diff -r 000000000000 -r 6474c204b198 mobile/android/base/sync/middleware/Crypto5MiddlewareRepositorySession.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mobile/android/base/sync/middleware/Crypto5MiddlewareRepositorySession.java	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,175 @@
+/* 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.middleware;
+
+import java.io.UnsupportedEncodingException;
+import java.util.concurrent.ExecutorService;
+
+import org.mozilla.gecko.sync.CryptoRecord;
+import org.mozilla.gecko.sync.crypto.CryptoException;
+import org.mozilla.gecko.sync.crypto.KeyBundle;
+import org.mozilla.gecko.sync.repositories.InactiveSessionException;
+import org.mozilla.gecko.sync.repositories.NoStoreDelegateException;
+import org.mozilla.gecko.sync.repositories.RecordFactory;
+import org.mozilla.gecko.sync.repositories.RepositorySession;
+import org.mozilla.gecko.sync.repositories.delegates.RepositorySessionFetchRecordsDelegate;
+import org.mozilla.gecko.sync.repositories.delegates.RepositorySessionStoreDelegate;
+import org.mozilla.gecko.sync.repositories.domain.Record;
+
+/**
+ * It's a RepositorySession that accepts Records as input, producing CryptoRecords
+ * for submission to a remote service.
+ * Takes a RecordFactory as a parameter. This is in charge of taking decrypted CryptoRecords
+ * as input and producing some expected kind of Record as output for local use.
+ *
+ *
+
+
+
+                 +------------------------------------+
+                 |    Server11RepositorySession       |
+                 +-------------------------+----------+
+                           ^               |
+                           |               |
+                        Encrypted CryptoRecords
+                           |               |
+                           |               v
+                 +---------+--------------------------+
+                 | Crypto5MiddlewareRepositorySession |
+                 +------------------------------------+
+                           ^               |
+                           |               |  Decrypted CryptoRecords
+                           |               |
+                           |            +---------------+
+                           |            | RecordFactory |
+                           |            +--+------------+
+                           |               |
+                          Local Record instances
+                           |               |
+                           |               v
+                 +---------+--------------------------+
+                 |  Local RepositorySession instance  |
+                 +------------------------------------+
+
+
+ * @author rnewman
+ *
+ */
+public class Crypto5MiddlewareRepositorySession extends MiddlewareRepositorySession {
+  private KeyBundle keyBundle;
+  private RecordFactory recordFactory;
+
+  public Crypto5MiddlewareRepositorySession(RepositorySession session, Crypto5MiddlewareRepository repository, RecordFactory recordFactory) {
+    super(session, repository);
+    this.keyBundle = repository.keyBundle;
+    this.recordFactory = recordFactory;
+  }
+
+  public class DecryptingTransformingFetchDelegate implements RepositorySessionFetchRecordsDelegate {
+    private RepositorySessionFetchRecordsDelegate next;
+    private KeyBundle keyBundle;
+    private RecordFactory recordFactory;
+
+    DecryptingTransformingFetchDelegate(RepositorySessionFetchRecordsDelegate next, KeyBundle bundle, RecordFactory recordFactory) {
+      this.next = next;
+      this.keyBundle = bundle;
+      this.recordFactory = recordFactory;
+    }
+
+    @Override
+    public void onFetchFailed(Exception ex, Record record) {
+      next.onFetchFailed(ex, record);
+    }
+
+    @Override
+    public void onFetchedRecord(Record record) {
+      CryptoRecord r;
+      try {
+        r = (CryptoRecord) record;
+      } catch (ClassCastException e) {
+        next.onFetchFailed(e, record);
+        return;
+      }
+      r.keyBundle = keyBundle;
+      try {
+        r.decrypt();
+      } catch (Exception e) {
+        next.onFetchFailed(e, r);
+        return;
+      }
+      Record transformed;
+      try {
+        transformed = this.recordFactory.createRecord(r);
+      } catch (Exception e) {
+        next.onFetchFailed(e, r);
+        return;
+      }
+      next.onFetchedRecord(transformed);
+    }
+
+    @Override
+    public void onFetchCompleted(final long fetchEnd) {
+      next.onFetchCompleted(fetchEnd);
+    }
+
+    @Override
+    public RepositorySessionFetchRecordsDelegate deferredFetchDelegate(ExecutorService executor) {
+      // Synchronously perform *our* work, passing through appropriately.
+      RepositorySessionFetchRecordsDelegate deferredNext = next.deferredFetchDelegate(executor);
+      return new DecryptingTransformingFetchDelegate(deferredNext, keyBundle, recordFactory);
+    }
+  }
+
+  private DecryptingTransformingFetchDelegate makeUnwrappingDelegate(RepositorySessionFetchRecordsDelegate inner) {
+    if (inner == null) {
+      throw new IllegalArgumentException("Inner delegate cannot be null!");
+    }
+    return new DecryptingTransformingFetchDelegate(inner, this.keyBundle, this.recordFactory);
+  }
+
+  @Override
+  public void fetchSince(long timestamp,
+                         RepositorySessionFetchRecordsDelegate delegate) {
+    inner.fetchSince(timestamp, makeUnwrappingDelegate(delegate));
+  }
+
+  @Override
+  public void fetch(String[] guids,
+                    RepositorySessionFetchRecordsDelegate delegate) throws InactiveSessionException {
+    inner.fetch(guids, makeUnwrappingDelegate(delegate));
+  }
+
+  @Override
+  public void fetchAll(RepositorySessionFetchRecordsDelegate delegate) {
+    inner.fetchAll(makeUnwrappingDelegate(delegate));
+  }
+
+  @Override
+  public void setStoreDelegate(RepositorySessionStoreDelegate delegate) {
+    // TODO: it remains to be seen how this will work.
+    inner.setStoreDelegate(delegate);
+    this.delegate = delegate;             // So we can handle errors without involving inner.
+  }
+
+  @Override
+  public void store(Record record) throws NoStoreDelegateException {
+    if (delegate == null) {
+      throw new NoStoreDelegateException();
+    }
+    CryptoRecord rec = record.getEnvelope();
+    rec.keyBundle = this.keyBundle;
+    try {
+      rec.encrypt();
+    } catch (UnsupportedEncodingException e) {
+      delegate.onRecordStoreFailed(e, record.guid);
+      return;
+    } catch (CryptoException e) {
+      delegate.onRecordStoreFailed(e, record.guid);
+      return;
+    }
+    // Allow the inner session to do delegate handling.
+    inner.store(rec);
+  }
+}