"Technical assistance" is very vague. If the FBI can legally compel Apple to produce a backdoored firmware for their phones, they can also compel Open Whisper

"Technical assistance" is very vague. If the FBI can legally compel Apple to produce a backdoored firmware for their phones, they can also compel Open Whisper Systems to produce a backdoored version of the Signal app to intercept all plaintext on the client side. Since almost everybody has automatic updates turned on, they won't even need to find a way to push the rogue version to the target's device. Every service that relies on a vendor-provided app is open to this kind of "technical assistance". Ditto for any webapp that relies on vendor-provided JavaScript crypto libraries. The vendor can "technically assist" themselves at any time to gain surveillance capabilities they previously did not have.