Secure session capability using public-key cryptography without access to the private key

• US 9,553,856 B2
• Filed: 06/25/2014
• Issued: 01/24/2017
• Est. Priority Date: 03/07/2013
• Status: Active Grant

• Current Assignee: CloudFlare Incorporated
• Original Assignee: CloudFlare Incorporated
• Inventors: Pahl, Sbastien Andreas Henry, Tourne, Matthieu Philippe Franois, Sikora, Piotr, Bejjani, Ray Raymond, Knecht, Dane Orion, Prince, Matthew Browning, Graham-Cumming, John, Holloway, Lee Hahn, Strasheim, Albertus
• Primary Examiner(s): Najjar, Saleh
• Assistant Examiner(s): Pan, Peiliang
• Application Number:
  US14/315,241
• Publication Number:
  US 20140310526A1
• Time in Patent Office: 944 Days
• Field of Search: 713/171, 380/44, 380/281, 380/282
• US Class Current: 1/1
• CPC Class Codes: G06F 21/335 for accessing specific resources, e.g. using Kerberos tickets
• CPC Class Codes: H04L 2463/061 applying further key derivation, e.g. deriving traffic keys from a pair-wise master key
• CPC Class Codes: H04L 63/0435 wherein the sending and receiving network entities apply symmetric encryption, i.e. same key used for encryption and decryption cryptographic mechanisms or cryptographic arrangements for symmetric key encryption H04L9/06
• CPC Class Codes: H04L 63/0442 wherein the sending and receiving network entities apply asymmetric encryption, i.e. different keys for encryption and decryption cryptographic mechanisms or cryptographic arrangements for public-key encryption H04L9/30
• CPC Class Codes: H04L 63/061 for key exchange, e.g. in peer-to-peer networks cryptographic mechanisms or cryptographic arrangements for key agreement H04L9/0838
• 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 63/0823 using certificates cryptographic mechanisms or cryptographic arrangements for entity authentication involving certificates H04L9/3263
• CPC Class Codes: H04L 63/0869 for achieving mutual authentication cryptographic mechanisms or cryptographic arrangements for mutual authentication H04L9/3273
• CPC Class Codes: H04L 63/166 at the transport layer
• CPC Class Codes: H04L 9/0825 using asymmetric-key encryption or public key infrastructure [PKI], e.g. key signature or public key certificates
• CPC Class Codes: H04L 9/0841 involving Diffie-Hellman or related key agreement protocols
• CPC Class Codes: H04L 9/0869 involving random numbers or seeds
• 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

Abstract

A server establishes a secure session with a client device where a private key used in the handshake when establishing the secure session is stored in a different server. During the handshake procedure, the server receives a premaster secret that has been encrypted using a public key bound with a domain for which the client device is attempting to establish a secure session with. The server transmits the encrypted premaster secret to another server for decryption. The server receives the decrypted premaster secret and continues with the handshake procedure including generating a master secret from the decrypted premaster secret and generating one or more session keys that are used in the secure session for encrypting and decrypting communication between the client device and the server.

Claims

1. A method in a first server for establishing a secure session with a client device where a private key used for the secure session is stored in a second server, the method comprising the first server performing the following:

receiving a message from the client device that initiates a procedure to establish a secure session between the client device and the first server;

transmitting a digital certificate to the client device that includes a public key;

generating a set of cryptographic parameters;

transmitting, to the second server, a message that includes the set of cryptographic parameters, wherein the second server has a private key that corresponds to the public key;

receiving from the second server, a message that includes the set of cryptographic parameters that have been signed using the private key;

transmitting, to the client device, the set of cryptographic parameters that have been signed using the private key;

receiving, from the client device, a value generated by the client device based in part on the set of cryptographic parameters;

generating, using the received value and at least some of the set of cryptographic parameters, a premaster secret;

generating a master secret using the premaster secret; and

generating, using the generated master secret, a set of one or more session keys to be used in the secure session for encrypting and decrypting communication between the client device and the first server.

2. The method of claim 1, wherein the first server and the second server are owned by different entities.

3. The method of claim 1, wherein the first server receives the message from the client device that initiates the procedure to establish the secure session between the client device and the first server as a result of a Domain Name System (DNS) request for a domain, for which the client device is attempting to establish the secure session, resolving to the first server.

4. The method of claim 1, wherein the message that includes the set of cryptographic parameters that have been signed using the private key is received over a secure session between the first server and the second server.

5. The method of claim 4, further comprising:

as part of establishing the secure session between the first server and the second server, the first server transmitting a digital certificate of the first server to the second server.

6. The method of claim 1, wherein the second server is an origin server, and wherein the method further comprises the first server performing the following:

receiving, from the client device over the secure session, an encrypted request for a resource of a domain of the second server;

decrypting the encrypted request;

retrieving the requested resource from the second server;

generating a response that includes the retrieved resource;

encrypting the generated response; and

transmitting, to the client device over the secure session, the encrypted response.

7. The method of claim 6, wherein retrieving the requested resource from the second server includes transmitting an encrypted request for the requested resource over a secure session between the first server and the second server.

