The GNU Transport Layer Security Library is used to enable TLS decryption using an RSA private key.
If this library isn’t already installed or available as a package for your platform, you can get it at https://gnutls.org/.
We provide packages cross-compiled using MinGW32 at https://anonsvn.wireshark.org/wireshark-win64-libs/trunk/packages/ and https://anonsvn.wireshark.org/wireshark-win32-libs/trunk/packages/.