More recently , a 500-page technical report on the Tunny cipher and its cryptanalysis - entitled General Report on Tunny - was released by GCHQ to the national Public Record Office in October 2000 ; the complete report is available online , and it contains a fascinating paean to Colossus by the cryptographers who worked with it : Construction of a fully functional replica of a Colossus Mark 2 was undertaken by a team led by Tony Sale .
A 500-page technical report on the Tunny cipher and its code breaking - entitled General Report on Tunny - was given by GCHQ to the national Public Record Office in October 2000 ; the complete technical report is online .