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Re: [IPsec] Question about RFC 5114

Joy Latten <latten@austin.ibm.com> Tue, 06 April 2010 21:40 UTC

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From: Joy Latten <latten@austin.ibm.com>
To: Richard Barnes <rbarnes@bbn.com>
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Subject: Re: [IPsec] Question about RFC 5114
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On Tue, 2010-04-06 at 12:54 -0400, Richard Barnes wrote:
> > Thanks so much for the detail. It has helped greatly.
> > I did take a look at NIST SP 800-56A section 5.6.2.4 for validating  
> > the
> > public value. I am in learning mode, so I found the 2nd step
> > confusing...
> > 1. Verify that 2 <= y <= p - 2
> > 2. Verify that y^q = 1 (mod p)
> >
> > Are the parenthesis around "mod p" correct? This is how it is in the
> > NIST doc.
> 
> 
> Yes, the parens are correct.  That's just a more traditional notation  
> for modular equivalence:
> 
> A = B (mod p)
> 
> is the same as saying (in C notation)
> 
> A % p == B % p
> 
> So in your case you would want to check:
> 
> y^q % p == 1
> 

Thanks so much!!! This definitely cleared it up for me! :-)

regards,
Joy

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