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/*
 * Copyright (C) 2015 The Android Open Source Project
 *
 * Licensed 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.conscrypt.ct;

import java.io.OutputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.cert.CertificateEncodingException;
import java.security.cert.CertificateException;
import java.security.cert.X509Certificate;
import org.conscrypt.Internal;
import org.conscrypt.OpenSSLX509Certificate;

/**
 * CertificateEntry structure.
 * This structure describes part of the data which is signed over in SCTs.
 * It is not defined by the RFC6962, but it is useful to have.
 *
 * It's definition would be :
 * struct {
 *     LogEntryType entry_type;
 *     select(entry_type) {
 *         case x509_entry: ASN.1Cert;
 *         case precert_entry: PreCert;
 *     } signed_entry;
 * } CertificateEntry;
 *
 * @hide
 */
@Internal
public class CertificateEntry {
    public enum LogEntryType {
        X509_ENTRY,
        PRECERT_ENTRY
    }

    private final LogEntryType entryType;

    // Only used when entryType is LOG_ENTRY_TYPE_PRECERT
    private final byte[] issuerKeyHash;

    /* If entryType == PRECERT_ENTRY, this is the encoded TBS of the precertificate.
       If entryType == X509_ENTRY, this is the encoded leaf certificate. */
    private final byte[] certificate;

    private CertificateEntry(LogEntryType entryType, byte[] certificate, byte[] issuerKeyHash) {
        if (entryType == LogEntryType.PRECERT_ENTRY && issuerKeyHash == null) {
            throw new IllegalArgumentException("issuerKeyHash missing for precert entry.");
        } else if (entryType == LogEntryType.X509_ENTRY && issuerKeyHash != null) {
            throw new IllegalArgumentException("unexpected issuerKeyHash for X509 entry.");
        }
        
        if (issuerKeyHash != null && issuerKeyHash.length != CTConstants.ISSUER_KEY_HASH_LENGTH) {
            throw new IllegalArgumentException("issuerKeyHash must be 32 bytes long");
        }

        this.entryType = entryType;
        this.issuerKeyHash = issuerKeyHash;
        this.certificate = certificate;
    }

    /**
     * @throws IllegalArgumentException if issuerKeyHash isn't 32 bytes
     */
    public static CertificateEntry createForPrecertificate(byte[] tbsCertificate, byte[] issuerKeyHash) {
        return new CertificateEntry(LogEntryType.PRECERT_ENTRY, tbsCertificate, issuerKeyHash);
    }

    public static CertificateEntry createForPrecertificate(OpenSSLX509Certificate leaf,
            OpenSSLX509Certificate issuer) throws CertificateException {
        try {
            if (!leaf.getNonCriticalExtensionOIDs().contains(CTConstants.X509_SCT_LIST_OID)) {
                throw new CertificateException("Certificate does not contain embedded signed timestamps");
            }

            OpenSSLX509Certificate preCert = leaf.withDeletedExtension(CTConstants.X509_SCT_LIST_OID);
            byte[] tbs = preCert.getTBSCertificate();

            byte[] issuerKey = issuer.getPublicKey().getEncoded();
            MessageDigest md = MessageDigest.getInstance("SHA-256");
            md.update(issuerKey);
            byte[] issuerKeyHash = md.digest();

            return createForPrecertificate(tbs, issuerKeyHash);
        } catch (NoSuchAlgorithmException e) {
            // SHA-256 is guaranteed to be available
            throw new RuntimeException(e);
        }
    }

    public static CertificateEntry createForX509Certificate(byte[] x509Certificate) {
        return new CertificateEntry(LogEntryType.X509_ENTRY, x509Certificate, null);
    }

    public static CertificateEntry createForX509Certificate(X509Certificate cert)
            throws CertificateEncodingException {
        return createForX509Certificate(cert.getEncoded());
    }

    public LogEntryType getEntryType() {
        return entryType;
    }
    public byte[] getCertificate() {
        return certificate;
    }
    public byte[] getIssuerKeyHash() {
        return issuerKeyHash;
    }

    /**
     * TLS encode the CertificateEntry structure.
     */
    public void encode(OutputStream output) throws SerializationException {
        Serialization.writeNumber(output, entryType.ordinal(), CTConstants.LOG_ENTRY_TYPE_LENGTH);
        if (entryType == LogEntryType.PRECERT_ENTRY) {
            Serialization.writeFixedBytes(output, issuerKeyHash);
        }
        Serialization.writeVariableBytes(output, certificate, CTConstants.CERTIFICATE_LENGTH_BYTES);
    }
}