The short answer is that so long as the page is loaded entirely over TLS, and the TLS isn't stripped or subverted in any way, it's safe from MITM. Sharefest doesn't currently support TLS, so they would need to set that up prior to enabling end-to-end encryption.
The short answer is that so long as the page is loaded entirely over TLS, and the TLS isn't stripped or subverted in any way, it's safe from MITM. Sharefest doesn't currently support TLS, so they would need to set that up prior to enabling end-to-end encryption.