Cryptographic process

An apparatus comprising at least one processing core and at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus at least to:

• determine a first channel definition describing a first wireless communication channel between the apparatus and a second apparatus, the first wireless communication channel being on a first frequency band;
• determine a second channel definition describing a second wireless communication channel between the apparatus and the second apparatus, the second wireless communication channel being on a second frequency band which has a lower bound at a higher frequency than an upper bound of the first frequency band;
• and
• derive an encryption key at least partly based on the second channel definition, and use the encryption key to encrypt information before it is transmitted to the second apparatus over the first wireless communication channel,
• wherein the upper bound of the first frequency band is less than six gigahertz, and the lower bound of the second frequency band is more than twenty-four gigahertz, and a center frequency of the second wireless communication channel is at least four times a center frequency of the first wireless communication channel,
• wherein the first channel definition and the second channel definition each define a channel frequency response, a channel impulse response, a channel state information, an angle of arrival, a direction of arrival, a time of arrival, and an angle of departure,
• wherein the apparatus comprises a first user equipment configured to communicate via sidelink with a second user equipment as the second apparatus,
• wherein the apparatus is configured to perform the determining of the second channel definition by deriving the second channel definition from the first channel definition using a predetermined correlation function employing location-based information, the predetermined correlation function mapping definitions of wireless communication channels in the first frequency band to definitions of wireless communication channels in the second frequency band,
• wherein the apparatus is configured to obtain a plurality of predetermined correlation functions based on prior measurements of the first user equipment and a base station,
• wherein the apparatus is configured to store the plurality of predetermined correlation functions and a mapping between the plurality of predetermined correlation functions and a location of the first user equipment and a location of the second user equipment,
• wherein the apparatus selects the predetermined correlation function based on the location of the first user equipment and the location of the second user equipment,
• wherein the channel frequency response of the second channel definition is derived at the first user equipment according to Ĥ110,2=f(Ĥ110,1), where f is a first predetermined correlation function, Ĥ110,1 is the channel frequency response of the first channel definition, and Ĥ110,2 is the channel frequency response of the second channel definition,
• wherein the channel frequency response of the second channel definition is derived at the second user equipment according to Ĥ120,2=f(Ĥ120,1), where g is a second predetermined correlation function, Ĥ120,1 is the channel frequency response of the first channel definition, and Ĥ120,2 is the channel frequency response of the second channel definition,
• wherein the channel frequency response of the second channel definition is a discrete Fourier transform of the channel impulse response of the second channel definition,
• wherein quantization is applied to the second channel definition after the channel frequency response of the second channel definition is derived from the first channel definition using the predetermined correlation function, and
• wherein the apparatus is configured to perform encrypting of the information at a physical layer of the first wireless communication channel.