/*
 * Copyright (c) 1996, 2011, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package sun.security.pkcs;

import java.io.*;
import java.math.BigInteger;
import java.util.*;
import java.security.cert.X509Certificate;
import java.security.cert.CertificateException;
import java.security.cert.X509CRL;
import java.security.cert.CRLException;
import java.security.cert.CertificateFactory;
import java.security.*;

import sun.security.util.*;
import sun.security.x509.AlgorithmId;
import sun.security.x509.CertificateIssuerName;
import sun.security.x509.KeyUsageExtension;
import sun.security.x509.X509CertImpl;
import sun.security.x509.X509CertInfo;
import sun.security.x509.X509CRLImpl;
import sun.security.x509.X500Name;

/**
 * PKCS7 as defined in RSA Laboratories PKCS7 Technical Note. Profile
 * Supports only <tt>SignedData</tt> ContentInfo
 * type, where to the type of data signed is plain Data.
 * For signedData, <tt>crls</tt>, <tt>attributes</tt> and
 * PKCS#6 Extended Certificates are not supported.
 *
 * @author Benjamin Renaud
 */
public class PKCS7 {

    private ObjectIdentifier contentType;

    // the ASN.1 members for a signedData (and other) contentTypes
    private BigInteger version = null;
    private AlgorithmId[] digestAlgorithmIds = null;
    private ContentInfo contentInfo = null;
    private X509Certificate[] certificates = null;
    private X509CRL[] crls = null;
    private SignerInfo[] signerInfos = null;

    private boolean oldStyle = false; // Is this JDK1.1.x-style?

    private Principal[] certIssuerNames;

    /**
     * Unmarshals a PKCS7 block from its encoded form, parsing the
     * encoded bytes from the InputStream.
     *
     * @param in an input stream holding at least one PKCS7 block.
     * @exception ParsingException on parsing errors.
     * @exception IOException on other errors.
     */
    public PKCS7(InputStream in) throws ParsingException, IOException {
        DataInputStream dis = new DataInputStream(in);
        byte[] data = new byte[dis.available()];
        dis.readFully(data);

        parse(new DerInputStream(data));
    }

    /**
     * Unmarshals a PKCS7 block from its encoded form, parsing the
     * encoded bytes from the DerInputStream.
     *
     * @param derin a DerInputStream holding at least one PKCS7 block.
     * @exception ParsingException on parsing errors.
     */
    public PKCS7(DerInputStream derin) throws ParsingException {
        parse(derin);
    }

    /**
     * Unmarshals a PKCS7 block from its encoded form, parsing the
     * encoded bytes.
     *
     * @param bytes the encoded bytes.
     * @exception ParsingException on parsing errors.
     */
    public PKCS7(byte[] bytes) throws ParsingException {
        try {
            DerInputStream derin = new DerInputStream(bytes);
            parse(derin);
        } catch (IOException ioe1) {
            ParsingException pe = new ParsingException(
                "Unable to parse the encoded bytes");
            pe.initCause(ioe1);
            throw pe;
        }
    }

    /*
     * Parses a PKCS#7 block.
     */
    private void parse(DerInputStream derin)
        throws ParsingException
    {
        try {
            derin.mark(derin.available());
            // try new (i.e., JDK1.2) style
            parse(derin, false);
        } catch (IOException ioe) {
            try {
                derin.reset();
                // try old (i.e., JDK1.1.x) style
                parse(derin, true);
                oldStyle = true;
            } catch (IOException ioe1) {
                ParsingException pe = new ParsingException(
                    ioe1.getMessage());
                pe.initCause(ioe1);
                throw pe;
            }
        }
    }

