Chaffing and Winnowing

Chaffing and winnowing is a cryptographic technique for transmitting confidential information that works without encryption.

The chaffing and winnowing technique uses normal, unencrypted transmission channels. The confidential text is combined with similar texts before transmission and a cryptographic checksum is applied.

Each message packet is provided with a unique serial number and a MAC code (Message Authentication Code), which are communicated to the recipient in advance. Then, the invented data packets, which have the same format as the legitimate ones, are added source-side. The legitimate data packets also have a serial number, but an invalid MAC code. The receiver can distinguish the legitimate from the invalid data packets by the MAC codes and thus sort out the information content.