If you prefer an exceptionally spicy sauce, use 3 teaspoons of the crumbled dried chiles. For a medium-hot sauce, use 2 teaspoons.
Bring a saucepan of water to a boil. Add tomatoes, and cook until soft, about 5 minutes. Drain, and let cool slightly. Squeeze juice and seeds from tomatoes over a small bowl, and reserve. Coarsely chop tomato flesh.
Heat oil in a skillet over medium-high heat. Add cumin and chiles, and cook until chiles darken and become fragrant, about 1 minute. Add onion, garlic, and ginger, and cook until golden brown, about 3 minutes. Reduce heat to medium, and cook for 2 minutes. Add chopped tomatoes and salt, and cook for 2 minutes. Stir in reserved tomato juice and seeds, and cook until almost all of the liquid has evaporated, about 2 minutes. Remove from heat, and let cool slightly.
Puree mixture with the cilantro in a food processor until smooth. Add vinegar and more salt if desired. Sauce can be refrigerated in an airtight container for up to 2 weeks; bring to room temperature before serving.
