## Cryptology ePrint Archive: Report 2000/010

The Security of Chaffing and Winnowing

Mihir Bellare and Alexandra Boldyreva

Abstract: This paper takes a closer look at Rivest's chaffing-and-winnowing paradigm for data privacy. We begin with a \textit{definition} which enables one to determine clearly whether a given scheme qualifies as chaffing-and-winnowing.'' We then analyze Rivest's schemes to see what quality of data privacy they provide. His simplest scheme is easily proven secure but is ineffient. The security of his more efficient scheme ---based on all-or-nothing transforms (AONTs)--- is however more problematic. It can be attacked under Rivest's definition of security of an AONT, and even under stronger notions does not appear provable. We show however that by using a OAEP as the AONT one can prove security. We also present a different scheme, still using AONTs, that is equally efficient and easily proven secure even under the original weak notion of security of AONTs.

Category / Keywords: secret-key cryptography / Message authentication, symmetric