深入理解OkHttp3：（六）Https

OkHttp试图平衡两个相互竞争的关注点:

• 连接到尽可能多的主机。这包括运行最新版本boringssl的高级主机，以及运行旧版本OpenSSL的少数过时的主机。
• 连接的安全性。这包括使用证书验证远程web服务器，以及使用强大的密码体系保证交换数据的隐私性。

在与HTTPS服务器的连接时，OkHttp需要知道要提供哪些TLS版本和密码套件。客户端想要最大限度地连接服务器，不得不包括过时的TLS版本和设计不足的密码套件。一个想要最大限度地提高安全性的严格客户端将仅限于最新的TLS版本和最强的密码套件。

具体的安全性与连接性决策由ConnectionSpec实现。OkHttp包括四个内置连接规格:

• RESTRICTED_TLS是一个安全的配置，目的是满足更严格的遵从性要求。
• MODERN_TLS是一个连接到现代HTTPS服务器的安全配置。
• COMPATIBLE_TLS是一种安全配置，可以连接到安全但不是当前的Https服务器。
• CLEARTEXT是一个不安全的配置，用于http:// url。

它们大致遵循谷歌云策略中设置的模型。

默认情况下，OkHttp将尝试一个MODERN_TLS连接。然而，通过配置客户端connectionSpecs，如果现代配置失败，您可以允许返回到COMPATIBLE_TLS连接。

OkHttpClient client = new OkHttpClient.Builder() 
    .connectionSpecs(Arrays.asList(ConnectionSpec.MODERN_TLS, ConnectionSpec.COMPATIBLE_TLS))
    .build();

每个规范中的TLS版本和密码套件可以随着每个版本的不同而改变。例如，在OkHttp 2.2中，为了应对POODLE 攻击，我们放弃了对SSL 3.0的支持。在OkHttp 2.3中，我们放弃了对RC4的支持。与桌面web浏览器一样，使用OkHttp是保持安全的最佳方法。

您可以使用一组自定义的TLS版本和密码套件构建自己的连接规范。例如，这个配置仅限于三个备受关注的密码套件。它的缺点是需要Android 5.0+和一个类似的当前webserver。

ConnectionSpec spec = new ConnectionSpec.Builder(ConnectionSpec.MODERN_TLS)  
    .tlsVersions(TlsVersion.TLS_1_2)
    .cipherSuites(
          CipherSuite.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
          CipherSuite.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
          CipherSuite.TLS_DHE_RSA_WITH_AES_128_GCM_SHA256)
    .build();

OkHttpClient client = new OkHttpClient.Builder() 
    .connectionSpecs(Collections.singletonList(spec))
    .build();

固定证书

默认情况下，OkHttp信任主机平台的证书认证。这种策略最大化了连接性，但它会受到证书认证的攻击，比如2011年的DigiNotar攻击。它还假定HTTPS服务器的证书是由证书颁发机构签署的。

使用CertificatePinner来限制哪些证书和证书颁发机构值得信任。固定证书增加了安全性，但限制了服务器团队更新TLS证书的能力。如果没有服务器的TLS管理员的许可，不要使用固定证书!

import java.io.IOException;
import java.security.cert.Certificate;
import okhttp3.CertificatePinner;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;

public final class CertificatePinning {
  private final OkHttpClient client;

  public CertificatePinning() {
    client = new OkHttpClient.Builder()
        .certificatePinner(
            new CertificatePinner.Builder()
                .add("publicobject.com", "sha256/afwiKY3RxoMmLkuRW1l7QsPZTJPwDS2pdDROQjXw8ig=")
                .build())
        .build();
  }

  public void run() throws Exception {
    Request request = new Request.Builder()
        .url("https://publicobject.com/robots.txt")
        .build();

    try (Response response = client.newCall(request).execute()) {
      if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);

      for (Certificate certificate : response.handshake().peerCertificates()) {
        System.out.println(CertificatePinner.pin(certificate));
      }
    }
  }

  public static void main(String... args) throws Exception {
    new CertificatePinning().run();
  }
}

