A computer-implemented method of determining, at a first node, a common secret that is common with the first node and a second node, wherein the first node is associated with a first asymmetric cryptography pair having a first node master private key (V 1C) and a first node master public key (P 1C), and the second node is associated with a second asymmetric cryptography pair having a second node master private key (V 1S) and a second node master public key (Pis), wherein the first node master public key (P 1C) and second node master public key (P 1S) are based on elliptic curve point multiplication of respective first node master private key (V 1C) and second node master private key (V 1S) and a generator common with the first and second nodes using a common elliptic curve cryptography system with the first and second nodes, and wherein the method comprises: - determining a first node second private key (V 2C); - determining (370, 370') a second node second public key (P 2S); and - determining the common secret based on elliptic curve point multiplication of the first node second private key (V 2C) and the second node second public key (P 2S) using the common elliptic curve cryptography system, wherein the second node has the same common secret based on elliptic curve point multiplication of a first node second public key (P 2C) and a second node second private key (V 2S) using the common elliptic curve cryptography system: characterised in that the first node second private key (V 2C) is determined based on at least a scalar addition of the first node master private key (V 1C) and a deterministic key common with the first and second nodes; - the second node second public key (P 2S) is determined based on at least the second node master public key (P 1S) with elliptic curve point addition to the elliptic curve point multiplication of the common generator and the deterministic key using the common elliptic curve cryptography system; - the first node second public key (P 2C) is based on at least the first node master public key (P 1C) with elliptic curve point addition to the elliptic curve point multiplication of the common generator and the deterministic key using the common elliptic curve cryptography system; and - the second node second private key (V 2S) is based on at least a scalar addition of the second node master private key (V 1S) and the deterministic key. - determining a first node second private key (V 2C); - determining (370, 370') a second node second public key (P 2S); and - determining the common secret based on elliptic curve point multiplication of the first node second private key (V 2C) and the second node second public key (P 2S) using the common elliptic curve cryptography system, - the second node second public key (P 2S) is determined based on at least the second node master public key (P 1S) with elliptic curve point addition to the elliptic curve point multiplication of the common generator and the deterministic key using the common elliptic curve cryptography system; - the first node second public key (P 2C) is based on at least the first node master public key (P 1C) with elliptic curve point addition to the elliptic curve point multiplication of the common generator and the deterministic key using the common elliptic curve cryptography system; and - the second node second private key (V 2S) is based on at least a scalar addition of the second node master private key (V 1S) and the deterministic key.