use some covert communications channel to route sensitive information round the ring in a manner shielded from casual external inspection. There is a loose precedent in Chaum’s ‘dining cryptographers’ construction [@Chaum88], in which a number of cryptographers pass messages round a ring in such a way as to mask, from insiders, the source and destination of encrypted traffic. Can we build a similar construction, but in which the fact of systematic message routing is concealed from outsiders, with the result that the participants appear to be ‘ordinary’ nodes making a modest contribution in the network, rather than important nodes that should be targeted for close inspection and/or destruction?

Previous Work
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There has been rapid progress in recent years in understanding how networks can develop organically, how their growth influences their topology, and how the topology in turn affects both their capacity and their robustness. There is now a substantial literature: for a book-length introduction, see Watts [@Watts03], while literature surveys are [@AB02; @Newmann03]

Early work by Erdös and Renyi modelled networks as random graphs [@ER59; @Bollobas]; this is mathematically interesting but does not model most real-world networks accurately. In real networks, path lengths are generally shorter; it is well 