The development of digital operating automatic devices models of the systems with the property of high functional controllability of hardware and software tools for the performance of computational functions (operations) on a real scale becomes a priority task in the context of ensuring high efficiency and reliability of monitoring the functioning of digital metrological telemetric measurement and control systems of critical infrastructure problem growing relevance. In the article, based on a critical analysis of known methods for digital systems functional control, a method of ensuring the operational controllability of digital automatic devices is proposed based on the concept implementation of predicting (forecasting) control signatures of tuples and their state. Relevant concepts are introduced, and a structural-functional model of functional control for digital automatic device with «hard» logic based on the method of signature prediction is proposed. In the context of the practical implementation of the proposed method of predicting signatures on each operating cycle of the digital automatic device, a system of control signature equations formulas (signature functional control rules) is given for the basic types of digital automatic device register operations with «hard» logic. This makes it possible to implement a new functional control principle (signature functional control by the method of signature prediction) of digital automatic devices by introducing a unified hardware redundancy (synthesized hardware node of a signature functional control) from functionally complete elementary combinational structures from a finite set (standard set). In this regard, the relevance of functional control by the method of predicting signatures for generators of pseudorandom sequences of the maximum length in the digital automatic device of cryptographic encryption by jamming measurement information during its transmission in telecommunication channels of management systems of critical infrastructure objects in the conditions of possible cyberattacks is reasonably grounded. The scientific novelty of the obtained theoretical results is the authors' proof of the need to develop further the methodology of functional control of a general-purpose digital automatic device and, in particular, of telemetric measurement and control systems of critical infrastructure based on the use of the author's mathematical apparatus of synthesis «signature Boolean-polynomial algebra».