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Is verification of a blockchain computationally cheaper than recreating it?

What exactly is Mining?What is the Merkle root?can I use elements of the blockchain to protect the integrity of a leaderboard without central servers?How scalable is a Blockchain-based system?Exchange Transaction versus Blockchain VerificationHow Blockchain transaction verification takes place?Can a Blockchain be Built Like This?How do you get Sibling Hashed Values in a Merkle Proof?Blockchain and anonymous data inside the chainHow and why we need to validate a transaction?Why do we need to chain the blocks (creating blockchain) in a permissioned blockchain?

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1

1

One of the advantages of cryptocurrencies like Bitcoin that is often repeated is how hard it should be to manipulate past transactions. The reason that is often stated is that you would have to re-calculate all the headers with all the hash values of the whole chain which is practically un-doable.

My question is: How do you verify the blockchain integrity? Don't you also have to recalculate all the values to see whether they are valid? Or is the complexity class of verification different from creating a new chain? In other words is there some asymmetry at work here and if yes how does it work?

blockchain hash transaction-verification algorithms theory

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edited 7 hours ago

vonjd

asked 9 hours ago

vonjdvonjd

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1

1

One of the advantages of cryptocurrencies like Bitcoin that is often repeated is how hard it should be to manipulate past transactions. The reason that is often stated is that you would have to re-calculate all the headers with all the hash values of the whole chain which is practically un-doable.

My question is: How do you verify the blockchain integrity? Don't you also have to recalculate all the values to see whether they are valid? Or is the complexity class of verification different from creating a new chain? In other words is there some asymmetry at work here and if yes how does it work?

blockchain hash transaction-verification algorithms theory

share|improve this question

edited 7 hours ago

vonjd

asked 9 hours ago

vonjdvonjd

10855 bronze badges

New contributor

vonjd is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

add a comment | 

One of the advantages of cryptocurrencies like Bitcoin that is often repeated is how hard it should be to manipulate past transactions. The reason that is often stated is that you would have to re-calculate all the headers with all the hash values of the whole chain which is practically un-doable.

My question is: How do you verify the blockchain integrity? Don't you also have to recalculate all the values to see whether they are valid? Or is the complexity class of verification different from creating a new chain? In other words is there some asymmetry at work here and if yes how does it work?

blockchain hash transaction-verification algorithms theory

share|improve this question

edited 7 hours ago

vonjd

asked 9 hours ago

vonjdvonjd

10855 bronze badges

New contributor

vonjd is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

edited 7 hours ago

vonjd

asked 9 hours ago

vonjdvonjd

10855 bronze badges

New contributor

vonjd is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

edited 7 hours ago

vonjd

asked 9 hours ago

vonjdvonjd

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vonjd is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 9 hours ago

vonjdvonjd

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vonjd is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 9 hours ago

vonjdvonjd

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2 Answers
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Is verification of blockchain computationally cheaper than recreating it?

Yes, far easier

How do you verify the blockchain integrity? Don't you also have to recalculate all the values to see whether they are valid?

No.

The miner has to find a value for parts of the block they can choose a value for, such that a hash of the block has a certain number of leading zeroes. This is impossible to predict without actually calculating the hash. So miners have to try a very large number of different choices before finding one that produces the hash with the required number of leading zeroes.

The verifier only has to recalculate that hash once because they don't need to vary any part of the block.

(note, the above is a simplification but the principles apply)

---

Reference:

• Nonce


• What exactly is Mining?

share|improve this answer

edited 9 hours ago

answered 9 hours ago

RedGrittyBrickRedGrittyBrick

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3

The reason that is often stated is that you would have to re-calculate all the headers with all the hash values of the whole chain which is practically un-doable.

It's not the mere recalculation of new headers: miners currently create about 8×10^19 block candidates every second. However, at current difficulty levels, it takes about 4.8×10^22 block candidates until a valid block is found. E.g. to change the history five blocks back, you have to find six blocks (approximately 2.9×10^23 block candidates) before the whole network together finds one more block.

share|improve this answer

answered 8 hours ago

Murch♦Murch

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3

Is verification of blockchain computationally cheaper than recreating it?

Yes, far easier

How do you verify the blockchain integrity? Don't you also have to recalculate all the values to see whether they are valid?

No.

The miner has to find a value for parts of the block they can choose a value for, such that a hash of the block has a certain number of leading zeroes. This is impossible to predict without actually calculating the hash. So miners have to try a very large number of different choices before finding one that produces the hash with the required number of leading zeroes.

