<p>In Cardano, time is segmented into 5 day <em>epochs</em> and 1 second <em>slots</em>.</p>
<p>As users publish transactions on the network, pools distribute the transactions to their peers and store valid transactions locally in a queue, known as the <em>mempool</em>.</p>
<p>In each <em>slot</em>, one or more <em>validators</em> (pools) may be selected to forge a block. That block will contain transactions from the mempool, up to max block size.</p>
<p>Validators are able to independently check if they are elected as the slot leader. From the <a href="https://eprint.iacr.org/2017/573.pdf" rel="noreferrer">Ourobouros Praos paper</a>:</p>
<blockquote>
<p>only a slot leader is aware that it is indeed a leader for a given slot; this assignment is unknown to all the other stakeholders—including other slot leaders of the same slot—until the other stakeholders receive a valid block from this slot leader</p>
</blockquote>
<p>Blocks are signed by a validator with their <em>operational key</em> and includes the validator's <em>operational certificate</em>. The certificate is composed of the public portion of the operational key, certificate issue number, beginning KES period, and a cold key signature <a href="https://hydra.iohk.io/build/6173902/download/1/ledger-spec.pdf" rel="noreferrer">as defined in the ledger spec</a>.</p>
<p>Once the new block is distributed to the network, each other validator can verify that the new block is valid, and that the publisher was eligible to forge a block in that slot.</p>
<p>All of this happens automatically as part of the <code>cardano-node</code> software. Operators only need to update their certificate periodically.</p>
<p>The proof of this distributed random selection process is a bit much for this answer, as is the proof for how the network selects a longest chain and handles soft forks, but worth reading up on if you're interested in this topic!</p>

CC BY-SA 4.0
2021-05-28T17:58:11.777Z
Thank you kindly for the detailed and easy to understand answer.
Thomas
CC BY-SA 4.0
2021-05-27T16:26:49.743Z
2021-05-27T16:26:49.743Z
Ben NOBLE
<p>How does a stake pool node certify a block for the blockchain? What part is done manually by a human pool operator and what part is done by a machine through automation?</p>
<p>Say Peter pays Paul $10 ADA. A pool is selected to process that transaction. What happens next?</p>

<stake-pool>
How does a stake pool node certify a block for the block chain?
# How does a stake pool node certify a block for the block chain?

(Asked by: username_0 on 2021-05-27)

How does a stake pool node certify a block for the blockchain? What part is done manually by a human pool operator and what part is done by a machine through automation?

Say Peter pays Paul $10 ADA. A pool is selected to process that transaction. What happens next?

**Tags:** stake-pool

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## 1 answers

### Answer by username_1 on 2021-05-27. Score: 5 | Accepted answer

In Cardano, time is segmented into 5 day *epochs* and 1 second *slots*.

As users publish transactions on the network, pools distribute the transactions to their peers and store valid transactions locally in a queue, known as the *mempool*.

In each *slot*, one or more *validators* (pools) may be selected to forge a block. That block will contain transactions from the mempool, up to max block size.

Validators are able to independently check if they are elected as the slot leader. From the [Ourobouros Praos paper](https://eprint.iacr.org/2017/573.pdf):

> only a slot leader is aware that it is indeed a leader for a given slot; this assignment is unknown to all the other stakeholders—including other slot leaders of the same slot—until the other stakeholders receive a valid block from this slot leader

Blocks are signed by a validator with their *operational key* and includes the validator's *operational certificate*. The certificate is composed of the public portion of the operational key, certificate issue number, beginning KES period, and a cold key signature [as defined in the ledger spec](https://hydra.iohk.io/build/6173902/download/1/ledger-spec.pdf).

Once the new block is distributed to the network, each other validator can verify that the new block is valid, and that the publisher was eligible to forge a block in that slot.

All of this happens automatically as part of the `cardano-node` software. Operators only need to update their certificate periodically.

The proof of this distributed random selection process is a bit much for this answer, as is the proof for how the network selects a longest chain and handles soft forks, but worth reading up on if you're interested in this topic!

> **Comments:**
> **username_0**: Thank you kindly for the detailed and easy to understand answer.  

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