diff -r 000000000000 -r 6474c204b198 mobile/android/base/sync/crypto/CryptoInfo.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mobile/android/base/sync/crypto/CryptoInfo.java	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,240 @@
+/* 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.sync.crypto;
+
+import java.security.GeneralSecurityException;
+import java.security.InvalidKeyException;
+import java.security.NoSuchAlgorithmException;
+import java.util.Arrays;
+
+import javax.crypto.BadPaddingException;
+import javax.crypto.Cipher;
+import javax.crypto.IllegalBlockSizeException;
+import javax.crypto.Mac;
+import javax.crypto.NoSuchPaddingException;
+import javax.crypto.spec.IvParameterSpec;
+import javax.crypto.spec.SecretKeySpec;
+
+import org.mozilla.apache.commons.codec.binary.Base64;
+
+/*
+ * All info in these objects should be decoded (i.e. not BaseXX encoded).
+ */
+public class CryptoInfo {
+  private static final String TRANSFORMATION     = "AES/CBC/PKCS5Padding";
+  private static final String KEY_ALGORITHM_SPEC = "AES";
+
+  private byte[] message;
+  private byte[] iv;
+  private byte[] hmac;
+  private KeyBundle keys;
+
+  /**
+   * Return a CryptoInfo with given plaintext encrypted using given keys.
+   */
+  public static CryptoInfo encrypt(byte[] plaintextBytes, KeyBundle keys) throws CryptoException {
+    CryptoInfo info = new CryptoInfo(plaintextBytes, keys);
+    info.encrypt();
+    return info;
+  }
+
+  /**
+   * Return a CryptoInfo with given plaintext encrypted using given keys and initial vector.
+   */
+  public static CryptoInfo encrypt(byte[] plaintextBytes, byte[] iv, KeyBundle keys) throws CryptoException {
+    CryptoInfo info = new CryptoInfo(plaintextBytes, iv, null, keys);
+    info.encrypt();
+    return info;
+  }
+
+  /**
+   * Return a CryptoInfo with given ciphertext decrypted using given keys and initial vector, verifying that given HMAC validates.
+   */
+  public static CryptoInfo decrypt(byte[] ciphertext, byte[] iv, byte[] hmac, KeyBundle keys) throws CryptoException {
+    CryptoInfo info = new CryptoInfo(ciphertext, iv, hmac, keys);
+    info.decrypt();
+    return info;
+  }
+
+  /*
+   * Constructor typically used when encrypting.
+   */
+  public CryptoInfo(byte[] message, KeyBundle keys) {
+    this.setMessage(message);
+    this.setKeys(keys);
+  }
+
+  /*
+   * Constructor typically used when decrypting.
+   */
+  public CryptoInfo(byte[] message, byte[] iv, byte[] hmac, KeyBundle keys) {
+    this.setMessage(message);
+    this.setIV(iv);
+    this.setHMAC(hmac);
+    this.setKeys(keys);
+  }
+
+  public byte[] getMessage() {
+    return message;
+  }
+
+  public void setMessage(byte[] message) {
+    this.message = message;
+  }
+
+  public byte[] getIV() {
+    return iv;
+  }
+
+  public void setIV(byte[] iv) {
+    this.iv = iv;
+  }
+
+  public byte[] getHMAC() {
+    return hmac;
+  }
+
+  public void setHMAC(byte[] hmac) {
+    this.hmac = hmac;
+  }
+
+  public KeyBundle getKeys() {
+    return keys;
+  }
+
+  public void setKeys(KeyBundle keys) {
+    this.keys = keys;
+  }
+
+  /*
+   * Generate HMAC for given cipher text.
+   */
+  public static byte[] generatedHMACFor(byte[] message, KeyBundle keys) throws NoSuchAlgorithmException, InvalidKeyException {
+    Mac hmacHasher = HKDF.makeHMACHasher(keys.getHMACKey());
+    return hmacHasher.doFinal(Base64.encodeBase64(message));
+  }
+
+  /*
+   * Return true if generated HMAC is the same as the specified HMAC.
