Sambal Udang is an Indonesian sauce made from chiles, garlic, shallots, tamarind, tomatoes and either dried shimp or dried shrimp paste (blachan.)
The shrimp and tamarind are soaked in water to soften them, then drained, and ground to a paste.
The paste is added to shallots and chiles that have been stir fried. The mixture is then cooked a bit, then the tomato along with the tamarind soaking water is added, and the mixture is further simmered until thick.
Some recipes may add petai seeds and lime juice.