chaffing and winnowing

Does anyone know of any serious work being done on developing the concepts of winnowing and chaffing, as outlined in Ronald L. Rivest's 1998 paper 'Confidentiality without Encryption'? (Or any other similar creative uses of MACs and authentication keys, for that matter? This line of thought certainly seems to have some interesting policy implications, particularly re. making the idea of forced key recovery obsolete. Any references to further papers or applications would be most welcome...thanks! ~Faustine. **** 'We live in a century in which obscurity protects better than the law--and reassures more than innocence can.' Antoine Rivarol (1753-1801).