IOTA tutorial 15: BundleHash

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This is part 15 of the IOTA tutorial.

In this video series different topics will be explained which will help you to understand IOTA.
It is recommended to watch each video sequentially as I may refer to certain IOTA topics explained earlier.

How the bundleHash is created, see:
https://github.com/iotaledger/iota.lib.js/blob/v0.4.7/lib/crypto/bundle/bundle.js
Bundle.prototype.finalize = function()

To create the bundleHash the following transactionObject values are used:
address, value, obsoleteTag, currentIndex, lastIndex and timestamp.
See prepareTransfers demo (step 6):
https://www.mobilefish.com/download/iota/preparetransfers_demo.txt
Note: The currentIndex and lastIndex are array positions, that is why you will not see these fields in step 6.

For each transactionObject in the bundle, calculate:
* valueTrits = convertToTrits(value).
The length is always 81 trits (padded with 0).
Note:
The number of IOTAs created is: 2,779,530,283,277,761
This number converted to trits: 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1
That is 33 trits which means valueTrits can hold more than enough trits.

* timestampTrits = convertToTrits(timestamp).
This is the number of seconds elapsed since January 1, 1970 00:00:00 UTC.
The length is always 27 trits (padded with 0).
Note:
27 trits (1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1) converted to a decimal value is: 3,812,798,742,493

* currentIndex = bundle array index
currentIndexTrits = convertToTrits(currentIndex).
The length is always 27 trits (padded with 0).

* lastIndex = bundle.length – 1
lastIndexTrits = convertToTrits(lastIndex).
The length is always 27 trits (padded with 0).

* bundleEssence = convertToTrits(address + convertToTrytes(valueTrits) + obsoleteTag + convertToTrytes(timestampTrits) + convertToTrytes(currentIndexTrits) + convertToTrytes(lastIndexTrits))
The bundleEssence length is always 81 + 27 + 27 + 9 + 9 + 9 = 162 trytes = 162 x 3 = 486 trits
Use the cryptographic sponge construction to absorb the bundleEssences and squeeze the hash.

Convert the hash to trytes:
bundleHash = convertToTrytes(hash)
The bundleHash contains 243 / 3 = 81 trytes.
For example:
bundleHash = NBBKCKPFECRKCDIBKSTHZYZKSXFEUPTIJRK9FECFKPTTSWTLUWGIFS9AHSDT9LASABRD9KDVFJ9GT9CKA

Add the bundleHash for each transactionObject in the bundle (fieldname is bundle).
The bundleHash identifies which transactions belongs to the same bundle.
See prepareTransfers demo (step 7):
https://www.mobilefish.com/download/iota/preparetransfers_demo.txt

After the bundleHash is added in the transactionObjects, the normalizedBundleHash is calculated.
The normalizedBundleHash is explained in IOTA tutorial 16.
The normalizedBundleHash is used to create or validate a signature.

If the normalizedBundleHash has tryte value M:
* Update the obsoleteTag in the FIRST transactionObject in the bundle by converting the obsoleteTag to trits, add value 1 and convert the result back to trytes.
* After the obsoleteTag is updated:
– Calculate the bundleEssences.
– Apply the cryptographic sponge construction.
– Calculate the bundleHash.
– Calculate the normalizedBundleHash.
* Repeat these steps until the normalizedBundleHash has no tryte value M.

To check for tryte value M in the normalizedBundleHash, see:
https://github.com/iotaledger/iota.lib.js/blob/v0.4.7/lib/crypto/bundle/bundle.js
Bundle.prototype.finalize = function()

See example where the obsoleteTag was updated multiple times.
https://www.mobilefish.com/download/iota/data_transaction_example2.txt

Remarks:
The normalizedBundleHash is not stored in the bundle but it is calculated using the bundleHash which is stored in the bundle.
The obsoleteTag plays an important role in the creation of the bundleHash.
https://github.com/iotaledger/iota.lib.js/blob/v0.4.7/lib/crypto/bundle/bundle.js
Bundle.prototype.finalize = function()

Check out all my other IOTA tutorial videos:
https://goo.gl/aNHf1y

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The presentation used in this video tutorial can be found at:
https://www.mobilefish.com/developer/iota/iota_quickguide_tutorial.html

#mobilefish #howto #iota

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