22. A computer-implemented method for exchanging private data, comprising the steps of: registering a plurality of data providers and a plurality of data buyers, the registration of each data buyer of the plurality of data buyers comprising receiving a legal representation from the data buyer that the data buyer will use any private data requested only in accordance with stated permissible uses; building, by the computer, a searchable index for each of the data buyers based on at least one index of private data for sale provided from one or more of the data providers; for each searchable index of each of the data buyers, encrypting and decrypting the searchable index by a public key unique to a respective one of the data buyers, when building the searchable indexes; receiving an encrypted query that identifies a data buyer of the plurality of data buyers and defines a purchase request for private data; retrieving the searchable index associated with the data buyer; determining, by the computer, whether at least one of the data providers maintains the private data requested by the data buyer by comparing the purchase request to the searchable index associated with the data buyer; encrypting and decrypting the searchable index associated with the data buyer by a private key unique to the data buyer, when determining whether at least one of the data providers maintains the private data requested; and in response to determining that at least one of the data providers maintains the private data requested, transmitting a message to the data buyer comprising information about the private data requested, the cost of purchasing the private data requested, and an anonymous exchange identifier code for uniquely identifying the private data requested.
22. A computer-implemented method for exchanging private data, comprising the steps of: registering a plurality of data providers and a plurality of data buyers, the registration of each data buyer of the plurality of data buyers comprising receiving a legal representation from the data buyer that the data buyer will use any private data requested only in accordance with stated permissible uses; building, by the computer, a searchable index for each of the data buyers based on at least one index of private data for sale provided from one or more of the data providers; for each searchable index of each of the data buyers, encrypting and decrypting the searchable index by a public key unique to a respective one of the data buyers, when building the searchable indexes; receiving an encrypted query that identifies a data buyer of the plurality of data buyers and defines a purchase request for private data; retrieving the searchable index associated with the data buyer; determining, by the computer, whether at least one of the data providers maintains the private data requested by the data buyer by comparing the purchase request to the searchable index associated with the data buyer; encrypting and decrypting the searchable index associated with the data buyer by a private key unique to the data buyer, when determining whether at least one of the data providers maintains the private data requested; and in response to determining that at least one of the data providers maintains the private data requested, transmitting a message to the data buyer comprising information about the private data requested, the cost of purchasing the private data requested, and an anonymous exchange identifier code for uniquely identifying the private data requested. 23. The computer-implemented method recited by claim 22 , wherein the private data requested comprises at least one of an address, a telephone number, and a social security number.