Blockchain – Big Topic broken down to pieces Part 2 (Bag Custody Sample)


I will continue the exploration of the basic components of the blockchain technology started in the previous post, where I implemented a basic java class to visualize hashing and the linking of blocks (chain). To provide a sample for the aviation industry walking along the use-case of tracking the baggage custody changes during a flight journey .

3. Validation

A blockchain need to be validated otherwise we would not know if data was changed or corrupted. We have to iterate through the sequence of blocks, for this we create an array of bag transactions to allow easy iteration and compare the stored hash of each block with the recalculated hash. If the values match the blockchain is valid, if not it is corrupted (and all subsequent blocks). Ideally this would be event-driven, any change to the blockchain triggers the revalidation. In a real-world implementation changes through the endpoints would not be possible, something we will look at later when working with Corda or Ethereum.

		String currentBagBlockHash = "0";

		String myBagTag = randomBagTagID();
		String myPNR = randomPNR();

		ArrayList allBagTransactions = new ArrayList();
		BagTransaction tempBagTransaction = null;

		// Print Bag Tag (Genesis Block)
		tempBagTransaction = new BagTransaction(myBagTag, myPNR,,, 0, "0");
		currentBagBlockHash = tempBagTransaction.getHash();


public void checkBlockchainIntegrity(ArrayList allBagTransactions) {
	// Check Blockchain. Compare recalculated hash with hash attribute stored

	for (BagTransaction b : allBagTransactions){
		System.out.print("Block " + b.getBlockID() + " Stored Hash: " + b.getHash() + " -- Calculated Hash:" + b.createHash());
		if (b.getHash().equals(b.createHash()))
			System.out.println(" -- OK");
			System.out.println(" -- FAIL. Blockchain broken.");
	System.out.println(" -- ");

For better reading we convert each block into a JSON object.

  "timeStamp": "2018-08-26T09:18:09.227Z",
  "blockID": 0,
  "blockHash": "ce41abbf21a162152e30fc511eaf594db43c84948691d12ef78fad6f31fa6043",
  "previousBlockHash": "0",
  "bagTag": "5347241966",
  "pnr": "EONT9T",
  "custodyTransfer": [
    {"transferFrom": "NIL"},
    {"transferTo": "PAX"}
  "timeStamp": "2018-08-26T09:18:09.287Z",
  "blockID": 1,
  "blockHash": "6b6073122ef996acc1e3c3e74c3963b5903112800781b4ba88e96baf0a8e2e04",
  "previousBlockHash": "ce41abbf21a162152e30fc511eaf594db43c84948691d12ef78fad6f31fa6043",
  "bagTag": "5347241966",
  "pnr": "EONT9T",
  "custodyTransfer": [
    {"transferFrom": "PAX"},
    {"transferTo": "AIRP"}

Running the validation for a clean and corrupted blockchain

Block 0 Stored Hash: ce41abbf21a162152e30fc511eaf594db43c84948691d12ef78fad6f31fa6043 -- Calculated Hash:ce41abbf21a162152e30fc511eaf594db43c84948691d12ef78fad6f31fa6043 -- OK
Block 1 Stored Hash: 6b6073122ef996acc1e3c3e74c3963b5903112800781b4ba88e96baf0a8e2e04 -- Calculated Hash:6b6073122ef996acc1e3c3e74c3963b5903112800781b4ba88e96baf0a8e2e04 -- OK
Block 2 Stored Hash: a33bbb5ebdec589e9f1b7c7952d6fef3fae2235b5a0600b8755b07040bba8227 -- Calculated Hash:a33bbb5ebdec589e9f1b7c7952d6fef3fae2235b5a0600b8755b07040bba8227 -- OK
Block 2 Stored Hash: 464319fed3a2c49df9a1fbeedae3f3e7c6692db0f6ab97a4c983f9fdf4269e6d -- Calculated Hash:464319fed3a2c49df9a1fbeedae3f3e7c6692db0f6ab97a4c983f9fdf4269e6d -- OK
-- Now corrupt Block 1 by changing the data
Block 0 Stored Hash: ce41abbf21a162152e30fc511eaf594db43c84948691d12ef78fad6f31fa6043 -- Calculated Hash:ce41abbf21a162152e30fc511eaf594db43c84948691d12ef78fad6f31fa6043 -- OK
Block 1 Stored Hash: 6b6073122ef996acc1e3c3e74c3963b5903112800781b4ba88e96baf0a8e2e04 -- Calculated Hash:09fd4223571f079258bd69d935f99cb552cd3ac0854410b81a2313d215929ebd -- FAIL. Blockchain broken.


