agr@vaxine.UUCP (Arnold Reinhold) (01/27/84)
Recent press articles posted to net.crypt suggest that progress in factoring large numbers poses a threat to military cryptosystems, including nuclear launch codes. In fact the cryptosystems threatened are some of the "trapdoor" function public key systems that have been proposed in the open literature in the past few years. The idea of the prime number trapdoor function is that you can make up a large number that is the product of two primes and publish it. Someone who wants to send you a message uses the number in a encryption algorithm. The encrypted message can be unscrambled easily by you because you know the two factors of the number that you published. As long as it is too hard for the bad guys to factor the published number, the system is secure. The improved factoring technology suggests, at the least, numbers much larger than 100 digits must be used for a secure system. I know of no evidence that the US uses public key systems of this type for secure communications. While current methods are secret there is plenty of reason to believe that the people responsible for communication security are very conservative in their methods. Indeed the fact that they have not classified the work at Sandia suggests they are not too concerned. Unfortunately the published stories will no doubt never be corrected.