Wendy McElroy relates one of the earliest examples of private encryption in the young American republic:
In America, the tug of war between privacy and forced access to encrypted data is as old as the nation’s formation. As always, forced access was executed by authorities against individuals.
In 1785, a resolution authorized the secretary of the Department of Foreign Affairs to open and inspect any mail that related to the safety and interests of the United States. The ensuing inspections caused prominent men, like George Washington, to complain of mail tampering. According to various historians, it also led James Madison, Thomas Jefferson and James Monroe to correspond in code. That is, they encrypted their letters to preserve the privacy of their political discussions.
The need for Founding Fathers to encrypt their correspondence is high irony. The intrusive post office against which they rebelled had been established specifically to provide a free flow of political opinion. In the 1770′s, Sam Adams urged the 13 colonies to create an independent postal system because the existing post office, established by the British, acted as a barrier to the spread of rebellious sentiment. Dorothy Ganfield Fowler in her book Unmailable: Congress and the Post Office observed, “He [Adams] claimed the colonial post office was made use of for the purpose of stopping the ‘Channels of publick Intelligence and so in Effect of aiding the measures of Tyranny.’”
Alas, the more government changes, the more oppression remains the same. Soon the Continental Congress itself wanted to declare some types of matter ‘unmailable’ because their content were deemed dangerous. Anti-Federalist letters and periodicals became one of the first types of information to become de facto unmailable. (Anti-federalists resisted centralized government and rejected a Constitution without a Bill of Rights.) During the ratification debates on the Constitution, the Anti-Federalists were unable to circulate their material through the Federalist-controlled post office.