    /**
     * Parses a PKCS#7 block.
     *
     * @param derin the ASN.1 encoding of the PKCS#7 block.
     * @param oldStyle flag indicating whether or not the given PKCS#7 block
     * is encoded according to JDK1.1.x.
     */
    private void parse(DerInputStream derin, boolean oldStyle)
        throws IOException
    {
        contentInfo = new ContentInfo(derin, oldStyle);
        contentType = contentInfo.contentType;
        DerValue content = contentInfo.getContent();

        if (contentType.equals(ContentInfo.SIGNED_DATA_OID)) {
            parseSignedData(content);
        } else if (contentType.equals(ContentInfo.OLD_SIGNED_DATA_OID)) {
            // This is for backwards compatibility with JDK 1.1.x
            parseOldSignedData(content);
        } else if (contentType.equals(ContentInfo.NETSCAPE_CERT_SEQUENCE_OID)){
            parseNetscapeCertChain(content);
        } else {
            throw new ParsingException("content type " + contentType +
                                       " not supported.");
        }
    }

    /**
     * Construct an initialized PKCS7 block.
     *
     * @param digestAlgorithmIds the message digest algorithm identifiers.
     * @param contentInfo the content information.
     * @param certificates an array of X.509 certificates.
     * @param crls an array of CRLs
     * @param signerInfos an array of signer information.
     */
    public PKCS7(AlgorithmId[] digestAlgorithmIds,
                 ContentInfo contentInfo,
                 X509Certificate[] certificates,
                 X509CRL[] crls,
                 SignerInfo[] signerInfos) {

        version = BigInteger.ONE;
        this.digestAlgorithmIds = digestAlgorithmIds;
        this.contentInfo = contentInfo;
        this.certificates = certificates;
        this.crls = crls;
        this.signerInfos = signerInfos;
    }

    public PKCS7(AlgorithmId[] digestAlgorithmIds,
                 ContentInfo contentInfo,
                 X509Certificate[] certificates,
                 SignerInfo[] signerInfos) {
        this(digestAlgorithmIds, contentInfo, certificates, null, signerInfos);
    }

    private void parseNetscapeCertChain(DerValue val)
    throws ParsingException, IOException {
        DerInputStream dis = new DerInputStream(val.toByteArray());
        DerValue[] contents = dis.getSequence(2);
        certificates = new X509Certificate[contents.length];

        CertificateFactory certfac = null;
        try {
            certfac = CertificateFactory.getInstance("X.509");
        } catch (CertificateException ce) {
            // do nothing
        }

        for (int i=0; i < contents.length; i++) {
            ByteArrayInputStream bais = null;
            try {
                if (certfac == null)
                    certificates[i] = new X509CertImpl(contents[i]);
                else {
                    byte[] encoded = contents[i].toByteArray();
                    bais = new ByteArrayInputStream(encoded);
                    certificates[i] =
                        (X509Certificate)certfac.generateCertificate(bais);
                    bais.close();
                    bais = null;
                }
            } catch (CertificateException ce) {
                ParsingException pe = new ParsingException(ce.getMessage());
                pe.initCause(ce);
                throw pe;
            } catch (IOException ioe) {
                ParsingException pe = new ParsingException(ioe.getMessage());
                pe.initCause(ioe);
                throw pe;
            } finally {
                if (bais != null)
                    bais.close();
            }
        }
    }

    private void parseSignedData(DerValue val)
        throws ParsingException, IOException {

        DerInputStream dis = val.toDerInputStream();

        // Version
        version = dis.getBigInteger();

        // digestAlgorithmIds
        DerValue[] digestAlgorithmIdVals = dis.getSet(1);
        int len = digestAlgorithmIdVals.length;
        digestAlgorithmIds = new AlgorithmId[len];
        try {
            for (int i = 0; i < len; i++) {
                DerValue oid = digestAlgorithmIdVals[i];
                digestAlgorithmIds[i] = AlgorithmId.parse(oid);
            }

        } catch (IOException e) {
            ParsingException pe =
                new ParsingException("Error parsing digest AlgorithmId IDs: " +
                                     e.getMessage());
            pe.initCause(e);
            throw pe;
        }
        // contentInfo
        contentInfo = new ContentInfo(dis);

