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XMLTooling-J is a low-level library that may be used to construct libraries that allow developers to work with XML in a Java beans manner.
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/*
 * Licensed to the University Corporation for Advanced Internet Development, 
 * Inc. (UCAID) under one or more contributor license agreements.  See the 
 * NOTICE file distributed with this work for additional information regarding
 * copyright ownership. The UCAID licenses this file to You under the Apache 
 * License, Version 2.0 (the "License"); you may not use this file except in 
 * compliance with the License.  You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.opensaml.xml.signature.impl;

import org.opensaml.xml.security.CriteriaSet;
import org.opensaml.xml.security.SecurityException;
import org.opensaml.xml.security.SecurityHelper;
import org.opensaml.xml.security.SigningUtil;
import org.opensaml.xml.security.credential.Credential;
import org.opensaml.xml.security.credential.CredentialResolver;
import org.opensaml.xml.security.credential.UsageType;
import org.opensaml.xml.security.criteria.KeyAlgorithmCriteria;
import org.opensaml.xml.security.criteria.UsageCriteria;
import org.opensaml.xml.security.keyinfo.KeyInfoCredentialResolver;
import org.opensaml.xml.security.trust.ExplicitKeyTrustEvaluator;
import org.opensaml.xml.security.trust.TrustedCredentialTrustEngine;
import org.opensaml.xml.signature.Signature;
import org.opensaml.xml.signature.SignatureTrustEngine;
import org.opensaml.xml.util.DatatypeHelper;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * An implementation of {@link SignatureTrustEngine} which evaluates the validity and trustworthiness of XML and raw
 * signatures.
 * 
 * 
 * Processing is first performed as described in {@link BaseSignatureTrustEngine}. If based on this processing, it is
 * determined that the Signature's KeyInfo is not present or does not contain a resolveable valid (and trusted) signing
 * key, then all trusted credentials obtained by the trusted credential resolver will be used to attempt to validate the
 * signature.
 * 
 */
public class ExplicitKeySignatureTrustEngine extends BaseSignatureTrustEngine> implements
        TrustedCredentialTrustEngine {

    /** Class logger. */
    private final Logger log = LoggerFactory.getLogger(ExplicitKeySignatureTrustEngine.class);

    /** Resolver used for resolving trusted credentials. */
    private CredentialResolver credentialResolver;

    /** The external explicit key trust engine to use as a basis for trust in this implementation. */
    private ExplicitKeyTrustEvaluator keyTrust;

    /**
     * Constructor.
     * 
     * @param resolver credential resolver used to resolve trusted credentials.
     * @param keyInfoResolver KeyInfo credential resolver used to obtain the (advisory) signing credential from a
     *            Signature's KeyInfo element.
     */
    public ExplicitKeySignatureTrustEngine(CredentialResolver resolver, KeyInfoCredentialResolver keyInfoResolver) {
        super(keyInfoResolver);
        if (resolver == null) {
            throw new IllegalArgumentException("Credential resolver may not be null");
        }
        credentialResolver = resolver;

        keyTrust = new ExplicitKeyTrustEvaluator();
    }

    /** {@inheritDoc} */
    public CredentialResolver getCredentialResolver() {
        return credentialResolver;
    }

    /** {@inheritDoc} */
    public boolean validate(Signature signature, CriteriaSet trustBasisCriteria) throws SecurityException {

        checkParams(signature, trustBasisCriteria);

        CriteriaSet criteriaSet = new CriteriaSet();
        criteriaSet.addAll(trustBasisCriteria);
        if (!criteriaSet.contains(UsageCriteria.class)) {
            criteriaSet.add(new UsageCriteria(UsageType.SIGNING));
        }
        String jcaAlgorithm = SecurityHelper.getKeyAlgorithmFromURI(signature.getSignatureAlgorithm());
        if (!DatatypeHelper.isEmpty(jcaAlgorithm)) {
            criteriaSet.add(new KeyAlgorithmCriteria(jcaAlgorithm), true);
        }

        Iterable trustedCredentials = getCredentialResolver().resolve(criteriaSet);

        if (validate(signature, trustedCredentials)) {
            return true;
        }

        // If the credentials extracted from Signature's KeyInfo (if any) did not verify the
        // signature and/or establish trust, as a fall back attempt to verify the signature with
        // the trusted credentials directly.
        log.debug("Attempting to verify signature using trusted credentials");

        for (Credential trustedCredential : trustedCredentials) {
            if (verifySignature(signature, trustedCredential)) {
                log.debug("Successfully verified signature using resolved trusted credential");
                return true;
            }
        }
        log.debug("Failed to verify signature using either KeyInfo-derived or directly trusted credentials");
        return false;
    }

    /** {@inheritDoc} */
    public boolean validate(byte[] signature, byte[] content, String algorithmURI, CriteriaSet trustBasisCriteria,
            Credential candidateCredential) throws SecurityException {

        checkParamsRaw(signature, content, algorithmURI, trustBasisCriteria);

        CriteriaSet criteriaSet = new CriteriaSet();
        criteriaSet.addAll(trustBasisCriteria);
        if (!criteriaSet.contains(UsageCriteria.class)) {
            criteriaSet.add(new UsageCriteria(UsageType.SIGNING));
        }
        String jcaAlgorithm = SecurityHelper.getKeyAlgorithmFromURI(algorithmURI);
        if (!DatatypeHelper.isEmpty(jcaAlgorithm)) {
            criteriaSet.add(new KeyAlgorithmCriteria(jcaAlgorithm), true);
        }

        Iterable trustedCredentials = getCredentialResolver().resolve(criteriaSet);

        // First try the optional supplied candidate credential
        if (candidateCredential != null) {
            if (SigningUtil.verifyWithURI(candidateCredential, algorithmURI, signature, content)) {
                log.debug("Successfully verified signature using supplied candidate credential");
                log.debug("Attempting to establish trust of supplied candidate credential");
                if (evaluateTrust(candidateCredential, trustedCredentials)) {
                    log.debug("Successfully established trust of supplied candidate credential");
                    return true;
                } else {
                    log.debug("Failed to establish trust of supplied candidate credential");
                }
            }
        }

        // If the candidate verification credential did not verify the
        // signature and/or establish trust, or if no candidate was supplied,
        // as a fall back attempt to verify the signature with the trusted credentials directly.
        log.debug("Attempting to verify signature using trusted credentials");

        for (Credential trustedCredential : trustedCredentials) {
            if (SigningUtil.verifyWithURI(trustedCredential, algorithmURI, signature, content)) {
                log.debug("Successfully verified signature using resolved trusted credential");
                return true;
            }
        }
        log.debug("Failed to verify signature using either supplied candidate credential"
                + " or directly trusted credentials");
        return false;
    }

    /** {@inheritDoc} */
    protected boolean evaluateTrust(Credential untrustedCredential, Iterable trustedCredentials)
            throws SecurityException {

        return keyTrust.validate(untrustedCredential, trustedCredentials);
    }
}