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I am trying to check KCVs of a few keys.

I am generating the KCV for the keys using the method mentioned here https://crypto.stackexchange.com/a/11873/115990

Question: Can KCVs of two different AES keys be the same? It's a hash but we take only the first 3 bytes so there is a chance right in case there are millions of keys?

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Yes, there are many keys with the same KCV value. To be precise, there are $2^{24}$ possible KCV values. This means collisions are unlikely to occur by chance unless you generate $2^{12}$ or so (a few thousand) keys, but could easily be constructed maliciously.

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  • $\begingroup$ What I have now found with practical data is that the collisions happen quite a lot as only 16 ^ 6 (i.e. 2 ^ 24 as you have mentioned) combinations are possible which is only 16 mill. For a large dataset that's too small and collisions will happen. $\endgroup$
    – humbleCoder
    Commented Apr 16 at 3:36

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