A method of transferring access to a digital asset is disclosed. The method comprises receiving a first blockchain transaction (4) from a first participant (6) by each of a plurality of second participants (8), (10). The first participant (6) has a first private key of a first private-public key pair of a cryptography system, and each participant (6), (8), (10) has a respective first share of a second private key of a second private-public key pair of the cryptography system, and the first blockchain transaction is signed with the first private key. Signature of the first blockchain transaction with the first private key is verified by each second participant (8), (10). A respective first share is applied to the first blockchain transaction to generate a respective second share of a second blockchain transaction signed with the second private key. Signature with the second private key is possible by means of a first threshold number of second shares and is inaccessible to less than the first threshold number of second shares. The first threshold number of second shares is combined from the first participant (6) and a plurality of the second participants (8), (10) generate the signature.