Sending an encrypted key pair and a secret shared by two devices to a trusted intermediary

• US 9,130,744 B1
• Filed: 09/22/2014
• Issued: 09/08/2015
• Est. Priority Date: 09/22/2014
• Status: Active Grant

• Current Assignee: Envelope LLC
• Original Assignee: Envelope LLC
• Inventors: Bergersen, Brad, King, Kevin
• Primary Examiner(s): Patel, Haresh N
• Application Number:
  US14/492,847
• Time in Patent Office: 351 Days
• Field of Search: 380/282, 380/258, 380/255, 713/156
• US Class Current: 1/1
• CPC Class Codes: H04L 2209/24 Key scheduling, i.e. generating round keys or sub-keys for block encryption
• CPC Class Codes: H04L 63/062 for key distribution, e.g. centrally by trusted party cryptographic mechanisms or cryptographic arrangements for key distribution involving a central third party H04L9/0819
• CPC Class Codes: H04L 9/083 involving central third party, e.g. key distribution center [KDC] or trusted third party [TTP]
• CPC Class Codes: H04L 9/0861 Generation of secret information including derivation or calculation of cryptographic keys or passwords
• CPC Class Codes: H04L 9/14 using a plurality of keys or algorithms
• CPC Class Codes: H04L 9/30 Public key, i.e. encryption algorithm being computationally infeasible to invert or user's encryption keys not requiring secrecy

Abstract

Key exchange methods, apparati, and computer-readable media for a cryptographic communication system. The system, which employs a novel combination of multiple channel communication, symmetric cryptography, and asymmetric cryptography, allows an entity A to bootstrap the exchange of cryptographic secrets EQ_B to a second entity B through an alternate communication channel 30 for the transmission of a cryptographically secure message M. The system is secure against various passive and active attacks. The encryption key transfer is briefly vulnerable to man-in-the-middle attacks, but this can be prevented in preferred embodiments.

Claims

1. At least one non-transitory computer-readable medium containing computer program instructions for performing the steps of:

a first entity A generates a private key/public key pair to be used by a second entity B in subsequent communications with A, where B has been selected by A to receive confidential communications from A;

A encrypts said key pair with P, where P is a secret shared by A and B;

A sends the encrypted key pair to a trusted intermediary L;

A encrypts a message M, and sends the encrypted M to B over a communications channel;

B retrieves B'"'"'s private key/public key pair from L, along with means to decrypt M; and

B decrypts M using B'"'"'s private key retrieved from L and said means to decrypt retrieved from L.

2. The at least one non-transitory computer-readable medium of claim 1 wherein the encryption of M comprises A encrypting M and A encrypting A'"'"'s public key with a randomly generated symmetric key R.

3. The at least one non-transitory computer-readable medium of claim 2 further comprising computer program instructions enabling A to encrypt R with B'"'"'s public key.

4. Apparatus for facilitating confidential communications between a first entity A and a second entity B, where B has been selected by A to be a recipient of confidential communications from A, said apparatus comprising:

coupled to A and to B, a shared secret P;

coupled to A, and accessible to B upon presentation of proper credentials, a trusted intermediary L;

associated with A, means for generating a public/private key pair to be used by B in subsequent confidential communications with A;

coupled to the generating means, means for encrypting the newly generated public/private key pair for B with P;

coupled to the encrypting means, means for transmitting the encrypted public/private key pair to L; and

associated with A, means for conveying to B a pointer to L and a randomly generated number Z adapted to enable B to retrieve B'"'"'s encrypted public/private key pair from L.

5. The apparatus of claim 4 further comprising means within A to encrypt a message destined for B and encrypt a public key of A with a randomly generated symmetric key R.

6. The apparatus of claim 5 further comprising, within A, means for encrypting R with B'"'"'s newly generated public key.

7. A computer-implemented method for a first entity A to initiate confidential communications with a second entity B that A has selected to be a recipient of said communications, said method comprising the steps of:

A generates a private key/public key pair to be used by B in subsequent communications with A, encrypts said key pair with P, and sends the encrypted key pair to a trusted intermediary L, where P is a secret shared by A and B;

A encrypts a message M, and sends the encrypted M to B over a communications channel;

B retrieves B'"'"'s private key/public key pair from L, along with means to decrypt M; and

B decrypts M using B'"'"'s private key retrieved from L and said means to decrypt retrieved from L.

8. The method of claim 7 wherein the communications channel comprises an open network.

9. The method of claim 8 wherein the open network comprises the Internet.

10. The method of claim 7 wherein the encryption with P uses symmetric key cryptography.

11. The method of claim 7 wherein the means to decrypt comprises an asymmetric key cryptographic algorithm.

12. The method of claim 7 wherein A'"'"'s encryption of M comprises A encrypting M and A encrypting A'"'"'s public key.

13. The method of claim 12 wherein the encryption of M and A'"'"'s public key comprises encrypting with a randomly generated symmetric key R.

14. The method of claim 13 further comprising the step of A sending to B, over the communications channel, R encrypted with B'"'"'s public key.

15. The method of claim 14 further comprising the steps of:

B using B'"'"'s private key to retrieve R; and

B using R to decrypt M and A'"'"'s public key.

16. The method of claim 7 further comprising the step of A sending to B over the communications channel a pointer to L and a random value Z.

17. The method of claim 16 further comprising the step of B using Z and the pointer to L to retrieve from L B'"'"'s public private key pair.

18. The method of claim 16 wherein Z is used once and then discarded.

19. The method of claim 7 wherein B does not use B'"'"'s public key for communicating with any entity other than A.

20. The method of claim 7 wherein M does not contain any non-random padding.

21. The computer-implemented method of claim 7, wherein;

there are N second entities B with whom A wishes to communicate confidentially, where N is an integer greater than or equal to 2; and

A sends to the trusted intermediary L a number N of encrypted private key/public key pairs, one pair for each B.

22. The computer-implemented method of claim 7, wherein:

there are a plurality of second entities B with whom A wishes to communicate confidentially;

for each B, A sends a public/private key pair to be used by that B to the trusted intermediary L, along with a unique random value derived from a master random value and from some identifiable information associated with that particular B; and

each B derives its unique random value from the master random value and from said identifiable information associated with that particular B.