自定义证书

完整的代码示例展示了如何用您自己的集合替换主机平台的证书颁发机构。如上所述，如果没有服务器的TLS管理员的许可，不要使用自定义证书!

import java.io.IOException;
import java.io.InputStream;
import java.security.GeneralSecurityException;
import java.security.KeyStore;
import java.security.cert.Certificate;
import java.security.cert.CertificateFactory;
import java.util.Arrays;
import java.util.Collection;
import javax.net.ssl.KeyManagerFactory;
import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLSocketFactory;
import javax.net.ssl.TrustManager;
import javax.net.ssl.TrustManagerFactory;
import javax.net.ssl.X509TrustManager;
import okhttp3.CertificatePinner;
import okhttp3.Headers;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;
import okio.Buffer;

public final class CustomTrust {
  private final OkHttpClient client;

  public CustomTrust() {
    X509TrustManager trustManager;
    SSLSocketFactory sslSocketFactory;
    try {
      trustManager = trustManagerForCertificates(trustedCertificatesInputStream());
      SSLContext sslContext = SSLContext.getInstance("TLS");
      sslContext.init(null, new TrustManager[] { trustManager }, null);
      sslSocketFactory = sslContext.getSocketFactory();
    } catch (GeneralSecurityException e) {
      throw new RuntimeException(e);
    }

    client = new OkHttpClient.Builder()
        .sslSocketFactory(sslSocketFactory, trustManager)
        .build();
  }

  public void run() throws Exception {
    Request request = new Request.Builder()
        .url("https://publicobject.com/helloworld.txt")
        .build();

    try (Response response = client.newCall(request).execute()) {
      if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);

      Headers responseHeaders = response.headers();
      for (int i = 0; i < responseHeaders.size(); i++) {
        System.out.println(responseHeaders.name(i) + ": " + responseHeaders.value(i));
      }

