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

1. A method in a first server for establishing and using a secure session with a client device, the method comprising:

transmitting, by the first server, a plurality of messages between the client device and a second server, the plurality of messages generated by the client device and the second server for establishing the secure session between the client device and the first server, wherein the second server has access to a private key used in establishing the secure session including signing a set of cryptographic parameters, included in the plurality of messages, that are to be used by the client device when generating a premaster secret and include a first Diffie-Hellman public value selected by the second server, and wherein the private key is not available on the first server;

receiving, from the second server, 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 that were generated at least using a master secret that is generated using a premaster secret that is generated using a second Diffie-Hellman public value selected by the client device and the first Diffie-Hellman public value selected by the second server;

receiving, from the client device over the secure session, an encrypted request for a resource,

decrypting, using the set of session keys, the encrypted request for the resource;

retrieving the requested resource locally on the first server;

generating a response that includes the retrieved resource;

encrypting the generated response using the set of session keys; and

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

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

3. The method of claim 1 , wherein the set of session keys are received from the second server over a secure session between the first server and the second server.

4. The method of claim 1 , wherein retrieving the requested resource includes transmitting the request for the resource to a third server and receiving the resource from the third server in response to the request, and wherein the second server and the third server are the same server.

5. The method of claim 1 , further comprising:

wherein the plurality of messages transmitted between the client device and the second server includes a Client Hello message received from the client device, a Server Hello message received from the second server, a Certificate message received from the second server, a Server Key Exchange message received from the second server, a Server Hello Done message received from the second server, a Client Key Exchange message received from the client device, a first and second Change Cipher Spec message, and a first and second Finished message;

receiving, from the second server, the master secret;

verifying information in the first Finished message including,

calculating a first value using a function that takes as input at least the master secret and a hash of the Client Hello message, Server Hello message, Certificate message, Server Key Exchange message, Server Hello Done message, Client Key Exchange message, and first Change Cipher Spec message, and

comparing the calculated first value with a second value included in the first Finished message, wherein a same first value and second value indicates a successful key exchange;

calculating a third value using a function that takes as input at least the master secret and a hash of the Client Hello message, Server Hello message, Certificate message, Server Key Exchange message, Server Hello Done message, Client Key Exchange message, first Change Cipher Spec message, first Finished message, and second Change Cipher Spec message; and

including the third value in the second Finished message.

6. A non-transitory computer-readable medium storing instructions, which when executed by a set of one or more processors of a first server, cause the set of processors to perform operations comprising:

transmitting, by the first server, a plurality of messages between a client device and a second server, the plurality of messages generated by the client device and the second server for establishing a secure session between the client device and the first server, wherein the second server has access to a private key used in establishing a secure session between the client device and the first server including signing a set of cryptographic parameters, included in the plurality of messages, that are to be used by the client device when generating a premaster secret and include a first Diffie-Hellman public value selected by the second server, and wherein the private key is not available on the first server;

receiving, from the second server, 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 that were generated at least using a master secret that is generated using a premaster secret that is generated using a first second Diffie-Hellman public value selected by the client device and the first Diffie-Hellman public value selected by the second server;

receiving, from the client device over the secure session, an encrypted request for a resource,

decrypting, using the set of session keys, the encrypted request for the resource;

retrieving the requested resource locally on the first server;

generating a response that includes the retrieved resource;

encrypting the generated response using the set of session keys; and

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

7. The non-transitory computer-readable medium of claim 6 , wherein the first server and the second server are owned or operated by different entities.

8. The non-transitory computer-readable medium of claim 6 , wherein the set of session keys are received from the second server over a secure session between the first server and the second server.

9. The non-transitory computer-readable medium of claim 6 , wherein retrieving the requested resource includes transmitting the request for the resource to a third server and receiving the resource from the third server in response to the request, and wherein the second server and the third server are the same server.

10. The non-transitory computer-readable medium of claim 6 , further storing instructions that, when executed by the set of processors, cause the set of processors to perform the following operations:

wherein the plurality of messages transmitted between the client device and the second server includes a Client Hello message received from the client device, a Server Hello message received from the second server, a Certificate message received from the second server, a Server Key Exchange message received from the second server, a Server Hello Done message received from the second server, a Client Key Exchange message received from the client device, a first and second Change Cipher Spec message, and a first and second Finished message;

receiving, from the second server, the master secret;

verifying information in the first Finished message including,

calculating a first value using a function that takes as input at least the master secret and a hash of the Client Hello message, Server Hello message, Certificate message, Server Key Exchange message, Server Hello Done message, Client Key Exchange message, and first Change Cipher Spec message, and

comparing the calculated first value with a second value included in the first Finished message, wherein a same first value and second value indicates a successful key exchange;

calculating a third value using a function that takes as input at least the master secret and a hash of the Client Hello message, Server Hello message, Certificate message, Server Key Exchange message, Server Hello Done message, Client Key Exchange message, first Change Cipher Spec message, first Finished message, and second Change Cipher Spec message; and

including the third value in the second Finished message.

11. 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:

transmit a plurality of messages between a client device and a second server, the plurality of messages generated by the client device and the second server for establishing a secure session between the client device and the first server, wherein the second server has access to a private key used in establishing a secure session between the client device and the first server including signing a set of cryptographic parameters, included in the plurality of messages, that are to be used by the client device when generating a premaster secret and include a first Diffie-Hellman public value selected by the second server, and wherein the private key is not available on the first server;

receive, from the second server, 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 that were generated at least using a master secret that is generated using a premaster secret that is generated using a second Diffie-Hellman public value selected by the client device and the first Diffie-Hellman public value selected by the second server;

receive, from the client device over the secure session, an encrypted request for a resource,

decrypt, using the set of session keys, the encrypted request for the resource;

retrieve the requested resource locally on the first server;

generate a response that includes the retrieved resource;

encrypt the generated response using the set of session keys; and

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

12. The apparatus of claim 11 , wherein the first server and the second server are owned or operated by different entities.

13. The apparatus of claim 11 , wherein the set of session keys are to be received from the second server over a secure session between the first server and the second server.

14. The apparatus of claim 11 , wherein retrieval of the requested resource includes transmission of the request for the resource to a third server and receipt of the resource from the third server in response to the request, wherein the second server and the third server are the same server.

15. The apparatus of claim 11 , 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:

wherein the plurality of messages to be transmitted between the client device and the second server includes a Client Hello message received from the client device, a Server Hello message received from the second server, a Certificate message received from the second server, a Server Key Exchange message received from the second server, a Server Hello Done message received from the second server, a Client Key Exchange message received from the client device, a first and second Change Cipher Spec message, and a first and second Finished message;

receive, from the second server, the master secret;

verify information in the first Finished message including,

calculate a first value using a function that takes as input at least the master secret and a hash of the Client Hello message, Server Hello message, Certificate message, Server Key Exchange message, Server Hello Done message, Client Key Exchange message, and first Change Cipher Spec message, and

compare the calculated first value with a second value included in the first Finished message, wherein a same first value and second value indicates a successful key exchange;

calculate a third value using a function that takes as input at least the master secret and a hash of the Client Hello message, Server Hello message, Certificate message, Server Key Exchange message, Server Hello Done message, Client Key Exchange message, first Change Cipher Spec message, first Finished message, and second Change Cipher Spec message; and

include the third value in the second Finished message.