System and method for certificate exchange

1. A method performed by a trusted party for exchanging a plurality of certificates together certifying a principal's public key for a single substitute certificate, comprising the steps of:

receiving a plurality of certificates each comprising a respective public key and signature of a corresponding distinct certificate signer;

determining whether the plurality of certificates forms a certification chain that begins with a root certificate and ends with a final certificate, wherein (1) the certificate signer for the root certificate is trusted by the trusted party, and the respective certificate signers for all the certificates except the root certificate are not required to be trusted by the trusted party, and (2) each certificate in the chain, starting with the root certificate, is unexpired and attests for the validity of a subsequent certificate in the chain, and wherein only the final certificate attests to the validity of the principal's public key; and

only if the plurality of certificates forms such a certificate chain, then subsequently issuing a single substitute certificate signed by the trusted party and certifying the principal's public key, in exchange for the plurality of certificates.

2. The method of claim 1 wherein the signature on at least the final certificate comprises the signature of a certification authority on the certificate using the certification authority's private key.

3. The method of claim 1 wherein each certificate further comprises a serial number, an issuer name, and expiration time, and an algorithm identifier.

4. The method of claim 1 wherein each certificate satisfies the X.509 standard.

5. The method of claim 1 wherein the single substitute certificate has a relatively short expiration period.

6. The method of claim 1 wherein the receiving step comprises receiving a plurality of certificates from a principal.

7. The method of claim 1 wherein the receiving step comprises receiving a single certificate from a principal and receiving at least one other certificate from a certificate server.

8. The method of claim 1 wherein the verifying step comprises:

authenticating the digital signature that signed each certificate;

checking for each certificate in an appropriate certificate revocation list; and

verifying that the certificate has not been revoked.

9. The method of claim 1 wherein the method further comprises the step of determining the principal's access privileges;

and wherein the issuing step comprises issuing a single substitute certificate certifying the principal's public key and listing the principal's access privileges.

10. The method of claim 9 , wherein the determining step comprises: verifying a privilege attributes certificate by authenticating the signature on the privilege attributes certificate and determining that the privilege attributes certificate has not expired.

11. The method of claim 10 wherein the determining step comprises: receiving the privilege attributes certificate from a server.

12. A system including a trusted party for exchanging a plurality of certificates together certifying a principal's public key for a single certificate, comprising:

a receiver receiving a plurality of certificates, each comprising a respective public key and a signature of a corresponding distinct certificate signer;

a verification module for determining whether the plurality of certificates forms a certification chain that begins with a root certificate and ends with a final certificate, wherein (1) the certificate signer for the root certificate is trusted by the trusted party, and the respective certificate signers for all the certificates except the root certificate are not required to be trusted by the trusted party, and (2) each certificate in the chain, starting with the root certificate, is unexpired and attests for the validity of a subsequent certificate in the chain, and wherein only the final certificate attests to the validity of the principal's public key; and

a certification module operative, only if the plurality of certificates forms such a certificate chain, to issue a single substitute certificate signed by the trusted party and certifying the principal's public key, in exchange for the plurality of certificates.

13. The system of claim 12 wherein the signature on at least the final certificate comprises the signature of a certification authority on the certificate using the certification authority's private key.

14. The system of claim 12 wherein each certificate further comprises a serial number, an issuer name, and expiration time, and an algorithm identifier.

15. The system of claim 12 wherein each certificate satisfies the X.509 standard.

16. The system of claim 12 wherein the single substitute certificate has a relatively short expiration period.

17. The system of claim 12 wherein the verification module comprises:

a comparator for checking for each certificate in an appropriate certificate revocation list and verifying that the certificate has not expired; and

an authenticator for authenticating the digital signature that signed each certificate.

18. The system of claim 12 wherein the system further comprises:

a receiver receiving a privilege attribute certificate for the principal, the privilege attribute certificate describing the principal's access privileges; and

a verification module for verifying the privilege attribute certificate by authenticating the signature on the privilege attribute certificate and determining that the privilege attribute certificate has not expired;

and wherein the certification module issues a single substitute certificate certifying the principal's public key and listing the principal's access privileges.

19. The system of claim 12 wherein the system further comprises:

a receiver receiving access information for the principal, the access information describing the principal's access privileges; and

and wherein the certification module issues a single substitute certificate certifying the principal's public key and listing the principal's access privileges.