  We provide a UTXO model of blockchain transactions that is able to represent
both credit and debt on the same blockchain. Ordinarily, the UTXO model is
solely used to represent credit and the representation of credit and debit
together is achieved using the account model because of its support for
balances. However, the UTXO model provides superior privacy, safety, and
scalability when compared to the account model. In this work, we introduce a
UTXO model that has the flexibility of balances with the usual benefits of the
UTXO model. This model extends the conventional UTXO model, which represents
credits as unmatched outputs, by representing debts as unmatched inputs. We
apply our model to solving the problem of transparency in reverse mortgage
markets, in which some transparency is necessary for a healthy market but
complete transparency leads to adverse outcomes. Here the pseudonymous
properties of the UTXO model protect the privacy of loan recipients while still
allowing an aggregate view of the loan market. We present a prototype of our
implementation in Tendermint and discuss the design and its benefits.
