Botan is a BSD-licensed crypto library written in C++. It provides a wide variety of cryptographic algorithms, formats, and protocols. It has been considered stable since 2002. The license makes it free for use as part of any commercial or free software without restriction. Those who desire it can also purchase a commercial support contract, or arrange for custom development work.

Botan runs on Linux and most Unix systems, MacOS X, and Microsoft Windows. It is written with portability in mind, and has been used on x86, x86-64, IA-64, PowerPC, SPARC, Alpha, MIPS, and ARM processors, with a number of different C++ compilers. The library also includes optional platform-specific modules which provide services such as compression (using zlib or bzip2), entropy gathering, secure memory allocation, and support for hardware crypto devices. It also includes assembly implementations of key algorithms like low level MPI routines and SHA-1 for x86 and x86-64 processors.