4. Mining Blocks

Now we get to the first more complex concepts of the blockchain, the mining process. We are still operating at a very basic level though with a single node, but we can introduce the mining operation. Without going into too much detail, mining blocks is the step to close/hash a block and creating a new one as part of the consensus process. The incentive to the miner community is a transaction fee given to that miner that solves a hard cryptographic problem first. The more computing power you invested in, the higher chance you have as miner to solve the problem and get the fee. Based on scarcity this consensus approach is called Proof-of-Work (recommended reading). Unfortunately this lead to the current hardware race consuming vast amount of energy for literally no purpose (you let CPU/GPU’s guess numbers basically). This is seen as limitation, together with the long transaction times, and some blockchain start to move to other concepts, such as Proof-of-Stake.

Breaking down the Proof-of-Work to a simple algorithm, we build a hash function that need to create a certain pattern before being accepted. The hash of (data current block + hash previous block + a nonce value) need to have a number of leading “0” in front. The number of “0” is the difficulty and the nonce is an integer value that is changed/increased until the hash matches the required pattern.

public String mineHash(int difficulty) {
	String returnHash = "";
	String tempHash = "";

	String target = new String(new char[difficulty]).replace('\0', '0');
	tempHash = createHash();

	while (!tempHash.substring(0, difficulty).equals(target)) {
		tempHash = createHash();

	return tempHash;

With a growing difficulty (more leading “0”) it takes obviously longer to crack the challenge and with more CPU power you can run through the guessing cycle faster. Some samples below with increasing difficulty running on an ordinary notebook i7 CPU (java executing on a single core/thread in this case).

Difficulty: 1
Attempts: 11
Milliseconds: 10

Difficulty: 2
Attempts: 393
Milliseconds: 30

Difficulty: 3
Attempts: 1.794
Milliseconds: 40

Difficulty: 4
Attempts: 115.756
Milliseconds: 230

Difficulty: 5
Attempts: 3.366.041
Milliseconds: 3.210

Difficulty: 6
Attempts: 5.322.279
Milliseconds: 4.530

Difficulty: 7
Attempts: 76.339.743
Milliseconds: 60.850

  "timeStamp": "2018-08-26T10:38:36.734Z",
  "blockID": 0,
  "blockHash": "0000000158d606c953a5df346d459aad949e9dbb4abe74f30ecf225c23112b14",
  "previousBlockHash": "0",
  "bagTag": "7821666095",
  "pnr": "ZHY4RT",
  "custodyTransfer": [
    {"transferFrom": "NIL"},
    {"transferTo": "PAX"}

Have a look at the below website for the current real life difficulty for bitcoin (hashing algorithm not implemented in the simple way we did it here for illustration purpose). Looking at the current difficulty (6,727,225,469,722) you can guess what kind of hardware setup you need to be fast. I gave up beyond difficulty 7 with the algorithm above.

Bitcoin Difficulty

Stay tuned for more blockchain.

Disclaimer: This discussion, datamodel and sourcecode or application is for study purpose solely. It does not reflect or replicate any existing commercial product.

Sourcecode at github


IATA Type B Bag Messages and Baggage Messaging Refresher

There is quite some movement in baggage handling and its associated messaging needs and requirements at the moment.  Though the IATA recommended practices RP 1745 and RP 1800 are around for quite a while, the IATA Resolution 753 (baggage tracking and custody) has to be implemented by June 2018 and the new BAG XML message standard is shaping up and will most likely released first time in 2017. Traditionally any handling of baggage requires a type-B message to be sent to the relevant parties. This is a push-based approach and due to the nature of type-B messages prone to errors (format) and accumulate costs by the distributing network operators and its transaction based charges. According to a IATA study/business case in the year 2012 26 million of bags have been mishandled, mostly for transfer bag handling and a good share of this is caused by missing or wrong messages.

