Patent ID: 8638940

Claim:
A method of checking an entity to be checked by a checking entity where the first entity to be checked comprises a first electronic chip and the checking entity comprises a second electronic chip; a secret key being associated with the checking entity and stored at the second electronic chip; said entity to be checked and said checking entity sharing a plurality of public parameters, a second public parameter of said plurality being a combination of a first public parameter of said plurality with the secret key of the checking entity; said method comprising the following steps in the entity to be checked: /a/ generating first and second random values and storing the first and second random values at the first electronic chip, in which at least one of the values based on the second public parameter is furthermore based on the second random value and is transmitted in the first message; /b/ transmitting a first message to the checking entity, said first message comprising at least one combined value obtained by combining the first public parameter with the at least one random value; and /c/ transmitting a second message to the checking entity, said second message comprising at least one combined value obtained by combining the at least one random value, a secret key of the entity to be checked and a value received from the checking entity; in which at least one of the values included in the first or the second message is based on the second public parameter; and in which it is decided that the entity to be checked is checked on the basis of the following equation: J =(( g v ) y ) x −v z −1 ) 1/vc where J is a public key of the entity to be checked or a value in a database accessible from the checking entity; where g is the first public parameter; where g v is the second public parameter; where x is a combined value transmitted in the first message; where y a combined value transmitted in the second message; where z is the value based on the second public parameter; where c is the value received from the checking entity; and where v is the secret key of the checking entity.