Steven Bellovin on a recent find he made:
While doing some research on cryptographic history, I stumbled on what may be
one of the oldest algorithmic patents. That is, what is patented is an
algorithm, rather than a physical, biological, or electronic device. It’s US
patent 1,356,546, filed on December 4, 1918, and issued on October 26, 1920.
It’s Lyman Morehouse’s two-tape variant of Vernam’s one-time pad encryptor,
and is thus historically significant as well.