<i>Even Williamson believed that the whole venture was too risky. When he finally wrote up a revised version of his key scheme, he cited these reservations as the reason for the two-year delay. "I find myself in an embarrassing position," he wrote. "I have come to doubt the whole theory of nonsecret encryption. The trouble is that I have no proof that the method ... is genuinely secure." He conceded he could not find anything wrong with the system, though, "and would be grateful if anyone else can." No one did. But by then the GCHQ had tacitly concluded it wasn't worth the effort to implement a public key crypto system.</i><p>They tried, hard, to find weaknesses, but they couldn't, <i>this was the problem</i>.