cert-d-java/pgp-cert-d-java/src/test/java/pgp/cert_d/PGPCertificateDirectoryTest.java

// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
//
// SPDX-License-Identifier: Apache-2.0

package pgp.cert_d;

import org.bouncycastle.util.io.Streams;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.MethodSource;
import pgp.cert_d.backend.FileBasedCertificateDirectoryBackend;
import pgp.cert_d.dummy.TestKeyMaterialMerger;
import pgp.cert_d.dummy.TestKeyMaterialReaderBackend;
import pgp.cert_d.subkey_lookup.InMemorySubkeyLookup;
import pgp.certificate_store.certificate.Certificate;
import pgp.certificate_store.certificate.Key;
import pgp.certificate_store.certificate.KeyMaterial;
import pgp.certificate_store.certificate.KeyMaterialMerger;
import pgp.certificate_store.exception.BadDataException;
import pgp.certificate_store.exception.BadNameException;
import pgp.certificate_store.exception.NotAStoreException;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import java.util.stream.Stream;

import static org.junit.jupiter.api.Assertions.assertArrayEquals;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertFalse;
import static org.junit.jupiter.api.Assertions.assertNotEquals;
import static org.junit.jupiter.api.Assertions.assertNotNull;
import static org.junit.jupiter.api.Assertions.assertNull;
import static org.junit.jupiter.api.Assertions.assertThrows;
import static org.junit.jupiter.api.Assertions.assertTrue;

public class PGPCertificateDirectoryTest {

    @SuppressWarnings("CharsetObjectCanBeUsed")
    private static final Charset UTF8 = Charset.forName("UTF8");

    private static final String HARRY_KEY = "-----BEGIN PGP PRIVATE KEY BLOCK-----\n" +
            "Comment: 2357 8FD1 7F20 7FDF 62F7  976C 4E9D 9891 7AD8 4522\n" +
            "Comment: Harry Potter <harry@potter.more>\n" +
            "\n" +
            "xVgEYwTP0hYJKwYBBAHaRw8BAQdAPVcWeaMiUVG+vECWpoytSoF3wNJQG/JsnCbj\n" +
            "uQtv0REAAP0cS3GCmrIMO/FqNm1FG1mKw4P+mvZ1JBFILN7Laooq7A/QwsARBB8W\n" +
            "CgCDBYJjBM/SBYkFn6YAAwsJBwkQTp2YkXrYRSJHFAAAAAAAHgAgc2FsdEBub3Rh\n" +
            "dGlvbnMuc2VxdW9pYS1wZ3Aub3JnRSvJhQu9P/3bpFqFdB2c5Mfg9JIdyic1tsAt\n" +
