This changes the TLS and certificate handling in a few ways:
- We always use TLS 1.2, both for sync connections (as previously) and
the GUI/REST/discovery stuff. This is a tightening of the requirements
on the GUI. AS far as I can tell from caniusethis.com every browser from
2013 and forward supports TLS 1.2, so I think we should be fine.
- We always greate ECDSA certificates. Previously we'd create
ECDSA-with-RSA certificates for sync connections and pure RSA
certificates for the web stuff. The new default is more modern and the
same everywhere. These certificates are OK in TLS 1.2.
- We use the Go CPU detection stuff to choose the cipher suites to use,
indirectly. The TLS package uses CPU capabilities probing to select
either AES-GCM (fast if we have AES-NI) or ChaCha20 (faster if we
don't). These CPU detection things aren't exported though, so the tlsutil
package now does a quick TLS handshake with itself as part of init().
If the chosen cipher suite was AES-GCM we prioritize that, otherwise we
prefer ChaCha20. Some might call this ugly. I think it's awesome.
The intention for this package is to provide a combination of the
security of crypto/rand and the convenience of math/rand. It should be
the first choice of random data unless ultimate performance is required
and the usage is provably irrelevant from a security standpoint.
GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3186
This replaces the current 3072 bit RSA certificates with 384 bit ECDSA
certificates. The advantage is these certificates are smaller and
essentially instantaneous to generate. According to RFC4492 (ECC Cipher
Suites for TLS), Table 1: Comparable Key Sizes, ECC has comparable
strength to 3072 bit RSA at 283 bits - so we exceed that.
There is no compatibility issue with existing Syncthing code - this is
verified by the integration test ("h2" instance has the new
certificate).
There are browsers out there that don't understand ECC certificates yet,
although I think they're dying out. In the meantime, I've retained the
RSA code for the HTTPS certificate, but pulled it down to 2048 bits. I
don't think a higher security level there is motivated, is this matches
current industry standard for HTTPS certificates.
