add bitcoin header

Author: geraldb

README.md

@@ -1038,7 +1038,7 @@ d2.to_s                  # convert 32-byte (256-bit) binary to hex string
 ```
 
 Note: Classic bitcoin uses a double hash, that is,
-for even higher security the hash gets hashed twice with the SHA256 algorithm 
+for even higher security the hash gets hashed twice with the SHA256 algorithm
 e.g. `sha256(sha256(header))`.
 
 In practice let's deal with the different byte order conversions
@@ -1184,13 +1184,125 @@ bin_to_hex32( d2 )
 ```
 
 
+Bonus. For easy (re)use let's package up the bitcoin block header code into a class:
+
+``` ruby
+require 'digest'
+
+module Bitcoin
+  class Header
+    attr_reader :version
+    attr_reader :prev
+    attr_reader :merkleroot
+    attr_reader :time
+    attr_reader :bits
+    attr_reader :nonce
+
+    def initialize( version, prev, merkleroot, time, bits, nonce )
+       @version    = version
+       @prev       = prev
+       @merkleroot = merkleroot
+       @time       = time
+       @bits       = bits
+       @nonce      = nonce
+    end
+
+    ## lets add a convenience c'tor helper
+    def self.from_hash( h )
+      new( h[:version],
+           h[:prev],
+           h[:merkleroot],
+           h[:time],
+           h[:bits],
+           h[:nonce] )
+    end
+
+    def to_bin
+       i4( version )       +
+      h32( prev )          +
+      h32( merkleroot )    +
+       i4( time )          +
+       i4( bits.to_i(16) ) +
+       i4( nonce )
+    end
+
+    def hash
+      bytes = sha256(sha256( to_bin ))
+      bin_to_h32( bytes )
+    end
+
+    def sha256( bytes )
+       Digest::SHA256.digest( bytes )
+    end
+
+    ## binary pack/unpack conversion helpers
+    def i4( num )   ##  integer (4 byte / 32bit) to binary (in little endian)
+      [num].pack( 'V' )
+    end
+
+    def h32( hex )   ## hex string (32 byte / 256 bit / 64 hex chars) to binary
+      [hex].pack( 'H*' ).reverse     ## change byte order (w/ reverse)
+    end
+
+    def bin_to_h32( bytes )
+      bytes.reverse.unpack( 'H*' )[0]   ## note: change byte order (w/ reverse)
+    end
+  end # class Header
+end # module Bitcoin
+```
+
+and let's test drive it with the genesis block #0 and block #125552:
+
+``` ruby
+b0 =
+Bitcoin::Header.from_hash(
+  version:     1,
+  prev:       '0000000000000000000000000000000000000000000000000000000000000000',
+  merkleroot: '4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b',
+  time:        1231006505,
+  bits:       '1d00ffff',
+  nonce:       2083236893 )
+
+b0.hash
+#=> "000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f"
+
+b125552 =
+Bitcoin::Header.from_hash(
+  version:     1,
+  prev:       '00000000000008a3a41b85b8b29ad444def299fee21793cd8b9e567eab02cd81',
+  merkleroot: '2b12fcf1b09288fcaff797d71e950e71ae42b91e8bdb2304758dfcffc2b620e3',
+  time:        1305998791,
+  bits:       '1a44b9f2',
+  nonce:       2504433986 )
+
+b125552.hash
+#=> "00000000000000001e8d6829a8a21adc5d38d0a473b144b6765798e61f98bd1d"
+```
+
+
+
 
 
 ## (Crypto) Block with Transactions (Tx)
 
 To be continued.
 
 
+
+
+
+
+
+
+## References / Links
+
+- [Programming Cryptocurrencies and Blockchains in Ruby](http://yukimotopress.github.io/blockchains)
+@ [Yuki & Moto Press Bookshelf](http://yukimotopress.github.io), Free (Online) Booklet
+- [Awesome Blockchains](https://github.com/openblockchains/awesome-blockchains) @ [Open Bockchains](https://github.com/openblockchains)
+- [Awesome Crypto](https://github.com/planetruby/awesome-crypto) @ [Planet Ruby](https://github.com/planetruby)
+
+
+
 ## Questions? Comments?
 
 Send them to the [ruby-talk mailing list](https://www.ruby-lang.org/en/community/mailing-lists/)

bitcoin_header.rb

@@ -0,0 +1,90 @@
+require 'digest'
+require 'pp'
+
+
+module Bitcoin
+  class Header
+    attr_reader :version
+    attr_reader :prev
+    attr_reader :merkleroot
+    attr_reader :time
+    attr_reader :bits
+    attr_reader :nonce
+
+    def initialize( version, prev, merkleroot, time, bits, nonce )
+       @version    = version
+       @prev       = prev
+       @merkleroot = merkleroot
+       @time       = time
+       @bits       = bits
+       @nonce      = nonce
+    end
+
+    ## lets add a convenience c'tor helper
+    def self.from_hash( h )
+      new( h[:version],
+           h[:prev],
+           h[:merkleroot],
+           h[:time],
+           h[:bits],
+           h[:nonce] )
+    end
+
+    def to_bin
+       i4( version )       +
+      h32( prev )          +
+      h32( merkleroot )    +
+       i4( time )          +
+       i4( bits.to_i(16) ) +
+       i4( nonce )
+    end
+
+    def hash
+      bytes = sha256(sha256( to_bin ))
+      bin_to_h32( bytes )
+    end
+
+    def sha256( bytes )
+       Digest::SHA256.digest( bytes )
+    end
+
+    ## binary pack/unpack conversion helpers
+    def i4( num )   ##  integer (4 byte / 32bit) to binary (in little endian)
+      [num].pack( 'V' )
+    end
+
+    def h32( hex )   ## hex string (32 byte / 256 bit / 64 hex chars) to binary
+      [hex].pack( 'H*' ).reverse     ## change byte order (w/ reverse)
+    end
+
+    def bin_to_h32( bytes )
+      bytes.reverse.unpack( 'H*' )[0]   ## note: change byte order (w/ reverse)
+    end
+  end # class Header
+end # module Bitcoin
+
+
+
+## test
+
+pp b0 =
+Bitcoin::Header.from_hash(
+  version:     1,
+  prev:       '0000000000000000000000000000000000000000000000000000000000000000',
+  merkleroot: '4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b',
+  time:        1231006505,
+  bits:       '1d00ffff',
+  nonce:       2083236893 )
+
+pp b0.hash
+
+pp b125552 =
+Bitcoin::Header.from_hash(
+  version:     1,
+  prev:       '00000000000008a3a41b85b8b29ad444def299fee21793cd8b9e567eab02cd81',
+  merkleroot: '2b12fcf1b09288fcaff797d71e950e71ae42b91e8bdb2304758dfcffc2b620e3',
+  time:        1305998791,  ## 2011-05-21 17:26:31
+  bits:       '1a44b9f2',
+  nonce:       2504433986 )
+
+pp b125552.hash