diff --git a/delta_performer.cc b/delta_performer.cc
index 1a98102..54a69fb 100644
--- a/delta_performer.cc
+++ b/delta_performer.cc
@@ -601,7 +601,8 @@
   OmahaHashCalculator signed_hasher;
   TEST_AND_RETURN_FALSE(signed_hasher.SetContext(signed_hash_context_));
   TEST_AND_RETURN_FALSE(signed_hasher.Finalize());
-  const vector<char>& hash_data = signed_hasher.raw_hash();
+  vector<char> hash_data = signed_hasher.raw_hash();
+  PayloadSigner::PadRSA2048SHA256Hash(&hash_data);
   TEST_AND_RETURN_FALSE(!hash_data.empty());
   TEST_AND_RETURN_FALSE(hash_data == signed_hash_data);
   return true;
diff --git a/delta_performer_unittest.cc b/delta_performer_unittest.cc
index 586d582..0c2d9b9 100755
--- a/delta_performer_unittest.cc
+++ b/delta_performer_unittest.cc
@@ -149,7 +149,7 @@
     LOG(INFO) << "Generating a mismatched private key.";
     ASSERT_EQ(0,
               System(StringPrintf(
-                  "/usr/bin/openssl genrsa -out %s 1024",
+                  "/usr/bin/openssl genrsa -out %s 2048",
                   private_key_path.c_str())));
   }
   int signature_size = GetSignatureSize(private_key_path);
@@ -164,12 +164,18 @@
                 signature_size,
                 hash_file.c_str())));
 
+  // Pad the hash
+  vector<char> hash;
+  ASSERT_TRUE(utils::ReadFile(hash_file, &hash));
+  ASSERT_TRUE(PayloadSigner::PadRSA2048SHA256Hash(&hash));
+  ASSERT_TRUE(WriteFileVector(hash_file, hash));
+
   string sig_file;
   ASSERT_TRUE(utils::MakeTempFile("/tmp/signature.XXXXXX", &sig_file, NULL));
   ScopedPathUnlinker sig_unlinker(sig_file);
   ASSERT_EQ(0,
             System(StringPrintf(
-                "/usr/bin/openssl rsautl -pkcs -sign -inkey %s -in %s -out %s",
+                "/usr/bin/openssl rsautl -raw -sign -inkey %s -in %s -out %s",
                 private_key_path.c_str(),
                 hash_file.c_str(),
                 sig_file.c_str())));
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
diff --git a/payload_signer.h b/payload_signer.h
index eb0663d..ee1bee9 100644
--- a/payload_signer.h
+++ b/payload_signer.h
@@ -67,6 +67,12 @@
   static bool VerifySignedPayload(const std::string& payload_path,
                                   const std::string& public_key_path);
 
+  // Pads a SHA256 hash so that it may be encrypted/signed with RSA2048
+  // using the PKCS#1 v1.5 scheme.
+  // hash should be a pointer to vector of exactly 256 bits. The vector
+  // will be modified in place and will result in having a length of
+  // 2048 bits. Returns true on success, false otherwise.
+  static bool PadRSA2048SHA256Hash(std::vector<char>* hash);
  private:
   // This should never be constructed
   DISALLOW_IMPLICIT_CONSTRUCTORS(PayloadSigner);
diff --git a/payload_signer_unittest.cc b/payload_signer_unittest.cc
index f803156..f7c59a6 100644
--- a/payload_signer_unittest.cc
+++ b/payload_signer_unittest.cc
@@ -14,7 +14,7 @@
 using std::vector;
 
 // Note: the test key was generated with the following command:
-// openssl genrsa -out unittest_key.pem 1024
+// openssl genrsa -out unittest_key.pem 2048
 
