Communication system and method for securely communicating a message between correspondents through an intermediary terminal

1. A method, performed at an intermediary terminal, of communicating a message between correspondents in a communication system through the intermediary terminal, the method comprising:

registering a certificate of a public key of a first correspondent in a table in the intermediary terminal, the first correspondent being a wireless subscriber unit;

receiving from the first correspondent, subsequent to registering the certificate, a secure communication including said message, the message being a signed encrypted message comprising ciphertext encrypted under a public key of a recipient and a signature of the first correspondent on the message using a private key of the first correspondent;

receiving, along with the secure communication, a signature component comprising a hash of the signed encrypted message concatenated with a nonce and an identifier of the first correspondent, signed by the first correspondent using the private key of the first correspondent;

verifying said signature component;

recovering, when the signature component is verified, said identifier from said signature component;

retrieving the certificate of the public key of said first correspondent from the table using the recovered identifier;

signing the certificate with a private key of the intermediary terminal;

attaching to said secure communication said signed certificate; and

forwarding said secure communication and said signed certificate to a second correspondent

wherein registering comprises:

transferring by the intermediary terminal a public key of said intermediary terminal to said first correspondent; and

receiving at the intermediary terminal from said first correspondent, said public key of said first correspondent,

wherein said first correspondent has stored in memory a public key of a trusted party and said intermediary terminal has a certificate of said public key of said intermediary terminal signed by said trusted party,

wherein said first correspondent is arranged to verify said public key of said intermediary terminal with said public key of said trusted party, and

wherein said public key of said intermediary terminal is used by said first correspondent to sign said public key of said first correspondent for secure transfer to said intermediary terminal.

2. The method according to claim 1 wherein said nonce is unique to each communication.

3. The method according to claim 1 wherein said identifier is unique to said first correspondent and is associated with said first correspondent.

4. The method according to claim 1 wherein said second correspondent is a second intermediary terminal, which utilizes said certificate to determine the public key of said first correspondent.

5. The method according to claim 4 wherein said second intermediary terminal signs another message including said public key of said first correspondent to generate a signature of said another message, and forwards said secure communication and said signature of said another message to said recipient.

6. The method according to claim 5 wherein said recipient retrieves said public key of said first correspondent using said signature of said another message, and extracts said message from said secure communication.

7. The method according to claim 1 wherein said first correspondent forwards authorization information to said intermediary terminal during registration and said intermediary terminal verifies that said first correspondent is not prior registered with a certifying authority.

8. The method according to claim 7 wherein said authorization information includes an address particular to said first correspondent for identification by said certifying authority.

9. The method according to claim 1 wherein said identifier is transferred from said intermediary terminal to said first correspondent upon verification by a certifying authority.

10. The method according to claim 9 wherein transfer of said identifier is secured by the public key of said first correspondent and said private key of said intermediary terminal.

11. An intermediary terminal arranged for communicating a message between correspondents, the intermediary terminal comprising processing circuitry and memory arranged to:

register a certificate of a public key of a first correspondent in a table in the intermediary terminal, the first correspondent being a wireless subscriber unit;

receive from the first correspondent, subsequent to registering the certificate, a secure communication including said message, the message being a signed encrypted message comprising ciphertext encrypted under a public key of a recipient and a signature of the first correspondent on the message using a private key of the first correspondent;

receive, along with the secure communication, a signature component comprising a hash of the signed encrypted message concatenated with a nonce and an identifier of the first correspondent, signed by the first correspondent using the private key of the first correspondent;

verify said signature component;

recover, when the signature component is verified, said identifier from said signature component;

retrieve the certificate of the public key of said first correspondent from the table using the recovered identifier;

sign the certificate with a private key of the intermediary terminal;

attach to said secure communication said signed certificate; and

forward said secure communication and said signed certificate to a second of said correspondents,

wherein to register the certificate, the intermediary terminal is arranged to:

transfer a public key of said intermediary terminal to said first correspondent; and

receive from said first correspondent, said public key of said first correspondent,

wherein said first correspondent has stored in memory a public key of a trusted party and said intermediary terminal has a certificate of said public key of said intermediary terminal signed by said trusted party,

wherein said first correspondent is arranged to verify said public key of said intermediary terminal with said public key of said trusted party, and

wherein said public key of said intermediary terminal is used by said first correspondent to sign said public key of said first correspondent for secure transfer to said intermediary terminal.

12. The intermediary terminal according to claim 11 wherein said a nonce is unique to each communication.

13. The intermediary terminal according to claim 11 wherein said identifier is unique to said first correspondent and is associated with said one of said correspondents.

14. The intermediary terminal according to claim 11 wherein said second correspondent is a second intermediary terminal, which utilizes said certificate to determine the public key of said first correspondent.

15. The intermediary terminal according to claim 14 wherein said second intermediary terminal is configured to sign another message including said public key of said first correspondent to generate a signature of said another message, and forward said secure communication and said signature of said another message to said recipient.

16. The intermediary terminal according to claim 15 wherein said recipient is configured to retrieve said public key of said first correspondent using said signature of said another message, and extract said message from said secure communication.

17. A non-transitory computer-readable storage medium that stores instructions for execution by one or more processors to perform operations at an intermediary terminal for communicating a message between correspondents in a communication system through the intermediary terminal, the operations comprising:

registering a certificate of a public key of a first correspondent in a table in the intermediary terminal, the first correspondent being a wireless subscriber unit;

receiving from the first correspondent, subsequent to registering the certificate, a secure communication including said message, the message being a signed encrypted message comprising ciphertext encrypted under a public key of a recipient and a signature of the first correspondent on the message using a private key of the first correspondent;

receiving, along with the secure communication, a signature component comprising a hash of the signed encrypted message concatenated with a nonce and an identifier of the first correspondent, signed by the first correspondent using the private key of the first correspondent;

verifying said signature component;

recovering, when the signature component is verified, said identifier from said signature component;

retrieving the certificate of the public key of said first correspondent from the table using the recovered identifier;

signing the certificate with a private key of the intermediary terminal;

attaching to said secure communication said signed certificate; and

forwarding said secure communication and said signed certificate to a second correspondent,

wherein registering comprises:

transferring by the intermediary terminal a public key of said intermediary terminal to said first correspondent; and

receiving at the intermediary terminal from said first correspondent, said public key of said first correspondent,

wherein said first correspondent has stored in memory a public key of a trusted party and said intermediary terminal has a certificate of said public key of said intermediary terminal signed by said trusted party,

wherein said first correspondent is arranged to verify said public key of said intermediary terminal with said public key of said trusted party, and

wherein said public key of said intermediary terminal is used by said first correspondent to sign said public key of said first correspondent for secure transfer to said intermediary terminal.