<p>The current block is the child and the previous block the parent. If the parent changes in any way then this will cause a change in the previous block hash pointer of the child. So the change does not ripple back to the genesis block. However what this does do is that once a block has many generations following it then it makes it very difficult to change. So the genesis block as the first block is impossible to change because changing it would make it necessary to change the previous hash of every block that followed it. </p>

CC BY-SA 3.0
2018-03-06T18:28:22.370Z
2018-03-06T18:28:22.370Z
John Singh
<p>We know that the hash of the previous block is included in the header of the next block. So, if an adversary change the data in the block no. 10, then they hash of it will be changed and the header of the block no. 11 will be no longer  true. 
But, in the textbooks that I read to understand the blockchain, the said that the change in block no. 10 will change the whole blocks till the header of the genesis block prevent.
Why the change of the data do backward from no 10 to the first not from no. 10 to 11 and so?</p>

<p>See this for example:
Imagine this for a second, a hacker attacks block 3 and tries to change the data. Because of the properties of hash functions, a slight change in data will change the hash drastically. This means that any slight changes made in block 3, will change the hash which is stored in block 2, now that in turn will change the data and the hash of block 2 which will result in changes in block 1 and so on and so forth. This will completely change the chain, which is impossible. This is exactly how blockchains attain immutability.</p>

<change>
Tamper - evident log with hash pointer
SayyedAli
# Tamper - evident log with hash pointer

(Asked by: username_0 on 2018-03-06)

We know that the hash of the previous block is included in the header of the next block. So, if an adversary change the data in the block no. 10, then they hash of it will be changed and the header of the block no. 11 will be no longer true.
But, in the textbooks that I read to understand the blockchain, the said that the change in block no. 10 will change the whole blocks till the header of the genesis block prevent.
Why the change of the data do backward from no 10 to the first not from no. 10 to 11 and so?

See this for example:
Imagine this for a second, a hacker attacks block 3 and tries to change the data. Because of the properties of hash functions, a slight change in data will change the hash drastically. This means that any slight changes made in block 3, will change the hash which is stored in block 2, now that in turn will change the data and the hash of block 2 which will result in changes in block 1 and so on and so forth. This will completely change the chain, which is impossible. This is exactly how blockchains attain immutability.

**Tags:** change


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## 1 answers

### Answer by username_1 on 2018-03-06. Score: 1 | Accepted answer

The current block is the child and the previous block the parent. If the parent changes in any way then this will cause a change in the previous block hash pointer of the child. So the change does not ripple back to the genesis block. However what this does do is that once a block has many generations following it then it makes it very difficult to change. So the genesis block as the first block is impossible to change because changing it would make it necessary to change the previous hash of every block that followed it.


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