We study a class of measures on the real line with a kind of self-similar structure, which we call dynamically driven self-similar measures, and contain proper self-similar measures such as Bernoulli convolutions as special cases. Our main result gives an expression for the L q dimensions of such dynamically driven self-similar measures, under certain conditions. As an application, we settle Furstenberg's longstanding conjecture on the dimension of the intersections of ×p and ×q-invariant sets. Among several other applications, we also show that Bernoulli convolutions have an L q density for all finite q, outside of a zero-dimensional set of exceptions.The proof of the main result is inspired by M. Hochman's approach to the dimensions of self-similar measures and his inverse theorem for entropy. Our method can be seen as an extension of Hochman's theory from entropy to L q norms, and likewise relies on an inverse theorem for the decay of L q norms of discrete measures under convolution. This central piece of our approach may be of independent interest, and is an application of well-known methods and results in additive combinatorics: the asymmetric version of the Balog-Szemerédi-Gowers Theorem due to Tao-Vu, and some constructions of Bourgain.