Method of verifying the integrity of an encryption key obtained by combining key parts

1. A 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, the method comprising 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 a symmetrical encryption algorithm 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 the verification encryption key (Kv).

2. The method according to claim 1 , wherein at least one of the combinations preceding the last combination (Mv) between the key portions (KM, M) and the verification key (Kv) is performed outside the protected zone ( 3 ).