This article is meant to provide an overview or general introduction, aka baggage messaging for starters. Baggage Handling is very complex process with dependencies and actors, including airlines, airport, handling agent and eventually the passenger and his baggage.

Main Systems involved in the process of baggage handling

DCS Departure Control System
BHS Baggage Handling System
BRS Baggage Reconciliation System

The Departure Control System is the operational backbone of every airline. It supports the check-in, baggage acceptance, boarding process and other related activities like load control, immigration.

The Baggage Handling System (usually owned by the airport) is a complex system of conveyor belts, chutes and bag drops that transports and buffers any checked-in luggage. It ensures that luggage that is checked-in, transferred or received from arriving flights is tracked, counted, scanned, screened and transported to the right bag chute or belt.

The Baggage Reconciliation System, usually used by the handling agent, helps to match passenger, bag, flight and container.

Traditional Type-B Messages for Baggage Handling (defined in IATA RP 1745)
RP 1745 defines the formats of the messages exchanged between the systems for automated baggage and passenger reconciliation, baggage sortation and other baggage services.

BTM Baggage Transfer Message
BSM Baggage Source Message
BPM Baggage Processed Message
BUM Baggage Unload Message
BNS Baggage Not Seen Message
BCM Baggage Control Message
BMM Baggage Manifest Message
BRQ Baggage Request

Baggage Tag Number or License Plate Code
A unique 10 digit number as reference for each piece of baggage, defined in IATA RP 740.
The bag tag number is part of the baggage messages.
According to resolution 751, effective June 1st 2013, the format contains only numbers.
Sample: 0220208212 (0-220-208212)

1 1 digit Leading digit 0
2 3 digit Airline code 220 Lufthansa
3 6 digit Bag number 208212

The printed barcode is a regular ITF-14 code, any smartphone can read the barcode. The number is also printed on the bag tag.

KLM is printing a “KL” in between but the barcode only contains numbers. “074” for KLM.

The Transfer Message contains bag information for the outbound carrier of incoming transfer passengers. Part of a through check-in transaction.

The Source Message is sent from the DCS to the baggage handling system upon checkin at the airport or bag drop.

The Processed Message is an status update sent locally, eg. baggage handling to carrier. BPM’s are often batched.

The Unload Message is the instruction to unload (or not to load) a specific bag, eg. no-show PAX at the gate.

The Not Seen Message contains bag info for baggage that could not been transported together with the passenger.

The Control Message serves secondary level information, such as
BAM Baggage Acknowledgement
FOM Flight Open
FMM Final Match
DBM Delete Baggage

The Baggage Manifest contains baggage details for down line stations.

The Baggage Request asks for bag info from a baggage handling system.

Sample Message
A very simple sample of a transfer message

1 .V Version and suppl. data Transfer Station FRA (Frankfurt)
2 .I Inbound Flight Number and date CPH (Copenhagen)
3 .F Outbound Flight Number and date SIN (Singapore)
4 .N Baggage Details 10 digit bag tag id 0220588615021
5 .P Passenger Name John Smith
6 .L PNR Passenger Name Record 7FABC

Message Flow for interline flight

The below is rather simplistic view (sunshine scenario) of the messaging that happens around bag management for a 2 segment interline flight with through-check-in of bags.

Message Flow for interline flight
A passenger is flying on LH 401 from JFK to FRA and SQ 025 from FRA to SIN. An interline flight with baggage checked through Singapore.

Relevant Documentation or References

IATA RP 1745 Baggage Service Messages
IATA RP 1796
Baggage System Interface
IATA RP 1701f
Self Service Baggage Process
IATA RP 1800
Baggage Process Description for Self-Service Check-in
Baggage Tracking

Online References
Remark: Most of the IATA documents are not available freely and have to be purchased, here only links to public documents or pages.

IATA BAG XML Initiative

Disclaimer: The information provided here might not be correct or complete. It is for educational purpose only. For reliable information please refer to the IATA manuals.