The rarity of that scenario is dictated by there rarely being a need for the security it offers. But that, in turn, is a function of our knowledge of cryptography, and may change over time. Who knows; perhaps someday we'll see something like what Vinge described in AFutD:

"Our main cargo is a one-time cryptographic pad. The source is Commercial Security at Sjandra Kei; the destination is the certificants' High colony. It was the usual arrangement: We're carrying a one-third xor of the pad. Independent shippers are carrying the others. At the destination, the three parts would be xor'd together. The result could supply a dozen worlds' crypto needs on the Net for ..."