      System.out.println(response.body().string());
    }
  }

  /**
   * Returns an input stream containing one or more certificate PEM files. This implementation just
   * embeds the PEM files in Java strings; most applications will instead read this from a resource
   * file that gets bundled with the application.
   */
  private InputStream trustedCertificatesInputStream() {
    // PEM files for root certificates of Comodo and Entrust. These two CAs are sufficient to view
    // https://publicobject.com (Comodo) and https://squareup.com (Entrust). But they aren't
    // sufficient to connect to most HTTPS sites including https://godaddy.com and https://visa.com.
    // Typically developers will need to get a PEM file from their organization's TLS administrator.
    String comodoRsaCertificationAuthority = ""
        + "-----BEGIN CERTIFICATE-----\n"
        + "MIIF2DCCA8CgAwIBAgIQTKr5yttjb+Af907YWwOGnTANBgkqhkiG9w0BAQwFADCB\n"
        + "hTELMAkGA1UEBhMCR0IxGzAZBgNVBAgTEkdyZWF0ZXIgTWFuY2hlc3RlcjEQMA4G\n"
        + "A1UEBxMHU2FsZm9yZDEaMBgGA1UEChMRQ09NT0RPIENBIExpbWl0ZWQxKzApBgNV\n"
        + "BAMTIkNPTU9ETyBSU0EgQ2VydGlmaWNhdGlvbiBBdXRob3JpdHkwHhcNMTAwMTE5\n"
        + "MDAwMDAwWhcNMzgwMTE4MjM1OTU5WjCBhTELMAkGA1UEBhMCR0IxGzAZBgNVBAgT\n"
        + "EkdyZWF0ZXIgTWFuY2hlc3RlcjEQMA4GA1UEBxMHU2FsZm9yZDEaMBgGA1UEChMR\n"
        + "Q09NT0RPIENBIExpbWl0ZWQxKzApBgNVBAMTIkNPTU9ETyBSU0EgQ2VydGlmaWNh\n"
        + "dGlvbiBBdXRob3JpdHkwggIiMA0GCSqGSIb3DQEBAQUAA4ICDwAwggIKAoICAQCR\n"
        + "6FSS0gpWsawNJN3Fz0RndJkrN6N9I3AAcbxT38T6KhKPS38QVr2fcHK3YX/JSw8X\n"
        + "pz3jsARh7v8Rl8f0hj4K+j5c+ZPmNHrZFGvnnLOFoIJ6dq9xkNfs/Q36nGz637CC\n"
        + "9BR++b7Epi9Pf5l/tfxnQ3K9DADWietrLNPtj5gcFKt+5eNu/Nio5JIk2kNrYrhV\n"
        + "/erBvGy2i/MOjZrkm2xpmfh4SDBF1a3hDTxFYPwyllEnvGfDyi62a+pGx8cgoLEf\n"
        + "Zd5ICLqkTqnyg0Y3hOvozIFIQ2dOciqbXL1MGyiKXCJ7tKuY2e7gUYPDCUZObT6Z\n"
        + "+pUX2nwzV0E8jVHtC7ZcryxjGt9XyD+86V3Em69FmeKjWiS0uqlWPc9vqv9JWL7w\n"
        + "qP/0uK3pN/u6uPQLOvnoQ0IeidiEyxPx2bvhiWC4jChWrBQdnArncevPDt09qZah\n"
        + "SL0896+1DSJMwBGB7FY79tOi4lu3sgQiUpWAk2nojkxl8ZEDLXB0AuqLZxUpaVIC\n"
        + "u9ffUGpVRr+goyhhf3DQw6KqLCGqR84onAZFdr+CGCe01a60y1Dma/RMhnEw6abf\n"
        + "Fobg2P9A3fvQQoh/ozM6LlweQRGBY84YcWsr7KaKtzFcOmpH4MN5WdYgGq/yapiq\n"
        + "crxXStJLnbsQ/LBMQeXtHT1eKJ2czL+zUdqnR+WEUwIDAQABo0IwQDAdBgNVHQ4E\n"
        + "FgQUu69+Aj36pvE8hI6t7jiY7NkyMtQwDgYDVR0PAQH/BAQDAgEGMA8GA1UdEwEB\n"
        + "/wQFMAMBAf8wDQYJKoZIhvcNAQEMBQADggIBAArx1UaEt65Ru2yyTUEUAJNMnMvl\n"
        + "wFTPoCWOAvn9sKIN9SCYPBMtrFaisNZ+EZLpLrqeLppysb0ZRGxhNaKatBYSaVqM\n"
        + "4dc+pBroLwP0rmEdEBsqpIt6xf4FpuHA1sj+nq6PK7o9mfjYcwlYRm6mnPTXJ9OV\n"
        + "2jeDchzTc+CiR5kDOF3VSXkAKRzH7JsgHAckaVd4sjn8OoSgtZx8jb8uk2Intzna\n"
        + "FxiuvTwJaP+EmzzV1gsD41eeFPfR60/IvYcjt7ZJQ3mFXLrrkguhxuhoqEwWsRqZ\n"
        + "CuhTLJK7oQkYdQxlqHvLI7cawiiFwxv/0Cti76R7CZGYZ4wUAc1oBmpjIXUDgIiK\n"
        + "boHGhfKppC3n9KUkEEeDys30jXlYsQab5xoq2Z0B15R97QNKyvDb6KkBPvVWmcke\n"
        + "jkk9u+UJueBPSZI9FoJAzMxZxuY67RIuaTxslbH9qh17f4a+Hg4yRvv7E491f0yL\n"
        + "S0Zj/gA0QHDBw7mh3aZw4gSzQbzpgJHqZJx64SIDqZxubw5lT2yHh17zbqD5daWb\n"
        + "QOhTsiedSrnAdyGN/4fy3ryM7xfft0kL0fJuMAsaDk527RH89elWsn2/x20Kk4yl\n"
        + "0MC2Hb46TpSi125sC8KKfPog88Tk5c0NqMuRkrF8hey1FGlmDoLnzc7ILaZRfyHB\n"
        + "NVOFBkpdn627G190\n"
        + "-----END CERTIFICATE-----\n";
    String entrustRootCertificateAuthority = ""
        + "-----BEGIN CERTIFICATE-----\n"
        + "MIIEkTCCA3mgAwIBAgIERWtQVDANBgkqhkiG9w0BAQUFADCBsDELMAkGA1UEBhMC\n"
        + "VVMxFjAUBgNVBAoTDUVudHJ1c3QsIEluYy4xOTA3BgNVBAsTMHd3dy5lbnRydXN0\n"
        + "Lm5ldC9DUFMgaXMgaW5jb3Jwb3JhdGVkIGJ5IHJlZmVyZW5jZTEfMB0GA1UECxMW\n"
        + "KGMpIDIwMDYgRW50cnVzdCwgSW5jLjEtMCsGA1UEAxMkRW50cnVzdCBSb290IENl\n"
        + "cnRpZmljYXRpb24gQXV0aG9yaXR5MB4XDTA2MTEyNzIwMjM0MloXDTI2MTEyNzIw\n"
        + "NTM0MlowgbAxCzAJBgNVBAYTAlVTMRYwFAYDVQQKEw1FbnRydXN0LCBJbmMuMTkw\n"
        + "NwYDVQQLEzB3d3cuZW50cnVzdC5uZXQvQ1BTIGlzIGluY29ycG9yYXRlZCBieSBy\n"
        + "ZWZlcmVuY2UxHzAdBgNVBAsTFihjKSAyMDA2IEVudHJ1c3QsIEluYy4xLTArBgNV\n"
        + "BAMTJEVudHJ1c3QgUm9vdCBDZXJ0aWZpY2F0aW9uIEF1dGhvcml0eTCCASIwDQYJ\n"
        + "KoZIhvcNAQEBBQADggEPADCCAQoCggEBALaVtkNC+sZtKm9I35RMOVcF7sN5EUFo\n"
        + "Nu3s/poBj6E4KPz3EEZmLk0eGrEaTsbRwJWIsMn/MYszA9u3g3s+IIRe7bJWKKf4\n"
        + "4LlAcTfFy0cOlypowCKVYhXbR9n10Cv/gkvJrT7eTNuQgFA/CYqEAOwwCj0Yzfv9\n"
        + "KlmaI5UXLEWeH25DeW0MXJj+SKfFI0dcXv1u5x609mhF0YaDW6KKjbHjKYD+JXGI\n"
        + "rb68j6xSlkuqUY3kEzEZ6E5Nn9uss2rVvDlUccp6en+Q3X0dgNmBu1kmwhH+5pPi\n"
        + "94DkZfs0Nw4pgHBNrziGLp5/V6+eF67rHMsoIV+2HNjnogQi+dPa2MsCAwEAAaOB\n"
        + "sDCBrTAOBgNVHQ8BAf8EBAMCAQYwDwYDVR0TAQH/BAUwAwEB/zArBgNVHRAEJDAi\n"
        + "gA8yMDA2MTEyNzIwMjM0MlqBDzIwMjYxMTI3MjA1MzQyWjAfBgNVHSMEGDAWgBRo\n"
        + "kORnpKZTgMeGZqTx90tD+4S9bTAdBgNVHQ4EFgQUaJDkZ6SmU4DHhmak8fdLQ/uE\n"
        + "vW0wHQYJKoZIhvZ9B0EABBAwDhsIVjcuMTo0LjADAgSQMA0GCSqGSIb3DQEBBQUA\n"
        + "A4IBAQCT1DCw1wMgKtD5Y+iRDAUgqV8ZyntyTtSx29CW+1RaGSwMCPeyvIWonX9t\n"
        + "O1KzKtvn1ISMY/YPyyYBkVBs9F8U4pN0wBOeMDpQ47RgxRzwIkSNcUesyBrJ6Zua\n"
        + "AGAT/3B+XxFNSRuzFVJ7yVTav52Vr2ua2J7p8eRDjeIRRDq/r72DQnNSi6q7pynP\n"
        + "9WQcCk3RvKqsnyrQ/39/2n3qse0wJcGE2jTSW3iDVuycNsMm4hH2Z0kdkquM++v/\n"
        + "eu6FSqdQgPCnXEqULl8FmTxSQeDNtGPPAUO6nIPcj2A781q0tHuu2guQOHXvgR1m\n"
        + "0vdXcDazv/wor3ElhVsT/h5/WrQ8\n"
        + "-----END CERTIFICATE-----\n";
    return new Buffer()
        .writeUtf8(comodoRsaCertificationAuthority)
        .writeUtf8(entrustRootCertificateAuthority)
        .inputStream();
  }

