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judymcconville@roadrunner.com 2017-05-02 11:13:16 -07:00
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@ -416,7 +416,7 @@ With all the other fields filled, the block header is now complete and the proce
==== Proof-of-Work Algorithm
A hash algorithm takes an arbitrary-length data input and produces a fixed-length deterministic result, a digital fingerprint of the input. For any specific input, the resulting hash will always be the same and can be easily calculated and verified by anyone implementing the same hash algorithm. The key characteristic of a cryptographic hash algorithm is that it is computationally infeasible to find two different inputs that produce the same fingerprint (known as a _collision_). As a corollary, it is also virtually impossible to select an input in such a way as to produce a desired fingerprint, other than trying random inputs.
((("mining and consensus", "mining the block", "Proof-of-Work algorithm")))((("Proof-of-Work algorithm", id="proof10")))((("consensus", "Proof-of-Work algorithm", id="Cproof10")))A hash algorithm takes an arbitrary-length data input and produces a fixed-length deterministic result, a digital fingerprint of the input. For any specific input, the resulting hash will always be the same and can be easily calculated and verified by anyone implementing the same hash algorithm. The key characteristic of a cryptographic hash algorithm is that it is computationally infeasible to find two different inputs that produce the same fingerprint (known as a _collision_). As a corollary, it is also virtually impossible to select an input in such a way as to produce a desired fingerprint, other than trying random inputs.
With SHA256, the output is always 256 bits long, regardless of the size of the input. In <<sha256_example1>>, we will use the Python interpreter to calculate the SHA256 hash of the phrase, "I am Satoshi Nakamoto."
@ -587,7 +587,7 @@ Hashing Power: 127141 hashes per second
As you can see, increasing the difficulty by 1 bit causes a doubling in the time it takes to find a solution. If you think of the entire 256-bit number space, each time you constrain one more bit to zero, you decrease the search space by half. In <<pow_example_outputs>>, it takes 84 million hash attempts to find a nonce that produces a hash with 26 leading bits as zero. Even at a speed of more than 120,000 hashes per second, it still requires 10 minutes on a laptop to find this solution.
At the time of writing, the network is attempting to find a block whose header hash is less than +0000000000000000029AB9000000000000000000000000000000000000000000+. As you can see, there are a lot of zeros at the beginning of that target, meaning that the acceptable range of hashes is much smaller, hence it's more difficult to find a valid hash. It will take on average more than 1.8 septa-hashes (thousand billion billion hashes) per second for the network to discover the next block. That seems like an impossible task, but fortunately the network is bringing 3 exa-hashes per second (EH/sec) of processing power to bear, which will be able to find a block in about 10 minutes on average.
At the time of writing, the network is attempting to find a block whose header hash is less than +0000000000000000029AB9000000000000000000000000000000000000000000+. As you can see, there are a lot of zeros at the beginning of that target, meaning that the acceptable range of hashes is much smaller, hence it's more difficult to find a valid hash. It will take on average more than 1.8 septa-hashes (thousand billion billion hashes) per second for the network to discover the next block. That seems like an impossible task, but fortunately the network is bringing 3 exa-hashes per second (EH/sec) of processing power to bear, which will be able to find a block in about 10 minutes on average.((("", startref="Cproof10")))((("", startref="proof10")))
[[target_bits]]
==== Target Representation