On the influence of probabilistic characteristics of discrete sources forming cryptographic keys on the practical secrecy of the key

The mathematical model of a binary discrete source is proposed, which is close to the practical conditions for the operation of cryptographic key generation devices. The model takes into account the non-stationarity of such devices, as well as the presence of statistical dependencies between their output bits. Within the framework of the model, an achievable and easily computable lower estimate of the practical secrecy of the key is obtained. It is shown that with certain parameters of the model, the assessment allows us to draw meaningful conclusions about the cryptographic quality of keys, while other well-known estimates do not cope with this.