            "lZ7o4k4DFQoIApsBAh4BFiEEI1eP0X8gf99i95dsTp2YkXrYRSIAAK2cAP9juDnY\n" +
            "qB6XuXVx76MzDlFemqJ/r2TIlN22O33ITp23cQEAiMk/rULVdfmlFi3QBvXgtPI2\n" +
            "QQYFI0UnyGLmJSa1cwzNIEhhcnJ5IFBvdHRlciA8aGFycnlAcG90dGVyLm1vcmU+\n" +
            "wsAUBBMWCgCGBYJjBM/SBYkFn6YAAwsJBwkQTp2YkXrYRSJHFAAAAAAAHgAgc2Fs\n" +
            "dEBub3RhdGlvbnMuc2VxdW9pYS1wZ3Aub3Jn0o9na1p+a9kY3y3+xUSFFnxbuxNM\n" +
            "5zvth0SAfJIH2C8DFQoIApkBApsBAh4BFiEEI1eP0X8gf99i95dsTp2YkXrYRSIA\n" +
            "AC1zAP0e2qRXH4zCnjvdYwGP0tIY3dwBsm1bvk+wVFHm8h68iwEAh2uyyQ+O5iQH\n" +
            "7NN/lV5dUKKsKaimj/vVGpSW3NtFZQDHWARjBM/SFgkrBgEEAdpHDwEBB0BUqcZu\n" +
            "VsEO6fmW8q3S5ll9WohcTOWRX7Spg5wS3DIqPgABALzJ9ZImb4U94WqRtftSSaeF\n" +
            "0w6rHCn2DiTT8pxjefGQEW7CwMUEGBYKATcFgmMEz9IFiQWfpgAJEE6dmJF62EUi\n" +
            "RxQAAAAAAB4AIHNhbHRAbm90YXRpb25zLnNlcXVvaWEtcGdwLm9yZ+HPX0u5kyKR\n" +
            "5IwErbomgGKVCGuvR6oSKc7CDQYMJS9eApsCvqAEGRYKAG8FgmMEz9IJEKk0hrvR\n" +
            "6Jc7RxQAAAAAAB4AIHNhbHRAbm90YXRpb25zLnNlcXVvaWEtcGdwLm9yZ8Chba26\n" +
            "1nQ6ZEZ/rVH8wMhYznGNa/Ux28sodM04wU6dFiEEli7ijJ6quX9gSoSbqTSGu9Ho\n" +
            "lzsAAG1wAQDVvKVWaMOBELROkF72oBH58X6lrOmr08W5FJQxehywhQEAwetpgL1V\n" +
            "DNj4qcvuCJJ2agAM1tA22WMPpQQeA5CCgwcWIQQjV4/RfyB/32L3l2xOnZiRethF\n" +
            "IgAAsWEA/RfOKexMYEtzlpM71MB9SL+emHXf+w1TNAvBxrifU8bMAPoDmWHkWjZQ\n" +
            "N6upbHKssRywPLKCMPLnFYtBNxDrMYr0BMddBGMEz9ISCisGAQQBl1UBBQEBB0CR\n" +
            "p5dCIlSpV/EvXX2+YZnZSRtc8eTFXkph8RArNi0QPAMBCAcAAP9seqRo6mbmvS4h\n" +
            "fkxmV5zap3wIemzW4iabNU2VbWJbEBALwsAGBBgWCgB4BYJjBM/SBYkFn6YACRBO\n" +
            "nZiRethFIkcUAAAAAAAeACBzYWx0QG5vdGF0aW9ucy5zZXF1b2lhLXBncC5vcmdx\n" +
            "uRLJ/h81azzvGn5zgJ+jdfkdM6iO+f1CLgfnHUH9ugKbDBYhBCNXj9F/IH/fYveX\n" +
            "bE6dmJF62EUiAACObgEAk4whKEo2nzpWht65tpFjrEXdakj00mA/P612P2CUdPQB\n" +
            "ANNn+VUiu9rtnLcP4NlaUVOwsgN7yyed0orbmG1VvSMF\n" +
            "=cBAn\n" +
            "-----END PGP PRIVATE KEY BLOCK-----\n";
    private static final String HARRY_FP = "23578fd17f207fdf62f7976c4e9d98917ad84522";

