gecko/mobile/android/base/background/fxa/FxAccountUtils.java

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

package org.mozilla.gecko.background.fxa;

import java.io.UnsupportedEncodingException;
import java.math.BigInteger;
import java.net.URI;
import java.net.URISyntaxException;
import java.security.GeneralSecurityException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;

import org.mozilla.gecko.background.common.log.Logger;
import org.mozilla.gecko.background.nativecode.NativeCrypto;
import org.mozilla.gecko.sync.Utils;
import org.mozilla.gecko.sync.crypto.HKDF;
import org.mozilla.gecko.sync.crypto.KeyBundle;
import org.mozilla.gecko.sync.crypto.PBKDF2;

public class FxAccountUtils {
  private static final String LOG_TAG = FxAccountUtils.class.getSimpleName();

  public static final int SALT_LENGTH_BYTES = 32;
  public static final int SALT_LENGTH_HEX = 2 * SALT_LENGTH_BYTES;

  public static final int HASH_LENGTH_BYTES = 16;
  public static final int HASH_LENGTH_HEX = 2 * HASH_LENGTH_BYTES;

  public static final int CRYPTO_KEY_LENGTH_BYTES = 32;
  public static final int CRYPTO_KEY_LENGTH_HEX = 2 * CRYPTO_KEY_LENGTH_BYTES;

  public static final String KW_VERSION_STRING = "identity.mozilla.com/picl/v1/";

  public static final int NUMBER_OF_QUICK_STRETCH_ROUNDS = 1000;

  public static String bytes(String string) throws UnsupportedEncodingException {
    return Utils.byte2Hex(string.getBytes("UTF-8"));
  }

  public static byte[] KW(String name) throws UnsupportedEncodingException {
    return Utils.concatAll(
        KW_VERSION_STRING.getBytes("UTF-8"),
        name.getBytes("UTF-8"));
  }

  public static byte[] KWE(String name, byte[] emailUTF8) throws UnsupportedEncodingException {
    return Utils.concatAll(
        KW_VERSION_STRING.getBytes("UTF-8"),
        name.getBytes("UTF-8"),
        ":".getBytes("UTF-8"),
        emailUTF8);
  }

  /**
   * Calculate the SRP verifier <tt>x</tt> value.
   */
  public static BigInteger srpVerifierLowercaseX(byte[] emailUTF8, byte[] srpPWBytes, byte[] srpSaltBytes)
      throws NoSuchAlgorithmException, UnsupportedEncodingException {
    byte[] inner = Utils.sha256(Utils.concatAll(emailUTF8, ":".getBytes("UTF-8"), srpPWBytes));
    byte[] outer = Utils.sha256(Utils.concatAll(srpSaltBytes, inner));
    return new BigInteger(1, outer);
  }

  /**
   * Calculate the SRP verifier <tt>v</tt> value.
   */
  public static BigInteger srpVerifierLowercaseV(byte[] emailUTF8, byte[] srpPWBytes, byte[] srpSaltBytes, BigInteger g, BigInteger N)
      throws NoSuchAlgorithmException, UnsupportedEncodingException {
    BigInteger x = srpVerifierLowercaseX(emailUTF8, srpPWBytes, srpSaltBytes);
    BigInteger v = g.modPow(x, N);
    return v;
  }

  /**
   * Format x modulo N in hexadecimal, using as many characters as N takes (in hexadecimal).
   * @param x to format.
   * @param N modulus.
   * @return x modulo N in hexadecimal.
   */
  public static String hexModN(BigInteger x, BigInteger N) {
    int byteLength = (N.bitLength() + 7) / 8;
    int hexLength = 2 * byteLength;
    return Utils.byte2Hex(Utils.hex2Byte((x.mod(N)).toString(16), byteLength), hexLength);
  }

  /**
   * The first engineering milestone of PICL (Profile-in-the-Cloud) was
   * comprised of Sync 1.1 fronted by a Firefox Account. The sync key was
   * generated from the Firefox Account password-derived kB value using this
   * method.
   */
  public static KeyBundle generateSyncKeyBundle(final byte[] kB) throws InvalidKeyException, NoSuchAlgorithmException, UnsupportedEncodingException {
    byte[] encryptionKey = new byte[32];
    byte[] hmacKey = new byte[32];
    byte[] derived = HKDF.derive(kB, new byte[0], FxAccountUtils.KW("oldsync"), 2*32);
    System.arraycopy(derived, 0*32, encryptionKey, 0, 1*32);
    System.arraycopy(derived, 1*32, hmacKey, 0, 1*32);
    return new KeyBundle(encryptionKey, hmacKey);
  }

