At least the Keybase code is open, so even if you can't personally validate that it's secure, someone else can.
Neither Dropbox nor Google encrypts and keeps the keys client side, so not trusting them is probably the right thing to do (also Dropbox has been misleading in the past about their security, so that's another reason one should be careful).
Neither Dropbox nor Google encrypts and keeps the keys client side, so not trusting them is probably the right thing to do (also Dropbox has been misleading in the past about their security, so that's another reason one should be careful).