We don't guarantee fips140=only support in x/crypto, but chacha20poly1305 is special in that it's vendored into the standard library. We could wrap all the callsites, but it's more robust to just error out at construction time. Change-Id: I4b1e451bd250429c4c5c5b61c8b2141c6a6a6964 Reviewed-on: https://go-review.googlesource.com/c/crypto/+/728480 Reviewed-by: Roland Shoemaker <roland@golang.org> LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: David Chase <drchase@google.com> Auto-Submit: Filippo Valsorda <filippo@golang.org>