Encryption to BCC recipients with S/MIME

• US 7,293,171 B2
• Filed: 01/21/2004
• Issued: 11/06/2007
• Est. Priority Date: 01/21/2004
• Status: Expired due to Fees

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Williams, Roy, Batthish, Karim, Davis, Malcolm, Wu, Jean
• Primary Examiner(s): Barron, Jr.; Gilberto
• Assistant Examiner(s): SAN JUAN, MARTINJERIKO P
• Application Number:
  US10/762,094
• Publication Number:
  US 20050160292A1
• Time in Patent Office: 1,385 Days
• Field of Search: 713/151, 713/152, 709/206
• US Class Current: 713/152
• CPC Class Codes: H04L 2209/16 Obfuscation or hiding, e.g. involving white box
• CPC Class Codes: H04L 2209/60 Digital content management, e.g. content distribution
• 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
• CPC Class Codes: H04L 63/065 for group communications cryptographic mechanisms or cryptographic arrangements for key management involving conference or group key H04L9/0833
• CPC Class Codes: H04L 63/0823 using certificates cryptographic mechanisms or cryptographic arrangements for entity authentication involving certificates H04L9/3263
• CPC Class Codes: H04L 9/302 involving the integer factorization problem, e.g. RSA or quadratic sieve [QS] schemes
• CPC Class Codes: H04L 9/3249 using RSA or related signature schemes, e.g. Rabin scheme
• 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
• CPC Class Codes: H04L 9/50 using hash chains, e.g. blockchains or hash trees

Abstract

Encrypted email message structures can contain recipient information that can reveal, to any recipient, all of the other recipients of an email message. Because some recipients, such as recipients to whom the message was “blind carbon-copied”, should remain hidden from the other recipients, individual encrypted messages can be created. One encrypted message can be created for all of the recipients who are intended to be revealed, such as the recipients listed in the TO and CC fields of an email header. A second encrypted message can be created for all of the recipients of the message who are intended to be hidden, such as the recipient listed in the BCC field of an email header. Alternatively, multiple encrypted messages can be created individually for each recipient in the BCC field, if the BCC recipients are to be hidden even from other BCC recipients.

Claims

1. A method for protecting the identity of one or more hidden recipients of an email message, the email message comprising an email header and an email body, the method comprising:

creating a first encrypted email body by encrypting the email body using a first encryption key;

creating a second encrypted email body by encrypting the email body using a second encryption key;

creating a first encrypted email message, said first encrypted email message comprising a first email header referencing one or more revealed recipients, said first encrypted email message further comprising the first encrypted email body and, for each of the one or more revealed recipients, an encrypted version of the first encryption key;

creating a second encrypted email message, said second encrypted email message comprising a second email header referencing one or more hidden recipients, said second encrypted email message further comprising the second encrypted email body and, for each of the one or more hidden recipients, an encrypted version of the second encryption key;

transmitting the first encrypted email message to the one or more revealed recipients referenced by the first email header; and

transmitting the second encrypted email message to the one or more hidden recipients referenced by the first email header.

2. The method of claim 1 further comprising:

determining the one or more revealed recipients of the email message and determining the one or more hidden recipients of the email message.

3. The method of claim 2, wherein the email header comprises a TO field, a CC field, and a BCC field, and wherein further the one or more revealed recipients are determined by reference to the TO field and the CC field and the one or more hidden recipients are determined by reference to the BCC field.

4. The method of claim 1, wherein the first encryption key and the second encryption key are equivalent, and wherein the first encrypted email body and the second encrypted email body are equivalent.

5. The method of claim 1, wherein the creating the first encrypted email message comprises:

locating one or more revealed recipient certificates corresponding to the one or more revealed recipients;

obtaining one or more revealed recipient public keys corresponding to the one or more revealed recipients from the one or more revealed recipients, the first encryption key using the one or more revealed recipient public keys;

and wherein the creating the second encrypted email message comprises;

locating one or more hidden recipient certificates corresponding to the one or more hidden recipients;

obtaining one or more hidden recipient public keys corresponding to the one or more hidden recipients from the one or more hidden recipient certificates; and

encrypting, for each of one or more hidden recipients, the second encryption key using the one or more hidden recipient public keys.

6. The method of claim 1, wherein the creating the second encrypted email message comprises creating one or more encrypted email messages corresponding to the one or more hidden recipients, wherein each encrypted email message of the one or more encrypted email messages comprises the second encrypted email body and the second encryption key encrypted for a corresponding hidden recipient;

and wherein the transmitting the second encrypted email message comprises transmitting the one or more encrypted email messages to the corresponding one or more hidden recipients.

7. The method of claim 6, wherein the one or more hidden recipients are members of an email mailing list referenced in the email header.

