Building The Library

This document describes how to build Botan on Unix/POSIX and Windows systems. The POSIX oriented descriptions should apply to most common Unix systems (including OS X), along with POSIX-ish systems like BeOS, QNX, and Plan 9. Currently, systems other than Windows and POSIX (such as VMS, MacOS 9, OS/390, OS/400, …) are not supported by the build system, primarily due to lack of access. Please contact the maintainer if you would like to build Botan on such a system.

Botan’s build is controlled by, which is a Python script. Python 2.6 or later is required.

For the impatient, this works for most systems:

$ ./ [--prefix=/some/directory]
$ make
$ make install

Or using nmake, if you’re compiling on Windows with Visual C++. On platforms that do not understand the ‘#!’ convention for beginning script files, or that have Python installed in an unusual spot, you might need to prefix the command with python or /path/to/python:

$ python ./ [arguments]

Configuring the Build

The first step is to run, which is a Python script that creates various directories, config files, and a Makefile for building everything. This script should run under a vanilla install of Python 2.6, 2.7, or 3.x.

The script will attempt to guess what kind of system you are trying to compile for (and will print messages telling you what it guessed). You can override this process by passing the options --cc, --os, and --cpu.

You can pass basically anything reasonable with --cpu: the script knows about a large number of different architectures, their sub-models, and common aliases for them. You should only select the 64-bit version of a CPU (such as “sparc64” or “mips64”) if your operating system knows how to handle 64-bit object code - a 32-bit kernel on a 64-bit CPU will generally not like 64-bit code.

By default the script tries to figure out what will work on your system, and use that. It will print a display at the end showing which algorithms have and have not been enabled. For instance on one system we might see lines like:

INFO: Skipping (dependency failure): certstor_sqlite3 sessions_sqlite3
INFO: Skipping (incompatible CPU): aes_power8
INFO: Skipping (incompatible OS): darwin_secrandom getentropy win32_stats
INFO: Skipping (incompatible compiler): aes_armv8 pmull sha1_armv8 sha2_32_armv8
INFO: Skipping (no enabled compression schemes): compression
INFO: Skipping (requires external dependency): bearssl boost bzip2 lzma openssl sqlite3 tpm zlib

The ones that are skipped because they are require an external dependency have to be explicitly asked for, because they rely on third party libraries which your system might not have or that you might not want the resulting binary to depend on. For instance to enable zlib support, add --with-zlib to your invocation of All available modules can be listed with --list-modules.

You can control which algorithms and modules are built using the options --enable-modules=MODS and --disable-modules=MODS, for instance --enable-modules=zlib and --disable-modules=xtea,idea. Modules not listed on the command line will simply be loaded if needed or if configured to load by default. If you use --minimized-build, only the most core modules will be included; you can then explicitly enable things that you want to use with --enable-modules. This is useful for creating a minimal build targeting to a specific application, especially in conjunction with the amalgamation option; see The Amalgamation Build.

For instance:

$ ./ --minimized-build --enable-modules=rsa,eme_oaep,emsa_pssr

will set up a build that only includes RSA, OAEP, PSS along with any required dependencies. Note that a minimized build does not by default include any random number generator, which is needed for example to generate keys, nonces and IVs. See Random Number Generators on which random number generators are available.

The option --module-policy=POL enables modules required by and disables modules prohibited by a text policy in src/build-data/policy. Additional modules can be enabled if not prohibited by the policy. Currently available policies include bsi, nist and modern:

$ ./ --module-policy=bsi --enable-modules=tls,xts

Cross Compiling

Cross compiling refers to building software on one type of host (say Linux x86-64) but creating a binary for some other type (say MinGW x86-32). This is completely supported by the build system. To extend the example, we must tell to use the MinGW tools:

$ ./ --os=mingw --cpu=x86_32 --cc-bin=i686-w64-mingw32-g++ --ar=i686-w64-mingw32-ar
$ make
$ file botan.exe
botan.exe: PE32 executable (console) Intel 80386, for MS Windows

You can also specify the alternate tools by setting the CXX and AR environment variables (instead of the –cc-bin and –ar-command options), as is commonly done with autoconf builds.

On Unix

The basic build procedure on Unix and Unix-like systems is:

$ ./ [--enable-modules=<list>] [--cc=CC]
$ make
$ ./botan-test

If that fails with an error about not being able to find, you may need to set LD_LIBRARY_PATH:

$ LD_LIBRARY_PATH=. ./botan-test

If the tests look OK, install:

$ make install

On Unix systems the script will default to using GCC; use --cc if you want something else. For instance use --cc=icc for Intel C++ and --cc=clang for Clang.

The make install target has a default directory in which it will install Botan (typically /usr/local). You can override this by using the --prefix argument to, like so:

$ ./ --prefix=/opt <other arguments>

On some systems shared libraries might not be immediately visible to the runtime linker. For example, on Linux you may have to edit /etc/ and run ldconfig (as root) in order for new shared libraries to be picked up by the linker. An alternative is to set your LD_LIBRARY_PATH shell variable to include the directory that the Botan libraries were installed into.

