ISO 8583 Decoder

ISO 8583 is the message format most national financial switches and card networks still speak — a fixed MTI, a bitmap declaring which fields are present, then fields packed back to back with no delimiters. This decodes a common subset of fields used in a card-present financial transaction, the same shape I built a jPOS bridge for against Zambia's National Financial Switch.

Supported fields: 2, 3, 4, 7, 11, 12, 13, 32, 37, 39, 41, 42, 49 — everything else stops the decode with a warning, same as a real packager would if it didn't recognize a field.