The TcpListener needs an X509Certificate to use for encryption. An easy way to set this up is to use the makecert.exe utility from Mircosoft.
First, you create a trusted root certificate:
makecert -pe -n "CN=Test And Dev Root Authority" -ss my -sr LocalMachine -sky signature -r "Test And Dev Root Authority.cer",Then you use this created cert to create a certificate for encryption:
makecert -pe -n "CN=apptest.com" -ss my -sr LocalMachine -sky exchange -eku 1.3.6.1.5.5.7.3.1 -is MY -ir LocalMachine -sp "Microsoft RSA SChannel Cryptographic Provider" -sy 12 apptest.com.cer
Be sure to copy the root authority certificate into you trusted root store.
An example of setting up a server is below, copied directly from here.