 namespace chromeos_update_engine {
 
@@ -23,29 +23,55 @@
 
 // Some data and its corresponding hash and signature:
 const char kDataToSign[] = "This is some data to sign.";
+
+// Generated by:
+// echo -n 'This is some data to sign.' | openssl dgst -sha256 -binary |
+//   hexdump -v -e '" " 8/1 "0x%02x, " "\n"'
 const char kDataHash[] = {
   0x7a, 0x07, 0xa6, 0x44, 0x08, 0x86, 0x20, 0xa6,
   0xc1, 0xf8, 0xd9, 0x02, 0x05, 0x63, 0x0d, 0xb7,
   0xfc, 0x2b, 0xa0, 0xa9, 0x7c, 0x9d, 0x1d, 0x8c,
   0x01, 0xf5, 0x78, 0x6d, 0xc5, 0x11, 0xb4, 0x06
 };
+
+// Generated with openssl 1.0, which at the time of this writing, you need
+// to download and install yourself. Here's my command:
+// echo -n 'This is some data to sign.' | openssl dgst -sha256 -binary |
+//    ~/local/bin/openssl pkeyutl -sign -inkey unittest_key.pem -pkeyopt
+//    digest:sha256 | hexdump -v -e '" " 8/1 "0x%02x, " "\n"'
 const char kDataSignature[] = {
-  0xa4, 0xbc, 0x8f, 0xeb, 0x81, 0x05, 0xaa, 0x56,
-  0x1b, 0x56, 0xe5, 0xcb, 0x9b, 0x1a, 0x00, 0xd7,
-  0x1d, 0x87, 0x8e, 0xda, 0x5e, 0x90, 0x09, 0xb8,
-  0x15, 0xf4, 0x25, 0x97, 0x2f, 0x3c, 0xa1, 0xf3,
-  0x02, 0x75, 0xcd, 0x67, 0x4b, 0x0c, 0x1f, 0xf5,
-  0x6e, 0xf1, 0x58, 0xd7, 0x0d, 0x8c, 0x18, 0x91,
-  0x52, 0x30, 0x98, 0x64, 0x58, 0xc0, 0xe2, 0xb5,
-  0x77, 0x3b, 0x96, 0x8f, 0x05, 0xc4, 0x7f, 0x7a,
-  0x9a, 0x44, 0x0f, 0xc7, 0x1b, 0x90, 0x83, 0xf8,
-  0x69, 0x05, 0xa8, 0x02, 0x57, 0xcd, 0x2e, 0x5b,
-  0x96, 0xc7, 0x77, 0xa6, 0x1f, 0x97, 0x97, 0x05,
-  0xb3, 0x30, 0x1c, 0x27, 0xd7, 0x2d, 0x31, 0x60,
-  0x84, 0x7e, 0x99, 0x00, 0xe6, 0xe1, 0x39, 0xa6,
-  0xf3, 0x3a, 0x72, 0xba, 0xc4, 0xfe, 0x68, 0xa9,
-  0x08, 0xfa, 0xbc, 0xa8, 0x44, 0x66, 0xa0, 0x60,
-  0xde, 0xc9, 0xb2, 0xba, 0xbc, 0x80, 0xb5, 0x55
+  0x9f, 0x86, 0x25, 0x8b, 0xf3, 0xcc, 0xe3, 0x95,
+  0x5f, 0x45, 0x83, 0xb2, 0x66, 0xf0, 0x2a, 0xcf,
+  0xb7, 0xaa, 0x52, 0x25, 0x7a, 0xdd, 0x9d, 0x65,
+  0xe5, 0xd6, 0x02, 0x4b, 0x37, 0x99, 0x53, 0x06,
+  0xc2, 0xc9, 0x37, 0x36, 0x25, 0x62, 0x09, 0x4f,
+  0x6b, 0x22, 0xf8, 0xb3, 0x89, 0x14, 0x98, 0x1a,
+  0xbc, 0x30, 0x90, 0x4a, 0x43, 0xf5, 0xea, 0x2e,
+  0xf0, 0xa4, 0xba, 0xc3, 0xa7, 0xa3, 0x44, 0x70,
+  0xd6, 0xc4, 0x89, 0xd8, 0x45, 0x71, 0xbb, 0xee,
+  0x59, 0x87, 0x3d, 0xd5, 0xe5, 0x40, 0x22, 0x3d,
+  0x73, 0x7e, 0x2a, 0x58, 0x93, 0x8e, 0xcb, 0x9c,
+  0xf2, 0xbb, 0x4a, 0xc9, 0xd2, 0x2c, 0x52, 0x42,
+  0xb0, 0xd1, 0x13, 0x22, 0xa4, 0x78, 0xc7, 0xc6,
+  0x3e, 0xf1, 0xdc, 0x4c, 0x7b, 0x2d, 0x40, 0xda,
+  0x58, 0xac, 0x4a, 0x11, 0x96, 0x3d, 0xa0, 0x01,
+  0xf6, 0x96, 0x74, 0xf6, 0x6c, 0x0c, 0x49, 0x69,
+  0x4e, 0xc1, 0x7e, 0x9f, 0x2a, 0x42, 0xdd, 0x15,
+  0x6b, 0x37, 0x2e, 0x3a, 0xa7, 0xa7, 0x6d, 0x91,
+  0x13, 0xe8, 0x59, 0xde, 0xfe, 0x99, 0x07, 0xd9,
+  0x34, 0x0f, 0x17, 0xb3, 0x05, 0x4c, 0xd2, 0xc6,
+  0x82, 0xb7, 0x38, 0x36, 0x63, 0x1d, 0x9e, 0x21,
+  0xa6, 0x32, 0xef, 0xf1, 0x65, 0xe6, 0xed, 0x95,
+  0x25, 0x9b, 0x61, 0xe0, 0xba, 0x86, 0xa1, 0x7f,
+  0xf8, 0xa5, 0x4a, 0x32, 0x1f, 0x15, 0x20, 0x8a,
+  0x41, 0xc5, 0xb0, 0xd9, 0x4a, 0xda, 0x85, 0xf3,
+  0xdc, 0xa0, 0x98, 0x5d, 0x1d, 0x18, 0x9d, 0x2e,
+  0x42, 0xea, 0x69, 0x13, 0x74, 0x3c, 0x74, 0xf7,
+  0x6d, 0x43, 0xb0, 0x63, 0x90, 0xdb, 0x04, 0xd5,
+  0x05, 0xc9, 0x73, 0x1f, 0x6c, 0xd6, 0xfa, 0x46,
+  0x4e, 0x0f, 0x33, 0x58, 0x5b, 0x0d, 0x1b, 0x55,
+  0x39, 0xb9, 0x0f, 0x43, 0x37, 0xc0, 0x06, 0x0c,
+  0x29, 0x93, 0x43, 0xc7, 0x43, 0xb9, 0xab, 0x7d
 };
 
