Cut dried chilies into 1/4-inch pieces with kitchen shears and soak in warm water until softened for about 20 minutes. Drain well in a sieve.

While chiles soak, toast coriander and peppercorns in a dry small heavy skillet over moderate heat, shaking the skillet until fragrant, 3 to 4 minutes, then cool. Thinly slice lower 6 inches of lemongrass stalks and finely chop. Finely grind the coriander and peppercorns in a spice grinder.

In a food processor fitted with a metal blade, pulse together the lemongrass, galangal, lime leaves, cilantro, shallot, garlic, fresh chilies, and soaked dried chilies. Add a tablespoon or more of water if the mixture is too thick. Add in the coriander-peppercorn mixture, shrimp paste, and salt and pulse until combined well.