Fair Public-Key Cryptosystems

W e show how co construct public-key cryptosysterns that are fair, that is, strike a good balance, in a democratic country, between the needs of the Government and those of the Citizens. Fair public-key cryptosystems guarantee that: (1) the systcm cannot be misused by criminal organizations and ( 2 ) the Citizens rnantain exactly the same rights to privacy they currently have under the law. We actually show how to transform any public-key cryptosystem into a fair one. The transformed systems preserve the security and efficiency of the original ones. Thus one can still US^ whatever system he believes to be more secure, and enjoy the additional properties of fairness. Moreover, for today's best known cryptosystems. w e show that the transformation to fair ones is particulariy efficient and convenient. As we shall explain, our solution compares favorably with the Clipper Chip, the encryption proposal more recently p u t forward by the Clinton Administration for solving similar problems. Note For The Reader. Since privacy and law enforcement interest most of society, and since we would welcome an informed debate before m h g crucial policy decisions in this area. we have made a sincere attempt to reach a broad audience. W e thus hope that at least the goals and the properties of our approach will he understandable by the Government official and the Citizen who do not have any familiarity with cryptography. Further, the basic technical ideas of our solution --which are quite simple to begin with-are presented at a very intuitive level. so 3s to be enjoyable for the reader generally familiar with the field of cryptography, though not necessarily an expert in secure protocol design. Such an expert will not have great difficulty in filling in the formalization and the occasionally subtle technical details that have been omitted in this draft. (We actually hope to have given her sufficient indications to make her journey through this draft as short as possible.) W e apologize for not having the lime to write different versions of this paper for different audiences. E.F. Brlckell (Ed.): Advances In Cryptology CRYPT0 '92, LNCS 740, pp. 113-138, 1993. 0 Spnnger-Verlag Berlln Heidelberg 1993