In C++, a program to decrypt a substitution cipher can begin with a letter frequency analysis by reading the ciphertext, computing frequencies using a map, and then taking the necessary steps for decryption.
To write a program in C++ that decrypts a simple substitution cipher, and computes and displays the letter frequency counts, here's a high-level description:
- Accept the ciphertext as input from the user.
- Iterate through the ciphertext to compute the frequency of each letter.
- Display the letter frequencies to the user.
An example code snippet to count letter frequencies would look like this:
#include<iostream>
#include<string>
#include<map>
int main() {
std::string ciphertext;
std::map<char, int> frequency;
std::cout << "Enter the ciphertext: ";
std::cin >> ciphertext;
for (char c : ciphertext) {
if(isalpha(c)) {
frequency[tolower(c)]++;
}
}
for (auto& pair : frequency) {
std::cout << pair.first << ": " << pair.second << std::endl;
}
return 0;
}
The actual decryption would require a defined key or an analysis of the frequencies compared to the expected frequencies in regular text to guess the most likely
substitution. Physical decryption methods may vary based on the context and key.
Letter frequency analysis is a critical step in the decryption of simple substitution ciphers. In C++, one can achieve this using maps to store and count occurrences of each letter effectively.