8. A computer-readable medium having computer-executable instructions for protecting the identity of one or more hidden recipients of an email message, the email message comprising an email header and an email body, the computer-readable instructions performing steps comprising:

creating a first encrypted email body by encrypting the email body using a first encryption key;

creating a second encrypted email body by encrypting the email body using a second encryption key;

creating a first encrypted email message, said first encrypted email message comprising a first email header referencing one or more revealed recipients, said first encrypted email message further comprising the first encrypted email body and, for each of the one or more revealed recipients, an encrypted version of the first encryption key;

creating a second encrypted email message, said second encrypted email message comprising a second email header referencing one or more hidden recipients, said second encrypted email message further comprising the second encrypted email body and, for each of the one or more hidden recipients, an encrypted version of the second encryption key;

transmitting the first encrypted email message to the one or more revealed recipients referenced by the first email header; and

transmitting the second encrypted email message to the one or more hidden recipients referenced by the second email header.

9. The computer-readable medium of claim 8 having further computer-executable instructions for performing steps comprising:

determining the one or more revealed recipients of the email message and determining the one or more hidden recipients of the email message.

10. The computer-readable medium of claim 9, wherein the email header comprises a TO field, a CC field, and a BCC field, and wherein further the one or more revealed recipients are determined by reference to the TO field and the CC field and the one or more hidden recipients are determined by reference to the BCC field.

11. The computer-readable medium of claim 8, wherein the first encryption key and the second encryption key are equivalent, and wherein the first encrypted email body and the second encrypted email body are equivalent.

12. The computer-readable medium of claim 8, wherein the creating the first encrypted email message comprises:

locating one or more revealed recipient certificates corresponding to the one or more revealed recipients;

obtaining one or more revealed recipient public keys corresponding to the one or more revealed recipients from the one or more revealed recipient certificates; and

encrypting, for each of one or more revealed recipients, the first encryption key using the one or more revealed recipient public keys;

and wherein the creating the second encrypted email message comprises;

locating one or more hidden recipient certificates corresponding to the one or more hidden recipients;

obtaining one or more hidden recipient public keys corresponding to the one or more hidden recipients from the one or more hidden recipient certificates; and

encrypting, for each of one or more hidden recipients, the second encryption key using the one or more hidden recipient public keys.

13. The computer-readable medium of claim 8, wherein the creating the second encrypted email message comprises creating one or more encrypted email messages corresponding to the one or more hidden recipients, wherein each encrypted email message of the one or more encrypted email messages comprises the second encrypted email body and the second encryption key encrypted for a corresponding hidden recipient;

and wherein the transmitting the second encrypted email message comprises transmitting the one or more encrypted email messages to the corresponding one or more hidden recipients.

14. The computer-readable medium of claim 13, wherein the one or more hidden recipients are members of an email mailing list referenced in the email header.

15. A computer-readable medium having computer-executable instructions for protecting the identity of one or more hidden recipients of an email message, the email message comprising an email header and an email body, the computer-readable instructions performing steps comprising:

determining one or more revealed recipients of the email message;

determining the one or more hidden recipients of the email message; and

selecting a hidden recipients concealment option;

wherein the one or more revealed recipients will receive a first encrypted email message comprising, for each of one or more revealed recipients, an encrypted version of a first encryption keys, a first encrypted email body created by encrypting the email body using the first encryption key, and the first email header of revealed recipients; and

wherein further each of the one or more hidden recipients will receive, depending on the selected hidden recipients concealment option, either a second encrypted email message comprising, for each of one or more hidden recipients, an encrypted version of a second encryption key, a second encrypted email body created by encrypting the email body using the second encryption key, and the second email header of hidden recipients, or a corresponding one or more encrypted email messages corresponding to the one or more hidden recipients,

wherein each encrypted email message of the corresponding one or more encrypted email messages comprises the second encryption key encrypted for a corresponding hidden recipient, a second encrypted email body created by encrypting the email body using the second encryption key, and the second email header of the corresponding hidden recipient.

16. The computer-readable medium of claim 15, wherein the email header comprises a TO field, a CC field, and a BCC field, and wherein further the one or more revealed recipients are determined by reference to the TO field and the CC field and the one or more hidden recipients are determined by reference to the BCC field.

17. The computer-readable medium of claim 15, wherein the first encryption key and the second encryption key are equivalent, and wherein the first encrypted email body and the second encrypted email body are equivalent.

18. The computer-readable medium of claim 15 having further computer-executable instructions for performing steps comprising:

encrypting the first encryption key for each of the one or more revealed recipients;

encrypting the second encryption key for each of the one or more hidden recipients; and

transmitting the encrypted first encryption keys, the encrypted second encryption keys, and an indication of the revealed recipients, the hidden recipients and the selected hidden recipients concealment option to a computing device, the computing device creating and transmitting the first encrypted email message and either the second encrypted email message or the corresponding one or more encrypted email messages depending on the selected hidden recipients concealment option.

19. The computer-readable medium of claim 18, wherein the encrypting the first encryption key comprises:

locating one or more revealed recipient certificates corresponding to the one or more revealed recipients;

obtaining one or more revealed recipient public keys corresponding to the one or more revealed recipients from the one or more revealed recipient certificates; and

encrypting, for each of one or more revealed recipients, the first encryption key using the one or more revealed recipient public keys;

and wherein the encrypting the second encryption key comprises;

locating one or more hidden recipient certificates corresponding to the one or more hidden recipients;

encrypting, for each of one or more hidden recipients, the second encryption key using the one or more hidden recipient public keys.