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Hi I found this question which I am currently struggling with. How to handle IKEv1 and IKEv2 diffie-hellman shared secret bits length not multiple of 8?

In ACVP, the input diffe-hellman shared secret bits isn't multiple of 8, for example, 521 in bits. The given gxy is 9E50F9E86DAF773F657F5F32BA4C84E707284843F422A74DFC6877D236020F86B115230C3BA57A680AED1AF2F0CE59CBB3C5755D80EFCCC1DD350DE79781AC807180. tried this input and also >> 7, none of them is correct.

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The given gxy is 9E50F9E86DAF773F657F5F32BA4C84E707284843F422A74DFC6877D236020F86B115230C3BA57A680AED1AF2F0CE59CBB3C5755D80EFCCC1DD350DE79781AC807180. tried this input and also >> 7, none of them is correct.

That value is suspicious; it is larger than $2^{521}-1$, which is the largest value a coordinate on the curve P-521 can be.

Are you sure that is the correct value?

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  • $\begingroup$ pages.nist.gov/ACVP/draft-celi-acvp-kdf-ikev1.html. In my demo files, the given dhlen is 521, the given gxy is 66 bytes, but most significant 7 bits are not 0. there must be some way to convert this given inpug gxy. I tried shift, cutoff, none of them are correct. $\endgroup$
    – Fiona
    Feb 22 at 20:34

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