    private static final String RON_CERT = "-----BEGIN PGP PUBLIC KEY BLOCK-----\n" +
            "Comment: B798 AF18 6BFE 4C19 902D  4950 5647 F001 37EF 4C41\n" +
            "Comment: Ron Weasley <ron@weasley.burrow>\n" +
            "\n" +
            "xjMEYwTRXBYJKwYBBAHaRw8BAQdAPHyiu4nwvo3OY3wLG1tUmS6qeTeT1zd3BrL+\n" +
            "6/5Ys3jCwBEEHxYKAIMFgmME0VwFiQWfpgADCwkHCRBWR/ABN+9MQUcUAAAAAAAe\n" +
            "ACBzYWx0QG5vdGF0aW9ucy5zZXF1b2lhLXBncC5vcmfEPNi/1ObPMwDwS094Lcyq\n" +
            "dRNRk2FRzvhoXKrqF/GHfQMVCggCmwECHgEWIQS3mK8Ya/5MGZAtSVBWR/ABN+9M\n" +
            "QQAAR/oBAJWxxUJqOAzYG4uAd6SSF55LZVl00t3bGhgEyGmrB/ppAQCZTpWu0rwU\n" +
            "GVv/MoeqRwX+P8sHS4FSu/hSYJpbNwysCM0gUm9uIFdlYXNsZXkgPHJvbkB3ZWFz\n" +
            "bGV5LmJ1cnJvdz7CwBQEExYKAIYFgmME0VwFiQWfpgADCwkHCRBWR/ABN+9MQUcU\n" +
            "AAAAAAAeACBzYWx0QG5vdGF0aW9ucy5zZXF1b2lhLXBncC5vcmf43PjsP9w1eGYP\n" +
            "CLm6O+K27EQPiCf2cW71QnQ0RunupgMVCggCmQECmwECHgEWIQS3mK8Ya/5MGZAt\n" +
            "SVBWR/ABN+9MQQAA7rYA/3U2aaw5PFa9L90PbxygOwFrgIVWLiOpnKfjqDJqEgva\n" +
            "AQDxTIbpUYEAYmTpmAm1tiQSlpp9P96vqCMIj2OqtYCNAs4zBGME0VwWCSsGAQQB\n" +
            "2kcPAQEHQGzhRPzKRkkce0v1NjuTV2stn8CEMVgnUxsMPtd0h2M9wsDFBBgWCgE3\n" +
            "BYJjBNFcBYkFn6YACRBWR/ABN+9MQUcUAAAAAAAeACBzYWx0QG5vdGF0aW9ucy5z\n" +
            "ZXF1b2lhLXBncC5vcmd6UNkzsh0jKRPQAKX2PoUhMN4QfhTK9IC6L+QbyL1rFgKb\n" +
            "Ar6gBBkWCgBvBYJjBNFcCRCuGMJD3GUsUUcUAAAAAAAeACBzYWx0QG5vdGF0aW9u\n" +
            "cy5zZXF1b2lhLXBncC5vcmcUTns9+sw7XKKO5ZOYQninRAchypKHbqV2LinV46Hi\n" +
            "bxYhBI+SjTgn0fulukOYj64YwkPcZSxRAADZtAEApse3UJi1iuSFvnyXxuYIOm4d\n" +
            "0sOaOtd18venqfWGyX4BALf7T7LknMY688vaW6/xkw2fonG6Y5VxreIHlMZAcX0H\n" +
            "FiEEt5ivGGv+TBmQLUlQVkfwATfvTEEAAFQ3AQCGSLEt8wgJZXlljPdk1eQ3uvW3\n" +
            "VHryNAc3/vbSOvByFAD/WKXY8Pqki2r9XVUW33Q88firoiKVuGmBxklEG3ACjALO\n" +
            "OARjBNFcEgorBgEEAZdVAQUBAQdARnMlx3ST0EHPiErN7lOF+lhtJ8FmW9arc46u\n" +
            "sHFMgUMDAQgHwsAGBBgWCgB4BYJjBNFcBYkFn6YACRBWR/ABN+9MQUcUAAAAAAAe\n" +
            "ACBzYWx0QG5vdGF0aW9ucy5zZXF1b2lhLXBncC5vcmfv1PKQX1GMihAdj3ftW/yS\n" +
            "bnPYdE+0h5rGCuhYl7sjaQKbDBYhBLeYrxhr/kwZkC1JUFZH8AE370xBAABWugEA\n" +
            "rWOEHQjzoQkxxsErVEVZjqr05SLMmo6+HMJ/4Sgur10A/0+4FSbaKKNGiCnCMRsZ\n" +
            "BEswoD99mUaBXl1nPH+Hg38O\n" +
            "=+pb5\n" +
            "-----END PGP PUBLIC KEY BLOCK-----\n";
    private static final String RON_FP = "b798af186bfe4c19902d49505647f00137ef4c41";

