diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -1316,6 +1316,7 @@
     'PhabricatorAuthLinkController' => 'applications/auth/controller/PhabricatorAuthLinkController.php',
     'PhabricatorAuthListController' => 'applications/auth/controller/config/PhabricatorAuthListController.php',
     'PhabricatorAuthLoginController' => 'applications/auth/controller/PhabricatorAuthLoginController.php',
+    'PhabricatorAuthManagementCachePKCS8Workflow' => 'applications/auth/management/PhabricatorAuthManagementCachePKCS8Workflow.php',
     'PhabricatorAuthManagementLDAPWorkflow' => 'applications/auth/management/PhabricatorAuthManagementLDAPWorkflow.php',
     'PhabricatorAuthManagementListFactorsWorkflow' => 'applications/auth/management/PhabricatorAuthManagementListFactorsWorkflow.php',
     'PhabricatorAuthManagementRecoverWorkflow' => 'applications/auth/management/PhabricatorAuthManagementRecoverWorkflow.php',
@@ -4429,6 +4430,7 @@
     'PhabricatorAuthLinkController' => 'PhabricatorAuthController',
     'PhabricatorAuthListController' => 'PhabricatorAuthProviderConfigController',
     'PhabricatorAuthLoginController' => 'PhabricatorAuthController',
+    'PhabricatorAuthManagementCachePKCS8Workflow' => 'PhabricatorAuthManagementWorkflow',
     'PhabricatorAuthManagementLDAPWorkflow' => 'PhabricatorAuthManagementWorkflow',
     'PhabricatorAuthManagementListFactorsWorkflow' => 'PhabricatorAuthManagementWorkflow',
     'PhabricatorAuthManagementRecoverWorkflow' => 'PhabricatorAuthManagementWorkflow',
diff --git a/src/applications/auth/management/PhabricatorAuthManagementCachePKCS8Workflow.php b/src/applications/auth/management/PhabricatorAuthManagementCachePKCS8Workflow.php
new file mode 100644
--- /dev/null
+++ b/src/applications/auth/management/PhabricatorAuthManagementCachePKCS8Workflow.php
@@ -0,0 +1,96 @@
+<?php
+
+final class PhabricatorAuthManagementCachePKCS8Workflow
+  extends PhabricatorAuthManagementWorkflow {
+
+  protected function didConstruct() {
+    $this
+      ->setName('cache-pkcs8')
+      ->setExamples('**cache-pkcs8** --public __keyfile__ --pkcs8 __keyfile__')
+      ->setSynopsis(
+        pht(
+          'Cache the PKCS8 format of a public key. When developing on OSX, '.
+          'this can be used to work around issues with ssh-keygen. Use '.
+          '`ssh-keygen -e -m PKCS8 -f key.pub` to generate a PKCS8 key to '.
+          'feed to this command.'))
+      ->setArguments(
+        array(
+          array(
+            'name' => 'public',
+            'param' => 'keyfile',
+            'help' => pht('Path to public keyfile.'),
+          ),
+          array(
+            'name' => 'pkcs8',
+            'param' => 'keyfile',
+            'help' => pht('Path to corresponding PKCS8 key.'),
+          ),
+        ));
+  }
+
+  public function execute(PhutilArgumentParser $args) {
+    $console = PhutilConsole::getConsole();
+
+    $public_keyfile = $args->getArg('public');
+    if (!strlen($public_keyfile)) {
+      throw new PhutilArgumentUsageException(
+        pht(
+          'You must specify the path to a public keyfile with --public.'));
+    }
+
+    if (!Filesystem::pathExists($public_keyfile)) {
+      throw new PhutilArgumentUsageException(
+        pht(
+          'Specified public keyfile "%s" does not exist!',
+          $public_keyfile));
+    }
+
+    $public_key = Filesystem::readFile($public_keyfile);
+
+    $pkcs8_keyfile = $args->getArg('pkcs8');
+    if (!strlen($pkcs8_keyfile)) {
+      throw new PhutilArgumentUsageException(
+        pht(
+          'You must specify the path to a pkcs8 keyfile with --pkc8s.'));
+    }
+
+    if (!Filesystem::pathExists($pkcs8_keyfile)) {
+      throw new PhutilArgumentUsageException(
+        pht(
+          'Specified pkcs8 keyfile "%s" does not exist!',
+          $pkcs8_keyfile));
+    }
+
+    $pkcs8_key = Filesystem::readFile($pkcs8_keyfile);
+
+    $warning = pht(
+      'Adding a PKCS8 keyfile to the cache can be very dangerous. If the '.
+      'PKCS8 file really encodes a different public key than the one '.
+      'specified, an attacker could use it to gain unautorized access.'.
+      "\n\n".
+      'Generally, you should use this option only in a development '.
+      'environment where ssh-keygen is broken and it is inconvenient to '.
+      'fix it, and only if you are certain you understand the risks. You '.
+      'should never cache a PKCS8 file you did not generate yourself.');
+
+    $console->writeOut(
+      "%s\n",
+      phutil_console_wrap($warning));
+
+    $prompt = pht('Really trust this PKCS8 keyfile?');
+    if (!phutil_console_confirm($prompt)) {
+      throw new PhutilArgumentUsageException(
+        pht('Aborted workflow.'));
+    }
+
+    $key = PhabricatorAuthSSHPublicKey::newFromRawKey($public_key);
+    $key->forcePopulatePKCS8Cache($pkcs8_key);
+
+    $console->writeOut(
+      "%s\n",
+      pht('Cached PKCS8 key for public key.'));
+
+    return 0;
+  }
+
+}
diff --git a/src/applications/auth/sshkey/PhabricatorAuthSSHPublicKey.php b/src/applications/auth/sshkey/PhabricatorAuthSSHPublicKey.php
--- a/src/applications/auth/sshkey/PhabricatorAuthSSHPublicKey.php
+++ b/src/applications/auth/sshkey/PhabricatorAuthSSHPublicKey.php
@@ -108,17 +108,48 @@
   }
 
