Skype to use the Industry standard Signal Protocol that developed by Open Whisper Systems in 2013 for end-to-end encryption for voice calls.
At this time the user’s can make only one private conversation from a single device at a time and the messages will strike at the same device, but you can switch the conversations.
During the skype private conversation all the calls, messages and image/audio/video are encrypted.
How to Start Skype Private Conversation
1. Click on the +chat icon next to New Private Conversation.
2. Select the contact your list and invite to accept your invitation for Private Conversation.
3. Once the invitation accepted you can start the private conversation with the specific device. Note the invitation is valid only for 7 days.
4. During the conversation, you can switch anytime between the Skype and private conversation by hitting the tabs.
5. Deleting the conversation works same as like the regular chat and to end the private communication select “End Conversation” from chat header.