diff --git a/payload_signer.cc b/payload_signer.cc
index 60a80d1..ef9791d 100644
--- a/payload_signer.cc
+++ b/payload_signer.cc
@@ -23,6 +23,28 @@
 const uint32_t kSignatureMessageVersion = 1;
 
 namespace {
+
+const char kRSA2048SHA256Padding[] = {
+  0x00, 0x01, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+  0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+  0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+  0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+  0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+  0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+  0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+  0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+  0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+  0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+  0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+  0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+  0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+  0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+  0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+  0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x00, 0x30, 0x31, 0x30,
+  0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01, 0x05,
+  0x00, 0x04, 0x20
+};
+
 // Given a raw |signature|, packs it into a protobuf and serializes it into a
 // binary blob. Returns true on success, false otherwise.
 bool ConvertSignatureToProtobufBlob(const vector<char> signature,
@@ -113,14 +135,18 @@
   TEST_AND_RETURN_FALSE(
       utils::MakeTempFile("/tmp/hash.XXXXXX", &hash_path, NULL));
   ScopedPathUnlinker hash_path_unlinker(hash_path);
+  // We expect unpadded SHA256 hash coming in
+  TEST_AND_RETURN_FALSE(hash.size() == 32);
+  vector<char> padded_hash(hash);
+  PadRSA2048SHA256Hash(&padded_hash);
   TEST_AND_RETURN_FALSE(utils::WriteFile(hash_path.c_str(),
-                                         hash.data(),
-                                         hash.size()));
+                                         padded_hash.data(),
+                                         padded_hash.size()));
 
   // 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",
+  SplitString("/usr/bin/openssl rsautl -raw -sign -inkey x -in x -out x",
               ' ',
               &cmd);
   cmd[cmd.size() - 5] = private_key_path;
@@ -220,7 +246,7 @@
       reinterpret_cast<const unsigned char*>(sig_data.data()),
       reinterpret_cast<unsigned char*>(hash_data.data()),
       rsa,
-      RSA_PKCS1_PADDING);
+      RSA_NO_PADDING);
   RSA_free(rsa);
   TEST_AND_RETURN_FALSE(decrypt_size > 0 &&
                         decrypt_size <= static_cast<int>(hash_data.size()));
@@ -251,6 +277,7 @@
   vector<char> hash;
   TEST_AND_RETURN_FALSE(OmahaHashCalculator::RawHashOfBytes(
       payload.data(), metadata_size + manifest.signatures_offset(), &hash));
+  PadRSA2048SHA256Hash(&hash);
   TEST_AND_RETURN_FALSE(hash == signed_hash);
   return true;
 }
@@ -299,4 +326,13 @@
   return true;
 }
 
+bool PayloadSigner::PadRSA2048SHA256Hash(std::vector<char>* hash) {
+  TEST_AND_RETURN_FALSE(hash->size() == 32);
+  hash->insert(hash->begin(),
+               kRSA2048SHA256Padding,
+               kRSA2048SHA256Padding + sizeof(kRSA2048SHA256Padding));
+  TEST_AND_RETURN_FALSE(hash->size() == 256);
+  return true;
+}
+
 }  // namespace chromeos_update_engine