On macOS

A build on macOS works much like that on any other Unix-like system.

To build a universal binary for macOS, you need to set some additional build flags. Do this with the flag –cc-abi-flags:

--cc-abi-flags="-force_cpusubtype_ALL -mmacosx-version-min=10.4 -arch i386 -arch ppc"

On Windows


The earliest versions of Windows supported are Windows 7 and Windows 2008 R2

You need to have a copy of Python installed, and have both Python and your chosen compiler in your path. Open a command shell (or the SDK shell), and run:

$ python --cc=msvc --os=windows
$ nmake
$ botan-test.exe
$ nmake install

Botan supports the nmake replacement Jom which enables you to run multiple build jobs in parallel.

For MinGW, use:

$ python --cc=gcc --os=mingw
$ make

By default the install target will be C:\botan; you can modify this with the --prefix option.

When building your applications, all you have to do is tell the compiler to look for both include files and library files in C:\botan, and it will find both. Or you can move them to a place where they will be in the default compiler search paths (consult your documentation and/or local expert for details).

For iOS using XCode

For iOS, you typically build for 3 architectures: armv7 (32 bit, older iOS devices), armv8-a (64 bit, recent iOS devices) and x86_64 for the iPhone simulator. You can build for these 3 architectures and then create a universal binary containing code for all of these architectures, so you can link to Botan for the simulator as well as for an iOS device.

To cross compile for armv7, configure and make with:

$ ./ --os=ios --prefix="iphone-32" --cpu=armv7 --cc=clang \
                 --cc-abi-flags="-arch armv7"
xcrun --sdk iphoneos make install

To cross compile for armv8-a, configure and make with:

$ ./ --os=ios --prefix="iphone-64" --cpu=armv8-a --cc=clang \
                 --cc-abi-flags="-arch arm64"
xcrun --sdk iphoneos make install

To compile for the iPhone Simulator, configure and make with:

$ ./ --os=ios --prefix="iphone-simulator" --cpu=x86_64 --cc=clang \
                 --cc-abi-flags="-arch x86_64"
xcrun --sdk iphonesimulator make install

Now create the universal binary and confirm the library is compiled for all three architectures:

$ xcrun --sdk iphoneos lipo -create -output libbotan-2.a \
               iphone-32/lib/libbotan-2.a \
               iphone-64/lib/libbotan-2.a \
$ xcrun --sdk iphoneos lipo -info libbotan-2.a
Architectures in the fat file: libbotan-2.a are: armv7 x86_64 armv64

The resulting static library can be linked to your app in Xcode.

For Android

Instructions for building the library on Android can be found here.

Emscripten (WebAssembly)

To build for WebAssembly using Emscripten, try:

CXX=em++ ./ --cc=clang --cpu=llvm --os=emscripten

This will produce bitcode files botan-test.bc and botan.bc along with a static archive libbotan-2.a which can linked with other modules. To convert the tests into a WASM file which can be executed on a browser, use:

   --preload-file src/tests/data botan-test.bc -o botan-test.html

Supporting Older Distros

Some “stable” distributions, notably RHEL/CentOS, ship very obsolete versions of binutils, which do not support more recent CPU instructions. As a result when building you may receive errors like:

Error: no such instruction: `sha256rnds2 %xmm0,%xmm4,%xmm3'

Depending on how old your binutils is, you may need to disable BMI2, AVX2, SHA-NI, and/or RDSEED. These can be disabled by passing the flags --disable-bmi2, --disable-avx2, --disable-sha-ni, and --disable-rdseed to

Building Applications


Botan usually links in several different system libraries (such as librt or libz), depending on which modules are configured at compile time. In many environments, particularly ones using static libraries, an application has to link against the same libraries as Botan for the linking step to succeed. But how does it figure out what libraries it is linked against?

The answer is to ask the botan command line tool using the config and version commands.

botan version: Print the Botan version number.

botan config prefix: If no argument, print the prefix where Botan is installed (such as /opt or /usr/local).

botan config cflags: Print options that should be passed to the compiler whenever a C++ file is compiled. Typically this is used for setting include paths.

botan config libs: Print options for which libraries to link to (this will include a reference to the botan library itself).

Your Makefile can run botan config and get the options necessary for getting your application to compile and link, regardless of whatever crazy libraries Botan might be linked against.


No special help exists for building applications on Windows. However, given that typically Windows software is distributed as binaries, this is less of a problem - only the developer needs to worry about it. As long as they can remember where they installed Botan, they just have to set the appropriate flags in their Makefile/project file.

Language Wrappers

Building the Python wrappers

The Python wrappers for Botan use ctypes and the C89 API so no special build step is required, just import

See Python Bindings for more information about the Python bindings.