Your passport is full of codes and secret numbers. A look at what many of these strings of digits mean.

Harris remembered an Air Force instructor who had shown him a secret code based on a five-by-five alphabet matrix. Each letter was communicated by tapping two numbers: the first designated the ...

The researchers believe that before her death, Mary began secret correspondence with her supporter Michel de Castelnau de Mauvissière, the French ambassador to England and the recipient of most of her ...