    private static final String CEDRIC_CERT = "-----BEGIN PGP PUBLIC KEY BLOCK-----\n" +
            "Comment: 5E75 BF20 646B C1A9 8D3B  1BC2 FE9C D472 987C 4021\n" +
            "Comment: Cedric Diggory <cedric@diggo.ry>\n" +
            "\n" +
            "xjMEYwTIyhYJKwYBBAHaRw8BAQdA80cyaoAEfh/ENuHw8XtWqrxDoPQ/x44LQzyO\n" +
            "TLhMN+PCwBEEHxYKAIMFgmMEyMoFiQWfpgADCwkHCRD+nNRymHxAIUcUAAAAAAAe\n" +
            "ACBzYWx0QG5vdGF0aW9ucy5zZXF1b2lhLXBncC5vcmf0ckQJQzwOKkXPe8rFP5B+\n" +
            "CbAshRG5OKD3Dp+hScGFXgMVCggCmwECHgEWIQRedb8gZGvBqY07G8L+nNRymHxA\n" +
            "IQAA9WYBAP5rQCq/W3KV90T/wpxf5pcXoCB4tCC9Gi/1AiuGhQdAAP48PIX9fH+T\n" +
            "g7N+tU0xzzCc2nWxG3cIuvGFsg94pKL8As0gQ2VkcmljIERpZ2dvcnkgPGNlZHJp\n" +
            "Y0BkaWdnby5yeT7CwBQEExYKAIYFgmMEyMoFiQWfpgADCwkHCRD+nNRymHxAIUcU\n" +
            "AAAAAAAeACBzYWx0QG5vdGF0aW9ucy5zZXF1b2lhLXBncC5vcmdkUL5mF5SwIXja\n" +
            "bCxhI3lvqiUURSoLY13K6YvHYLz7bwMVCggCmQECmwECHgEWIQRedb8gZGvBqY07\n" +
            "G8L+nNRymHxAIQAA6SwA/jiM8k/Z0ljnHdFxsdoLhdnTZ0yJT/7RxreSZ3aITrDs\n" +
            "AP9V8bAYy4hK0C7i4FmNcos3HQs2Si6ee2/EZjo8LqxeCc4zBGMEyMoWCSsGAQQB\n" +
            "2kcPAQEHQIu0hKMngTnmIPXlZ/p9WOZmLB0s9v9yZJLdZ5ICKn7jwsDFBBgWCgE3\n" +
            "BYJjBMjKBYkFn6YACRD+nNRymHxAIUcUAAAAAAAeACBzYWx0QG5vdGF0aW9ucy5z\n" +
            "ZXF1b2lhLXBncC5vcmdCT1SyOVJwTPp4OEDWFNEgxKD12H+Dya9EzOMJ3I9frwKb\n" +
            "Ar6gBBkWCgBvBYJjBMjKCRDNPli8d9EIkUcUAAAAAAAeACBzYWx0QG5vdGF0aW9u\n" +
            "cy5zZXF1b2lhLXBncC5vcmccLTSNIhZOiNFaTj76iAutuAkUCImFp5ptMICZRo7E\n" +
            "TRYhBESzEAYRbxRfM3ub5c0+WLx30QiRAAAZtwD/WRJrSxzJRsnZs4w+QgZjqOZx\n" +
            "bOGwGObfbEHaExG0cKEA/R+BFODg5oPOvK9W7n0Kt9O171Po+zXB0UDmBiEhh0YL\n" +
            "FiEEXnW/IGRrwamNOxvC/pzUcph8QCEAAEneAQDnOv/cf1/qmjfLnorEi+Z4gRWQ\n" +
            "fp3Rp/gI4SLUQxT0PQD/USZIP0bNMGGC1TRQa+8nK6opSqtIvsatt0tQuu178A7O\n" +
            "OARjBMjKEgorBgEEAZdVAQUBAQdAazcEUsYtY9f9o4A+ePR7ACMIDScVEUWS83+I\n" +
            "SwJQz3QDAQgHwsAGBBgWCgB4BYJjBMjKBYkFn6YACRD+nNRymHxAIUcUAAAAAAAe\n" +
            "ACBzYWx0QG5vdGF0aW9ucy5zZXF1b2lhLXBncC5vcmc/qxMatwD+6zaKDZGlVdn/\n" +
            "TWumSgLtuyYonaOupIfMEAKbDBYhBF51vyBka8GpjTsbwv6c1HKYfEAhAADPiwEA\n" +
            "vQ7fTnAHcdZlMVnNPkc0pZSp1+kO5Z789I5Pp4HloNIBAMoC84ja83PjvcpIyxgR\n" +
            "kspLC9BliezVbFSHIK9NQ/wC\n" +
            "=VemI\n" +
            "-----END PGP PUBLIC KEY BLOCK-----\n";
    private static final String CEDRIC_FP = "5e75bf20646bc1a98d3b1bc2fe9cd472987c4021";

