>From: [email protected] On Behalf Of azhar jodatti
>Sent: Saturday, 16 March, 2013 14:00
>I am working on application which has android and iPhone client.
>Both the client talk to my server which is written in JAVA. I am
>using JCE implementation of DH algorithm and X509EncodedkeySpec
>for generating public and private key. code below
> X509EncodedKeySpec x509Spec = new
X509EncodedKeySpec(this.clientPublicKey);
> PublicKey pk = kf.generatePublic(x509Spec);
(I assume this is on the server, kf is a KeyFactory.getInstance("DH")
and this.clientPublicKey contains client DH public key in X509-ki form.)
In spite of the name, that doesn't generate a key, it only converts it
from an external form (X509) to an internal form JCE can use directly.
DH key(pair) generation is done with a KeyPairGenerator.getInstance("DH").
It can use parameters from several sources; which are you using?
>for iPhone client I wrote a C programme which makes use of openSSl
>implementation of DH algorithm. The problem I am facing is when
>I generate DH params (prime,generator,pulickey) at client and pass
>them to server to calculate server's public and secret key, my server
>(JAVA) throws invalidKeySpecification exception. below are steps.
> //client is DH *client.
> //also tried with 1024 bits and DH_GENERATOR_5
> DH_generate_parameters_ex(client,512,DH_GENERATOR_2,NULL);
You don't need to generate new parameters each time, as I said before.
And for secure sizes it's usually rather costly/slow to do so.
If you do generate new parameters, the server side Java *must* use
parameters sent by the client as input to server KeyPairGenerator.
OTOH DH-512 is almost certainly not secure. I don't understand all
the math, but the authorities I trust say that discrete-log (DH) is
only a few bits better than factoring (RSA), and RSA-512 is fallen.
> 2. then generating DH public and private key
> DH_generate_key(client)
That is actual key generation, like KeyPairGenerator.generate.
>when I pass these (prime,generator,publickey ) generated keys to
>server which is written in JAVA , It won't work. server (JAVA)
>throws invalidKeySpecification exception.
Then you're not doing what I described. See next.
>One more point I would like to mention here is, When I use
>DHPublicKeySpec instead of X509EncodedKeySpec at server (JAVA)
>it won't throw invalidKeySpecification exception. <snip rest>
Those are different data formats. X509EncodedKeySpec is correct
if you have a DH public key (or other public key) *in X.509
SubjectPublicKeyInfo format* which Openssl calls PUBKEY and
can do with no additional code. In another email you show
that you are using a JSON format with separate fields (which
you didn't mention before), which contains the same data as
X.509-keyinfo but is not even remotely the same format,
so for your format yes DHPublicKeySpec is correct.
See other response for more about parameters and key values.
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