I wonder if there is an open API to access WhatsApp through an internet protocol? The concrete question is:
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whatsapp
1) It looks possible. This info on Github describes how to create a java program to send a message using the whatsapp encryption protocol from WhisperSystems.
2) No. See the whatsapp security white paper.
3) See #1.
WhatsApp does not have a API available for public use. As you put it, it's a closed system.
However, they provide several other ways in which your iPhone application can interact with WhatsApp: through custom URL schemes, share extension and through the Document Interaction API.
There were several projects available that reverse engineered the WhatsApp webservice interfaces. However, to my knowledge all of them are now discontinued/defunct due to legal action against them from WhatsApp.
For mobile phone applications there is a limited URL-Scheme-API available on IPhone and Android (Android-intent possible as well).
Source: Stackoverflow.com