Index: resources/sql/patches/20131106.diffphid.1.col.sql
===================================================================
--- /dev/null
+++ resources/sql/patches/20131106.diffphid.1.col.sql
@@ -0,0 +1,2 @@
+ALTER TABLE {$NAMESPACE}_differential.differential_diff
+  ADD phid VARCHAR(64) NOT NULL COLLATE utf8_bin AFTER id;
Index: resources/sql/patches/20131106.diffphid.2.mig.php
===================================================================
--- /dev/null
+++ resources/sql/patches/20131106.diffphid.2.mig.php
@@ -0,0 +1,47 @@
+<?php
+
+$diff_table = new DifferentialDiff();
+$conn_w = $diff_table->establishConnection('w');
+
+$size = 1000;
+
+$row_iter = id(new LiskMigrationIterator($diff_table))->setPageSize($size);
+$chunk_iter = new PhutilChunkedIterator($row_iter, $size);
+
+foreach ($chunk_iter as $chunk) {
+  $sql = array();
+
+  foreach ($chunk as $diff) {
+    $id = $diff->getID();
+    echo "Migrating diff ID {$id}...\n";
+
+    $phid = $diff->getPHID();
+    if (strlen($phid)) {
+      continue;
+    }
+
+    $type_diff = DifferentialPHIDTypeDiff::TYPECONST;
+    $new_phid = PhabricatorPHID::generateNewPHID($type_diff);
+
+    $sql[] = qsprintf(
+      $conn_w,
+      '(%d, %s)',
+      $id,
+      $new_phid);
+  }
+
+  if (!$sql) {
+    continue;
+  }
+
+  foreach (PhabricatorLiskDAO::chunkSQL($sql, ', ') as $sql_chunk) {
+    queryfx(
+      $conn_w,
+      'INSERT IGNORE INTO %T (id, phid) VALUES %Q
+        ON DUPLICATE KEY UPDATE phid = VALUES(phid)',
+      $diff_table->getTableName(),
+      $sql_chunk);
+  }
+}
+
+echo "Done.\n";
Index: resources/sql/patches/20131106.diffphid.3.key.sql
===================================================================
--- /dev/null
+++ resources/sql/patches/20131106.diffphid.3.key.sql
@@ -0,0 +1,2 @@
+ALTER TABLE {$NAMESPACE}_differential.differential_diff
+  ADD UNIQUE KEY `key_phid` (phid);
Index: src/__phutil_library_map__.php
===================================================================
--- src/__phutil_library_map__.php
+++ src/__phutil_library_map__.php
@@ -396,6 +396,7 @@
     'DifferentialMailPhase' => 'applications/differential/constants/DifferentialMailPhase.php',
     'DifferentialManiphestTasksFieldSpecification' => 'applications/differential/field/specification/DifferentialManiphestTasksFieldSpecification.php',
     'DifferentialNewDiffMail' => 'applications/differential/mail/DifferentialNewDiffMail.php',
+    'DifferentialPHIDTypeDiff' => 'applications/differential/phid/DifferentialPHIDTypeDiff.php',
     'DifferentialPHIDTypeRevision' => 'applications/differential/phid/DifferentialPHIDTypeRevision.php',
     'DifferentialParseRenderTestCase' => 'applications/differential/__tests__/DifferentialParseRenderTestCase.php',
     'DifferentialPathFieldSpecification' => 'applications/differential/field/specification/DifferentialPathFieldSpecification.php',
@@ -2606,6 +2607,7 @@
     'DifferentialMail' => 'PhabricatorMail',
     'DifferentialManiphestTasksFieldSpecification' => 'DifferentialFieldSpecification',
     'DifferentialNewDiffMail' => 'DifferentialReviewRequestMail',
+    'DifferentialPHIDTypeDiff' => 'PhabricatorPHIDType',
     'DifferentialPHIDTypeRevision' => 'PhabricatorPHIDType',
     'DifferentialParseRenderTestCase' => 'PhabricatorTestCase',
     'DifferentialPathFieldSpecification' => 'DifferentialFieldSpecification',
Index: src/applications/differential/phid/DifferentialPHIDTypeDiff.php
===================================================================
--- /dev/null
+++ src/applications/differential/phid/DifferentialPHIDTypeDiff.php
@@ -0,0 +1,45 @@
+<?php
+
+final class DifferentialPHIDTypeDiff extends PhabricatorPHIDType {
+
+  const TYPECONST = 'DIFF';
+
+  public function getTypeConstant() {
+    return self::TYPECONST;
+  }
+
+  public function getTypeName() {
+    return pht('Differential Diff');
+  }
+
+  public function newObject() {
+    return new DifferentialDiff();
+  }
+
+  protected function buildQueryForObjects(
+    PhabricatorObjectQuery $query,
+    array $phids) {
+
+    return id(new DifferentialDiffQuery())
+      ->withPHIDs($phids);
+  }
+
+  public function loadHandles(
+    PhabricatorHandleQuery $query,
+    array $handles,
+    array $objects) {
+
+    foreach ($handles as $phid => $handle) {
+      $diff = $objects[$phid];
+
+      $id = $diff->getID();
+
+      $handle->setName(pht('Diff %d', $id));
+    }
+  }
+
+  public function canLoadNamedObject($name) {
+    return false;
+  }
+
+}
Index: src/applications/differential/query/DifferentialDiffQuery.php
===================================================================
--- src/applications/differential/query/DifferentialDiffQuery.php
+++ src/applications/differential/query/DifferentialDiffQuery.php
@@ -4,6 +4,7 @@
   extends PhabricatorCursorPagedPolicyAwareQuery {
 
