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at IPsec, Diffie-hellman is used in framework ISAKMP resulting shared secret. some of Diffie-Hellman group may define the length of the prime number of q and the size of the secret key of K: group 1 (768 bit),Group 2 (1024 bit), atau Group 5 (1536 bit).

a. what is the prime number of group 1 at decimal and hexadecimal b. what is the maximum length primitive root of q in decimal?

Diffie-Hellman Key Exchange

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  • $\begingroup$ A possible duplicate What Diffie-Hellman parameters should I use? $\endgroup$
    – kelalaka
    Commented Mar 2, 2020 at 19:04
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    $\begingroup$ If you're asking what the group parameters that IKE uses, group 1, 2 is listed in sections 6.1, 6.2 of datatracker.ietf.org/doc/rfc2409 and group 5 is listed in section 2 of datatracker.ietf.org/doc/rfc3526 . BTW: in all three cases, the value 'a' (the generator) is not a primitive root. In addition, nowadways all three groups is considered too small; we generally advise to use group 14 or bigger, or an elliptic curve group $\endgroup$
    – poncho
    Commented Mar 2, 2020 at 19:07
  • $\begingroup$ why the value of 'a' is not a primitive root? $\endgroup$ Commented Mar 2, 2020 at 19:17
  • $\begingroup$ @LeeHyeWon: because they deliberately selected a value that was a Quadratic Residue, and QRs are never primitive roots $\endgroup$
    – poncho
    Commented Mar 2, 2020 at 20:00

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