  /**
   * Firefox Accounts are password authenticated, but clients should not store
   * the plain-text password for any amount of time. Equivalent, but slightly
   * more secure, is the quickly client-side stretched password.
   * <p>
   * We separate this since multiple login-time operations want it, and the
   * PBKDF2 operation is computationally expensive.
   */
  public static byte[] generateQuickStretchedPW(byte[] emailUTF8, byte[] passwordUTF8) throws GeneralSecurityException, UnsupportedEncodingException {
    byte[] S = FxAccountUtils.KWE("quickStretch", emailUTF8);
    try {
      return NativeCrypto.pbkdf2SHA256(passwordUTF8, S, NUMBER_OF_QUICK_STRETCH_ROUNDS, 32);
    } catch (final LinkageError e) {
      // This will throw UnsatisifiedLinkError (missing mozglue) the first time it is called, and
      // ClassNotDefFoundError, for the uninitialized NativeCrypto class, each subsequent time this
      // is called; LinkageError is their common ancestor.
      Logger.warn(LOG_TAG, "Got throwable stretching password using native pbkdf2SHA256 " +
          "implementation; ignoring and using Java implementation.", e);
      return PBKDF2.pbkdf2SHA256(passwordUTF8, S, NUMBER_OF_QUICK_STRETCH_ROUNDS, 32);
    }
  }

  /**
   * The password-derived credential used to authenticate to the Firefox Account
   * auth server.
   */
  public static byte[] generateAuthPW(byte[] quickStretchedPW) throws GeneralSecurityException, UnsupportedEncodingException {
    return HKDF.derive(quickStretchedPW, new byte[0], FxAccountUtils.KW("authPW"), 32);
  }

  /**
   * The password-derived credential used to unwrap keys managed by the Firefox
   * Account auth server.
   */
  public static byte[] generateUnwrapBKey(byte[] quickStretchedPW) throws GeneralSecurityException, UnsupportedEncodingException {
    return HKDF.derive(quickStretchedPW, new byte[0], FxAccountUtils.KW("unwrapBkey"), 32);
  }

  public static byte[] unwrapkB(byte[] unwrapkB, byte[] wrapkB) {
    if (unwrapkB == null) {
      throw new IllegalArgumentException("unwrapkB must not be null");
    }
    if (wrapkB == null) {
      throw new IllegalArgumentException("wrapkB must not be null");
    }
    if (unwrapkB.length != CRYPTO_KEY_LENGTH_BYTES || wrapkB.length != CRYPTO_KEY_LENGTH_BYTES) {
      throw new IllegalArgumentException("unwrapkB and wrapkB must be " + CRYPTO_KEY_LENGTH_BYTES + " bytes long");
    }
    byte[] kB = new byte[CRYPTO_KEY_LENGTH_BYTES];
    for (int i = 0; i < wrapkB.length; i++) {
      kB[i] = (byte) (wrapkB[i] ^ unwrapkB[i]);
    }
    return kB;
  }

  /**
   * The token server accepts an X-Client-State header, which is the
   * lowercase-hex-encoded first 16 bytes of the SHA-256 hash of the
   * bytes of kB.
   * @param kB a byte array, expected to be 32 bytes long.
   * @return a 32-character string.
   * @throws NoSuchAlgorithmException
   */
  public static String computeClientState(byte[] kB) throws NoSuchAlgorithmException {
    if (kB == null ||
        kB.length != 32) {
      throw new IllegalArgumentException("Unexpected kB.");
    }
    byte[] sha256 = Utils.sha256(kB);
    byte[] truncated = new byte[16];
    System.arraycopy(sha256, 0, truncated, 0, 16);
    return Utils.byte2Hex(truncated);    // This is automatically lowercase.
  }

  /**
   * Given an endpoint, calculate the corresponding BrowserID audience.
   * <p>
   * This is the domain, in web parlance.
   *
   * @param serverURI endpoint.
   * @return BrowserID audience.
   * @throws URISyntaxException
   */
  public static String getAudienceForURL(String serverURI) throws URISyntaxException {
    URI uri = new URI(serverURI);
    return new URI(uri.getScheme(), null, uri.getHost(), uri.getPort(), null, null, null).toString();
  }
}