A security device performing flow classification and storing flow information in a flow table includes a flow engine generating a flow key identifying a flow to which a received data packet belongs, the flow engine applying a hash function to the flow key to generate a flow hash value and an entry hash value being orthogonal to each other. The security device includes a hash map and a flow data table. The hash map table is indexed by the flow hash value and an entry index value is derived from the entry hash value. The flow data table is indexed by the flow hash value and the entry index value to return at least a retrieved flow key from a flow record of an indexed entry.