Acidus wrote:
] ] The complex version: Onion Routing is a connection-oriented
] ] anonymizing communication service. Users choose a
] ] source-routed path through a set of nodes, and negotiate a
] ] "virtual circuit" through the network, in which each node
] ] knows its predecessor and successor, but no others. Traffic
] ] flowing down the circuit is unwrapped by a symmetric key at
] ] each node, which reveals the downstream node.
]
] What about traffic analysis? While I don't know much about
] this, I had a talk about this very same thing with Decius not
] too long ago. Don't you need some type of anonymous cloud
] takes and "holds" your request for some random length of time?
] That way if enough people are inject requests into the cloud,
] there is no way to match an incoming transmition cloud with
] one leaving the cloud.

It's a performance tradeoff, and it is thought that even the typical padding and reordering is not sufficient. The design document has this to say:

No mixing, padding, or traffic shaping (yet): Onion Routing originally called for batching and reordering cells as they arrived, assumed padding between ORs, and in later designs added padding between onion proxies (users) and ORs [27,41]. Tradeoffs between padding protection and cost were discussed, and traffic shaping algorithms were theorized [49] to provide good security without expensive padding, but no concrete padding scheme was suggested. Recent research [1] and deployment experience [4] suggest that this level of resource use is not practical or economical; and even full link padding is still vulnerable [33]. Thus, until we have a proven and convenient design for traffic shaping or low-latency mixing that improves anonymity against a realistic adversary, we leave these strategies out.

They suggest (but dont say outright) that reordering & batching may occur at some point. It would certainly give me more warm fuzzies if it did.

http://freehaven.net/tor/cvs/doc/design-paper/tor-design.html

makes for an interesting read...

RE: Onion Routing 2.0: tor