Per discussion, implement the Omaha Client Update Protocol (CUP) in src/crypto.

crypto/cup_nss.cc

+// Copyright (c) 2013 The Chromium 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 "crypto/cup.h"
+
+#include <base64.h>
+#include <keyhi.h>
+#include <pk11pub.h>
+#include <seccomon.h>
+
+#include "base/logging.h"
+#include "crypto/nss_util.h"
+#include "crypto/scoped_nss_types.h"
+
+namespace crypto {
+
+typedef scoped_ptr_malloc<
+    CERTSubjectPublicKeyInfo,
+    NSSDestroyer<CERTSubjectPublicKeyInfo, SECKEY_DestroySubjectPublicKeyInfo> >
+    ScopedCERTSubjectPublicKeyInfo;
+
+typedef scoped_ptr_malloc<
+    unsigned char,
+    NSSDestroyer<void, PORT_Free> >
+    ScopedPORTAllocUnsignedChar;
+
+size_t ClientUpdateProtocol::LoadPublicKey(const char* public_key) {
+  EnsureNSSInit();
+
+  // The string |public_key| is expected to be a Base64-encoded DER public key.
+

[Ryan Sleevi, 2013/05/30 02:28:08]

style: delete blank line.

[Ryan Myers (chromium), 2013/05/30 21:01:10]

Done.

+  unsigned int der_encoded_spki_len = 0;
+  ScopedPORTAllocUnsignedChar der_encoded_spki(
+      ATOB_AsciiToData(public_key, &der_encoded_spki_len));

[Ryan Sleevi, 2013/05/30 02:28:08]

eg: using DER you don't have to go through these hijinks.

Especially because we have base::Base64Encode/Decode.

[Ryan Myers (chromium), 2013/05/30 21:01:10]

Done.

+  if (der_encoded_spki_len == 0 || !der_encoded_spki.get()) {
+    return 0;
+  }
+
+  SECItem spki_item;
+  spki_item.type = siBuffer;
+  spki_item.data = der_encoded_spki.get();
+  spki_item.len = der_encoded_spki_len;
+
+  ScopedCERTSubjectPublicKeyInfo spki(
+      SECKEY_DecodeDERSubjectPublicKeyInfo(&spki_item));
+  if (!spki.get()) {
+    return 0;
+  }
+
+  pkv_.reset(SECKEY_ExtractPublicKey(spki.get()));
+  if (!pkv_.get()) {
+    return 0;
+  }
+
+  return SECKEY_PublicKeyStrength(pkv_.get());
+}
+
+bool ClientUpdateProtocol::EncryptSharedKey() {
+  // WARNING: This call bypasses the usual PKCS padding and does direct RSA
+  // exponentiation.  This not secure without taking measures to ensure that
+  // the contents of r are suitable.  We do this to remain compatible with the
+  // implementation on the Google Update servers; don't copy-paste this code
+  // arbitrarily and expect it to work and/or remain secure!

[Ryan Sleevi, 2013/05/30 02:28:08]

Comment nit: Avoid "we" in comments.

[Ryan Myers (chromium), 2013/05/30 21:01:10]

Done.

+
+  SECKEYPublicKey* pkv = pkv_.get();
+  if (!pkv) {
+    return false;
+  }
+  size_t keysize = SECKEY_PublicKeyStrength(pkv);
+  if (r_.size() != keysize) {
+    return false;
+  }
+
+  w_.resize(keysize);
+  return SECSuccess == PK11_PubEncryptRaw(pkv,
+                                          &w_.front(),
+                                          &r_.front(),
+                                          r_.size(),
+                                          NULL);
+}
+
+}  // namespace crypto
+