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The Bouncy Castle Java APIs for the TLS, including a JSSE provider. The APIs are designed primarily to be used in conjunction with the BC LTS provider but may also be used with other providers providing cryptographic services.

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package org.bouncycastle.tls;

import java.math.BigInteger;
import java.util.Vector;

import org.bouncycastle.tls.crypto.SRP6Group;
import org.bouncycastle.tls.crypto.SRP6StandardGroups;
import org.bouncycastle.tls.crypto.TlsSRPConfig;

public class DefaultTlsSRPConfigVerifier
    implements TlsSRPConfigVerifier
{
    private static final Vector DEFAULT_GROUPS = new Vector();

    static
    {
        DEFAULT_GROUPS.addElement(SRP6StandardGroups.rfc5054_1024);
        DEFAULT_GROUPS.addElement(SRP6StandardGroups.rfc5054_1536);
        DEFAULT_GROUPS.addElement(SRP6StandardGroups.rfc5054_2048);
        DEFAULT_GROUPS.addElement(SRP6StandardGroups.rfc5054_3072);
        DEFAULT_GROUPS.addElement(SRP6StandardGroups.rfc5054_4096);
        DEFAULT_GROUPS.addElement(SRP6StandardGroups.rfc5054_6144);
        DEFAULT_GROUPS.addElement(SRP6StandardGroups.rfc5054_8192);
    }

    // Vector is (SRP6Group)
    protected final Vector groups;

    /**
     * Accept only the group parameters specified in RFC 5054 Appendix A.
     */
    public DefaultTlsSRPConfigVerifier()
    {
        this(DEFAULT_GROUPS);
    }

    /**
     * Specify a custom set of acceptable group parameters.
     * 
     * @param groups a {@link Vector} of acceptable {@link SRP6Group}.
     */
    public DefaultTlsSRPConfigVerifier(Vector groups)
    {
        this.groups = new Vector(groups);
    }

    public boolean accept(TlsSRPConfig srpConfig)
    {
        for (int i = 0; i < groups.size(); ++i)
        {
            if (areGroupsEqual(srpConfig, (SRP6Group)groups.elementAt(i)))
            {
                return true;
            }
        }
        return false;
    }

    protected boolean areGroupsEqual(TlsSRPConfig a, SRP6Group b)
    {
        BigInteger[] ng = a.getExplicitNG();
        return areParametersEqual(ng[0], b.getN()) && areParametersEqual(ng[1], b.getG());
    }

    protected boolean areParametersEqual(BigInteger a, BigInteger b)
    {
        return a == b || a.equals(b);
    }
}