    private static final KeyMaterialMerger merger = new TestKeyMaterialMerger();

    private static Stream<PGPCertificateDirectory> provideTestSubjects()
            throws IOException, NotAStoreException {
        PGPCertificateDirectory inMemory = PGPCertificateDirectories.inMemoryCertificateDirectory(
                new TestKeyMaterialReaderBackend());

        File tempDir = Files.createTempDirectory("pgp-cert-d-test").toFile();
        tempDir.deleteOnExit();
        PGPCertificateDirectory fileBased = PGPCertificateDirectories.fileBasedCertificateDirectory(
                new TestKeyMaterialReaderBackend(),
                tempDir,
                new InMemorySubkeyLookup());

        return Stream.of(inMemory, fileBased);
    }

    @ParameterizedTest
    @MethodSource("provideTestSubjects")
    public void lockDirectoryAndInsertWillFail(PGPCertificateDirectory directory)
            throws IOException, InterruptedException, BadDataException {
        // Manually lock the dir
        assertFalse(directory.backend.getLock().isLocked());
        directory.backend.getLock().lockDirectory();
        assertTrue(directory.backend.getLock().isLocked());
        assertFalse(directory.backend.getLock().tryLockDirectory());

        Certificate inserted = directory.tryInsert(new ByteArrayInputStream(CEDRIC_CERT.getBytes(UTF8)), merger);
        assertNull(inserted);

        directory.backend.getLock().releaseDirectory();
        inserted = directory.tryInsert(new ByteArrayInputStream(CEDRIC_CERT.getBytes(UTF8)), merger);
        assertNotNull(inserted);
    }

    @ParameterizedTest
    @MethodSource("provideTestSubjects")
    public void getByInvalidNameFails(PGPCertificateDirectory directory) {
        assertThrows(BadNameException.class, () -> directory.getBySpecialName("invalid"));
    }

    @ParameterizedTest
    @MethodSource("provideTestSubjects")
    public void testInsertAndGetSingleCert(PGPCertificateDirectory directory)
            throws BadDataException, IOException, InterruptedException, BadNameException {
        assertNull(directory.getByFingerprint(CEDRIC_FP), "Empty directory MUST NOT contain certificate");

        ByteArrayInputStream bytesIn = new ByteArrayInputStream(CEDRIC_CERT.getBytes(UTF8));

        Certificate certificate = directory.insert(bytesIn, merger);
        assertEquals(CEDRIC_FP, certificate.getFingerprint(), "Fingerprint of inserted cert MUST match");

        Certificate get = directory.getByFingerprint(CEDRIC_FP);
        assertEquals(CEDRIC_FP, get.getFingerprint(), "Fingerprint of retrieved cert MUST match");

        byte[] expected = CEDRIC_CERT.getBytes(UTF8);
        ByteArrayOutputStream actual = new ByteArrayOutputStream();
        Streams.pipeAll(get.getInputStream(), actual);
        assertArrayEquals(expected, actual.toByteArray(), "InputStream of cert MUST match what we gave in");
    }

    @ParameterizedTest
    @MethodSource("provideTestSubjects")
    public void testInsertAndGetTrustRootAndCert(PGPCertificateDirectory directory)
            throws BadDataException, IOException, InterruptedException {
        assertNull(directory.getTrustRoot());

        KeyMaterial trustRootMaterial = directory.insertTrustRoot(
                new ByteArrayInputStream(HARRY_KEY.getBytes(UTF8)), merger);
        assertNotNull(trustRootMaterial);
        assertTrue(trustRootMaterial instanceof Key);
        assertEquals(HARRY_FP, trustRootMaterial.getFingerprint());

        Key trustRoot = (Key) directory.getTrustRoot();
        assertEquals(HARRY_FP, trustRoot.getFingerprint());
        Certificate trustRootCert = directory.getTrustRootCertificate();
        assertEquals(HARRY_FP, trustRootCert.getFingerprint());

        directory.tryInsert(new ByteArrayInputStream(RON_CERT.getBytes(UTF8)), merger);
        directory.insert(new ByteArrayInputStream(CEDRIC_CERT.getBytes(UTF8)), merger);

        Set<String> expected = new HashSet<>(Arrays.asList(RON_FP, CEDRIC_FP));

        Set<String> actual = new HashSet<>();
        Iterator<String> fingerprints = directory.fingerprints();
        actual.add(fingerprints.next());
        actual.add(fingerprints.next());
        assertFalse(fingerprints.hasNext());

        assertEquals(expected, actual);
    }

    @ParameterizedTest
    @MethodSource("provideTestSubjects")
    public void testGetTrustRootIfChanged(PGPCertificateDirectory directory)
            throws BadDataException, IOException, InterruptedException {
        KeyMaterial trustRootMaterial = directory.insertTrustRoot(
                new ByteArrayInputStream(HARRY_KEY.getBytes(UTF8)), merger);

        assertNotNull(trustRootMaterial.getTag());
        Long tag = trustRootMaterial.getTag();
        assertNull(directory.getTrustRootCertificateIfChanged(tag));
        assertNotNull(directory.getTrustRootCertificateIfChanged(tag + 1));

