Hi Heiner, have had the same problems as Jazzfood,
Installing the 2 SSL pakages didn’t solve the install problem for me.
At the end I made a remote desktop connection to the Pi and entered the install command for shell in a box
„sudo apt-get install shellinabox“
To be sure I installed open ssl (again?), don’t know if it was nessecary
„apt-get install openssl“
Remote control is working now.