Method for certifying public keys in a digital signature scheme

• US 5,717,759 A
• Filed: 01/31/1997
• Issued: 02/10/1998
• Est. Priority Date: 04/23/1996
• Status: Expired due to Term

• Current Assignee: Assa Abloy AB
• Original Assignee: Silvio Micali
• Inventors: Micali, Silvio
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US08/792,974
• Time in Patent Office: 375 Days
• Field of Search: 380/9, 380/21, 380/23, 380/25, 380/29, 380/30, 380/49, 380/50
• US Class Current: 713/157
• CPC Class Codes: G06Q 20/02 involving a neutral party, e.g. certification authority, notary or trusted third party [TTP]
• CPC Class Codes: H04L 9/3255 using group based signatures, e.g. ring or threshold signatures
• CPC Class Codes: H04L 9/3263 involving certificates, e.g. public key certificate [PKC] or attribute certificate [AC]; Public key infrastructure [PKI] arrangements network architectures or network communication protocols for supporting authentication of entities using certificates in a packet data network H04L63/0823

Abstract

A method for certifying public keys of a digital signature scheme in a communications system is provided. The secure communications system is one in which there are at least two levels of authorities. A user presents a piece of data to an intermediate level authority who, upon verifying the data, causes an issuing authority to issue a certificate that the piece of data posses a given property. Although the certificate is compacted by not having it contain a pubic key of the intermediate authority, nonetheless, information is stored in order to keep the intermediate authority accountable.

Claims

1. A method for certifying a user public key in a system having a first authority with a first public key of a digital signature scheme and a second authority with a second public key of a digital signature scheme, the method comprising the steps of:

(a) presenting the user public key to the first authority for inspection of a given property;

(b) if the user public key passes inspection of the first authority, causing the second authority to receive an indication that the user public key has passed inspection of the first authority;

(c) having the second authority issue a compact certificate that indicates that the user public key possesses the given property, the compact certificate including a signature of the second authority but not including a public key of the first authority, wherein the compact certificate is equivalent to a conventional certificate containing the signature of the first authority, the public key of the first authority, and the public key of the second authority; and

(d) storing information in order to keep at least the first authority accountable for pieces of data that the first authority contributes to certify.

2. A method for certifying a user public key according to claim 1, wherein the given property of the user public key includes a given user choosing the user public key as his own public key in connection with at least one of:

a digital signature system and a public key encryption system.

3. A method for certifying a user public key according to claim 2, wherein inspection of the first authority includes identifying the user.

4. A method for certifying a user public key according to claim 3, wherein identifying the user includes verifying that the user knows the secret key associated with the user public key.

5. A method for certifying a user public key according to claim 2, wherein the information that is stored includes a signature of the first authority.

6. A method for certifying a user public key according to claim 1, wherein a certified public verification key of the second authority is sufficient to verify the certificate.

7. A method for certifying a user public key according to claim 1, wherein at least a portion of the information that is stored is stored in the certificate.

8. A method for certifying a user public key according to claim 7, wherein the at least a portion of the information that is stored identifies the first level authority.

9. A method for certifying a user public key according to claim 1, wherein the compact certificate includes a digital signature of the first authority.

10. A method for certifying a user public key PK_U where there are a plurality of authorities A_l, . . . , A_n that certify user public keys, where for each i<

n, authority A_i is configured to send authority A_i+l authenticated messages that are verifiable by A_i+l as having genuinely come from A_i, and authority A_n has a signing key SK_n and an associated certified public key PK_n, the method comprising the steps of;

(a) having a verification key PK_U presented to authority A_l ;

(b) having authority A_l verify, by means of a predetermined procedure, that PK_U possesses some properties out of a set of given properties;

(c) for all i<

n, having authority A_i send authority A_i+l a message indicating that PK_U has been verified to possess the given properties;

(d) issuing a compact certificate for PK_U that includes a signature provided using SK_n and does not include a public key of at least one authority A_i for some j<

n, wherein the compact certificate is equivalent to a conventional certificate containing the public key of A_j ; and

(e) storing accountability information that renders A_j accountable for keys that A_j contributes to certify.

11. A method for certifying a user public key according to claim 10, wherein the given property of PK_u includes a given user choosing PK_U as his own public key in connection with at least one of:

a digital signature system and a public key encryption system.

12. A method for certifying a user public key according to claim 11, wherein the inspection authority A₁ includes identifying the user.

13. A method for certifying a user public key according to claim 12, wherein the inspection includes verifying that the user knows the secret key associated with the user public key.

14. A method for certifying a user public key according to claim 11, wherein the certificate does not include public keys of any authorities A₁, . . . , A_n-1.

15. A method for certifying a user public key according to claim 10, wherein the certificate does not include the public key of at least some other authority A_j.

16. A method for certifying a user public key according to claim 10, wherein at least a portion of the information that is stored is stored in the certificate.

17. A method for certifying a user public key according to claim 16, wherein the at least a portion of the information that is stored in the certificate identifies authority A_k.

18. A method for certifying a user public key according to claim 10, wherein the certificate includes a digital signature of authority A_k.

19. A method for certifying a user public key according to claim 10, wherein at least one authority A_j+1 contributes additional data that is included in the certificate.

20. A method for certifying a user public key according to claim 10, wherein at least an authority A_j+1 sends authority A_j+2 a digital signature of authority A_j.

21. A method for certifying a user public key according to claim 10, wherein information is stored in the certificate that identifies all authorities A_j whose public key is not included in the certificate.

22. A method for certifying a user public key according to claim 10, wherein information is stored in the certificate that identifies all authorities who have contributed to certifying the user public key.