Encrypted keyword search allows a server to perform a search over a set of encrypted documents on behalf of a client without learning the contents of the documents or the words being searched for. Designing a practical system is challenging because the privacy constraint thwarts standard indexing and ranking techniques. We present Mafdet, an encrypted keyword search system we have implemented. Our system makes the search practical even for large data sets. We evaluated Mafdet's performance on a set of queries and a large collection of documents. In these queries, Mafdet's accuracy is within 6% of Google Desktop, and the search time is on the order of seconds for document sets as large as 2.6 GB.