smb@research.att.com writes:

Btw -- I found the patent online via WWW; see http://town.hall.org/ and do the obvious. If you want just that single patent, go to ftp://ftp.town.hall.org/patent/data1/05276/05276737, or do the obvious ftp.

Following smb's suggestion, I WWW'ed to town.hall.org and started poking around. I found a second Micali "fair crypto-system" patent that also looks like it would cover Clipper. It is patent number 05315658 (the other was 05276737). I found it by traversing to http://town.hall.org/cgi-bin/srch-patent and searching using "public key" as the search criteria. The two patents seem vary similar, but it seems to me that the second patent more closely describes a system similar to Clipper: ----- NUM Claim Number: 7. Claim 7 7. A method, using a cryptosystem, for enabling a predetermined entity to monitor communications of users suspected of unlawful activities while protecting the privacy of law-abiding users, wherein one user has at least a secret decryption key, comprising the steps of: having trustees hold pieces of information that are guaranteed to include shares of a secret decryption key; and upon a predetermined request, having a given number of trustees each reveal the piece of information that includes the share of the secret decryption key to enable the entity to attempt to monitor communications to the user suspected of unlawful activities. NUM Claim Number: 8. 8. The method as described in claim 7 wherein upon the predetermined request all of the trustees each reveal the piece of information. [..] NUM Claim Number: 12. 12. A method, using a cryptosystem, for enabling a predetermined entity to confirm that users of a system exchange messages encrypted according to a predetermined algorithm, comprising the steps of: providing each user in the system with a secure chip containing at least one secret key unknown to the user; and having the user send encrypted messages using the secure chip; and with each encrypted message sent by a user, having the secure chip also send a data string, computed using the secret key, to guarantee the entity that the encrypted message was generated by the secure chip using the predetermined algorithm. NUM Claim Number: 13. 13. The method as described in claim 12 further including the steps of: providing trustees with pieces of information including shares of a secret key; and upon a predetermined request, having a given number of trustees send information including shares of the secret key to allow the entity to monitor communications to a suspect user. Jim_Miller@suite.com