Although the generator g can be any number, it is typically 2 or 5.
In fact, this is all that OpenSSL supports (values 2 or 5 for g). The
typical situation is this:
(1) Alice and Bob generate random secret values a and b. If a or b
happen to be prime, that is fine - but they need not be.
(2) Alice sends Bob A=g^a(mod p) and Bob sends Alice B=g^b(mod p).
(3) Alice calculates S=B^a(mod p) and Bob calculates S=A^b(mod p) and
they are both left with the secret S.
The key thing to notice is that the DH parameters are *public*. That
means that the modulus and generator can be known by anyone without
compromising the integrity of the DH transaction.
I've generated a few 8192-bit moduli using openssl, and those jobs
tend to take about 3 days to complete on a 2.4GHz core. If you need a
large modulus, say 4096 bits or higher, you're best off generating it
once on a fast machine and embedding it in your application as a byte
array.
On Tue, Mar 22, 2011 at 5:12 PM, ikuzar razuk...@gmail.com wrote:
Hello,
I 'd like to know :
1) if exponent x in g^x must be a great prime number. In some docs I saw, it
is said that x must b a GREAT number but no information about primality ..
2) May generation of 'x' run for hours like related here :
http://www.openssl.org/docs/crypto/DH_generate_parameters.html ( in NOTES)
Thanks for your help.
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