        CertificateFactory certfac = null;
        try {
            certfac = CertificateFactory.getInstance("X.509");
        } catch (CertificateException ce) {
            // do nothing
        }

        /*
         * check if certificates (implicit tag) are provided
         * (certificates are OPTIONAL)
         */
        if ((byte)(dis.peekByte()) == (byte)0xA0) {
            DerValue[] certVals = dis.getSet(2, true);

            len = certVals.length;
            certificates = new X509Certificate[len];

            for (int i = 0; i < len; i++) {
                ByteArrayInputStream bais = null;
                try {
                    if (certfac == null)
                        certificates[i] = new X509CertImpl(certVals[i]);
                    else {
                        byte[] encoded = certVals[i].toByteArray();
                        bais = new ByteArrayInputStream(encoded);
                        certificates[i] =
                            (X509Certificate)certfac.generateCertificate(bais);
                        bais.close();
                        bais = null;
                    }
                } catch (CertificateException ce) {
                    ParsingException pe = new ParsingException(ce.getMessage());
                    pe.initCause(ce);
                    throw pe;
                } catch (IOException ioe) {
                    ParsingException pe = new ParsingException(ioe.getMessage());
                    pe.initCause(ioe);
                    throw pe;
                } finally {
                    if (bais != null)
                        bais.close();
                }
            }
        }

        // check if crls (implicit tag) are provided (crls are OPTIONAL)
        if ((byte)(dis.peekByte()) == (byte)0xA1) {
            DerValue[] crlVals = dis.getSet(1, true);

            len = crlVals.length;
            crls = new X509CRL[len];

            for (int i = 0; i < len; i++) {
                ByteArrayInputStream bais = null;
                try {
                    if (certfac == null)
                        crls[i] = new X509CRLImpl(crlVals[i]);
                    else {
                        byte[] encoded = crlVals[i].toByteArray();
                        bais = new ByteArrayInputStream(encoded);
                        crls[i] = (X509CRL) certfac.generateCRL(bais);
                        bais.close();
                        bais = null;
                    }
                } catch (CRLException e) {
                    ParsingException pe =
                        new ParsingException(e.getMessage());
                    pe.initCause(e);
                    throw pe;
                } finally {
                    if (bais != null)
                        bais.close();
                }
            }
        }

        // signerInfos
        DerValue[] signerInfoVals = dis.getSet(1);

        len = signerInfoVals.length;
        signerInfos = new SignerInfo[len];

        for (int i = 0; i < len; i++) {
            DerInputStream in = signerInfoVals[i].toDerInputStream();
            signerInfos[i] = new SignerInfo(in);
        }
    }

    /*
     * Parses an old-style SignedData encoding (for backwards
     * compatibility with JDK1.1.x).
     */
    private void parseOldSignedData(DerValue val)
        throws ParsingException, IOException
    {
        DerInputStream dis = val.toDerInputStream();

        // Version
        version = dis.getBigInteger();

        // digestAlgorithmIds
        DerValue[] digestAlgorithmIdVals = dis.getSet(1);
        int len = digestAlgorithmIdVals.length;

        digestAlgorithmIds = new AlgorithmId[len];
        try {
            for (int i = 0; i < len; i++) {
                DerValue oid = digestAlgorithmIdVals[i];
                digestAlgorithmIds[i] = AlgorithmId.parse(oid);
            }
        } catch (IOException e) {
            throw new ParsingException("Error parsing digest AlgorithmId IDs");
        }

        // contentInfo
        contentInfo = new ContentInfo(dis, true);

