arno/bitcoinbook
1
0
Fork 0
mirror of https://github.com/bitcoinbook/bitcoinbook synced 2024-11-12 02:49:26 +00:00
Code Issues Releases Wiki Activity

Merge pull request #143 from cgodley/develop

Browse Source 
Clarify the phrase "the same block as its parent" since it is ambiguous ...
This commit is contained in:
Minh T. Nguyen 2014-10-19 22:50:37 -04:00
commit c95b2b15d4
1 changed files with 1 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
ch07.asciidoc
View File

@ -9,7 +9,7 @@ The blockchain data structure is an ordered back-linked list of blocks of transa
Each block within the blockchain is identified by a hash, generated using the SHA256 cryptographic hash algorithm on the header of the block. Each block also references a previous block, known as the _parent_ block, through the "previous block hash" field in the block header. In other words, each block contains the hash of its parent inside its own header. The sequence of hashes linking each block to its parent, creates a chain going back all the way to the first block ever created, known as the _genesis block_.
While a block has just one parent, it can temporarily have multiple children. Each of the children refers to the same block as its parent and contains the same (parent) hash in the "previous block hash" field. Multiple children arise during a blockchain "fork", a temporary situation that occurs when different blocks are discovered almost simultaneously by different miners (see <<forks>>). Eventually, only one child block becomes part of the blockchain and the "fork" is resolved. Even though a block may have more than one child, each block can have only one parent. This is because a block has one single "previous block hash" field referencing its single parent.
While a block has just one parent, it can temporarily have multiple children. Each of the children refers to the same (parent) block and contains the same (parent) hash in the "previous block hash" field. Multiple children arise during a blockchain "fork", a temporary situation that occurs when different blocks are discovered almost simultaneously by different miners (see <<forks>>). Eventually, only one child block becomes part of the blockchain and the "fork" is resolved. Even though a block may have more than one child, each block can have only one parent. This is because a block has one single "previous block hash" field referencing its single parent.
The "previous block hash" field is inside the block header and thereby affects the _current_ block's hash. The child's own identity changes if the parent's identity changes. When the parent is modified in any way, the parent's hash changes. The parent's changed hash necessitates a change in the "previous block hash" pointer of the child. This in turn causes the child's hash to change, which requires a change in the pointer of the grandchild, which in turn changes the grandchild and so on. This cascade effect ensures that once a block has many generations following it, it cannot be changed without forcing a recalculation of all subsequent blocks. Because such a recalculation would require enormous computation, the existence of a long chain of blocks makes the blockchain's deep history immutable, a key feature of bitcoin's security.