Bitcoin/address validation http://rosettacode.org/wiki/Bitcoin/address_validation

bitcoin_validate.rb

require 'digest/sha2'
module BitcoinAddress
  extend self
  N = [0,1,2,3,4,5,6,7,8,nil,nil,nil,nil,nil,nil,nil,9,10,11,12,13,14,15,16,nil,17,18,19,20,21,nil,22,23,24,25,26,27,28,29,30,31,32,nil,nil,nil,nil,nil,nil,33,34,35,36,37,38,39,40,41,42,43,nil,44,45,46,47,48,49,50,51,52,53,54,55,56,57]
  def validate? address
    g = address.bytes.inject(0){|g,n| g*58+N[n-49]}.to_s(16)
    n = g.slice!(0..-9)
    (n.length...42).each{n.insert(0,'0')}
    caculate = Digest::SHA256.hexdigest(Digest::SHA256.digest(convert(n)))[0,8]
    g == caculate ? true : false
  end

  private

  def convert g
    i,e = '',[]
    (0...g.length/2).each{|n| e[n] = g[n+=n]+g[n+1]; i+='H2'}
    e.pack(i)
  end
end