Merkle root proof of existence OP_RETURN data at vout=3 is a hash of the filenames, as H = SHA-256d(NAME1 || 0x20 || NAME2 || 0x20 || NAME3) OP_RETURN data at vout=4 is the Merkle root of the files, as H = SHA-256d(0x01 || SHA-256d(0x01 || SHA-256d(0x00 || F1) || SHA-256d(0x00 || F2)) || SHA-256d(0x01 || SHA-256d(0x00 || F3) || SHA-256d(0x00 || F3)))