Are libtorrent transfers by default encrypted?

Sorry if this sounds blunt, still I wish to ask this question as I am new to libtorrent. I am trying to write a file transfer mechanism using libtorrent but I run to this interesting error while doing a CMake Build :

CMake Error at C:/Program Files (x86)/CMake/share/cmake-3.2/Modules/FindPackageHandleStandardArgs.cmake:138 (message):
  Could NOT find OpenSSL, try to set the path to OpenSSL root folder in the
  system variable OPENSSL_ROOT_DIR (missing: OPENSSL_LIBRARIES
  OPENSSL_INCLUDE_DIR)
Call Stack (most recent call first):
  C:/Program Files (x86)/CMake/share/cmake-3.2/Modules/FindPackageHandleStandardArgs.cmake:374 (_FPHSA_FAILURE_MESSAGE)
  C:/Program Files (x86)/CMake/share/cmake-3.2/Modules/FindOpenSSL.cmake:334 (find_package_handle_standard_args)
  CMakeLists.txt:162 (FIND_PACKAGE)

The error is pretty much understood - I have a missing dependancy and I could install it. But what I am wondering is whether the torrent traffic using the libtorrent is by default encrypted. I have already implemented an encryption scheme in my program and I wouldn't want to encrypt already encrypted data!