Similar to other chat services, Skype users can now also have end-to-end encrypted conversations, but Microsoft has not enabled the functionality by default. Earlier this year it already became known that Microsoft and Open Whisper Systems partnered on adding end-to-end encryption to Skype.
Open Whisper System is the developer of the Signal Protocol that is used by e.g. WhatsApp, Facebook Messenger, Google Allo and Signal for end-to-end encryption of conversations. With end-to-end encryption the content of messages can only be accessed by the sender and the receiver of the message. Skype users who want to have end-to-end encrypted conversations have to choose, "New Private Conversation" from the compose menu or the recipients profile.
The receiver then has to accept an invitation for an encrypted conversation after which all messages in that conversation are end-to-end encrypted, until the users end the conversation. An user can only have one encrypted conversation on a single device at any given time. It's possible to continue the conversation on another device, but the messages that are sent and received are only available on the currently used device.
