Schneier's law
expressioncryptographysecurity
'Anyone can invent a security system so clever that he can't think of how to break it.'
Bruce Schneier stated the observation in 1998 and Cory Doctorow later attached Schneier's name to it: the designer's inability to break a cipher is evidence about the designer, not the cipher. It is the working argument for public review, open competitions, and hiring people whose job is to break your own designs. Corollary in practice: never ship cryptography you invented yourself.