This is the 'null cipher' [1]. A modern, digital scheme similar to this is called 'chaffing and winnowing' [2]. Both are steganography rather than encryption,

This is the 'null cipher' [1]. A modern, digital scheme similar to this is called 'chaffing and winnowing' [2]. Both are steganography rather than encryption, but the intent is the same -- to communicate securely over an insecure channel. [1] https://en.wikipedia.org/wiki/Null_cipher https://en.wikipedia.org/wiki/Null_cipher [2] https://en.wikipedia.org/wiki/Chaffing_and_winnowing https://en.wikipedia.org/wiki/Chaffing_and_winnowing