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copied!<p>I think the part of the example</p> <pre><code>private static BigInteger g512 = new BigInteger("1234567890", 16); private static BigInteger p512 = new BigInteger("1234567890", 16); </code></pre> <p>is completely bogus. <code>p</code> needs to be prime and <code>g</code>needs to be a generator. When I try running the example I get an exception. <a href="http://www.exampledepot.com/egs/javax.crypto/KeyAgree.html" rel="nofollow">This</a> seems to be a more reasonable example (but I haven't tested it myself yet).</p> <p>Basically the interesting input to the DH exchange is that (<code>p,g</code>) pair which needs to be generated and must have some unique properties. Clearly, the example above shows just place holder values which will not produce a correctly functioning algorithm (<code>p</code> can not be equal to <code>g</code> and <code>p</code> should be prime, while in the example it is clearly divisible by 10). The example I linked to shows how to use the libraries to generate a correct (<code>p, g</code>) pair. </p> <p>It is also worth noting that DH parameter generation is usually a separate step from generating the secret key. While DH parameters are somewhat private, they are not as sensitive as your private key and can be generated once and then reused.</p> <p><strong>(Edit: <a href="http://www.exampledepot.com/egs/javax.crypto/GenDhParams.html" rel="nofollow">Example</a>)</strong></p> <pre><code>AlgorithmParameterGenerator paramGen = AlgorithmParameterGenerator.getInstance("DH"); paramGen.init(512); // number of bits AlgorithmParameters params = paramGen.generateParameters(); DHParameterSpec dhSpec = params.getParameterSpec(DHParameterSpec.class); BigInteger p512 = dhSpec.getP(); BigInteger g512 = dhSpec.getG(); int l = dhSpec.getL(); ... </code></pre>

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