In food processor, grind shrimp paste, lemon grass, shallots, garlic, chiles, cilantro, cumin, pepper, and galangal to a smooth paste. Add 1/2 cup of coconut milk to the paste and transfer to a saucepan. Bring to a boil and simmer until liquid evaporates and the paste changes color. Add chicken pieces and stir to coat them. Add remaining coconut milk and stir until the mixture starts to thicken. Reduce heat to low and simmer for 20 minutes. Add tomatoes and bring to a boil. Reduce heat and simmer for 5 minutes. Add fish sauce, tamarind liquid and sugar. Stir and simmer for 5 minutes. Pour into a serving bowl.