   public function toPKCS8() {
+    $entire_key = $this->getEntireKey();
+    $cache_key = $this->getPKCS8CacheKey($entire_key);
 
-    // TODO: Put a cache in front of this.
+    $cache = PhabricatorCaches::getImmutableCache();
+    $pkcs8_key = $cache->getKey($cache_key);
+    if ($pkcs8_key) {
+      return $pkcs8_key;
+    }
 
     $tmp = new TempFile();
     Filesystem::writeFile($tmp, $this->getEntireKey());
-    list($pem_key) = execx(
-      'ssh-keygen -e -m PKCS8 -f %s',
-      $tmp);
+    try {
+      list($pkcs8_key) = execx(
+        'ssh-keygen -e -m PKCS8 -f %s',
+        $tmp);
+    } catch (CommandException $ex) {
+      unset($tmp);
+      throw new PhutilProxyException(
+        pht(
+          'Failed to convert public key into PKCS8 format. If you are '.
+          'developing on OSX, you may be able to use `bin/auth cache-pkcs8` '.
+          'to work around this issue. %s',
+          $ex->getMessage()),
+        $ex);
+    }
     unset($tmp);
 
-    return $pem_key;
+    $cache->setKey($cache_key, $pkcs8_key);
+
+    return $pkcs8_key;
+  }
+
+  public function forcePopulatePKCS8Cache($pkcs8_key) {
+    $entire_key = $this->getEntireKey();
+    $cache_key = $this->getPKCS8CacheKey($entire_key);
+
+    $cache = PhabricatorCaches::getImmutableCache();
+    $cache->setKey($cache_key, $pkcs8_key);
+  }
+
+  private function getPKCS8CacheKey($entire_key) {
+    return 'pkcs8:'.PhabricatorHash::digestForIndex($entire_key);
   }
 
 }