lib25519: Install

Prerequisites:

python3 (for: build, test)
recommended python3-capstone (for: build)
gcc and/or clang (for: build)
valgrind (for: build, test)
libcpucycles (for: build, bench)
librandombytes (for: build, test, bench, run)

Make sure to test the compiled library. The tests check for subtle security problems that can be created by compilers. A compiled version of lib25519 is not supported unless it passes the full test suite.

For sysadmins

To install in /usr/local/{include,lib,bin,man}:

./configure && make -j8 install

For developers with an unprivileged account

Typically you'll already have

export LD_LIBRARY_PATH="$HOME/lib"
export LIBRARY_PATH="$HOME/lib"
export CPATH="$HOME/include"
export MANPATH="$HOME/man"
export PATH="$HOME/bin:$PATH"

in $HOME/.profile. To install in $HOME/{include,lib,bin,man}:

./configure --prefix=$HOME && make -j8 install

For distributors creating a package

Run

./configure --prefix=/usr && make -j8

and then follow your usual packaging procedures for the build/0/package files:

build/0/package/include/lib25519.h
build/0/package/lib/lib25519*
build/0/package/bin/lib25519*
build/0/package/man/man3/*.3
build/0/package/man/man1/*.1

More options, part 1: s2n-bignum

Before ./configure you can run ./use-s2n-bignum to download various assembly implementations from s2n-bignum and integrate them into lib25519. These implementations save time on some CPUs, but the more important feature of these implementations is that they are formally verified to work correctly on all inputs. The implementations cover, for 64-bit Intel/AMD/ARM, the main nG and nP subroutines used in X25519 key generation and shared-secret generation, along with a lower-level pow/inv25519 subroutine having further applications.

You can run

./configure --prioritizeverified

to prioritize implementations marked as verified even when they are slower. Beware that this will still fall back to unverified implementations for primitives and CPUs that do not have verified implementations.

More options, part 2: architectures

You can run

./configure --host=amd64

to override ./configure's guess of the architecture that it should compile for.

Inside the build directory, 0 is symlinked to amd64 for --host=amd64. Running make clean removes build/amd64. Re-running ./configure automatically starts with make clean.

A subsequent ./configure --host=arm64 will create build/arm64 and symlink 0 -> arm64, without touching an existing build/amd64. However, cross-compilers aren't yet selected automatically.

More options, part 3

One further ./configure option is supported for developers: --no-trim.

All ./configure options not listed above are experimental and not supported. Use them at your own risk.

Version: This is version 2026.06.13 of the "Install" web page.