Following the natural asymmetry of USB, the host initiates all processes (except signaling), security being no exception. Security requests are made to devices to find their security capabilities, after which the appropriate devices can be chosen. The standard, symmetric encryption method is AES-128 with CCM, though Public key encryption may be used for initial authentication (namely, only the sending of the initial CCM key), provided that the achieved security level is comparable (in practice by using 3072-bit RSA and SHA-256 for hashing).