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end-to-end
End-To-End is a crypto library to encrypt, decrypt, digital sign, and verify signed messages (implementing OpenPGP)
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SurveyJS
Open-Source JSON Form Builder to Create Dynamic Forms Right in Your App. With SurveyJS form UI libraries, you can build and style forms in a fully-integrated drag & drop form builder, render them in your JS app, and store form submission data in any backend, inc. PHP, ASP.NET Core, and Node.js.
With that in mind, secure messaging in a browser is a nightmare. Google tried to figure out a way to do end-to-end in a browser, mostly in the context of e-mail but it could be extended to chat applications. They wrote up a threat model that you really should read. They identified five threat sources within the architecture and six more that they acknowledge but don't delve into. They also discuss four UI-based threats, four message-based, four key-based, and two cryptographic threats, and each of those threats has subthreats. Finally, they wrap with three "Other" threats. They dropped the project soon after.