There is no such thing as the Whisper protocol, AFAIK. Signal uses the [_Signal_ protocol](https://en.wikipedia.org/wiki/Signal_Protocol#Properties%3Fwprov=sfla1), formerly known as _TextSecure_ due to Signal being a merge of the earlier (proprietary) projects _[TextSecure](https://en.wikipedia.org/wiki/TextSecure?wprov=sfla1)_ for encrypted messaging and _RedPhone_ for encrypted voice calls. The two projects were initially started by Whisper Systems, co-founded by Moxie Marlinspike and Stuart Anderson. The name of this company may be the cause of confusion, but the protocol has to my knowledge never been called anything else than TextSecure and subsequently Signal. Whisper Systems was acqui-hired by Twitter who then open-sourced both projects under the GPL license, after which the _Open Whisper Systems_ organization was created by Moxie to continue development on what later got merged into the Signal project as we see it today. The protocol uses the _[Double Ratchet](https://en.wikipedia.org/wiki/Double_Ratchet_Algorithm?wprov=sfla1)_ algorithm (a.k.a. _Axolotl Ratchet_) for cryptographic key exchange, invented specifically for secure messaging and use in Signal (although naturally open source and applicable for oher use cases too). Wikipedia (understandably) has a nice timeline over the various projects: https://en.wikipedia.org/wiki/File%3ASignal_timeline.svg End of nerd snipe transmission, over and out. :-)