Cipher Library — OOP Encryption in C++ with a C API

A C++ cipher library built around OOP principles (encapsulation, inheritance, polymorphism), exposed as a cross-compiler-safe dynamic library (DLL) through a C-style factory API, plus a CLI application that loads the library at runtime.

Features

• Abstract Cipher base class with pure virtual encrypt/decrypt methods and a virtual destructor for safe polymorphic cleanup.
• Caesar Cipher — letter-shift encryption with wraparound; non-letter characters pass through unchanged.
• Vigenère Cipher — keyword-based shifting cipher, cycling through the key while skipping non-letter characters.
• Bonus: a third cipher implementation (extra credit), added on top of the required two.
• C library API (factory pattern) — cipher_api.h exposes only extern "C" functions (cipher_create_caesar, cipher_create_vigenere, cipher_encrypt, cipher_decrypt, cipher_destroy, cipher_free), returning opaque handles so callers never touch C++ internals directly. This avoids name-mangling and vtable incompatibilities across compilers.
• Dynamic library loading at runtime — the CLI executable loads the DLL via LoadLibrary/dlopen, resolves function pointers manually, and unloads the library cleanly on exit.
• Memory-safe usage — every encrypt/decrypt call is paired with proper cipher_destroy/cipher_free cleanup to avoid leaks.

Tech Stack

C++ (library, OOP) / C (public API) — Windows (MSVC/MinGW)

How to Build & Run

Windows (MSVC):

cl /LD /EHsc cipher.cpp /Fe:cipher.dll
cl /EHsc main.cpp cipher.lib /Fe:cipher_app.exe
cipher_app.exe

Windows (MinGW):

g++ -shared -o cipher.dll cipher.cpp
g++ -o cipher_app.exe main.cpp -L. -lcipher

CLI Usage

The console application lets the user:

• choose a cipher type (Caesar / Vigenère / bonus cipher) and provide a key
• encrypt a message
• decrypt a message

Project Structure

• cipher.h — Cipher base class and derived cipher implementations
• cipher_api.h / cipher_api.cpp — C-style factory API, extern "C" exports
• main.cpp — CLI executable, dynamic library loading and function resolution

Author

Solo project completed as part of a Programming Languages Principles and Paradigms (PLPP) course, focused on object-oriented programming.