What is the rocket fuel used in the solid boosters for the space shuttle?

The two reusable SRBs provide the main thrust to lift the Space Shuttle off the pad and up to an altitude of about 150,000 feet (45.7 km). In addition, the two SRBs carry the entire weight of the external tank and orbiter and transmit the weight load through their structure to the mobile launcher platform. Each booster has a (sea level) liftoff thrust of approximately 3,300,000 lbf at launch. They are ignited after the three space shuttle main engines' thrust level is verified. The two SRBs provide 83 % of the thrust at lift-off. Seventy five seconds after SRB separation, SRB apogee occurs at an altitude of approximately 220,000 feet (67 km), after which they land on parachutes; impact occurs in the ocean approximately 122 nautical miles (226 km) downrange, after which the two are recovered.