Skype supports private message. It looks like its private message is encrypted using Signal Protocol.
I have this sample of Skype private message and need to decrypt the "content".
"clientmessageid": "10507111498039774744",
"messagetype": "EndToEndEncryption/EncryptedText",
"originalarrivaltime": "2020-01-27T05:53:17.571Z",
"encryptedkey": {
"d79ee36f-a499-49b7-ac9d-6091362e141a": "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"
},
"version": "1580104398186",
"fromdeviceid": "aee59f97-e1e9-4561-af80-4a0b4c6f2156",
"from": "https://azwcus1-client-s.gateway.messenger.live.com/v1/users/ME/contacts/8:prakash.tandukar",
"id": "1580104398186",
"conversationLink": "https://azwcus1-client-s.gateway.messenger.live.com/v1/users/ME/conversations/19:cd600a6ac9fd0fc43098250d506519ea3fae996a9ab5ed32b81734696b6e8325@encrypted.skype",
"type": "Message",
"conversationid": "19:cd600a6ac9fd0fc43098250d506519ea3fae996a9ab5ed32b81734696b6e8325@encrypted.skype",
"content": "UVpLGf93DMdW5sNpO+XnHp7xHpq5LtgZM/TcvxE9nT8M7ElyNiOVQWGB933cw/Cn",
"composetime": "2020-01-27T05:53:17.571Z"
The content is encrypted. There is also encryptedkey. I have been looking signal-protocol-pcl package for decyrpting content in c# but have not able to decrypt the content.