def encrypt(field)
      return if field !~ /\S/
      aes = OpenSSL::Cipher.new(symmetric_algorithm)
      aes_key = aes.random_key
      iv = aes.random_iv
      encrypt_data(iv, aes_key, field.force_encoding(encoding))
    end
def encrypt(field)
      return if field !~ /\S/
      aes = OpenSSL::Cipher.new(symmetric_algorithm)
      aes_key = aes.random_key
      iv = aes.random_iv
      encrypt_data(iv, aes_key, field.force_encoding(encoding))
    end
Return encrypted string according to specified format.
 Return nil if field is whitespace.