It is the right of the people to overthrow a barbaric government. When a government makes it their main concern to prevent dissent, rather than to uphold the constitution of our nation, they have strayed from their rights and duties as governors. There is nothing elegant about the government having the twitch ability to single-out every dissenting "radical" and efficiently terminate their "threat." A sudden change in political wind, and you could see your neighbor disappear because he was a "communist" rebel. Take the current wiretaps and surveillance and channel them back 40 years, and imagine the consequence on the populace. We need to prevent our government from being able to destroy dissent, and that includes invasive invasion of privacy, regardless of its current use and form. It will always be a horrendous potential energy, a spring ready to swallow up the good will of the nation.
Unless of course you mean common knowledge among computer scientists and cryptographers, in which case "common" is rather rare.