Ah now that makes sense, if I remember the algorithm correctly they do
need to agree on p and g first, g being primitive to mod p. Then they
choose their own random integer, i, and sends pow (g, i) % p. Or
something like that.
Cheers, I'll have another go. However, I'd still like to know why these
specific values in the validat2 test file (as mentioned eariler):
memset(val1.begin(), 0x10, val1.size());
memset(val2.begin(), 0x11, val2.size());
Are they important? Anyone!?
Jim
On Wed, 2004-03-10 at 23:10, Mike Marshall wrote:
> It took me a while to figure out how to do this too.
> The key is that both DH objects need to be initialized
> with the same Generator and Modulus, here is some
> sample code, which you should be able to extrapolate
> to a two machine scenario:
>
> AutoSeededRandomPool asrp;
>
> DH dh(dynamic_cast<RandomNumberGenerator&>(asrp),
> 128);
>
> Integer iPrime, iGenerator;
> if (dh.AccessGroupParameters().GetValue("Modulus",
> iPrime))
> {
> if
> (dh.AccessGroupParameters().GetValue("SubgroupGenerator",
> iGenerator))
> {
>
> // important line is here
> DH dhB(iPrime, iGenerator);
>
> SecByteBlock privA(dh.PrivateKeyLength());
> SecByteBlock pubA(dh.PublicKeyLength());
> SecByteBlock privB(dhB.PrivateKeyLength());
> SecByteBlock pubB(dhB.PublicKeyLength());
> SecByteBlock val1(dh.AgreedValueLength());
> SecByteBlock val2(dhB.AgreedValueLength());
>
> dh.GenerateKeyPair(rndPoolA, privA, pubA);
> dhB.GenerateKeyPair(rndPoolB, privB, pubB);
>
> if (!dh.Agree(val1, privA, pubB))
> {
> cout << "First agreement failed" << endl;
> return 0;
> }
>
> if (!dhB.Agree(val2, privB, pubA))
> {
> cout << "Second agreement failed" << endl;
> return 0;
> }
>
>
> }
> --- James Vanns <[EMAIL PROTECTED]> wrote:
> > I am having trouble getting to processes (running on
> > different machines)
> > to agree on a value using their Diffie-Hellman keys.
> >
> > Do the different DH objects need the same
> > RandomNumber objects? I send
> > their public keys over the network and try to
> > Agree() them with the
> > opposite private key (as in the crypto++ example).
> > However, this always
> > fails. The only thing I can see that's different is
> > that I am using a
> > different PRNG object (obviously, as they're on
> > different machines!).
> >
> > Also can you explain what this does (well, I know
> > what memset does), and
> > more importantly why the specific values:
> >
> > Line 198 in validat2.cpp
> >
> > memset(val1.begin(), 0x10, val1.size());
> > memset(val2.begin(), 0x11, val2.size());
> >
> > The code I'm using (or a snippet of as I don't want
> > to swamp the list)
> > is:
> >
> > string data;
> > // Setup the pseudo random number generator
> > AutoSeededRandomPool *arng = new
> > AutoSeededRandomPool;
> > RandomNumberGenerator &rng =
> > *dynamic_cast<RandomNumberGenerator *>
> > (arng);
> >
> > // declare a diffie-hellman object
> > DH dh (rng, 128);
> >
> > // declare the local validation and public-private
> > key pair
> > SecByteBlock local_validate (dh.AgreedValueLength
> > ());
> > SecByteBlock local_public_key (dh.PublicKeyLength
> > ());
> > SecByteBlock local_private_key (dh.PrivateKeyLength
> > ());
> >
> > // clear the validation object
> > fill (local_validate.begin (), local_validate.end
> > (), 0x11);
> >
> > // generate the public-private key pair
> > dh.GenerateKeyPair (rng, local_private_key,
> > local_public_key);
> >
> > delete arng;
> >
> > // encode the local public key to a hexed-string
> > StringSource (local_public_key, true, new HexEncoder
> > (new StringSink
> > (data)));
> > cout << "Local public key: " << data << endl;
> >
> > // connect to the server
> > JClientSocket c ("eeyore", 50000);
> >
> > // send the local public key
> > c << data;
> > // clear the string
> > data.clear ();
> > // receive the server's public key
> > c >> data;
> >
> > cout << "Foreign public key: " << data << endl;
> >
> > // decode the hexed-string to the foreign public key
> > SecByteBlock foreign_public_key (dh.PublicKeyLength
> > ());
> > StringSource (foreign_public_key, true, new
> > HexDecoder (new StringSink
> > (data)));
> >
> > // clear the string
> > data.clear ();
> >
> > // agreement method with the local private and the
> > foreign public key
> > if (!dh.Agree (local_validate, local_private_key,
> > foreign_public_key)) {
> > cout << "Key agreement failed." << endl;
> > return 1;
> > }
> >
> > The server has similar code (this is the client)
> >
> > Regards
> >
> > Jim
> >
> > --
> > James Vanns BSc (Hons) MCP
> > Linux Systems Administrator
> > Senior Software Engineer (Linux / C & C++)
> > Canterbury Christ Church University College
> > Public Key:
> >
> http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x24045370
> >
--
James Vanns BSc (Hons) MCP
Linux Systems Administrator
Senior Software Engineer (Linux / C & C++)
Canterbury Christ Church University College
Public Key: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x24045370
