[tech] Integrity checks for Gemini pages

[nervuri]

On Thu, 2021-05-20, nothien@uber.space wrote:
> Sorry, but that's just wrong.  TLS already provides the mandatory
> close_notify signal (and there have been discussions about it before on
> this ML) for indicating that the complete text has been transferred.

We can't rely on close_notify, unfortunately.  According to Lupa [1],
"33.3 % of URLs do NOT send a proper TLS shutdown (application close).
Even 26.7 % of those who return status 20 are in that case."

[1] gemini://gemini.bortzmeyer.org/software/lupa/stats.gmi

> And every single authenticated encryption method provided with TLS
> ensures that the communicated data is the same at both ends - bit flips
> and the like are detected and such malformed packets are dropped
> appropriately.  One of the mechanisms for this verification is Poly1305
> - check it out if you're interested in how and why these work.

You're referring to the transfer, but data may be corrupted server-side,
on disk or in RAM.