        // certificates
        CertificateFactory certfac = null;
        try {
            certfac = CertificateFactory.getInstance("X.509");
        } catch (CertificateException ce) {
            // do nothing
        }
        DerValue[] certVals = dis.getSet(2);
        len = certVals.length;
        certificates = new X509Certificate[len];

        for (int i = 0; i < len; i++) {
            ByteArrayInputStream bais = null;
            try {
                if (certfac == null)
                    certificates[i] = new X509CertImpl(certVals[i]);
                else {
                    byte[] encoded = certVals[i].toByteArray();
                    bais = new ByteArrayInputStream(encoded);
                    certificates[i] =
                        (X509Certificate)certfac.generateCertificate(bais);
                    bais.close();
                    bais = null;
                }
            } catch (CertificateException ce) {
                ParsingException pe = new ParsingException(ce.getMessage());
                pe.initCause(ce);
                throw pe;
            } catch (IOException ioe) {
                ParsingException pe = new ParsingException(ioe.getMessage());
                pe.initCause(ioe);
                throw pe;
            } finally {
                if (bais != null)
                    bais.close();
            }
        }

        // crls are ignored.
        dis.getSet(0);

        // signerInfos
        DerValue[] signerInfoVals = dis.getSet(1);
        len = signerInfoVals.length;
        signerInfos = new SignerInfo[len];
        for (int i = 0; i < len; i++) {
            DerInputStream in = signerInfoVals[i].toDerInputStream();
            signerInfos[i] = new SignerInfo(in, true);
        }
    }

    /**
     * Encodes the signed data to an output stream.
     *
     * @param out the output stream to write the encoded data to.
     * @exception IOException on encoding errors.
     */
    public void encodeSignedData(OutputStream out) throws IOException {
        DerOutputStream derout = new DerOutputStream();
        encodeSignedData(derout);
        out.write(derout.toByteArray());
    }

    /**
     * Encodes the signed data to a DerOutputStream.
     *
     * @param out the DerOutputStream to write the encoded data to.
     * @exception IOException on encoding errors.
     */
    public void encodeSignedData(DerOutputStream out)
        throws IOException
    {
        DerOutputStream signedData = new DerOutputStream();

        // version
        signedData.putInteger(version);

        // digestAlgorithmIds
        signedData.putOrderedSetOf(DerValue.tag_Set, digestAlgorithmIds);

        // contentInfo
        contentInfo.encode(signedData);

        // certificates (optional)
        if (certificates != null && certificates.length != 0) {
            // cast to X509CertImpl[] since X509CertImpl implements DerEncoder
            X509CertImpl implCerts[] = new X509CertImpl[certificates.length];
            for (int i = 0; i < certificates.length; i++) {
                if (certificates[i] instanceof X509CertImpl)
                    implCerts[i] = (X509CertImpl) certificates[i];
                else {
                    try {
                        byte[] encoded = certificates[i].getEncoded();
                        implCerts[i] = new X509CertImpl(encoded);
                    } catch (CertificateException ce) {
                        IOException ie = new IOException(ce.getMessage());
                        ie.initCause(ce);
                        throw ie;
                    }
                }
            }

            // Add the certificate set (tagged with [0] IMPLICIT)
            // to the signed data
            signedData.putOrderedSetOf((byte)0xA0, implCerts);
        }

        // CRLs (optional)
        if (crls != null && crls.length != 0) {
            // cast to X509CRLImpl[] since X509CRLImpl implements DerEncoder
            Set<X509CRLImpl> implCRLs = new HashSet<>(crls.length);
            for (X509CRL crl: crls) {
                if (crl instanceof X509CRLImpl)
                    implCRLs.add((X509CRLImpl) crl);
                else {
                    try {
                        byte[] encoded = crl.getEncoded();
                        implCRLs.add(new X509CRLImpl(encoded));
                    } catch (CRLException ce) {
                        IOException ie = new IOException(ce.getMessage());
                        ie.initCause(ce);
                        throw ie;
                    }
                }
            }

            // Add the CRL set (tagged with [1] IMPLICIT)
            // to the signed data
            signedData.putOrderedSetOf((byte)0xA1,
                    implCRLs.toArray(new X509CRLImpl[implCRLs.size()]));
        }

        // signerInfos
        signedData.putOrderedSetOf(DerValue.tag_Set, signerInfos);

