Method and apparatus for encrypting and transferring electronic mails

• US 6,289,105 B1
• Filed: 07/26/1996
• Issued: 09/11/2001
• Est. Priority Date: 07/28/1995
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Murota, Masao
• Primary Examiner(s): Barrón, Jr., Gilberto
• Assistant Examiner(s): Seal, James
• Application Number:
  US08/690,169
• Time in Patent Office: 1,873 Days
• Field of Search: 380/21, 380/49, 380/286, 380/282, 380/285, 379/100.08, 379/93.24, 455/412, 709/206, 709/207, 713/152, 713/167, 713/176, 713/181
• US Class Current: 380/286
• CPC Class Codes: H04L 2463/062 applying encryption of the keys cryptographic mechanisms or cryptographic arrangements for key distribution using key encryption key H04L9/0822
• CPC Class Codes: H04L 51/00 User-to-user messaging in packet-switching networks, transmitted according to store-and-forward or real-time protocols, e.g. e-mail
• CPC Class Codes: H04L 63/045 wherein the sending and receiving network entities apply hybrid encryption, i.e. combination of symmetric and asymmetric encryption cryptographic mechanisms or cryptographic arrangements using a plurality of keys or algorithms H04L9/14

Abstract

A scheme for encrypting and transferring electronic mails which enables the realization of the information management regarding encrypted electronic mails by an electronic mail manager, and the transfer control regarding encrypted electronic mails. A management encryption key information is produced by encrypting the message encrypting key according to a public-key cryptography by using a prescribed management public key, in addition to the usual sender'"'"'s encryption key information and each receiver'"'"'s encryption key information. The encrypted electronic mail is then constructed from the encrypted message, the sender'"'"'s encryption key information, each receiver'"'"'s encryption key information and the management encryption key information. At a time of transferring the electronic mail, whether this electronic mail is an encrypted electronic mail or not is identified and whether a transfer of this electronic mail is permitted or not is judged according an identification result.

Claims

1. An electronic mail encryption apparatus, comprising:

message encrypting means for encrypting a message of an electronic mail according to a secret-key cryptography by using an encryption key, to produce an encrypted message;

encryption key encrypting means for encrypting the encryption key according to a public-key cryptography by using each one of public keys of a sender and receivers of the electronic mail and a management public key corresponding to an electronic mail manager, to respectively produce encryption key information for each one of the sender and the receivers of the electronic mail and a management encryption key information; and

encrypted electronic mail constructing means for constructing an encrypted electronic mail by using the encrypted message, the encryption key information for each one of the sender and the receivers of the electronic mail, and the management encryption key information.

2. The apparatus of claim 1, further comprising:

public key acquisition means for acquiring the public keys of the sender and the receivers of the electronic mail according to a header information of the electronic mail; and

management public key acquisition means for acquiring the prescribed management public key independently from the public key acquisition means.

3. The apparatus of claim 1, further comprising:

management header information adding means for adding the electronic mail manager to a receiver information in a header information of the electronic mail.

4. The apparatus of claim 3, further comprising:

public key acquisition means for acquiring the public keys of the sender and the receivers of the electronic mail and the prescribed management public key according to the header information of the electronic mail to which the electronic mail manager is added by the management header information adding means.

5. The apparatus of claim 3, wherein the encrypted electronic mail constructing means constructs the encrypted electronic mail by also using the header information of the electronic mail to which the electronic mail manager is added by the management header information adding means.

6. The apparatus of claim 3, wherein the encrypted electronic mail constructing means constructs the encrypted electronic mail by also using the header information of the electronic mail to which the electronic mail manager is not yet added by the management header information adding means.

7. A method for encrypting an electronic mail, comprising the steps of:

(a) encrypting a message of the electronic mail according to a secret-key cryptography by using an encryption key, to produce an encrypted message;

(b) encrypting the encryption key according to a public-key cryptography by using each one of public keys of a sender and receivers of the electronic mail and a management public key corresponding to an electronic mail manager, to respectively produce encryption key information for each one of the sender and the receivers of the electronic mail and a management encryption key information; and

(c) constructing an encrypted electronic mail by using the encrypted message produced at the step (a), and the encryption key information for each one of the sender and the receivers of the electronic mail and the management encryption key information produced at the step (b).

8. The method of claim 7, further comprising the steps of:

(d) acquiring the public keys of the sender and the receivers of the electronic mail according to a header information of the electronic mail; and

(e) acquiring the prescribed management public key independently from the step (d).

9. The method of claim 7, further comprising the step of:

(f) adding the electronic mail manager to a receiver information in a header information of the electronic mail.

10. The method of claim 9, further comprising the steps of:

(g) acquiring the public keys of the sender and the receivers of the electronic mail and the prescribed management public key according to the header information of the electronic mail to which the electronic mail manager is added by the step (f).

11. The method of claim 9, wherein the step (c) constructs the encrypted electronic mail by also using the header information of the electronic mail to which the electronic mail manager is added by the step (g).

12. The method of claim 9, wherein the step (c) constructs the encrypted electronic mail by also using the header information of the electronic mail to which the electronic mail manager is not yet added by the step (g).

13. An electronic mail encryption and transfer apparatus, comprising:

message encrypting means for encrypting a message of an electronic mail according to a secret-key cryptography by using an encryption key, to produce an encrypted message;

encryption key encrypting means for encrypting the encryption key according to a public-key cryptography by using each one of public keys of a sender and receivers of the electronic mail and a management public key corresponding to an electronic mail manager, to respectively produce encryption key information for each one of the sender and the receivers of the electronic mail and a management encryption key information;

encrypted electronic mail constructing means for constructing an encrypted electronic mail by using the encrypted message, the encryption key information for each one of the sender and the receivers of the electronic mail, and the management encryption key information; and

transfer means for transferring said encrypted electronic mail constructed by the encrypted electronic mail constructing means by checking whether said encrypted electronic mail contains the management encryption key information or not, and judging that a transfer of said encrypted electronic mail to be transferred is permitted unless said encrypted electronic mail is found to be not containing the management encryption key information.

14. A method for encrypting and transferring an electronic mail, comprising the steps of:

(a) encrypting a message of the electronic mail according to a secret-key cryptography by using an encryption key, to produce an encrypted message;

(b) encrypting the encryption key according to a public-key cryptography by using each one of public keys of a sender and receivers of the electronic mail and a management public key corresponding to an electronic mail manager, to respectively produce encryption key information for each one of the sender and the receivers of the electronic mail and a management encryption key information;

(c) constructing an encrypted electronic mail by using the encrypted message produced at the step (a), and the encryption key information for each one of the sender and the receivers of the electronic mail and the management encryption key information produced at the step (b); and

(d) transferring said encrypted electronic mail constructed at the step (c) by checking whether said encrypted electronic mail contains the management encryption key information or not, and judging that a transfer of said encrypted electronic mail to be transferred is permitted unless said encrypted electronic mail is found to be not containing the management encryption key information.