What Is An Orphaned Block?
An orphaned block is a block that has been successfully mined but does not get added to the blockchain.
What Is A Block?
Before exploring orphaned blocks in detail, what is a regular block in a blockchain?
A block in a blockchain is a batch of transactions that happens on that network. Using cryptography, each batch of transactions is securely linked to the previous batch in a “chain” of blocks.
These links ensure that network participants are alerted if anyone tampers with data in a block.
Orphaned Blocks
An orphaned block is, as mentioned, a successfully mined block but is yet to be added to the blockchain.
This happens when two different miners produce blocks at the same time. Only one can be added, even if they’re both valid.
The block that is rejected is left stranded alone, unattached to the rest of the chain. Its parent block—the block that precedes it—is unknown, which is why it is referred to as an “orphan.”
Any unprocessed transactions from the orphaned block will be returned to the memory pool, to be processed again.
Basic Dynamics of Blocks in a Blockchain
The batch of transaction information isn’t the only data that a block contains. It will also contain a comprehensive header and some additional metadata.
The Header
The header is a very important part of the block, as it is what links the block to the previous one.
This is done by including the “hash” (a fingerprint) of the last block. It will also include a timestamp that shows when the block was created, as well as a special number called a nonce.
Finally, the header will include a Merkle root – a cryptographic code that represents all of the block’s transactions in a single hash. This is what will tie this block to the next one.
Additional Metadata
The additional metadata attached to the block will carry general information about the block, which isn’t necessarily important to its data integrity.
This may include the size of the block in bytes, the mining difficulty at the time the block was created, and the version of the mining software being used.
How Are Blocks Linked In Blockchain?
Blocks are linked in a blockchain using special cryptography.
Each block is tagged with its own digital fingerprint, called a hash. When a new block is mined, it also records the hash of the previous block. This means that each block “remembers” the block that came before it.
Now, if someone tries to modify even the tiniest bit of information in any block, every block that comes after it will raise a warning flag that it is invalid. As a result, the rest of the network will know not to trust this particular version of the chain, and it will be thrown away.
How Is A Block Validated In Blockchain?
First, each and every transaction in a block is verified. This involves checking the transaction inputs and digital signatures.
Then, the block hash is checked. For a block to be valid, the hash needs to meet specific criteria, which depend on the particular blockchain at hand.
Following this, it is verified that the block points to the true last block on the blockchain.
Finally, validators check that the “Merkle Root” is correct, verifying that none of the transactions have been tampered with since the block was created.
How Are Orphan Blocks Different From Stale Blocks?
What Is A Stale Block?
A stale block is a very similar scenario to an orphan block.
Once again, two blocks were mined at almost the same time. Rather than one of them being discarded, each of these blocks is added to a version of the blockchain.
Both of these blockchains may continue growing for a short while. However, only one version of the blockchain can be kept alive – and that is the longest chain.
Whichever chain receives the next block will usually prevail, leaving one dead chain behind that ends with the “wrong” block. This is a stale block.
Orphan Block vs Stale Block
The common trait an orphan block and a stale block both share is that neither of the two will make up part of the longest valid blockchain.
However, a stale block actually makes it onto a version of the blockchain. On the other hand, an orphaned block was stranded altogether. It never gets the chance to link back to a previous “parent” block.
Article Sources
Howard L. Poston (2019). A Brief Introduction to Blockchain Concepts
https://ghostvolt.com/eBooks/eBook-Introduction-to-Blockchain-Concepts_Howard-L-Poston.pdf
The Institutes (2017). Blockchain Building Blocks: Creating a world of opportunity for insurance from an evolving area of technology.
https://theblockchaintest.com/uploads/resources/The%20Institutes%20-%20Blockchain%20Building%20Blocks-Creating%20a%20world%20of%20opportunity%20for%20insurance%20from%20an%20evolving%20area%20of%20technology%20-%202019.pdf