Substitute passphrase in my post with shared symmetric key. It is still a string you have to enter on both ends.
if the underlying mechanisms just work in every case except for key mismatch and give you a good error message in that case, requiring your contractors to enter the same string in two devices that they already have to program is going to be hard for them to justify as a great additional expense.
if the underlying mechanisms just work in every case except for key mismatch and give you a good error message in that case, requiring your contractors to enter the same string in two devices that they already have to program is going to be hard for them to justify as a great additional expense.