Passwords have been stolen just by listening to keyboard click noises. Why could a typewriter be any different? A relatively straightforward codebook analysis of keypress noises plus a hidden markov model plus a Viterbi algorithm will allow you calculate the highest probability sequence of letters for a given sequence of sounds and timings between sounds even in German!
Mind you, they have to be able to get a sound bug in there, but that might be malware-infected computers nearby the typewriters.
Anyhow, basically, the technology used to do automatic speech recognition would make short work of tapping typewriters, so they’re fooling themselves if they think this’ll make much difference.
BTW, I have a strong suspicion that the Germans’ outrage is all a big charade. Every major country has big spy operations. The NSA is neither unique nor the first of its kind. The Germans could not have been ignorant of at least the general nature NSA’s dealings before Snowden, so while they openly object, secretly, this is business as usual. By doing this, they fool their people into thinking they’re not being spied on by their own government and, using the US as a scapegoat, they also generate a degree of solidarity. Russians spy operations, of course, are way worse, so their objections are the same bullshit. And the Chinese government is all about lying to, well, basically everyone while they use both capitalism and cyberwarfare to take over the world and control everyone, so their recent statement about the iPhone is also a crock of shit.
This reminds me of Andrew Cuomo’s push to restore trust in government. The whole idea is disingenuous. Governments, like any large organization, are only going to do what the people need only with checks & balances and transparency.
And as a final note, I believe that the stated purpose of the NSA is a good one: Mine publically available data to identify terrorist activity. That sounds like a good thing to do. It’s the illegal violations of privacy that are wrong. They violate our rights because it’s inconvenient to get the info they need some other way. It’s also inconvenient for me to work a regular job instead of selling drugs. There are much more convenient ways to achieve my goals that I avoid because they are wrong. To do their job, the NSA needs to find clever ways to acquire the information they need WITHIN THE LAW.