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Users/user agents need to know whether to expect a connection to be secure. Unfortunately, you can't necessarily trust any random link you follow to reliably tell you. If I can get you to use HTTP when you should've used HTTPS, I might be able to sniff your traffic. If I can get you to use HTTPS when you should've used HTTP, it might be a DoS. Incidentally, this is the same problem as public key distribution. You need a trusted channel to receive public keys, and a trusted channel to know whether to use a public key. Why can't these be the same channel? Right now we have HSTS preloading[1] for the latter, but in that case why not preload certificates (or hashes thereof) too? Then we can finally cut out the middle-men and realize the truth: that the browser is the ultimate certificate authority. [1] https://hstspreload.appspot.com/ |
That is not worst case scenario. If someone can force http, they can also inject malicious code into the stream and do anything from bank transfers to create botnets. With the worst case scenario of always https being DoS, and worst case scenario of allowing http is code injection, I would prefer deprecating http in favor of https.