# 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.

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### Why is the Keyspace of a Substitution Cipher not 2^26 but 2^88

It is known that a cipher has a keyspace of cryptographic algorithm whose key length is $n$ is given by $2^n$, but the keyspace of the substitution cipher is $2^{88}$ which is an approximation of $26!$...
60 views

### How to decrypt a combination of transposition and substitution cipher text

I'm having problems decrypting a cipher text that has an transposition cipher applied to it but also a substitution cipher. I don't know in which order they were applied. Does anyone know what steps I ...
58 views

### Decrypting a substitution cipher, but with symbols instead of letters

I'm trying to decipher a message encrypted by a substitution cipher (probably a monosubstitution). But the problem is, that we have symbols instead of letters (letters were substituted for random ...
178 views

### How to distinguish a transposition cipher from a simple substitution cipher only given a ciphertext?

I am working on one interesting question. There is a ciphertext that has 10,000 letters. We need to distingish whether this ciphertext was encrypted by a transposition cipher or a simple subsitution ...
109 views

### Most efficient way to crack a monoalphabetic substitution cipher with spacing intact

I've got a cipher I've been challenged to crack by hand. It's a monoalphabetic substitution cipher, and the English spacing is intact, so all of the words are the right size. Is there a more ...
76 views

### What kind of decryption is used in this example? [closed]

I stumbled upon an encrypted text on a website, to which Google had brought me, showing me the plain text also. So does anyone know what kind of encryption was used here and how to decrypt it, so I ...
168 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?
119 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. ...
114 views

### modified substitution permutation networks

I have a model of substitution permutation networks, modified as follows: instead of iterating $n$ times a round(each of which is composed of the key mixing phase, substitution S-BOX) and ...
107 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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### Proving at most one affine permutation mapping $x$ to $u$ and $y$ to $v$ with $x,y \in \mathbb{Z}_n$ and $\gcd(x−y,n) = 1$

Suppose that $x,y \in \mathbb{Z}_n$ with $\gcd(x−y,n) = 1$. Prove that for any $u,v \in \mathbb{Z}_n$ there is at most one affine permutation mapping $x$ to $u$ and $y$ to $v$.
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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 ...
429 views

### Cryptoanalysis using Frequency Analysis

I have read some documents to decrypt ciphertext without a key using Frequency analysis. here are my questions: If the most occurring Char is not 'E' then how do we start? Let's say I have this ...
100 views

### How does an S-box introduce confusion

I'm trying to find the logic for introducing the S-box, but having trouble understanding why. In a simple cipher, e.g. c = pt xor key I understand that I can ...
56 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 ...
308 views

### Does Format Preserving Encryption have significant advantages over a randomly generated lookup table?

I have a need to anonymise phone numbers so that I can carry out testing and analysis work on telecoms data sets and comply with GDPR. I typically receive a batch of a few hundred thousand events ...
235 views

### How to decrypt a simple substitution cipher where space is also encrypted by a character

I am trying to decrypt a text data encrypted with a simple substitution method with 2 steps. First, shift the alphabet of the source text by a few characters. For example, if we shift by 2 characters,...
346 views

### What is an accurate definition for a 'Monoalphabetic substitution cipher' and why does it provide a poor level of security

From my research online, I am confused about the difference between a 'monoalphabetic cipher' and 'monoalphabetic substitution cipher'. However, I have got my answer from the websites Kifanga and ...
92 views

### Non-exact substitution cyphers

Picture a simple substitution cypher of text with length $N$(spaces optional): Plain : ATTACK AT DAWN Encrypted: ELLETI EL HEPG Another way to represent the encrypted text is with an $N \times N$ ...
739 views

### What's the difference between confusion/diffusion and mode of operation?

I understand the concepts of confusion (substitution) and diffusion (permutation). My understanding of what a mode is that it's an algorithm that lets us encrypt arbitrary message size. i.e. AES is ...
93 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 ...
50 views

### Common cyphers where the plaintext is the same length as the cyphertext

What are the common cyphers where the cyphertext is always the same length as the plaintext? I can think of XOR cyphers, and letter-substitution cyphers, what others are there?
106 views

### Cryptanalysis in the middle ages — publications

Are there any publications, articles or literature discussing cryptanalysis and crypt breaking techniques in the middle-ages? I have seen various manuals from the middle ages describing various types ...
582 views

### Decrypt Base64 Encoded Monoalphabetic Cipher

I'm attempting to decrypt a body of ciphertext which has been encrypted using a monoalphabetic cipher. The trouble I'm having is that the plaintext was base64 encoded before being encrypted. In this ...
304 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 ...
56 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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### Which cipher text is easiest to guess the plaintext?

I know that there are approximately 2^88 diff erent permutations of 26 characters. The stream cipher A5/1, which generates a binary keystream using three irregularly clocked LFSR, and has a 64-bit key....
397 views

### Cryptanalysis affine cipher and substitution cipher

1) Consider the chosen-plaintext attack on the simple substitution cipher. How many chosen plaintext characters suffice to uniquely determine the key? My answer was: 26! 2) Consider the chosen-...
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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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### Combine Sinkov score bigrams, trigrams and quadgrams

I am trying to break a special substitution cipher (where the text is divided into several columns and each column has its own substitution table). Currently I am trying hill-climbing. For the score, ...
95 views

### What effect does adding noise to a substitution cipher have?

Assume I assigned the letters A-Z to random numbers in the range of 0-100. The mapping of plaintext characters to ciphertext values constitutes my cipher alphabet(and key). I encrypt a message using ...
63 views

### A name for “word fingerprints” (technique for breaking monoalphabetic substitutional ciphers)

I have invented a technique for breaking monoalphabetic substitution ciphers. However, I believe that such simple thing must have been already invented. I wonder how is this called. I call it “word ...
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### Number of Substitution boxes

How many possible 16 bit S-boxes exist? (AES uses 8 bit substitution boxes) I first taught of calculating 128(keysize in bits)/8(bits) =16, but I believe it's wrong.
689 views

### XOR and cipher stream

I am new to cryptography and I am very confused. In fact, I am so confused that I have trouble providing a suitable title for my thread... I know that a Substitution Cipher is designed to substitute ...
608 views

### How does Permutation and Substitution work?

I'm a little confused on how permutation and substitution works, I've been reading about S-DES and how it goes through P-Boxes and S-Boxes but what goes on inside P or S in the algorithm? Are these p ...
41 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 ...
321 views

### Identifying and attacking a proposed cipher (multiple substitution)

I'm just beginning to dip my toes into cryptography and a friend has proposed a cipher and challenged me to figure out how to attack it. I know the process used to encrypt, but am having a hard time ...
378 views

### Relative security of this polyalphabetic cipher system?

A friend described this cipher to me the other day, but if it has an official name, I'm unaware of it. The same 26 cipher alphabets that are used in the Vigenère cipher are used here, but rather than ...
975 views

### How to encrypt this using caesar cipher?

I recently had an exercise that read: Encrypt the message "easy question" using Caesar Cipher defined as: C=E(P)=(Pi+3) mod 26 What is this formula and how to solve it?
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### How to start a classical cryptanalysis on a Substitution + Shift cipher? [closed]

i was thinked about problem of Cyrpto. At first glance, it looks like a simple classic password problem, but there are a lot of difficulties to think about the way the two encryption schemes are ...
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### I have a encryption png file [closed]

I have a encryption png. I open the file in hex editor and I saw it: ...
2k 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, ...
414 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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### 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 ...
386 views

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

Given a keyword, you can encrypt a message using alphabetical substitution like this: ...
145 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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### 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, /...
7k 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 ...