Back in the 1700s, if you wrote a private letter (on paper/parchment, with a feather ink pen as they had back then), in a foreign language, and the court system wanted to use this as evidence, could the government compel you to translate it?
Or, suppose you developed your own cipher (they had ciphers back then, I'm sure). Could the government compel you to decipher the message back then?
The use of encryption really isn't much different from this.
Back in the 1700s, if you wrote a private letter (on paper/parchment, with a feather ink pen as they had back then), in a foreign language, and the court system wanted to use this as evidence, could the government compel you to translate it?
Or, suppose you developed your own cipher (they had ciphers back then, I'm sure). Could the government compel you to decipher the message back then?
The use of encryption really isn't much different from this.