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

Patent metadata

Field	Value
Publication number	US-2015288514-A1
Application number	US-201414248254-A
Country	US
Kind code	A1
Filing date	Apr 8, 2014
Priority date	Apr 8, 2014
Publication date	Oct 8, 2015
Grant date	—

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. The server transmits the encrypted premaster secret to the different server for decryption along with other information necessary to compute a master secret and session keys for the secure session. The different server decrypts the encrypted premaster secret, generates the master secret, and generates session keys that are used in the secure session for encrypting and decrypting communication between the client device and the server and transmits those session keys to that server.

First claim

1 . A method in a first server for establishing a secure session with a client device, the method comprising:
receiving, from the client device, a Client Hello message that includes a first random value; in response to the received Client Hello message, transmitting a Server Hello message to the client device that includes a second random value; transmitting, to the client device, a Server Certificate message that includes one or more digital certificates; transmitting, to the client device, a Server Hello Done message; receiving, from the client device, a Client Key Exchange message that includes an encrypted premaster secret, wherein the first server does not include a private key that can decrypt the encrypted premaster secret; transmitting, to a second server that has access to a private key that is capable of decrypting the encrypted premaster secret, the encrypted premaster secret, the first random value, the second random value, and an indication of a negotiated cipher suite between the client device and the first server; receiving, from the second server, a set of 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 decrypted from the encrypted premaster secret, the first random value, the second random value, and the negotiated cipher suite between the client device and the first server; 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.

2 . The method of claim 1 , further comprising:
wherein prior to transmitting the Server Hello message to the client device, performing the following:
transmitting, to the second server, the Client Hello message, and
receiving, from the second server, the Server Hello message
wherein prior to transmitting the Server Certificate message to the client device, receiving the Server Certificate message from the second server; wherein prior to transmitting the Server Hello Done message to the client device, receiving the Server Hello Done message from the second server; transmitting the Client Key Exchange message to the second server; and wherein the encrypted premaster secret is transmitted in the Client Key Exchange message, the first random value is transmitted in the Client Hello message, the second random value is transmitted in the Server Hello message, and wherein the indication of the negotiated cipher suite between the client device and the first server is transmitted in the Server Hello message.

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

4 . The method of claim 3 , further comprising:
as part of establishing the secure session between the first server and the second server, transmitting, to the second server, a client Certificate message that includes a digital certificate of the first server.

5 . The method of claim 1 , further comprising:
after transmitting the second Finished message to the client device, receiving from the client device a request for a resource over the secure session, wherein the request is encrypted; decrypting, using the set of session keys, the request for the resource; transmitting the request for the resource to a third server; receiving the resource from the third server in response to the request; generating an encrypted response that includes the retrieved resource, wherein the encrypted response is encrypted with the set of session keys; and transmitting the encrypted response to the client device.

6 . The method of claim 5 , wherein the second server and the third server are the same server.

7 . The method of claim 1 , further comprising:
transmitting, to the second server, an indication of a domain for which the client device is attempting to establish the secure session that is to be used by the second server to identify the private key.

8 . The method of claim 1 , further comprising:
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, Server Certificate 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 Certificate message, Server Hello 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.

9 . The method of claim 1 , further comprising:
transmitting, to the second server, at least,
a first value included in the first Finished message that is used to verify a successful key exchange, and
a hash of the Client Hello message, Server Certificate message, Server Hello message, Server Hello Done message, Client Key Exchange message, and first Change Cipher Spec message;
receiving, from the second server, an indication that the key exchange is successful; transmitting, to the second server, a request to generate a second value to be included in the second Finished message that is calculated using a function that takes as input at least the master secret and a hash of the Client Hello message, Server Hello message, Server Certificate message, Server Hello Done message, Client Key Exchange message, first Change Cipher Spec message, first Finished message, and second Change Cipher Spec message; and receiving, from the second server, the second value and including the second value in the second Finished message.

10 . A method in a first server for establishing a secure session with a client device, the method comprising:
receiving a message from the client device that initiates a handshake procedure to establish a secure session between the client device and the first server; negotiating a set of cryptographic parameters between the client device and the first server for the secure session, wherein negotiating the set of cryptographic parameters includes the first server receiving an encrypted premaster secret from the client device, wherein the first server does not have access to a key to decrypt the encrypted premaster secret; transmitting at least some of the negotiated set of cryptographic parameters to a second server to create a set of one or more session keys to be used in the secure session, wherein the transmitted at least some of the negotiated set of cryptographic parameters includes the encrypted premaster secret; receiving, from the second server, the set of session keys; and completing the handshake procedure with the client device including installing the set of session keys to be used during the secure session with the client device.

11 . The method of claim 10 , wherein the transmitted at least some of the negotiated set of cryptographic parameters further includes a first random value selected by the client device, a second random value selected by the first server, and an indication of a ciphe

Assignees

• Cloudflare Inc

Inventors

• Pahl Sébastien Andreas Henry
• Tourne Matthieu Philippe François
• Sikora Piotr
• Bejjani Ray Raymond
• Knecht Dane Orion
• Prince Matthew Browning
• Graham-Cumming John
• Holloway Lee Hahn
• Sullivan Nicholas Thomas
• Strasheim Albertus

Classifications

• H04L63/164

  at the network layer · CPC title

• H04L63/16

  Implementing security features at a particular protocol layer · CPC title

• H04L63/166

  at the transport layer · CPC title

• H04L9/0844

  with user authentication or key authentication, e.g. ElGamal, MTI, MQV-Menezes-Qu-Vanstone protocol or Diffie-Hellman protocols using implicitly-certified keys · CPC title

• H04L63/045

  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 title