  /**
   * Returns a trust manager that trusts {@code certificates} and none other. HTTPS services whose
   * certificates have not been signed by these certificates will fail with a {@code
   * SSLHandshakeException}.
   *
   * <p>This can be used to replace the host platform's built-in trusted certificates with a custom
   * set. This is useful in development where certificate authority-trusted certificates aren't
   * available. Or in production, to avoid reliance on third-party certificate authorities.
   *
   * <p>See also {@link CertificatePinner}, which can limit trusted certificates while still using
   * the host platform's built-in trust store.
   *
   * <h3>Warning: Customizing Trusted Certificates is Dangerous!</h3>
   *
   * <p>Relying on your own trusted certificates limits your server team's ability to update their
   * TLS certificates. By installing a specific set of trusted certificates, you take on additional
   * operational complexity and limit your ability to migrate between certificate authorities. Do
   * not use custom trusted certificates in production without the blessing of your server's TLS
   * administrator.
   */
  private X509TrustManager trustManagerForCertificates(InputStream in)
      throws GeneralSecurityException {
    CertificateFactory certificateFactory = CertificateFactory.getInstance("X.509");
    Collection<? extends Certificate> certificates = certificateFactory.generateCertificates(in);
    if (certificates.isEmpty()) {
      throw new IllegalArgumentException("expected non-empty set of trusted certificates");
    }

