https://github.com/jedisct1/libsodium/blob/6d566070b48efd2fa099bbe9822914455150aba9/src/libsodium/crypto_sign/ed25519/ref10/keypair.c#L38
https://github.com/jedisct1/libsodium/blob/6d566070b48efd2fa099bbe9822914455150aba9/src/libsodium/crypto_kx/crypto_kx.c#L29