Ruby Quiz - Challenge #2 - Calculate the Bitcoin Genesis Block Hash (SHA-256)

[Gerald Bauer]

Hello,

To kick start the new Ruby Quiz let's add another "real world" puzzle.


Challenge #2 - Calculate the Bitcoin Genesis Block Hash (SHA-256)


Let's calculate the classic bitcoin (crypto) block hash from scratch (zero).
Let's start with the genesis block, that is block #0
with the unique block hash id
`000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f`.

Note: You can search and browse bitcoin blocks using (online)
block explorers. Example:

- blockchain.info/block/000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f
[1]
- blockexplorer.com/block/000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f
[2]
- and others.

The classic bitcoin (crypto) block hash gets calculated from
the 80-byte block header:

| Field | Size (Bytes) | Comments |
|------------|--------------|--------------------|
| version | 4 byte | Block version number |
| prev | 32 byte | 256-bit hash of the previous block header |
| merkleroot | 32 byte | 256-bit hash of all transactions in the block |
| time | 4 bytes | Current timestamp as seconds since
1970-01-01 00:00 |
| bits | 4 bytes | Current difficulty target in compact
binary format |
| nonce | 4 bytes | 32-bit number of the (mined) lucky
lottery number used once |

Note: 32 byte x 8 bit = 256 bit

Tip: Find out more about the Bitcoin Block hashing algorithm [3]
in the wiki page.

Using the data for the genesis block the setup is:

```
version = 1
prev = "0000000000000000000000000000000000000000000000000000000000000000"
merkleroot = "4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b"
time = 1231006505
bits = "1d00ffff"
nonce = 2083236893
```


The challenge: Code a calculate method that returns the Bitcoin hash.
Start from scratch or, yes, use any library / gem you can find.

```
def calculate( version, prev, merkleroot, time, bits, nonce )
# ...
end
```


To qualify for solving the code challenge / puzzle you must pass the test:

```
require 'minitest/autorun'


class RubyQuizTest < MiniTest::Test

def test_calculate

hash = "000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f"

version = 1
prev =
"0000000000000000000000000000000000000000000000000000000000000000"
merkleroot =
"4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b"
time = 1231006505
bits = "1d00ffff"
nonce = 2083236893

assert_equal hash, calculate( version, prev, merkleroot, time, bits, nonce )

end # method test_calculate
end # class RubyQuizTest
```

Post your code snippets on the "official" Ruby Quiz Channel,
that is, the ruby-talk mailing list.

Happy hacking and crypto mining with Ruby.


PS: The Ruby Quiz - #1 Challenge is still open too for new code
snippets / solutions! [4]


[1]: https://blockchain.info/block/000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f
[2]: https://blockexplorer.com/block/000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f
[3]: https://en.bitcoin.it/wiki/Block_hashing_algorithm
[4]: https://github.com/planetruby/quiz

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[Frank J. Cameron]

Post by Gerald Bauer
Challenge #2 - Calculate the Bitcoin Genesis Block Hash (SHA-256)

$ ruby lib/002.rb
Run options: --seed 62016
# Running:
.
Finished in 0.002718s, 367.9076 runs/s, 367.9076 assertions/s.
1 runs, 1 assertions, 0 failures, 0 errors, 0 skips

$ cat lib/002.rb
require_relative '../002/test.rb'
require 'digest'
class RubyQuizTest
def calculate(v, p, m, t, b, n)
Digest::SHA256.digest(
Digest::SHA256.digest(
[v].pack('V') \
+ [p].pack('H*').reverse \
+ [m].pack('H*').reverse \
+ [t].pack('V') \
+ [b].pack('H*').reverse \
+ [n].pack('V')
)
).reverse.unpack('H*')[0]
end
end
RubyQuizTest.new('fjc')



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