Given the Snowden leaks and everyone's experience with what Facebook etc. do with our data, I wouldn't call that a "benign" adversary at all. Besides, even if Signal itself is benign, someone who manages to hack the Signal infrastructure might not be.

> The alternative to using SGX in these situations is to hand over the data in the clear to Signal servers.

This is not correct. The alternative would be to tell users to choose a passphrase with enough entropy. In that case, SGX wouldn't be necessary. Unfortunately, they didn't do that, so now a lot of users have chosen a short PIN and their data will be compromised should SGX ever fail to live up to its promises. (This is what I meant by "Signal PIN UI fuckup" – the word "PIN" alone suggests choosing a short number over a long passphrase.)