        // making it a signed data block
        DerValue signedDataSeq = new DerValue(DerValue.tag_Sequence,
                                              signedData.toByteArray());

        // making it a content info sequence
        ContentInfo block = new ContentInfo(ContentInfo.SIGNED_DATA_OID,
                                            signedDataSeq);

        // writing out the contentInfo sequence
        block.encode(out);
    }

    /**
     * Verifying signed data using an external chunked data source.
     */
    public static class PKCS7Verifier {

        private final SignerInfo si;          // Signer to verify
        private final MessageDigest md;       // MessageDigest object for chunks
        private final Signature sig;          // Signature object for chunks

        private PKCS7Verifier(SignerInfo si, MessageDigest md, Signature sig) {
            this.si = si;
            this.md = md;
            this.sig = sig;
        }

        public static PKCS7Verifier from(PKCS7 block, SignerInfo si) throws
                SignatureException, NoSuchAlgorithmException {

            try {
                MessageDigest md = null;
                Signature sig;

                ContentInfo content = block.getContentInfo();
                String digestAlgname = si.getDigestAlgorithmId().getName();

                // if there are authenticate attributes, feed data chunks to
                // the message digest. In this case, pv.md is not null
                if (si.authenticatedAttributes != null) {
                    // first, check content type
                    ObjectIdentifier contentType = (ObjectIdentifier)
                           si.authenticatedAttributes.getAttributeValue(
                             PKCS9Attribute.CONTENT_TYPE_OID);
                    if (contentType == null ||
                        !contentType.equals(content.contentType))
                        return null;  // contentType does not match, bad SignerInfo

                    // now, check message digest
                    byte[] messageDigest = (byte[])
                        si.authenticatedAttributes.getAttributeValue(
                             PKCS9Attribute.MESSAGE_DIGEST_OID);

                    if (messageDigest == null) // fail if there is no message digest
                        return null;

                    md = MessageDigest.getInstance(digestAlgname);
                }

                // put together digest algorithm and encryption algorithm
                // to form signing algorithm
                String encryptionAlgname =
                    si.getDigestEncryptionAlgorithmId().getName();

                // Workaround: sometimes the encryptionAlgname is actually
                // a signature name
                String tmp = AlgorithmId.getEncAlgFromSigAlg(encryptionAlgname);
                if (tmp != null) encryptionAlgname = tmp;
                String algname = AlgorithmId.makeSigAlg(
                        digestAlgname, encryptionAlgname);

                sig = Signature.getInstance(algname);
                X509Certificate cert = si.getCertificate(block);

                if (cert == null) {
                    return null;
                }
                if (cert.hasUnsupportedCriticalExtension()) {
                    throw new SignatureException("Certificate has unsupported "
                                                 + "critical extension(s)");
                }

                // Make sure that if the usage of the key in the certificate is
                // restricted, it can be used for digital signatures.
                // XXX We may want to check for additional extensions in the
                // future.
                boolean[] keyUsageBits = cert.getKeyUsage();
                if (keyUsageBits != null) {
                    KeyUsageExtension keyUsage;
                    try {
                        // We don't care whether or not this extension was marked
                        // critical in the certificate.
                        // We're interested only in its value (i.e., the bits set)
                        // and treat the extension as critical.
                        keyUsage = new KeyUsageExtension(keyUsageBits);
                    } catch (IOException ioe) {
                        throw new SignatureException("Failed to parse keyUsage "
                                                     + "extension");
                    }

                    boolean digSigAllowed = ((Boolean)keyUsage.get(
                            KeyUsageExtension.DIGITAL_SIGNATURE)).booleanValue();

                    boolean nonRepuAllowed = ((Boolean)keyUsage.get(
                            KeyUsageExtension.NON_REPUDIATION)).booleanValue();

                    if (!digSigAllowed && !nonRepuAllowed) {
                        throw new SignatureException("Key usage restricted: "
                                                     + "cannot be used for "
                                                     + "digital signatures");
                    }
                }

