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Chaffing and winnowing

Chaffing and winnowing definition

Chaffing and winnowing is a cryptographic concept that provides confidentiality without using traditional encryption techniques.

The term originates from grain production. Chaff is the protective casing of the seeds. To winnow it, you have to throw it into the air so that the wind blows away the chaff, leaving only the grains.

In cybersecurity, chaffing means sending a message in plaintext but with a lot of noise added to the transmission. A cryptographic checksum accompanies each data packet. The receiver uses a secret key to calculate the correct checksums for each packet, winnowing the noise from the message.

Without the secret key, the wheat and the chaff packets look identical, so eavesdroppers can’t distinguish the real message from the noise.

History of chaffing and winnowing

Ronald L. Rivest, a professor at MIT, developed the concept of chaffing and winnowing in 1998. At the time, the export of strong encryption methods from the United States was highly regulated, and there was also a growing concern about the potential for domestic regulation and key escrow systems.

Rivest's proposal challenged the legal definition of encryption, demonstrating a way to provide confidentiality without technically encrypting data.

Chaffing and winnowing hasn’t been used widely — it’s a theoretical construct designed to provoke thought and challenge certain legal and regulatory ideas. Traditional encryption methods remain the standard for most applications that require data confidentiality.