   private $ids;
+  private $phids;
   private $revisionIDs;
   private $needChangesets = false;
   private $needArcanistProjects = false;
@@ -13,6 +14,11 @@
     return $this;
   }
 
+  public function withPHIDs(array $phids) {
+    $this->phids = $phids;
+    return $this;
+  }
+
   public function withRevisionIDs(array $revision_ids) {
     $this->revisionIDs = $revision_ids;
     return $this;
@@ -126,6 +132,13 @@
         $this->ids);
     }
 
+    if ($this->phids) {
+      $where[] = qsprintf(
+        $conn_r,
+        'phid IN (%Ls)',
+        $this->phids);
+    }
+
     if ($this->revisionIDs) {
       $where[] = qsprintf(
         $conn_r,
Index: src/applications/differential/storage/DifferentialDiff.php
===================================================================
--- src/applications/differential/storage/DifferentialDiff.php
+++ src/applications/differential/storage/DifferentialDiff.php
@@ -34,6 +34,17 @@
   private $arcanistProject = self::ATTACHABLE;
   private $revision = self::ATTACHABLE;
 
+  public function getConfiguration() {
+    return array(
+      self::CONFIG_AUX_PHID => true,
+    ) + parent::getConfiguration();
+  }
+
+  public function generatePHID() {
+    return PhabricatorPHID::generateNewPHID(
+      DifferentialPHIDTypeDiff::TYPECONST);
+  }
+
   public function addUnsavedChangeset(DifferentialChangeset $changeset) {
     if ($this->changesets === null) {
       $this->changesets = array();
Index: src/infrastructure/storage/patch/PhabricatorBuiltinPatchList.php
===================================================================
--- src/infrastructure/storage/patch/PhabricatorBuiltinPatchList.php
+++ src/infrastructure/storage/patch/PhabricatorBuiltinPatchList.php
@@ -1724,6 +1724,18 @@
         'type' => 'sql',
         'name' => $this->getPatchPath('20131105.buildstep.sql'),
       ),
+      '20131106.diffphid.1.col.sql' => array(
+        'type' => 'sql',
+        'name' => $this->getPatchPath('20131106.diffphid.1.col.sql'),
+      ),
+      '20131106.diffphid.2.mig.php' => array(
+        'type' => 'php',
+        'name' => $this->getPatchPath('20131106.diffphid.2.mig.php'),
+      ),
+      '20131106.diffphid.3.key.sql' => array(
+        'type' => 'sql',
+        'name' => $this->getPatchPath('20131106.diffphid.3.key.sql'),
+      ),
     );
   }
 }