A method of sharing a first common secret among a plurality of nodes, wherein each said node is associated with a respective asymmetric cryptography first key pair having a respective first private key and a respective first public key of a cryptography system common to said plurality of nodes, and wherein the first common secret is based on the first private key of each of said nodes, the method comprising:- determining, for at least one first node, a plurality of second common secrets (x 1, x 2, x 3), wherein each said second common secret is common to said first node and a respective second node, is determined at said first node on the basis of the first private key of the first node and the first public key of the second node, and is determined at the second node on the basis of the first private key of the second node and the first public key of the first node, wherein a plurality of shares of the first common secret are each based on at least one respective second common secret such that said first common secret is accessible to a threshold number of said shares but is inaccessible to less than said threshold number of shares; determining, for at least one second node, at least one respective third common secret, wherein the or each respective third common secret is common to said second node and a respective third node, is determined at said second node on the basis of the first private key of the second node and the first public key of the third node, and is determined at the third node on the basis of the first private key of the third node and the first public key of the second node, and wherein at least one share of the first common secret is based on at least one respective said third common secret; encrypting, at at least one said first node, at least one share of said first common secret known to said first node, on the basis of a respective encryption key common to said first node and a respective said second node, wherein said encryption key is based on a respective said second common secret known to said first node and said second node; sending at least one said encrypted share from said first node to the respective said second node with which the second common secret on which said encryption key is based is common; and receiving, at at least one said first node, from at least one said second node, at least one respective share of said first common secret known to said second node and encrypted on the basis of a respective encryption key common to said first node and said second node, wherein said encryption key is based on the second common secret common to said first node and said second node, to enable said first node to access at least one share of said first common secret known to said second node. determining, for at least one first node, a plurality of second common secrets (x 1, x 2, x 3), wherein each said second common secret is common to said first node and a respective second node, is determined at said first node on the basis of the first private key of the first node and the first public key of the second node, and is determined at the second node on the basis of the first private key of the second node and the first public key of the first node, wherein a plurality of shares of the first common secret are each based on at least one respective second common secret such that said first common secret is accessible to a threshold number of said shares but is inaccessible to less than said threshold number of shares; determining, for at least one second node, at least one respective third common secret, wherein the or each respective third common secret is common to said second node and a respective third node, is determined at said second node on the basis of the first private key of the second node and the first public key of the third node, and is determined at the third node on the basis of the first private key of the third node and the first public key of the second node, and wherein at least one share of the first common secret is based on at least one respective said third common secret; encrypting, at at least one said first node, at least one share of said first common secret known to said first node, on the basis of a respective encryption key common to said first node and a respective said second node, wherein said encryption key is based on a respective said second common secret known to said first node and said second node; sending at least one said encrypted share from said first node to the respective said second node with which the second common secret on which said encryption key is based is common; and receiving, at at least one said first node, from at least one said second node, at least one respective share of said first common secret known to said second node and encrypted on the basis of a respective encryption key common to said first node and said second node, wherein said encryption key is based on the second common secret common to said first node and said second node, to enable said first node to access at least one share of said first common secret known to said second node.