Knuth's TAOCP, Volume 2, Third Edition, Page 407:

"Historical note: It was revealed in 1998 that Clifford Cocks had considered encoding messages by the transformation $x^{pq} mod pq$ already in 1973, but his work was kept secret".

And that feels like the correct amount of recognition.

... apparently it was only discovered when he went for an unrelated consultation with a podiatrist.