64-bit SPIs

[DemiMarie]

64-bit SPIs would dramatically simplify implementations, at least inasmuch as they avoid needing premature key rotations.

[hlrichardson]

That is an interesting point, indeed there is a tradeoff to be made between increasing the header size (which impacts throughput) and rekeying overhead. When a unique SPI is used per connection, the 31-bit space can be exhausted in about a day at a connection rate of about 25K/second, which is entirely possible now and can only be expected to increase over time. On the other hand, periodic key rotation still needs to be supported in order to limit the amount of data encrypted by the same key, so it isn't clear that this would really help simplify implementations.

By the way, this might be a good topic to raise on the PSP discussion group, which has a larger audience than we do here:

https://groups.google.com/g/psp-discuss