The invention provides a secure method for exchanging entities via a blockchain. The invention incorporates tokenisation techniques, and also techniques for embedding metadata in a redeem script of a blockchain transaction. Embodiment(s) provide a method of: generating a first script, the first script comprising: a first set of metadata associated with a first invitation for the exchange of a first entity by a first user, the first set of metadata comprising an indication of the first entity to be offered for exchange and a first location condition for the exchange, a first user public key (P1A) associated with the first user, wherein the first user public key (P1A) is part of an asymmetric cryptographic pair comprising the first user public key (P1A) and a first user private key (V1A). The script may further comprise a first third-party public key (P1T) associated with a first third-party, wherein the first third-party public key (P1T) is part of an asymmetric cryptographic pair comprising the first third-party public key (P1T) and a first third-party private key (V1T) The method further comprises the steps of hashing the first script to generate a first script hash and publishing the first script and the first script hash on a distributed hash table (DHT).