Canonical Transaction Ordering


1. definition

Canonical Transaction Ordering (CTOR) is a rule implemented in the Bitcoin Cash (BCH) network that mandates transactions within each block to be ordered by their transaction IDs in lexicographical order. This specific ordering allows for more efficient block propagation, faster transaction lookup, and potential future scalability enhancements.


For instance, if a block contains three transactions with IDs 'a', 'b', and 'c', under CTOR, these transactions must be ordered as 'a', 'b', 'c' within the block. This order allows nodes to quickly verify the correctness of the transaction order in a block, and it simplifies the process of checking whether a specific transaction is included in a block.

2. implementation

CTOR was activated on the Bitcoin Cash network during the scheduled November 2018 hard fork. The implementation of CTOR was part of a broader effort to improve the scalability and efficiency of the BCH network, with the goal of enabling BCH to function as a global currency.


Prior to the implementation of CTOR, transactions in a block could be in any order, as long as the dependencies between transactions were respected. This old ordering system was known as Topological Transaction Ordering (TTOR). The switch to CTOR was a significant change in the block structure of BCH.

3. benefits

The benefits of CTOR are not just limited to faster transaction lookup. It also allows for enhanced compression techniques, which can reduce the amount of data that needs to be transmitted when propagating blocks across the network. This can lead to faster block propagation times, reducing the risk of stale blocks and improving the overall efficiency of the network.


With CTOR, it's possible to use techniques like Graphene for block propagation, which can significantly reduce the amount of data that needs to be transmitted. This is because with CTOR, the order of transactions in a block is known in advance, so only the presence or absence of transactions needs to be communicated, not their order.

* All terms and definitions may update as the Cryptionary improves.