The method of verifying the integrity of an encryption key (K) obtained by combining at least two key portions (KM, M) in a protected zone (3) by using a commutative operator, comprises the steps of: using the commutative operator to perform a first combination between a key portion (KM) and a verification encryption key (Kv); using the commutative operator to perform in succession a combination between a key portion that has not yet been combined and a result obtained by an immediately preceding combination, until a last combination (Mv) is performed that includes all of the key portions; performing a combination in the protected zone (3) between the encryption key (K) to be verified and the last combination (Mv) of the verification encryption key (Kv) and the key portions (KM, M) in order to obtain a final verification key (Kf); encrypting verification data (Dv) by means of a symmetrical encryption algorithm (DES) using the final verification key (Kf); and making a comparison with a verification encryption (Cv) obtained by direct encryption of the verification data (Dv) by means of the verification encryption key (Kv).