Method and apparatus for encrypting and transferring electronic mails

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).

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.

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.