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    tl;dr is that if you generate around 4.3 billion (2^32) keys, the lower 64 bits of two of them might be the same. This is a birthday attack so generating a key with some specified “long” ID is still going to require generating around 9.2 million billion (2^63) of them.

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      My software uses the medium-long key ID for identifying users. I guess I know now that I have to switch to long IDs.