                PublicKey key = cert.getPublicKey();
                sig.initVerify(key);
                return new PKCS7Verifier(si, md, sig);
            } catch (IOException e) {
                throw new SignatureException("IO error verifying signature:\n" +
                                             e.getMessage());

            } catch (InvalidKeyException e) {
                throw new SignatureException("InvalidKey: " + e.getMessage());

            }
        }

        public void update(byte[] data, int off, int end)
                throws SignatureException {
            if (md != null) {
                md.update(data, off, end-off);
            } else {
                sig.update(data, off, end-off);
            }
        }

        public SignerInfo verify() throws SignatureException {
            try {
                // if there are authenticate attributes, get the message
                // digest and compare it with the digest of data
                if (md != null) {
                    // now, check message digest
                    byte[] messageDigest = (byte[])
                        si.authenticatedAttributes.getAttributeValue(
                             PKCS9Attribute.MESSAGE_DIGEST_OID);

                    byte[] computedMessageDigest = md.digest();

                    if (!MessageDigest.isEqual(
                            messageDigest, computedMessageDigest)) {
                        return null;
                    }

                    // message digest attribute matched
                    // digest of original data

                    // the data actually signed is the DER encoding of
                    // the authenticated attributes (tagged with
                    // the "SET OF" tag, not 0xA0).
                    byte[] dataSigned = si.authenticatedAttributes.getDerEncoding();
                    sig.update(dataSigned);
                }

                if (sig.verify(si.getEncryptedDigest())) {
                    return si;
                }

            } catch (IOException e) {
                throw new SignatureException("IO error verifying signature:\n" +
                                             e.getMessage());
            }
            return null;
        }
    }

    /**
     * This verifies a given SignerInfo.
     *
     * @param info the signer information.
     * @param bytes the DER encoded content information.
     *
     * @exception NoSuchAlgorithmException on unrecognized algorithms.
     * @exception SignatureException on signature handling errors.
     */
    public SignerInfo verify(SignerInfo info, byte[] bytes)
    throws NoSuchAlgorithmException, SignatureException {
        return info.verify(this, bytes);
    }

    /**
     * Returns all signerInfos which self-verify.
     *
     * @param bytes the DER encoded content information.
     *
     * @exception NoSuchAlgorithmException on unrecognized algorithms.
     * @exception SignatureException on signature handling errors.
     */
    public SignerInfo[] verify(byte[] bytes)
    throws NoSuchAlgorithmException, SignatureException {

        List<SignerInfo> intResult = new ArrayList<>();
        for (int i = 0; i < signerInfos.length; i++) {

            SignerInfo signerInfo = verify(signerInfos[i], bytes);
            if (signerInfo != null) {
                intResult.add(signerInfo);
            }
        }
        if (!intResult.isEmpty()) {
            return intResult.toArray(new SignerInfo[intResult.size()]);
        }
        return null;
    }

    /**
     * Returns all signerInfos which self-verify.
     *
     * @exception NoSuchAlgorithmException on unrecognized algorithms.
     * @exception SignatureException on signature handling errors.
     */
    public SignerInfo[] verify()
    throws NoSuchAlgorithmException, SignatureException {
        return verify(null);
    }

    /**
     * Returns the version number of this PKCS7 block.
     * @return the version or null if version is not specified
     *         for the content type.
     */
    public  BigInteger getVersion() {
        return version;
    }

    /**
     * Returns the message digest algorithms specified in this PKCS7 block.
     * @return the array of Digest Algorithms or null if none are specified
     *         for the content type.
     */
    public AlgorithmId[] getDigestAlgorithmIds() {
        return  digestAlgorithmIds;
    }

    /**
     * Returns the content information specified in this PKCS7 block.
     */
    public ContentInfo getContentInfo() {
        return contentInfo;
    }

