Establishing a protected communication channel
To establish a first protected communication channel between a device D and a first server S, a symmetric key K S is derived at the device D, based on a device identifying key K D and public key information dependent on a first server public key S public of the first server S. The symmetric key K S is derived in a corresponding way at a second server T. The symmetric key K S is transmitted from the second server T to the first server S on a second protected communication channel. Communication on the first protected communication channel between the device D and the first server S is protected using a communication key K C which is dependent on the symmetric key K S . This can enable a device D lacking support for asymmetric key cryptography to securely enter into communication with the first server S.
1. A method for establishing a first protected communication channel between a device and a first server, the first server having a first server public key, and the device having a device identifying key shared with a second server different from the first server, the method comprising:
deriving a symmetric key at the device, based on the device identifying key and public key information dependent on the first server public key;
sending, by the device, a payload message to the first server on the first protected communication channel protected using a communication key which is dependent on the symmetric key;
in response to the payload message, the first server sends a key generation request to the second server to trigger the second server to derive the symmetric key and transmit the symmetric key to the first server on a second protected communication channel;
deriving the symmetric key at the second server, based on the device identifying key and the public key information; and
transmitting the symmetric key from the second server to the first server using the second protected communication channel.
2. The method of claim 1 , in which the second protected communication channel is protected using a public key infrastructure based on asymmetric keys.
3. The method of claim 2 , in which the asymmetric keys for the public key infrastructure comprise said first server public key and a first server private key.
4. The method of claim 1 , in which the communication key is the same as the symmetric key.
5. The method of claim 1 , in which the communication key is derived from the symmetric key based on information shared between the device and the first server.
6. The method of claim 5 , in which the information shared between the device and the first server comprises at least one of:
a class key associated with a class of devices including the device; and
a random or pseudorandom value.
7. The method of claim 1 , in which the public key information is the same as the first server public key.
8. The method of claim 1 , in which the public key information comprises a hash of the first server public key, and has fewer bits than the first server public key.
9. The method of claim 1 , in which the device is incapable of generation of asymmetric keys for supporting a public key infrastructure.
10. The method of claim 1 , in which the payload message and the key generation request each specify a device identifier of the device.
11. At least one non-transitory, computer-readable storage medium storing one or more computer programs, which when executed by one or more data processors in a device, a first server, and a second server different from the first server, cause the one or more data processors to establish a first protected communication channel between the device and the first server, where the first server has a first server public key and the device has a device identifying key shared with the second server by:
deriving a symmetric key at the device, based on the device identifying key and public key information dependent on the first server public key;
sending, by the device, a payload message to the first server on the first protected communication channel protected using a communication key which is dependent on the symmetric key;
in response to the payload message, the first server sending a key generation request to the second server to trigger the second server to derive the symmetric key and transmit the symmetric key to the first server on a second protected communication channel;
deriving the symmetric key at the second server, based on the device identifying key and the public key information; and
transmitting the symmetric key from the second server to the first server using the second protected communication channel.
12. A system comprising:
a device;
a first server; and
a second server different from the first server,
each of the device, the first server, and the second server comprising:
corresponding processing circuitry to perform data processing; and
data storage,
wherein each data storage stores one or more computer programs for controlling corresponding processing circuitry to establish a first protected communication channel between the device and the first server, the first server having a first server public key, and the device having a device identifying key shared with the second server by:
deriving a symmetric key at the device, based on the device identifying key and public key information dependent on the first server public key;
sending, by the device, a payload message to the first server on the first protected communication channel protected using a communication key which is dependent on the symmetric key;
in response to the payload message, the first server sends a key generation request to the second server to trigger the second server to derive the symmetric key and transmit the symmetric key to the first server on a second protected communication channel;
deriving the symmetric key at the second server, based on the device identifying key and the public key information; and
transmitting the symmetric key from the second server to the first server using the second protected communication channel.