+   */
+  public boolean generatedHMACIsHMAC() throws NoSuchAlgorithmException, InvalidKeyException {
+    byte[] generatedHMAC = generatedHMACFor(getMessage(), getKeys());
+    byte[] expectedHMAC  = getHMAC();
+    return Arrays.equals(generatedHMAC, expectedHMAC);
+  }
+
+  /**
+   * Performs functionality common to both encryption and decryption.
+   *
+   * @param cipher
+   * @param inputMessage non-BaseXX-encoded message
+   * @return encrypted/decrypted message
+   * @throws CryptoException
+   */
+  private static byte[] commonCrypto(Cipher cipher, byte[] inputMessage)
+                        throws CryptoException {
+    byte[] outputMessage = null;
+    try {
+      outputMessage = cipher.doFinal(inputMessage);
+    } catch (IllegalBlockSizeException e) {
+      throw new CryptoException(e);
+    } catch (BadPaddingException e) {
+      throw new CryptoException(e);
+    }
+    return outputMessage;
+  }
+
+  /**
+   * Encrypt a CryptoInfo in-place.
+   *
+   * @throws CryptoException
+   */
+  public void encrypt() throws CryptoException {
+
+    Cipher cipher = CryptoInfo.getCipher(TRANSFORMATION);
+    try {
+      byte[] encryptionKey = getKeys().getEncryptionKey();
+      SecretKeySpec spec = new SecretKeySpec(encryptionKey, KEY_ALGORITHM_SPEC);
+
+      // If no IV is provided, we allow the cipher to provide one.
+      if (getIV() == null || getIV().length == 0) {
+        cipher.init(Cipher.ENCRYPT_MODE, spec);
+      } else {
+        cipher.init(Cipher.ENCRYPT_MODE, spec, new IvParameterSpec(getIV()));
+      }
+    } catch (GeneralSecurityException ex) {
+      throw new CryptoException(ex);
+    }
+
+    // Encrypt.
+    byte[] encryptedBytes = commonCrypto(cipher, getMessage());
+    byte[] iv = cipher.getIV();
+
+    byte[] hmac;
+    // Generate HMAC.
+    try {
+      hmac = generatedHMACFor(encryptedBytes, keys);
+    } catch (NoSuchAlgorithmException e) {
+      throw new CryptoException(e);
+    } catch (InvalidKeyException e) {
+      throw new CryptoException(e);
+    }
+
+    // Update in place.  keys is already set.
+    this.setHMAC(hmac);
+    this.setIV(iv);
+    this.setMessage(encryptedBytes);
+  }
+
+  /**
+   * Decrypt a CryptoInfo in-place.
+   *
+   * @throws CryptoException
+   */
+  public void decrypt() throws CryptoException {
+
+    // Check HMAC.
+    try {
+      if (!generatedHMACIsHMAC()) {
+        throw new HMACVerificationException();
+      }
+    } catch (NoSuchAlgorithmException e) {
+      throw new CryptoException(e);
+    } catch (InvalidKeyException e) {
+      throw new CryptoException(e);
+    }
+
+    Cipher cipher = CryptoInfo.getCipher(TRANSFORMATION);
+    try {
+      byte[] encryptionKey = getKeys().getEncryptionKey();
+      SecretKeySpec spec = new SecretKeySpec(encryptionKey, KEY_ALGORITHM_SPEC);
+      cipher.init(Cipher.DECRYPT_MODE, spec, new IvParameterSpec(getIV()));
+    } catch (GeneralSecurityException ex) {
+      throw new CryptoException(ex);
+    }
+    byte[] decryptedBytes = commonCrypto(cipher, getMessage());
+    byte[] iv = cipher.getIV();
+
+    // Update in place.  keys is already set.
+    this.setHMAC(null);
+    this.setIV(iv);
+    this.setMessage(decryptedBytes);
+  }
+
+  /**
+   * Helper to get a Cipher object.
+   *
+   * @param transformation The type of Cipher to get.
+   */
+  private static Cipher getCipher(String transformation) throws CryptoException {
+    try {
+      return Cipher.getInstance(transformation);
+    } catch (NoSuchAlgorithmException e) {
+      throw new CryptoException(e);
+    } catch (NoSuchPaddingException e) {
+      throw new CryptoException(e);
+    }
+  }
+}