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Is my calculation correct that to bruteforce XTEA with 128 bit key:

https://www.wolframalpha.com/input/?i=number+of+4-permutations+of+4,294,967,295+objects

Would require that many permutations?

Are there any attacks known to bruteforce it or decrypt? Especially in context of RKE (Remote Key Entry)

Thanks,

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A 128-bit key contains 2128 possible combinations. Guessing the correct key in an exhaustive search will occur after approximately half that. This is true regardless of what cipher is used. Note that some ciphers are vulnerable to cryptanalysis which creates "shortcuts" to discovering the key. There are no known key recovery attacks against XTEA which can recover the key faster than an exhaustive search, though.

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  • $\begingroup$ Thanks. Hmm I looked at the code that implements XTEA and thought the key was 4 ints, so 4 x 32 bit. Hence my permutation on 4 elements of 2^32 objects. But this is wrong, right? $\endgroup$
    – dev
    Commented Jan 19, 2019 at 13:07
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    $\begingroup$ @android_dev Not quite as you can also permute within the objects (int) too. Simply think of it as a wide counter from 0 to $2^{128} -1$. $\endgroup$
    – Paul Uszak
    Commented Jan 19, 2019 at 13:22

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