We develop an algorithm for estimating the values of a vector x Rn over a support S of size k from a randomized sparse binary linear sketch Ax of size O(k). Given Ax and S, we can recover x with x - xS 2 x - xS 2 with probability at least 1 - k-(1) . The recovery takes O(k) time. While interesting in its own right, this primitive also has a number of applications. For example, we can: