Cryptography Stack Exchange
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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.

The term substitution cipher is mostly used for historical ciphers, in contrast to transposition ciphers. Substitution ciphers working on a small alphabet (i.e. small units, like characters or pairs of characters) are susceptible to statistical attacks, and should not be used.

Modern block ciphers (when used in ECB mode) are in principle substitution ciphers whose units are the blocks. These effectively have an alphabet size of 2block-size.

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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 substitution cipher? (Involutary keys are keys…
Cryptkeeper
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Existing dictionaries of popular words to help solve a random substitution cipher?

I'm trying to find faster ways to solve this: http://cryptogram.org/solve_cipher.html Actually lists of common words are good, but they are often limited to 1000 words. I found this, but I'm not sure which one to use, but the word list still seems…
jokoon
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Question on monoalphabetic substitution

Question: A stream of cipher operates on a data stream of 6-bit characters using a simple mono-alphabetic substitution technique. Estimate and explain the number of different substitution alphabets possible. The key is effectively the…
Aubergine
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symbol representation based cipher?

so i had an idea recently for a cipher. the idea is as follows: for every ascii character in the input, replace it with a corresponding sequence of 25 binary digits that, when arranged into a 5x5 grid, make an image that relates to the character.…
zackit
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Cracking a Shift Cipher that uses an Unknown Deterministic Scheduling Algorithm

Consider a shift cipher that has the following encryption scheme: The plaintext contains lowercase characters and spaces, is composed of English text, and is length 500. Thus, the message (and ciphertext) space is $\{\text{space}, a, b, ...,…
Dovi Salomon
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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 wrapping my head around a way to go about…
silentAitch
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I have a encryption png file

I have a encryption png. I open the file in hex editor and I saw it: 83 5A 44 4D 07 00 10 00 0A 0A 0A 07 43 42 4E 58 0A 0A 0B A5 0A 0A 0A D8 02 08 0A 0A 0A 78 C8 D2 F7 0A 0A 0A 0B 79 58 4D 48 0A A4 C4 16 E3 0A 0A 0A 0E 6D 4B 47 4B 0A 0A BB 85 01 F6…
Yair B.
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I Have An Encrypted Message

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 to complete the rest due to my incompetence. This…
Zack
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Substitution Cipher

For the Substitution Cipher, for functions such as $$f(x) = x^k \pmod{26}$$ or $$f(x) = x^k + k \pmod{26}$$ (functions that consist of x^k), why do the values of k=5 or k=7 or k > 10 have one-to-one mapping? I know 5 and 7 are relatively prime to…
bjpo027
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What is the difference between a substitution cipher and an oracle?

I was looking into the opaque authentication protocol and they discuss an oracle, which, if I understand it correctly is a projection $Z$ from $f$ to $g$ ($g$ at least the size of $f$), which maps inputs from $f$ to $g$. If $f$ and $g$ are the same,…
Koos Gadellaa
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How many different ciphertexts in repeated substitution cipher?

Consider an alphabet with 26 letters. Then a substitution cipher has $26!$ possible ciphertexts (with every letter substituted). What about repetive substitutions on a 5 letter word for example? How many different ciphertexts will result? Like…
cluster34
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Rotor that divides binary number by mod 3

Let's say we have transformer(?) A = $\{0;1 \}$, B = $\{0;1\}$, $Q = \{q_0,q_1,q_2\}$, where A - plaintext alphabet, B - encryption alphabet, Q - the set of states. The functions of the rotor are described as: $$q0 ◦ 0 → q0 \ \ \ q0 ∗ 0 → 0 \\ q0 ◦…
Gianni D'Adova
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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 symbols). What would be the best way to decrypt such…
Peter
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What kind of decryption is used in this example?

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 can decrypt the rest of the text? Encrypted…
Kaniee
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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 a normal substitution cipher. I then create a…
Chris
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