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Are there any security concerns with choosing highly structured or short connection IDs for use in DTLS? For example:

  • 32bit connection IDs handed out sequentially: There is obviously statistical data being revealed and wrapping around the range might inadvertently terminate old connections, but would it open up deeper threats as well?
  • On the other end of the spectrum, 128bit connection IDs, where the low bits are used for load balancing purposes and everything else is random: Identifying the server, where the cryptographic state of the connection resides, would really simplify load balancing. E.g. if the low bits are 0x015a, just forward the packet to the machine with DNS name backend_015a.

The DTLS 1.2 connection ID RFC does not list any concerns for how to choose IDs.

Meanwhile, the QUIC RFC demands:

Connection IDs MUST NOT contain any information that can be used by an external observer (that is, one that does not cooperate with the issuer) to correlate them with other connection IDs for the same connection. As a trivial example, this means the same connection ID MUST NOT be issued more than once on the same connection.

But it doesn't give any rational for this stipulation.

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