8. A method in a first server for establishing a secure session with a client device where a private key used for the secure session is stored in a second server, the method comprising the first server performing the following:

receiving, from the client device, a Client Hello message;

in response to the received Client Hello message, transmitting a Server Hello message to the client device;

transmitting, to the client device, a Server Certificate message that includes one or more digital certificates;

generating a set of server key exchange parameters used for generating a premaster secret;

transmitting, to the second server, a message requesting signing of the server key exchange parameters;

receiving, from the second server, a message that includes the server key exchange parameters that are signed;

transmitting, to the client device, a Server Key Exchange message that includes the signed server key exchange parameters;

transmitting, to the client device, a Server Hello Done message;

receiving, from the client device, a Client Key Exchange message that includes a value generated by the client device based in part on the server key exchange parameters;

generating, using the value generated by the client device and at least some of the server key exchange parameters, the premaster secret;

generating a master secret using the premaster secret;

receiving, from the client device, a first Change Cipher Spec message;

receiving, from the client device, a first Finished message;

transmitting, to the client device, a second Change Cipher Spec message; and

transmitting, to the client device, a second Finished message.

9. The method of claim 8, wherein the first server and the second server are owned or operated by different entities.

10. The method of claim 8, wherein the message that includes the server key exchange parameters that are signed is received over a secure session between the first server and the second server.

11. The method of claim 10, further comprising:

as part of establishing the secure session between the first server and the second server, the first server transmitting, to the second server, a client Certificate message that includes a digital certificate of the first server.

12. The method of claim 8, wherein the second server is an origin server, and wherein the method further comprises the first server performing the following:

receiving, from the client device over the secure session, an encrypted request for a resource of a domain of the second server;

decrypting the encrypted request;

retrieving the requested resource from the second server;

generating a response that includes the retrieved resource;

encrypting the generated response; and

transmitting, to the client device over the secure session, the encrypted response.

13. The method of claim 12, wherein retrieving the requested resource from the second server includes transmitting an encrypted request for the requested resource over a secure session between the first server and the second server.

14. A method in a first server, comprising the first server performing the following:

receiving a set of cryptographic parameters from a second server, wherein the set of cryptographic parameters is received from the second server as part of a secure session establishment between a client device and the second server;

accessing a private key, wherein the private key is not stored on the second server;

signing the set of cryptographic parameters using the private key; and

transmitting the signed set of cryptographic parameters to the second server for use in the secure session establishment between the client device and the second server including generation of a premaster secret.

15. The method of claim 14, further comprising the first server performing the following:

prior to transmitting the set of cryptographic parameters to the second server, participating in a secure session establishment procedure that establishes a secure session between the first server and the second server, wherein transmitting the set of cryptographic parameters to the second server is over secure session.

16. The method of claim 15, wherein as part of participating in the establishment of the secure session, the first server performs the following:

requesting a certificate from the second server;

receiving a certificate from the second server; and

using the received certificate to authenticate the second server.

17. The method of claim 14, further comprising the first server receiving, from the second server, an indication of a domain in which the client device is attempting to connect via the secure session, and wherein the accessed private key corresponds to a public key associated with the indicated domain.

18. The method of claim 14, wherein prior to transmitting the set of cryptographic parameters to the second server, the first server verifying that the second server is communicating with the first server with an IP address having a value expected by the first server.

19. An apparatus, comprising:

a first server including a set of one or more processors and a set of one or more non-transitory computer-readable storage mediums storing instructions, that when executed by the set of processors, cause the set of processors to perform the following operations;

receive a message from a client device that initiates a procedure to establish a secure session between the client device and the first server;

transmit a digital certificate to the client device that includes a public key;

generate a set of cryptographic parameters;

transmit, to a second server, a message that includes the set of cryptographic parameters, wherein the second server is configured to have a private key that corresponds to the public key;

receive from the second server, a message that includes the set of cryptographic parameters that have been signed using the private key;

transmit, to the client device, the set of cryptographic parameters that have been signed using the private key;

receive, from the client device, a value generated by the client device based in part on the set of cryptographic parameters;

generate, using the received value and at least some of the set of cryptographic parameters, a premaster secret;

generate a master secret using the premaster secret; and

generate, using the generated master secret, a set of one or more session keys to be used in the secure session for encrypting and decrypting communication between the client device and the first server.

20. The apparatus of claim 19, wherein the first server and the second server are owned by different entities.

21. The apparatus of claim 19, wherein the first server receives the message from the client device that initiates the procedure to establish the secure session between the client device and the first server as a result of a Domain Name System (DNS) request for a domain, in which the client device is attempting to establish the secure session, resolving to the first server.

22. The apparatus of claim 19, wherein the message that includes the set of cryptographic parameters that have been signed using the private key is received over a secure session between the first server and the second server.

23. The apparatus of claim 22, wherein the set of non-transitory computer-readable storage mediums further stores instructions, that when executed by the set of processors, cause the set of processors to perform the following operations:

as part of the establishment of the secure session between the first server and the second server, the first server transmits a digital certificate of itself to the second server for the second server to authenticate an identity of the first server.

24. The apparatus of claim 19, wherein the second server is an origin server, and wherein the set of non-transitory computer-readable storage mediums further stores instructions, that when executed by the set of processors, cause the set of processors to perform the following operations:

receive, from the client device over the secure session, an encrypted request for a resource of a domain of the origin server;

decrypt the encrypted request;

retrieve the requested resource from the origin server;

generate a response that includes the retrieved resource;

encrypt the generated response; and

transmit, to the client device over the secure session, the encrypted response.

25. The apparatus of claim 24, wherein the operation to retrieve the requested resource from the origin server includes a transmission of an encrypted request for the requested resource over a secure session between the first server and the origin server.