The verifier only has to recalculate that hash once because they don't need to vary any part of the block.

(note, the above is a simplification but the principles apply)

---

Reference:

• Nonce


• What exactly is Mining?

share|improve this answer

edited 9 hours ago

answered 9 hours ago

RedGrittyBrickRedGrittyBrick

3,60811 gold badge1010 silver badges2222 bronze badges

add a comment | 

3

Is verification of blockchain computationally cheaper than recreating it?

Yes, far easier

How do you verify the blockchain integrity? Don't you also have to recalculate all the values to see whether they are valid?

No.

The miner has to find a value for parts of the block they can choose a value for, such that a hash of the block has a certain number of leading zeroes. This is impossible to predict without actually calculating the hash. So miners have to try a very large number of different choices before finding one that produces the hash with the required number of leading zeroes.

The verifier only has to recalculate that hash once because they don't need to vary any part of the block.

(note, the above is a simplification but the principles apply)

---

Reference:

• Nonce


• What exactly is Mining?

share|improve this answer

edited 9 hours ago

answered 9 hours ago

RedGrittyBrickRedGrittyBrick

3,60811 gold badge1010 silver badges2222 bronze badges

add a comment | 

Is verification of blockchain computationally cheaper than recreating it?

Yes, far easier

How do you verify the blockchain integrity? Don't you also have to recalculate all the values to see whether they are valid?

No.

The miner has to find a value for parts of the block they can choose a value for, such that a hash of the block has a certain number of leading zeroes. This is impossible to predict without actually calculating the hash. So miners have to try a very large number of different choices before finding one that produces the hash with the required number of leading zeroes.

The verifier only has to recalculate that hash once because they don't need to vary any part of the block.

(note, the above is a simplification but the principles apply)

---

Reference:

• Nonce


• What exactly is Mining?

share|improve this answer

edited 9 hours ago

answered 9 hours ago

RedGrittyBrickRedGrittyBrick

3,60811 gold badge1010 silver badges2222 bronze badges

share|improve this answer

edited 9 hours ago

answered 9 hours ago

RedGrittyBrickRedGrittyBrick

3,60811 gold badge1010 silver badges2222 bronze badges

answered 9 hours ago

RedGrittyBrickRedGrittyBrick

3,60811 gold badge1010 silver badges2222 bronze badges

answered 9 hours ago

RedGrittyBrickRedGrittyBrick

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3

The reason that is often stated is that you would have to re-calculate all the headers with all the hash values of the whole chain which is practically un-doable.

It's not the mere recalculation of new headers: miners currently create about 8×10^19 block candidates every second. However, at current difficulty levels, it takes about 4.8×10^22 block candidates until a valid block is found. E.g. to change the history five blocks back, you have to find six blocks (approximately 2.9×10^23 block candidates) before the whole network together finds one more block.

share|improve this answer

answered 8 hours ago

Murch♦Murch

35.9k2727 gold badges119119 silver badges350350 bronze badges

add a comment | 

3

The reason that is often stated is that you would have to re-calculate all the headers with all the hash values of the whole chain which is practically un-doable.

It's not the mere recalculation of new headers: miners currently create about 8×10^19 block candidates every second. However, at current difficulty levels, it takes about 4.8×10^22 block candidates until a valid block is found. E.g. to change the history five blocks back, you have to find six blocks (approximately 2.9×10^23 block candidates) before the whole network together finds one more block.

share|improve this answer

answered 8 hours ago

Murch♦Murch

35.9k2727 gold badges119119 silver badges350350 bronze badges

add a comment | 

The reason that is often stated is that you would have to re-calculate all the headers with all the hash values of the whole chain which is practically un-doable.

It's not the mere recalculation of new headers: miners currently create about 8×10^19 block candidates every second. However, at current difficulty levels, it takes about 4.8×10^22 block candidates until a valid block is found. E.g. to change the history five blocks back, you have to find six blocks (approximately 2.9×10^23 block candidates) before the whole network together finds one more block.

share|improve this answer

answered 8 hours ago

Murch♦Murch

35.9k2727 gold badges119119 silver badges350350 bronze badges

share|improve this answer

answered 8 hours ago

Murch♦Murch

35.9k2727 gold badges119119 silver badges350350 bronze badges

answered 8 hours ago

Murch♦Murch

35.9k2727 gold badges119119 silver badges350350 bronze badges

answered 8 hours ago

Murch♦Murch

35.9k2727 gold badges119119 silver badges350350 bronze badges