We improve instruction cache data analysis techniques with a framework based on vector quantization and hidden Markov models. As a result, we are capable of carrying out efficient automated attacks using live I-cache timing data. Using this analysis technique, we run an I-cache attack on OpenSSL’s DSA implementation and recover keys using lattice methods. Previous I-cache attacks were proof-of-concept: we present results of an actual attack in a real-world setting, proving these attacks to be realistic. We also present general software countermeasures, along with their performance impact, that are not algorithm specific and can be employed at the kernel and/or compiler level.