Index: src/__phutil_library_map__.php
===================================================================
--- src/__phutil_library_map__.php
+++ src/__phutil_library_map__.php
@@ -1244,6 +1244,7 @@
     'PhabricatorBarePageView' => 'view/page/PhabricatorBarePageView.php',
     'PhabricatorBaseEnglishTranslation' => 'infrastructure/internationalization/translation/PhabricatorBaseEnglishTranslation.php',
     'PhabricatorBaseProtocolAdapter' => 'infrastructure/daemon/bot/adapter/PhabricatorBaseProtocolAdapter.php',
+    'PhabricatorBcryptPasswordHasher' => 'infrastructure/util/password/PhabricatorBcryptPasswordHasher.php',
     'PhabricatorBot' => 'infrastructure/daemon/bot/PhabricatorBot.php',
     'PhabricatorBotBaseStreamingProtocolAdapter' => 'infrastructure/daemon/bot/adapter/PhabricatorBotBaseStreamingProtocolAdapter.php',
     'PhabricatorBotChannel' => 'infrastructure/daemon/bot/target/PhabricatorBotChannel.php',
@@ -3915,6 +3916,7 @@
     'PhabricatorBarePageExample' => 'PhabricatorUIExample',
     'PhabricatorBarePageView' => 'AphrontPageView',
     'PhabricatorBaseEnglishTranslation' => 'PhabricatorTranslation',
+    'PhabricatorBcryptPasswordHasher' => 'PhabricatorPasswordHasher',
     'PhabricatorBot' => 'PhabricatorDaemon',
     'PhabricatorBotBaseStreamingProtocolAdapter' => 'PhabricatorBaseProtocolAdapter',
     'PhabricatorBotChannel' => 'PhabricatorBotTarget',
Index: src/applications/auth/provider/PhabricatorAuthProviderPassword.php
===================================================================
--- src/applications/auth/provider/PhabricatorAuthProviderPassword.php
+++ src/applications/auth/provider/PhabricatorAuthProviderPassword.php
@@ -264,6 +264,19 @@
             if ($user->comparePassword($envelope)) {
               $account = $this->loadOrCreateAccount($user->getPHID());
               $log_user = $user;
+
+              // If the user's password is stored using a less-than-optimal
+              // hash, upgrade them to the strongest available hash.
+
+              $hash_envelope = new PhutilOpaqueEnvelope(
+                $user->getPasswordHash());
+              if (PhabricatorPasswordHasher::canUpgradeHash($hash_envelope)) {
+                $user->setPassword($envelope);
+
+                $unguarded = AphrontWriteGuard::beginScopedUnguardedWrites();
+                  $user->save();
+                unset($unguarded);
+              }
             }
           }
         }
Index: src/applications/settings/panel/PhabricatorSettingsPanelPassword.php
===================================================================
--- src/applications/settings/panel/PhabricatorSettingsPanelPassword.php
+++ src/applications/settings/panel/PhabricatorSettingsPanelPassword.php
@@ -112,6 +112,15 @@
       }
     }
 
+    $hash_envelope = new PhutilOpaqueEnvelope($user->getPasswordHash());
+    if (PhabricatorPasswordHasher::canUpgradeHash($hash_envelope)) {
+      $best_hash = PhabricatorPasswordHasher::getBestHasher();
+      $errors[] = pht(
+        'The strength of your stored password hash can be upgraded. '.
+        'To upgrade, either: log out and log in using your password; or '.
+        'change your password.');
+    }
+
     $len_caption = null;
     if ($min_len) {
       $len_caption = pht('Minimum password length: %d characters.', $min_len);
@@ -146,7 +155,36 @@
     $form
       ->appendChild(
         id(new AphrontFormSubmitControl())
-          ->setValue(pht('Save')));
+          ->setValue(pht('Change Password')));
+
+    if (!strlen($user->getPasswordHash())) {
+      $current_name = pht('None');
+    } else {
+      try {
+        $current_hasher = PhabricatorPasswordHasher::getHasherForHash(
+          new PhutilOpaqueEnvelope($user->getPasswordHash()));
+        $current_name = $current_hasher->getHumanReadableName();
+      } catch (Exception $ex) {
+        $current_name = pht('Unknown');
+      }
+    }
+
+    $form->appendChild(
+      id(new AphrontFormStaticControl())
+        ->setLabel(pht('Current Algorithm'))
+        ->setValue($current_name));
+
+    try {
+      $best_hasher = PhabricatorPasswordHasher::getBestHasher();
+      $best_name = $best_hasher->getHumanReadableName();
+    } catch (Exception $ex) {
+      $best_name = pht('Unknown');
+    }
+
+    $form->appendChild(
+      id(new AphrontFormStaticControl())
+        ->setLabel(pht('Best Available Algorithm'))
+        ->setValue($best_name));
 
