Convert String to uint64_t

Hi, i need to convert a String to uint64_t and uint64_t to String

Example:

String direccion_1 = '28fff00364140368';
String direccion_2='';
const uint64_t direccion_final;

direccion_final = direccion_1;    //String to uint64_t
direccion_2 = direccion_final;    //uint64_t to String

Please help!!

The Arduino Yún is a microcontroller board based on the ATmega32u4 and the Atheros AR9331.

ATmega32u4: 8 bits MCU
AR9331: 32 bits CPU
Yún: in Chinese word is cloud, means cloud computing here.

"uint64_t" at 64 bits hardware (CPU) and 64 bits OS is home run, setup cloud computing with 64 bits box solve problem in no time.