class to convert the public key part of an RSA key to the .NET XML format

gistfile1.rb

require 'openssl'
require 'base64'

class RSAKeyToXmlConverter
  
  def initialize rsa_key_string
    @key = OpenSSL::PKey::RSA.new(rsa_key_string)
  end

  def to_public_key
    <<XML_KEY
    <RSAKeyValue>
      <Modulus>         
        #{to_base_64(@key.n)}
      </Modulus>
      <Exponent>
        #{to_base_64(@key.e)}
      </Exponent>
    </RSAKeyValue>
XML_KEY
  end

  private

  def to_base_64 num
    hexstring = num.to_s(16).downcase
    Base64.encode64([hexstring].pack('H*')).split("\n").join
  end
end