How to decode a (Vigenère?) substitution cipher? [closed]

I am trying to decode a message that I suspect has been encrypted with a Vigenère cipher: Utl zluuocp zsc rvzu hbcp ztvibfz vrabzz utl ilry. Utlal flal cb fbaiz, qszu zbsciz. Utvu cllihl vhzb dvil ...
4
votes
2answers
190 views

Research for video game: Novice cryptography concepts [closed]

I'm making a video game which has some basic cryptography as a main base for puzzle design. I'm hoping players will get great puzzle challenge and learn a few cryptography concepts through playing the ...
0
votes
0answers
57 views

How do substution-permutation networks work? [duplicate]

I understand what is going on in higher level. But I don't understand what's really going on in page 3 and 4 of this slide. Specifically, How $S_0$ and $S_1$ is used? What goes in what goes out? ...
2
votes
2answers
293 views

Determining Involutary Keys in Substitution Ciphers

How would I be able to show that a key $K=(a,b)$ is involutary for an Affine Cipher over the integers modulo n? Similarly, is there a way to generalize the conditions for a key to be involutary for a ...
3
votes
4answers
3k views

Can a book cipher be cracked without key?

Book cipher works this way : Choose a reference book. For each word find its position in the book. replace each word by its coordinates (ie: 2,3,4 = page 2, 3rd line, 4th word). How would somebody ...
-1
votes
1answer
167 views

Creating a custom 2 way encryption class [closed]

I am trying to make a simple 2 way encryption function that currently uses a substitute cipher for the encryption and an inverse substitution for the decryption. I want to move away from this ...
4
votes
1answer
831 views

Comparison Vigènere vs. Monoalphabetic cipher

I have a question for a class of secure communication, but I have no idea about how to proceed in order to answer it. I'll be very grateful to whom replies to me. Assuming that brute force attack ...
3
votes
1answer
141 views

What is the difference between LCG and Affine cipher?

What is the difference between LCG and Affine cipher? More specific: What are they used for, and what are the structural differences between them?
4
votes
1answer
82 views

Is frequency analysis a viable attack on non-text data encoded by substitution?

Is frequency analysis a viable attack on non-text data encoded by substitution (eg image and audio formats encoded with a substitution cipher)?
3
votes
0answers
127 views

How to overcome issues with big ciphers? E.g. with small vs. big Vigenére Ciphers

I understand that bigger ciphers show more recurring patterns and therefore should be easier (or at least faster) to decrypt as you'll have a better statistical analysis, being However if we use a ...
1
vote
0answers
424 views

Solving Vigenére with unknown alphabet

I'm trying to decrypt a cipher that I suppose has been encrypted with Vigenére. However I came about the following thought: The cipher consists of characters from [...
4
votes
1answer
796 views

Deciphering “easy” ciphers without hints

I've been keen on IT Security for a long time now and I've learned a lot about networking & security. However trying a "decryption challenge" I'm lacking what I think is basic encryption/...
2
votes
2answers
348 views

How exactly is an enigma simulation software supposed to encrypt alphabets?

EDIT: The model I'm trying to make is "Enigma 1". I learned initially about it from a book called "Code Book" and then looked at it in detail from its wikipedia page. The rotor wiring and other ...
7
votes
3answers
5k views

How does the ring settings of enigma change wiring tables?

EDIT: The model I'm trying to make is "Enigma 1". I learned initially about it from a book called "Code Book" and then looked at it in detail from its wikipedia page. The site wont allow me too add ...
1
vote
2answers
285 views

One time pad- XORing or substitution

I have come across 2 versions of otp while reading it and want to confirm it. they have taken a plain text consisting of alphabets where they are shifted and replaced by alphabets itself. XORing of ...
4
votes
4answers
3k views

Are specially designed fonts sometimes used in cryptography?

As a font designer, I was thinking that it would be very easy to design a special font that could either jumble characters of a language (or of a code) or simply (with the features offered by the OTF ...
2
votes
1answer
234 views

Compacting a substitution cipher key

In a substitution cipher, I recieve 3 bits and than I return another 3 bits. The key of this cipher could be a matrix represented as: ...
1
vote
1answer
1k views

Vigenère, auto-correlation vs Kasiski examination

What are the differences between 'Kasiski examination' and 'auto-correlation' ? In Cryptool site, they state that autocorrelation analysis is more efficient and clearer than the Friedman or Kasiski ...
1
vote
1answer
439 views

Why is a Feistel network not a type of substitution-permutation network?

I understand what substitution-permutation networks look like. I understand what Feistel networks and Feistel-like networks look like. A Feistel network or a Feistel-like network features substitution ...
1
vote
0answers
193 views

common ways / methods to try to break a SP network

I have a very little cryptography background (but a relatively solid maths background) so my below question is very general. Basically I have been given a SP network with an output to reverse. I ...
0
votes
1answer
90 views

One-one correspondance complete function

I am reading the paper by John B. Kam and Georges I. Davida (1979) titled Structured Design of Substitution-Permutation Encryption Networks. On page 749 it reads ...
1
vote
0answers
1k views

Deriving a decryption equation

Consider a very simple symmetric block encryption algorithm, in which 32-bits blocks of plaintext are encrypted using a 64-bit key. Encryption is defined as $C = (P\oplus K_L) \boxplus K_R$ where $...
1
vote
1answer
1k views

Base64 with shuffled alphabet

I have a base64 'cipher' text. I know that in clear text is a hidden XML document (I know nothing about its structure), but the base64 alphabet was somehow shuffled. Is there any smart way, how to ...
8
votes
3answers
5k views

How to perform frequency analysis of a substitution cipher using a Base64 alphabet

Let's imagine a cipher that works like the following: Plaintext is encoded to Base64. The characters in the encoded plaintext are substituted with a randomly shuffled character set(A-z, 0-9, -, _, =)....
1
vote
1answer
106 views

Available programs that can verify the working of a simple substitution cipher

Is there any tool available that can test whether a simple substitution cipher is working. I will put my scenario in detail. Lets say I built a simple substitution cipher that maps 8 bit data to 16 ...
0
votes
1answer
1k views

What is meaning of “Decipher the rest of the message by deducing additional words”?

I have an assignment in cryptography. I am not asking here answer, but meaning of question. This is a question : 2.4 The following ciphertext was generated using a simple substitution algorithm. ...