Securing a cryptographic device against implementation attacks

A computer-implemented method of providing a secure communication of data between a client device and a host device, wherein the client device is configured to use a plurality of keys with a single power trace per key against implementation attacks, said method comprising:

• providing the client device with a client microprocessor and a client memory, wherein the plurality of keys are stored within the client memory;
• providing the host device with a host microprocessor and a host memory;
• establishing a secure connection between the host device and the client device;
• supplying, for each key, at least one input vector to the client device from the host device;
• deriving an updated key and an updated output based on the input vector and a constant input, wherein an identical constant input is used for all keys of the plurality of keys and deriving the update key only produces the single power trace per key;
• and
• using said updated output to encrypt communication between the client device and the host device by using the updated output as a keystream.

A computer-implemented method of message authentication code generation, wherein a cryptographic device is configured to use a plurality of keys with a single power trace per key against implementation attacks, said method comprising:

• providing the cryptographic device configured to use the plurality of keys with an integrated circuit;
• supplying an input vector to the cryptographic device;
• supplying a constant input to the cryptographic device, wherein an identical constant input is used for all keys of the plurality of keys;
• deriving an updated key and an updated output, based on the input vector, wherein deriving the updated key only produces the single power trace per key;
• and
• using the updated output as a message authentication code.