The breaking of the Enigma codes at Bletchley Park is one of the most remarkable episodes of WW2. Gordon Welchman was instrumental in setting up Hut Six, where the mathematical miracles performed by the men and women who worked there led directly to our mastery of a whole range of German radio signals throughout the war. Their decipherment is an amazing story - one in which inspired psychology plays a part as well as mathematical genius - and the lessons learnt during those exciting days are, as Welchman points out, still relevant to the preservation of cypher security today...