        Long oldTag = tag;
        // "update" key
        trustRootMaterial = directory.insertTrustRoot(
                new ByteArrayInputStream(HARRY_KEY.getBytes(UTF8)), merger);
        tag = trustRootMaterial.getTag();

        assertNotEquals(oldTag, tag);
        assertNotNull(directory.getTrustRootCertificateIfChanged(oldTag));
    }

    @ParameterizedTest
    @MethodSource("provideTestSubjects")
    public void testGetBySpecialNameIfChanged(PGPCertificateDirectory directory)
            throws BadDataException, IOException, InterruptedException, BadNameException {
        KeyMaterial specialName = directory.insertWithSpecialName(SpecialNames.TRUST_ROOT,
                new ByteArrayInputStream(HARRY_KEY.getBytes(UTF8)), merger);

        assertNotNull(specialName.getTag());
        Long tag = specialName.getTag();
        assertNull(directory.getBySpecialNameIfChanged(SpecialNames.TRUST_ROOT, tag));
        assertNotNull(directory.getBySpecialNameIfChanged(SpecialNames.TRUST_ROOT, tag + 1));

        Long oldTag = tag;
        // "update" key
        specialName = directory.insertWithSpecialName(SpecialNames.TRUST_ROOT,
                new ByteArrayInputStream(HARRY_KEY.getBytes(UTF8)), merger);
        tag = specialName.getTag();

        assertNotEquals(oldTag, tag);
        assertNotNull(directory.getBySpecialNameIfChanged(SpecialNames.TRUST_ROOT, oldTag));
    }

    @ParameterizedTest
    @MethodSource("provideTestSubjects")
    public void testGetByFingerprintIfChanged(PGPCertificateDirectory directory)
            throws BadDataException, IOException, InterruptedException, BadNameException {
        Certificate certificate = directory.insert(new ByteArrayInputStream(CEDRIC_CERT.getBytes(UTF8)), merger);
        Long tag = certificate.getTag();
        assertNotNull(tag);

        assertNull(directory.getByFingerprintIfChanged(certificate.getFingerprint(), tag));
        assertNotNull(directory.getByFingerprintIfChanged(certificate.getFingerprint(), tag + 1));

        Long oldTag = tag;
        // "update" cert
        certificate = directory.insert(new ByteArrayInputStream(CEDRIC_CERT.getBytes(UTF8)), merger);
        tag = certificate.getTag();

        assertNotEquals(oldTag, tag);
        assertNull(directory.getByFingerprintIfChanged(certificate.getFingerprint(), tag));
        assertNotNull(directory.getByFingerprintIfChanged(certificate.getFingerprint(), oldTag));
    }

    @Test
    public void testFileBasedCertificateDirectoryTagChangesWhenFileChanges() throws IOException, NotAStoreException, BadDataException, InterruptedException, BadNameException {
        File tempDir = Files.createTempDirectory("file-based-changes").toFile();
        tempDir.deleteOnExit();
        PGPCertificateDirectory directory = PGPCertificateDirectories.fileBasedCertificateDirectory(
                new TestKeyMaterialReaderBackend(),
                tempDir,
                new InMemorySubkeyLookup());
        FileBasedCertificateDirectoryBackend.FilenameResolver resolver =
                new FileBasedCertificateDirectoryBackend.FilenameResolver(tempDir);

        // Insert certificate
        Certificate certificate = directory.insert(new ByteArrayInputStream(CEDRIC_CERT.getBytes(UTF8)), merger);
        Long tag = certificate.getTag();
        assertNotNull(tag);
        assertNull(directory.getByFingerprintIfChanged(certificate.getFingerprint(), tag));

        Long oldTag = tag;

        // Change the file on disk directly, this invalidates the tag due to changed modification date
        File certFile = resolver.getCertFileByFingerprint(certificate.getFingerprint());
        FileOutputStream fileOut = new FileOutputStream(certFile);
        Streams.pipeAll(certificate.getInputStream(), fileOut);
        fileOut.close();

        // Old invalidated tag indicates a change, so the modified certificate is returned
        certificate = directory.getByFingerprintIfChanged(certificate.getFingerprint(), oldTag);
        assertNotNull(certificate);

        // new tag is valid
        tag = certificate.getTag();
        assertNotEquals(oldTag, tag);
        assertNull(directory.getByFingerprintIfChanged(certificate.getFingerprint(), tag));
    }
}