    /**
     * Returns the X.509 certificates listed in this PKCS7 block.
     * @return a clone of the array of X.509 certificates or null if
     *         none are specified for the content type.
     */
    public X509Certificate[] getCertificates() {
        if (certificates != null)
            return certificates.clone();
        else
            return null;
    }

    /**
     * Returns the X.509 crls listed in this PKCS7 block.
     * @return a clone of the array of X.509 crls or null if none
     *         are specified for the content type.
     */
    public X509CRL[] getCRLs() {
        if (crls != null)
            return crls.clone();
        else
            return null;
    }

    /**
     * Returns the signer's information specified in this PKCS7 block.
     * @return the array of Signer Infos or null if none are specified
     *         for the content type.
     */
    public SignerInfo[] getSignerInfos() {
        return signerInfos;
    }

    /**
     * Returns the X.509 certificate listed in this PKCS7 block
     * which has a matching serial number and Issuer name, or
     * null if one is not found.
     *
     * @param serial the serial number of the certificate to retrieve.
     * @param issuerName the Distinguished Name of the Issuer.
     */
    public X509Certificate getCertificate(BigInteger serial, X500Name issuerName) {
        if (certificates != null) {
            if (certIssuerNames == null)
                populateCertIssuerNames();
            for (int i = 0; i < certificates.length; i++) {
                X509Certificate cert = certificates[i];
                BigInteger thisSerial = cert.getSerialNumber();
                if (serial.equals(thisSerial)
                    && issuerName.equals(certIssuerNames[i]))
                {
                    return cert;
                }
            }
        }
        return null;
    }

    /**
     * Populate array of Issuer DNs from certificates and convert
     * each Principal to type X500Name if necessary.
     */
    private void populateCertIssuerNames() {
        if (certificates == null)
            return;

        certIssuerNames = new Principal[certificates.length];
        for (int i = 0; i < certificates.length; i++) {
            X509Certificate cert = certificates[i];
            Principal certIssuerName = cert.getIssuerDN();
            if (!(certIssuerName instanceof X500Name)) {
                // must extract the original encoded form of DN for
                // subsequent name comparison checks (converting to a
                // String and back to an encoded DN could cause the
                // types of String attribute values to be changed)
                try {
                    X509CertInfo tbsCert =
                        new X509CertInfo(cert.getTBSCertificate());
                    certIssuerName = (Principal)
                        tbsCert.get(CertificateIssuerName.NAME + "." +
                                    CertificateIssuerName.DN_NAME);
                } catch (Exception e) {
                    // error generating X500Name object from the cert's
                    // issuer DN, leave name as is.
                }
            }
            certIssuerNames[i] = certIssuerName;
        }
    }

    /**
     * Returns the PKCS7 block in a printable string form.
     */
    public String toString() {
        String out = "";

        out += contentInfo + "\n";
        if (version != null)
            out += "PKCS7 :: version: " + Debug.toHexString(version) + "\n";
        if (digestAlgorithmIds != null) {
            out += "PKCS7 :: digest AlgorithmIds: \n";
            for (int i = 0; i < digestAlgorithmIds.length; i++)
                out += "\t" + digestAlgorithmIds[i] + "\n";
        }
        if (certificates != null) {
            out += "PKCS7 :: certificates: \n";
            for (int i = 0; i < certificates.length; i++)
                out += "\t" + i + ".   " + certificates[i] + "\n";
        }
        if (crls != null) {
            out += "PKCS7 :: crls: \n";
            for (int i = 0; i < crls.length; i++)
                out += "\t" + i + ".   " + crls[i] + "\n";
        }
        if (signerInfos != null) {
            out += "PKCS7 :: signer infos: \n";
            for (int i = 0; i < signerInfos.length; i++)
                out += ("\t" + i + ".  " + signerInfos[i] + "\n");
        }
        return out;
    }

    /**
     * Returns true if this is a JDK1.1.x-style PKCS#7 block, and false
     * otherwise.
     */
    public boolean isOldStyle() {
        return this.oldStyle;
    }
}