diff --git a/payload_signer.cc b/payload_signer.cc
new file mode 100644
index 0000000..03ff391
--- /dev/null
+++ b/payload_signer.cc
@@ -0,0 +1,79 @@
+// Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "update_engine/payload_signer.h"
+
+#include "base/logging.h"
+#include "base/string_util.h"
+#include "update_engine/subprocess.h"
+#include "update_engine/update_metadata.pb.h"
+#include "update_engine/utils.h"
+
+using std::string;
+using std::vector;
+
+namespace chromeos_update_engine {
+
+const uint32_t kSignatureMessageVersion = 1;
+
+bool PayloadSigner::SignPayload(const string& unsigned_payload_path,
+                                const string& private_key_path,
+                                vector<char>* out_signature_blob) {
+  string sig_path;
+  TEST_AND_RETURN_FALSE(
+      utils::MakeTempFile("/tmp/signature.XXXXXX", &sig_path, NULL));
+  ScopedPathUnlinker sig_path_unlinker(sig_path);
+  
+  // This runs on the server, so it's okay to cop out and call openssl
+  // executable rather than properly use the library
+  vector<string> cmd;
+  SplitString("/usr/bin/openssl rsautl -pkcs -sign -inkey x -in x -out x",
+              ' ',
+              &cmd);
+  cmd[cmd.size() - 5] = private_key_path;
+  cmd[cmd.size() - 3] = unsigned_payload_path;
+  cmd[cmd.size() - 1] = sig_path;
+  
+  int return_code = 0;
+  TEST_AND_RETURN_FALSE(Subprocess::SynchronousExec(cmd, &return_code));
+  TEST_AND_RETURN_FALSE(return_code == 0);
+  
+  vector<char> signature;
+  TEST_AND_RETURN_FALSE(utils::ReadFile(sig_path, &signature));
+  
+  // Pack it into a protobuf
+  Signatures out_message;
+  Signatures_Signature* sig_message = out_message.add_signatures();
+  sig_message->set_version(kSignatureMessageVersion);
+  sig_message->set_data(signature.data(), signature.size());
+  
+  // Serialize protobuf
+  string serialized;
+  TEST_AND_RETURN_FALSE(out_message.AppendToString(&serialized));
+  out_signature_blob->insert(out_signature_blob->end(),
+                             serialized.begin(),
+                             serialized.end());
+  return true;
+}
+
+bool PayloadSigner::SignatureBlobLength(
+    const string& private_key_path,
+    uint64_t* out_length) {
+  DCHECK(out_length);
+  
+  string x_path;
+  TEST_AND_RETURN_FALSE(
+      utils::MakeTempFile("/tmp/signed_data.XXXXXX", &x_path, NULL));
+  ScopedPathUnlinker x_path_unlinker(x_path);
+  TEST_AND_RETURN_FALSE(utils::WriteFile(x_path.c_str(), "x", 1));
+
+  vector<char> sig_blob;
+  TEST_AND_RETURN_FALSE(PayloadSigner::SignPayload(x_path,
+                                                   private_key_path,
+                                                   &sig_blob));
+  *out_length = sig_blob.size();
+  return true;
+}
+
+}  // namespace chromeos_update_engine