Soak the chiles in water for 20 minutes to soften, then remove and drain. Roast the coriander and cumin seeds for about 2 minutes in a dry skillet, and when they are cooled, grind to a fine powder in a spice mill.
Combine all ingredients in a food processor or blender and puree into a fine paste. Store it in a tightly sealed jar in the refrigerator.