    // Put the certificates a key store.
    char[] password = "password".toCharArray(); // Any password will work.
    KeyStore keyStore = newEmptyKeyStore(password);
    int index = 0;
    for (Certificate certificate : certificates) {
      String certificateAlias = Integer.toString(index++);
      keyStore.setCertificateEntry(certificateAlias, certificate);
    }

    // Use it to build an X509 trust manager.
    KeyManagerFactory keyManagerFactory = KeyManagerFactory.getInstance(
        KeyManagerFactory.getDefaultAlgorithm());
    keyManagerFactory.init(keyStore, password);
    TrustManagerFactory trustManagerFactory = TrustManagerFactory.getInstance(
        TrustManagerFactory.getDefaultAlgorithm());
    trustManagerFactory.init(keyStore);
    TrustManager[] trustManagers = trustManagerFactory.getTrustManagers();
    if (trustManagers.length != 1 || !(trustManagers[0] instanceof X509TrustManager)) {
      throw new IllegalStateException("Unexpected default trust managers:"
          + Arrays.toString(trustManagers));
    }
    return (X509TrustManager) trustManagers[0];
  }

  private KeyStore newEmptyKeyStore(char[] password) throws GeneralSecurityException {
    try {
      KeyStore keyStore = KeyStore.getInstance(KeyStore.getDefaultType());
      InputStream in = null; // By convention, 'null' creates an empty key store.
      keyStore.load(in, password);
      return keyStore;
    } catch (IOException e) {
      throw new AssertionError(e);
    }
  }

  public static void main(String... args) throws Exception {
    new CustomTrust().run();
  }
}

本文是翻译文章，英文原文地址：https://github.com/square/okhttp/wiki/HTTPS