A from scratch C++ (with slight inline assembly) implementation of ChaCha20 & Poly1305 stream cipher described in RFC - 8439.

tests:

All test from RFC-8439 is implemented here and is inside the tests folder.

• x86_64 or aarch64 architecture
• little endian system

If your system does not have these requirements, it might produce wrong results or might not even compile.

Note: one byte is equivalent to one unsigned char, If we have an array with a size of 5 bytes, that is an array of type unsigned char with 5 elements.

/**Encryption.
 * 
 * @param outputCipher resulting cipher text output, 
 * The size of outputCipher in bytes is equivalent to textLen.
 * 
 * @param outputTag resulting 128bit / 16 byte array,
 * GENERATED after ENCRYPTION.
 * 
 * @param inputText plain text to be ENCRYPTED.
 * 
 * @param textLen size of the inputText in bytes.
 * 
 * @param AAD Arbitrary length additional authenticated data.
 * 
 * @param AAD_len size of the AAD in bytes.
 * 
 * @param key a 256-bit key or 32 byte unsigned char array.
 * 
 * @param nonce number only once.
*/
ChaCha20_Poly1305::aead_encrypt(
    unsigned char       *outputCipher,
    unsigned char       *outputTag,
    const unsigned char *inputText,
    size_t               textLen,
    const unsigned char *AAD,
    size_t               AAD_len,
    const unsigned char *key,
    const unsigned char *nonce
);

/**Decryption.
 * 
 * @param outputText recovered plain text output, 
 * The size of outputText in bytes is equivalent to cipherLen.
 * 
 * @param outputTag resulting 128bit / 16 byte array,
 * GENERATED after DECRYPTION.
 * 
 * @param inputCipher cipher text to be DECRYPTED.
 * 
 * @param cipherLen size of the input inputCipher in bytes.
 * 
 * @param AAD Arbitrary length additional authenticated data.
 * 
 * @param AAD_len size of the AAD in bytes.
 * 
 * @param key a 256-bit key or 32 byte unsigned char array.
 * 
 * @param nonce number only once.
*/
ChaCha20_Poly1305::aead_decrypt(
    unsigned char       *outputText,
    unsigned char       *outputTag,
    const unsigned char *inputCipher,
    size_t               cipherLen,
    const unsigned char *AAD,
    size_t               AAD_len,
    const unsigned char *key,
    const unsigned char *nonce
);

To know if the message is authentic:

The outputTag of generated by encryption should match the outputTag generated by decryption.

1. The sender will send the encrypted cipher text along with the encrypted tag.

2. Then the receiver will decrypt the cipher text, the decryption function will generate the output recovered plain text and the output decryption tag.

3. The receiver then compares the sender's encryption tag to the generated output decryption tag; if both tag matched / is-equal then the message was authentic / not altered.

There are TWO WAYS to use the library, either using the header only mode, or building the static library.

• Using header only

  Directly include the Header-Mode-Chaha20-Poly1305.hpp in your source code, and you can directly compile it without building the static library.

  #include "Header-Mode-Chaha20-Poly1305.hpp"

  But you always need to enable the optimization flags for this method to work.

  g++ main.cpp main.out -O2

  clang++ main.cpp main.out -O2

• Static Build with GNU-GCC Linux makefiles

  Build & install static library

  make -f staticlib
  sudo make -f staticlib install

  Run tests (optional)

  make -f staticlib build_test
  

  Include #include <ChaCha20-Poly1305.hpp> in your program then compile with -lchacha20

  g++ main.cpp -o main.out -lchacha20
  

  To uninstall library

  sudo make -f staticlib uninstall
  

  Clean Up compiled objects

  make -f staticlib cleanup
  

• Static Build with Clang Linux makefiles

  Build static library with clang

  make -f staticlib CC=clang++
  sudo make -f staticlib install

  Run tests with clang (optional)

  make -f staticlib build_test CC=clang++
  

  Include #include <ChaCha20-Poly1305.hpp> in your program then compile with -lchacha20

  clang++ main.cpp -o main.out -lchacha20
  

  To uninstall library

  sudo make -f staticlib uninstall
  

  Clean Up compiled objects

  make -f staticlib cleanup
  

• Static Build with Mingw64 Windows makefiles

  Build & install static library

  mingw32-make -f staticlib
  mingw32-make -f staticlib install INSTALL_PREFIX=(path/to/mingw64)

  Run tests (optional)

  mingw32-make -f staticlib build_test
  

  Include #include <ChaCha20-Poly1305.hpp> in your program then compile with -lchacha20

  g++ main.cpp -o main.out -lchacha20
  

  To uninstall library

  mingw32-make -f staticlib uninstall INSTALL_PREFIX=(path/to/mingw64)
  

  Clean Up compiled objects

  mingw32-make -f staticlib cleanup
  

You can also modify the installation path in linux by setting up a new value for the INSTALL_PREFIX= when executing the make build commands similar to what is shown in the windows build.