Generator of physically unclonable cryptographic keys (PUF) has two adjustable speed ring oscillators (GPRS, GPRS′), which outputs (o-GPRS, o-GPRS′) are connected to inputs (i1-DF, i2-DF) of a phase detector (DF), which output (o-DF) is connected to control inputs of the adjustable speed ring oscillators (s-GPRS, s-GPRS′) through a control system (US) and is also connected to a output (o-PUF) of the generator of physically unclonable cryptographic keys (PUF) through a sample and compare circuit (URP). Generator has a initializing input (i-UCH) connected to both initializing inputs of the adjustable speed ring oscillators (i-GPRS, GPRS′) and to the first input of the sample and compare circuit (i-URP), which second input (z-URP) is connected to the output (o-GPRS′) of one of adjustable speed ring oscillators (GPRS′).