discuz暗号解読authcodeはRuby 1.9で実現(利用可能)

def self.authcode(str,decode=true,key='',expiry=0)
    return nil unless str
    str = decode ? str+'====' : str.gsub(/\\t/,"\t")
    require 'base64'
    ckey_length = 4

    key = Digest::MD5.hexdigest(!key.empty? ? key : 'asdf')
    keya = Digest::MD5.hexdigest(key[0,16])
    keyb = Digest::MD5.hexdigest(key[16,16])
   
    keyc = decode ? str[0,ckey_length] : Digest::MD5.hexdigest("#{Time.now.to_f} #{Time.now.to_i}")[-ckey_length,ckey_length]
    cryptkey = keya + Digest::MD5.hexdigest(keya+keyc)
    key_length = cryptkey.size
    str = decode ?  Base64.decode64(str[ckey_length..-1])  : format("%010d",(expiry!=0 ? expiry + Time.now.to_i : 0)).to_s  + Digest::MD5.hexdigest(str+keyb)[0,16]+str

    str_length = str.size


    result = ''
    box = {}
    (0..255).each  { |i| box[i] = i}

    rndkey = {}
    (0..255).each do |i| 
      rndkey[i] = (cryptkey[i % key_length,1]).ord   #cryptkey[0,i % key_length][0]    [0]  ord
    end

    j = 0
    (0..255).each do |i|
      j = (j + box[i].to_i + rndkey[i].to_i) % 256
      tmp = box[i]
      box[i] = box[j]
      box[j] = tmp
    end


    
    a=j=0
    (0..str_length-1).each do |i|
      a = (a+1) % 256
      j = (j + box[a]) % 256
      tmp = box[a]
      box[a] = box[j]
      box[j] = tmp
      ks = box[(box[a].to_i + box[j].to_i)%256]
      result  << (str[i].ord ^ ks.to_i ).chr         #( (str[i].to_i ^ ks ).to_s[0] % 256 ).chr     to_i  ord
    end



    if decode
    
    
      if (result[0,10].to_i ==0 || (result[0,10].to_i - Time.now.to_i) > 0) && result[10,16] == (Digest::MD5.hexdigest(result[26..-1] + keyb)[0,16])
        return result[26..-1]
      else
        return ''
      end
    else

      return keyc+Base64.encode64(result).sub('=','')
    end
  end