  Blockchain technology streamlines multi-party collaborations in decentralized
settings, especially where trust is limited. While public blockchains enhance
transparency and reliability, they conflict with confidentiality. To address
this, we introduce Multi-Authority Approach to Transaction Systems for
Interoperating Applications (MARTSIA). MARTSIA provides read-access control at
the message-part level through user-defined policies and certifier-declared
attributes, so that only authorized actors can interpret encrypted data while
all blockchain nodes can verify its integrity. To this end, MARTSIA resorts to
blockchain, Multi-Authority Attribute-Based Encryption and distributed
hash-table data-stores.
