credit card validation on ruby

gistfile1.rb

# References
# http://en.wikipedia.org/wiki/Bank_card_number
# http://en.wikipedia.org/wiki/Luhn_algorithm

def valid_credit_card?(number)
  number = number.to_s.gsub(/\D/, "")

  return false unless valid_association?(number)
  number.reverse!

  relative_number = {'0' => 0, '1' => 2, '2' => 4, '3' => 6, '4' => 8, '5' => 1, '6' => 3, '7' => 5, '8' => 7, '9' => 9}

  sum = 0 

  number.split("").each_with_index do |n, i|
    sum += (i % 2 == 0) ? n.to_i : relative_number[n]
  end 

  sum % 10 == 0
end

def valid_association?(number)
  number = number.to_s.gsub(/\D/, "") 

  return :dinners  if number.length == 14 && number =~ /^3(0[0-5]|[68])/   # 300xxx-305xxx, 36xxxx, 38xxxx
  return :amex     if number.length == 15 && number =~ /^3[47]/            # 34xxxx, 37xxxx
  return :visa     if [13,16].include?(number.length) && number =~ /^4/    # 4xxxxx
  return :master   if number.length == 16 && number =~ /^5[1-5]/           # 51xxxx-55xxxx
  return :discover if number.length == 16 && number =~ /^6011/             # 6011xx
  return nil
end

while(true)
  print ">> "
  begin
    number = gets.chomp
  rescue NoMethodError => e
    puts ""
    number = "exit"
  end
  break if number == "exit"
  puts "#{number} is #{valid_credit_card?(number) ? valid_association?(number) : 'frauld'}"
end

puts "Bye..."