Abstract: A method and apparatus for obtaining, while on a spacecraft, a random number and hence a secure cryptographic key. The method includes the steps of providing, on the spacecraft, a device capable of producing random information when subject to random space phenomena, obtaining the random information and producing a random number therefrom and using an algorithm to establish the secure key. The apparatus includes a random access memory which experiences bit-flips when struck by radiation such as cosmic rays. Changes in the RAM bits are propagated using a linear feedback shift register.