 //class PayloadSignerTest : public ::testing::Test {};
@@ -96,9 +122,11 @@
   EXPECT_TRUE(PayloadSigner::VerifySignature(signature_blob,
                                              kUnittestPublicKeyPath,
                                              &hash_data));
-  ASSERT_EQ(arraysize(kDataHash), hash_data.size());
-  for (size_t i = 0; i < arraysize(kDataHash); i++) {
-    EXPECT_EQ(kDataHash[i], hash_data[i]);
+  vector<char> padded_hash_data(kDataHash, kDataHash + sizeof(kDataHash));
+  PayloadSigner::PadRSA2048SHA256Hash(&padded_hash_data);
+  ASSERT_EQ(padded_hash_data.size(), hash_data.size());
+  for (size_t i = 0; i < padded_hash_data.size(); i++) {
+    EXPECT_EQ(padded_hash_data[i], hash_data[i]);
   }
 }
 
diff --git a/unittest_key.pem b/unittest_key.pem
index f3867e4..224d3c3 100644
--- a/unittest_key.pem
+++ b/unittest_key.pem
@@ -1,15 +1,27 @@
 -----BEGIN RSA PRIVATE KEY-----
-MIICXQIBAAKBgQDh27889vgney5Fmg89ZR80CFAhBWfj/33/6uRfWRs9tNP0kKpy
-Iml8Q4s6acPyp4VUlmfcayVKIkoNYhV+D9oRtNGmjosPCTRmupQ+55z0/FFHjtT5
-4sJShFvBcCofygvHeYqrzgpZdB8z1z/zhAfJc43hs2jFcr82UvkQ8XD3xwIDAQAB
-AoGAeiVwqFTcYeXBYYzu3wI4PNieFS2qQOjkyKnM9i/nhpir5GD0fSNVLwoMWvvm
-J+4nMlbhNpiPoycmK1S3UOTbxqFgw5b0DSUMiiGBdPIc7X0hPVIeR4I40g81fFl0
-3EyvZxlZexzfeTISbp+gpa+KW1bYoxY7e9TWCQDP+cuB34ECQQD5uJXzjU5AKTpA
-hgE1u2WetuGsnl95S96cBwuCiULAcbdFXQYip57eODfoNI2QDGyhdhcr3OBzhbR5
-ScK1qIXBAkEA54mPrA+65eEtv2fD4Iqt1qcvuVll/fSIdq6yQJEnzCUEsT7Ink0C
-WvAAHYlBISkc8onIagPowCQfGbVangQvhwJBAJ438HIOfpyyQmEtRkj4AausrZGE
-CnO8uT9cS1OaifuKURcWmFOOpl6fefSaj3LMHGu0eXvmByPKfA04ya/1JUECQQCX
-FQAW+jyue/zqBL+f6V39zyIpA9i1mbbiGqRd1Vnur8kcDyfBg+ahiDHLFCDXjohB
-Cv8njl114xwYHmp+6aRJAkAtumVpfP3KIAg7q7pXT5W1yTTqrzN/xAn4AQhnaXuh
-6Kt1dgWF7IQUEzoMKHBgciuwh2KjIxOx1/sMfLj3nz3H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 -----END RSA PRIVATE KEY-----
diff --git a/unittest_key.pub.pem b/unittest_key.pub.pem
deleted file mode 100644
index 10485f3..0000000
--- a/unittest_key.pub.pem
+++ /dev/null
@@ -1,6 +0,0 @@
------BEGIN PUBLIC KEY-----
-MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDh27889vgney5Fmg89ZR80CFAh
-BWfj/33/6uRfWRs9tNP0kKpyIml8Q4s6acPyp4VUlmfcayVKIkoNYhV+D9oRtNGm
-josPCTRmupQ+55z0/FFHjtT54sJShFvBcCofygvHeYqrzgpZdB8z1z/zhAfJc43h
-s2jFcr82UvkQ8XD3xwIDAQAB
------END PUBLIC KEY-----