Re: a question about Diffie-Hellman key exchange mode

> William,
>  
> have a look at MODP (Modular Exponential DH Groups) referenced in RFC5246:
>  
> RFC2409 defines primes for 768 and 1024 bit, and
> RFC3526 defines primes for 1536, 2048, and 3072 bit.
> (The generator is always 2.)
>  
> Peter-Michael
>
> ------------------------------------------------------------------------
> *From:* owner-openssl-users@...
> [mailto:owner-openssl-users@...]   *On Behalf Of *William Cai
> *Sent:* Monday, July 06, 2009 3:25 AM
> *To:* openssl-users@...
> *Subject:* Re: a question about Diffie-Hellman key exchange mode
>
> Thanks Michael! Could you please share me some information about
> when/how to agree upon p & g?
>
> Thanks,
> William
>
> ------------------------------------------------------------------------
> *From:* Michael Sierchio <kudzu@...>
> *To:* openssl-users@...
> *Sent:* Sunday, July 5, 2009 11:58:42 PM
> *Subject:* Re: a question about Diffie-Hellman key exchange mode
>
> William Cai wrote:
>
>> According to my understanding, Diffie-Hellman algorithm is based on
>> something like this,
>> 1. public prime number, p
>> 2. public base, g
>> 3. Side A's private key, a
>> 4. Side A's public key, A = g ^ a mod p
>> 5. Side B's private key, b
>> 6. Side B's public key, B = g ^ b mod p
>>
>> The question is that which items above the Diffie-Hellman public
>> parameters consist of? If they are 1, 2 and 4, then we need at least an
>> additional step pass the public prime number and public base to the
>> other side, otherwise, the other side cannot calculate its public key.
>> right? But I don't see such description in the paper. Are public prime
>> number and public base presetted?
>
> Yes, the p and g are well known and agreed upon in advance.
>
>
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