openssl_rsa_encrypt.rb

require 'openssl'

class Encryptor
  
  def initialize(key_pass, key_size = 1024, key_name = 'rsakey.sec', cipher = OpenSSL::Cipher.new('aes-256-cbc'))
    @key_size = key_size
    @cipher = cipher
    @key_name = key_name

    if( File.exists?(@key_name) )
      @rsakey = OpenSSL::PKey::RSA.new(File.read(@key_name), key_pass)
    else
      @rsakey = OpenSSL::PKey::RSA.generate(@key_size)
      File.open(@key_name,'w+') do |priv|
        priv.write(@rsakey.to_pem(@cipher, key_pass))
      end
    end
  end

  def encrypt_string(txt)
    begin
      @rsakey.public_encrypt(txt)
    rescue OpenSSL::PKey::RSAError => e
      if e.message == 'data too large for key size'
        STDERR.puts 'Your string is too large to encrypt'
      else
        raise
      end
    end
  end

  def decrypt_string(etxt)
    @rsakey.private_decrypt(etxt)
  end
end