The case this 2016 letter is about was not a request to break phone encryption in general. The government asked Apple to assist only in getting into a few specific phones for a specific reason, under the authority of a valid warrant. And many folks thought Apple had a strong legal case to say no.

Apple can’t search phones under the technology they announced, so the government can’t ask Apple for information about what is on people’s phones.

The government could only ask Apple to add hashes to an operating system that Apple runs. Structurally, this is the same as asking them to add functionality, which is what they objected to in 2016.

There is also a scope issue; if every iPhone has the same hash list, then the government is essentially fishing in everyone’s phone for a file. This is typically illegal. The government has to be specific about why they think a certain person/people have a piece of data before they can get a warrant to go get it.

Remember that (as the Twitter thread reminds us) the entire CSAM scanning effort is voluntary. The government is not forcing Apple to scan for CSAM, so how would they force Apple to scan for anything else?