     $form_box = id(new PHUIObjectBoxView())
       ->setHeaderText(pht('Change Password'))
Index: src/infrastructure/util/password/PhabricatorBcryptPasswordHasher.php
===================================================================
--- /dev/null
+++ src/infrastructure/util/password/PhabricatorBcryptPasswordHasher.php
@@ -0,0 +1,56 @@
+<?php
+
+final class PhabricatorBcryptPasswordHasher
+  extends PhabricatorPasswordHasher {
+
+  public function getHumanReadableName() {
+    return pht('bcrypt');
+  }
+
+  public function getHashName() {
+    return 'bcrypt';
+  }
+
+  public function getHashLength() {
+    return 60;
+  }
+
+  public function canHashPasswords() {
+    return function_exists('password_hash');
+  }
+
+  public function getInstallInstructions() {
+    return pht('Upgrade to PHP 5.5.0 or newer.');
+  }
+
+  public function getStrength() {
+    return 2.0;
+  }
+
+  public function getHumanReadableStrength() {
+    return pht("Good");
+  }
+
+  protected function getPasswordHash(PhutilOpaqueEnvelope $envelope) {
+    $raw_input = $envelope->openEnvelope();
+
+    // NOTE: The default cost is "10", but my laptop can do a hash of cost
+    // "12" in about 300ms. Since server hardware is often virtualized or old,
+    // just split the difference.
+
+    $options = array(
+      'cost' => 11,
+    );
+
+    $raw_hash = password_hash($raw_input, CRYPT_BLOWFISH, $options);
+
+    return new PhutilOpaqueEnvelope($raw_hash);
+  }
+
+  protected function verifyPassword(
+    PhutilOpaqueEnvelope $password,
+    PhutilOpaqueEnvelope $hash) {
+    return password_verify($password->openEnvelope(), $hash->openEnvelope());
+  }
+
+}
Index: src/infrastructure/util/password/PhabricatorIteratedMD5PasswordHasher.php
===================================================================
--- src/infrastructure/util/password/PhabricatorIteratedMD5PasswordHasher.php
+++ src/infrastructure/util/password/PhabricatorIteratedMD5PasswordHasher.php
@@ -12,7 +12,7 @@
   }
 
   public function getHashLength() {
-    return 40;
+    return 32;
   }
 
   public function canHashPasswords() {
Index: src/infrastructure/util/password/PhabricatorPasswordHasher.php
===================================================================
--- src/infrastructure/util/password/PhabricatorPasswordHasher.php
+++ src/infrastructure/util/password/PhabricatorPasswordHasher.php
@@ -108,6 +108,28 @@
   abstract protected function getPasswordHash(PhutilOpaqueEnvelope $envelope);
 
 
+  /**
+   * Verify that a password matches a hash.
+   *
+   * The default implementation checks for equality; if a hasher embeds salt in
+   * hashes it should override this method and perform a salt-aware comparison.
+   *
+   * @param   PhutilOpaqueEnvelope  Password to compare.
+   * @param   PhutilOpaqueEnvelope  Bare password hash.
+   * @return  bool                  True if the passwords match.
+   * @task hasher
+   */
+  protected function verifyPassword(
+    PhutilOpaqueEnvelope $password,
+    PhutilOpaqueEnvelope $hash) {
+
+    $actual_hash = $this->getPasswordHash($password)->openEnvelope();
+    $expect_hash = $hash->openEnvelope();
+
+    return ($actual_hash === $expect_hash);
+  }
+
+
 /* -(  Using Hashers  )------------------------------------------------------ */
 
 
@@ -236,7 +258,7 @@
    */
   public static function getBestHasher() {
     $hashers = self::getAllUsableHashers();
-    msort($hashers, 'getStrength');
+    $hashers = msort($hashers, 'getStrength');
 
     $hasher = last($hashers);
     if (!$hasher) {
@@ -292,7 +314,7 @@
    *              the hash strength.
    * @task hashing
    */
-  public static function canHashBeUpgraded(PhutilOpaqueEnvelope $hash) {
+  public static function canUpgradeHash(PhutilOpaqueEnvelope $hash) {
     $current_hasher = self::getHasherForHash($hash);
     $best_hasher = self::getBestHasher();
 
@@ -328,9 +350,9 @@
     PhutilOpaqueEnvelope $hash) {
 
     $hasher = self::getHasherForHash($hash);
-    $password_hash = $hasher->getPasswordHashForStorage($password);
+    $parts = self::parseHashFromStorage($hash);
 
-    return ($password_hash->openEnvelope() == $hash->openEnvelope());
+    return $hasher->verifyPassword($password, $parts['hash']);
   }
 
 }