This project contains the implementation of the popular RSA cryptosystem in C++.
Currently the cryptosystem supports en-/decryption of a single character or a whole string.

The RSA key-length is currently 256 bit. The boost multiprecision subset is used for that key length implementation.
(It is a dynamic key-length implementation planned)

The complete implementation and all source files are in the subdirectory src/.
Src contains the three "main" classes, which are RSA, Encryptor and Decryptor.
Also there are two additional subdirectories math and tests.
Below is described what are the three modules and what is living in the math and tests subdirectories.

This is the main class for the encryption and decryption process.

RSA uses this class to encrypt data.
Encryptor does all neccessary calculation to encrypt the data.

RSA uses this class to decrypt data.
Decryptor does all neccessary calculation to decrypt the data.

This directory contains all mathematical algorithms the RSA cryptosystem uses.
Containing algorithms are the basic euclidean algorithm to calculate the greatest common divisor of two integers and the extended euclidean algorithm to calculate the inverse representants of the two input integers. One use case of the extended euclidean algorithm is to calculate one member of the secret key.

Contains unit tests.

First of all an instance of RSA has to be created.
RSA has two main functions encrypt() and decrypt(). Each two times, one for en-/decrypt strings and one for en-/decrypt characters.
The method signatures are the following:

//-----------------------------------------------------
// Encrypts a string
//
// str: string to be encrypted
//
// return: CryptoString; Structure which contains
//         encrypted message
//
CryptoString encrypt(string str);

//-----------------------------------------------------
// Decrypts a string
//
// str: string to decrypt
//
// return: string; Decrypted message
//
string decrypt(CryptoString str);

//-----------------------------------------------------
// Encrypts a string
//
// ch: character to be encrypted
//
// return: CryptoChar; Boost's 256bit integer which contains
//         the encrypted character
//
CryptoChar encrypt(char ch);

//-----------------------------------------------------
// Decrypts a string
//
// str: character to decrypt;  Boost's 256bit integer which contains
//      the decrypted character
//
// return: char; Decrypted character
//
char decrypt(CryptoChar str);

All together an example for an en-/decryption of a string:

try
{
  Crypto::RSA rsa(6907, 7687, 24);

  // Message to encrypt
  string in_str = "This is a bretty long message, with extra special caharacters and no deeber meaning!";

  // Encrypt message
  Crypto::CryptoString out_str = rsa.encrypt(in_str);
  // Decrypt message
  string res_str = rsa.decrypt(out_str);

  // Print to console
  std::cout << "input: " << in_str << " | output: " << res_str << "\n";
}
catch (std::exception &e)
{
  std::cout << e.what();
}

MIT License

Copyright (c) 2020 Sebastian Weninger

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.