Common use of Indices Clause in Contracts

Indices. As it is crucial that the smart card cannot be coerced into re-using a leaf, the first operation should be incrementing the state index. Because Java Card does not guarantee a native 32-bit integer type, all indices are stored as tuples of two shorts, interpreted as 15-bit unsigned values (effectively ignoring the high bit). As a consequence, atomic increments are not possible without use of expensive transactions, and special care has to be taken in case of overflows – the conservative approach skips 215 leafs in case of card tear7, rather than rolling back. Similar considerations apply when deriving indices of ‘next’ and ‘previous’ nodes during state generation. As we have limited h/d previously, internal tree indices can be represented with a single short.