Chaffing and winnowing also bear some resemblance to encryption techniques. Indeed, the process of authenticating packets and then adding chaff achieves confidentiality, and so qualifies as encryption by anyone who uses a definition of encryption that is so broad as to include all techniques for achieving confidentiality. But this fails to note the special structure here, wherein a non-encrypting key-dependent first step (adding authentication) followed by a non-encrypting keyless second step (adding chaff) achieves confidentiality. Since the second step can be performed by anyone […], and since the first step (adding authentication) may be performed for other good reasons, we see something novel, where strong confidentiality can even be obtained without the knowledge and permission of the original sender.

Ronald L. Rivest, “Chaffing and Winnowing: Confidentiality without Encryption”