libtls is part of libressl: http://www.libressl.org/

> LibreSSL is composed of four parts:

> The openssl(1) utility, which provides tools for managing keys, certificates, etc. > libcrypto: a library of cryptography fundamentals > libssl: a TLS library, backwards-compatible with OpenSSL > libtls: a new TLS library, designed to make it easier to write foolproof applications