The invention relates to an electronic system comprising a casing consisting of at least first and second casing portions and containing a device for detecting the substitution of the first casing portion. The device comprises a first integrated circuit intended to be fixed to the first casing portion and a second integrated circuit intended to be fixed to the second casing portion. The second circuit is adapted to transmit to the first integrated circuit successive random or pseudo-random digital signals (R). The first integrated circuit is adapted to return to the second integrated circuit, for each digital signal, the first encrypted signature (S) from said digital signal. The second integrated circuit is adapted to determine a second encrypted signature (S′) from said digital signal and to detect a substitution of the first casing portion if the first and second encrypted signatures are different.