X509KeySelector.java

package helpers;
import java.security.Key;
import java.security.PublicKey;
import java.security.cert.X509Certificate;
import java.util.Iterator;

import javax.xml.crypto.AlgorithmMethod;
import javax.xml.crypto.KeySelector;
import javax.xml.crypto.KeySelectorException;
import javax.xml.crypto.KeySelectorResult;
import javax.xml.crypto.XMLCryptoContext;
import javax.xml.crypto.XMLStructure;
import javax.xml.crypto.dsig.SignatureMethod;
import javax.xml.crypto.dsig.keyinfo.KeyInfo;
import javax.xml.crypto.dsig.keyinfo.X509Data;

import com.sun.org.apache.xml.internal.security.signature.XMLSignature;

//Source:
/*http://www.oracle.com/technetwork/articles/javase/dig-signature-api-140772.html*/
//for Validation purposes only
public class X509KeySelector extends KeySelector {
    public KeySelectorResult select(KeyInfo keyInfo,
                                    KeySelector.Purpose purpose,
                                    AlgorithmMethod method,
                                    XMLCryptoContext context)
        throws KeySelectorException {
        @SuppressWarnings("rawtypes")
		Iterator ki = keyInfo.getContent().iterator();
        while (ki.hasNext()) {
            XMLStructure info = (XMLStructure) ki.next();
            if (!(info instanceof X509Data))
                continue;
            X509Data x509Data = (X509Data) info;
            @SuppressWarnings("rawtypes")
			Iterator xi = x509Data.getContent().iterator();
            while (xi.hasNext()) {
                Object o = xi.next();
                if (!(o instanceof X509Certificate))
                    continue;
                final PublicKey key = ((X509Certificate)o).getPublicKey();
                // Make sure the algorithm is compatible
                // with the method.
                if (algEquals(method.getAlgorithm(), key.getAlgorithm())) {
                    return new KeySelectorResult() {
                        public Key getKey() { return key; }
                    };
                }
            }
        }
        throw new KeySelectorException("No key found!");
    }

    static boolean algEquals(String algURI, String algName) {
        if ((algName.equalsIgnoreCase("DSA") &&
            algURI.equalsIgnoreCase(SignatureMethod.DSA_SHA1)) ||
            (algName.equalsIgnoreCase("RSA") &&
            algURI.equalsIgnoreCase(SignatureMethod.RSA_SHA1)) ||
            (algName.equalsIgnoreCase("RSA") &&
            algURI.equalsIgnoreCase(XMLSignature.ALGO_ID_SIGNATURE_RSA_SHA256))){
            return true;
        } else {
            return false;
        }
    }
}