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# block difficulties

we use [hashcash][1] as a mechanism to protect the blockchain from a Sybil Attack.

The difficulty is the number of hexadecimal digit we have to "resolve" in the block hash.

Finding a block hash than match the required difficuly is the "work"
and the hash itself is the [*proof of work*][1].

example: block [Z9Pa9kcag3TBc6EX671u6Zwk7N6M7jTuQ5HPtjzDrpx4f][2] has is matching a difficulty of 4








[1]: /docs/pow.html
[2]: /api/0.0/getblock?hash=Z9Pa9kcag3TBc6EX671u6Zwk7N6M7jTuQ5HPtjzDrpx4f