System for cryptocurrency transactions, includes a server configured to mediate exchange of data between user devices; an internal currency derivable from any cryptocurrency; each user device configured to issue, transfer rights, redemption and restoration of an internal currency unit. Issue includes creation of new addresses in blockchain, protected by splitting the private key PrivKey into first part (PrivKey1) and second part (PrivKey2), and requires connection to the blockchain only once, to generate PrivKey and to split PrivKey into PrivKey1 and PrivKey2, based on PrivKey*G=(PrivKey1*PrivKey2)*G. PrivKey1 is generated and stored in the server, PrivKey2 is generated on the user's device. The server stores all PrivKey1's device IDs of the user's device. Redemption requires both PrivKey1 and PrivKey2; public key PublicKey of each internal currencies unit is PrivKey1*(PrivKey2*G)=PrivKey2*(PrivKey1*G)=PublicKey; user with PublicKey can check balance for the corresponding private key PrivKey but needs PrivKey to redeem/transfer.