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I'm vaguely familiar with Bitcoin's UTXO-based transaction structure and Ethereum's account-based/gas-including transaction structure.

What does an IOTA transaction contain?

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Trinary Note

  • In the "normal" world we have bytes & bits, where 1 byte is 8 bits giving us 2^8 = 256 possible data values for 1 byte.
  • In the trinary world we have trytes & trits, where 1 tryte is 3 trits giving us 3^3 = 27 possible data values for 1 tryte. This is what IOTA uses to stores its transaction data.

Transaction Composition

One IOTA transaction consists of 2673 trytes. Note, however, that a user will usually broadcast a collection of multiple transactions (also called a bundle). One bundle could consist of

  1. Withdrawal transaction (acquire funds to be spent from some address)
  2. Payment transactions (pay some other address a sub or total amount of the funds withdrawn)
  3. Change transaction (deposit unspent funds back to one of the user's addresses)

Note that bundles are not restricted to a specific number of transactions. For exmaple, one could have a bundle that consists of just one transaction (when a value of 0 is "transferred").

The data segments within one transaction are as follows.

Core Data
  1. Signature Message Fragment contains the transaction signature = 2187 trytes
  2. Address is either receipt address (if value > 0) or withdrawal address (if value < 0) = 81 trytes
  3. Value is the amount of IOTA transferred = 27 trytes
  4. Obsolete Tag is some arbitrary user-defined value = 27 trytes
  5. Time Stamp of when the transaction was issued = 9 trytes
  6. Current Index of this transaction in its bundle = 9 trytes
  7. Last Index is the total number of transactions in the bundle = 9 trytes
Hashes
  1. Bundle Hash is the hash of the entire bundle = 81 trytes
  2. Trunk Hash is the hash of the 1st transaction referenced/approved = 81 trytes
  3. Branch Hash is the hash of the 2nd transaction referenced/approved = 81 trytes
Another Tag
  1. Tag is another arbitrary user-defined value = 27 trytes
Additional Time Stamps
  1. Attachment Time is the time stamp for when PoW is completed = 9 trytes
  2. Attachment Time (lower bound) is a slot for future use = 9 trytes
  3. Attachment Time (upper bound) is a slot for future use = 9 trytes
Proof-of-Work Data
  1. Nonce is the PoW nonce of the transaction = 27 trytes

Additional Links

https://github.com/iotaledger/iri/.../controllers/TransactionViewModel.java
https://github.com/alon-e/iotaWayback
https://iota.readme.io/docs/the-anatomy-of-a-transaction

  • Actually, the Nonce has been reduced to 27 trytes, and the remaining part of the (old) nonce is used for a second Tag field (27 trytes) and three timestamp fields (9 trytes each) – mihi Nov 29 '17 at 20:02
  • @mihi Do you have a source? Then I can update my answer accordingly. – Phil-ZXX Nov 29 '17 at 22:34
  • iri commit: github.com/iotaledger/iri/commit/… – mihi Nov 29 '17 at 22:46
  • Small clarification: 8. is the hash of the fields 2 to 7 of the entire bundle (it obviously cannot contain itself, the signature, or one of the other hashes, but it also does not include the additional timestamps) – mihi Dec 2 '17 at 23:50

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