[webcrypto] Add symmetric key export for NSS and OpenSSL.

content/renderer/webcrypto/webcrypto_impl_nss.cc

Index: content/renderer/webcrypto/webcrypto_impl_nss.cc
diff --git a/content/renderer/webcrypto/webcrypto_impl_nss.cc b/content/renderer/webcrypto/webcrypto_impl_nss.cc
index 73319df1a78b837fa4c7a93a762d6307cd06e3f8..3eb385d3ce192652d48b0d76aefb16f7cc0577cc 100644
--- a/content/renderer/webcrypto/webcrypto_impl_nss.cc
+++ b/content/renderer/webcrypto/webcrypto_impl_nss.cc
@@ -325,6 +325,31 @@ bool ImportKeyInternalRaw(
   return true;
 }
 
+bool ExportKeyInternalRaw(
+    const blink::WebCryptoKey& key,
+    blink::WebArrayBuffer* buffer) {
+
+  DCHECK(key.handle());
+  DCHECK(buffer);
+
+  if (key.type() != blink::WebCryptoKeyTypeSecret || !key.extractable())
+    return false;
+
+  SymKeyHandle* const sym_key = reinterpret_cast<SymKeyHandle*>(key.handle());

[eroman, 2013/12/05 01:47:53]

I don't see any value in making the pointer "const" here.
I wouldn't object to "const SymKeyHandle*" however.

[padolph, 2013/12/05 02:45:57]

The Scott Meyers books trained me to make as much stuff const as possible. It
can provide some safety in future modifications, in some (remote) cases can
allow compile time optimizations, and gives the reader the hint that I don't
plan on ever changing the value.

I can't use "const SymKeyHandle" in this case because PK11_ExtractKeyValue()
cannot support a const input. Strangely, it actually changes the underlying
PK11_SymKey structure, depositing the raw key bytes within it so they can then
be read by PK11_GetKeyData().

Anyway, I'll take out the const pointer stuff to maintain the style of the
chromium code as you mention below.

Done.

+
+  if (PK11_ExtractKeyValue(sym_key->key()) != SECSuccess)
+    return false;
+
+  SECItem* const key_data = PK11_GetKeyData(sym_key->key());

[eroman, 2013/12/05 01:47:53]

It is uncommon in chromium code to make the pointer itself const rather than a
pointer to const data. My suggestion is to remove it.

[padolph, 2013/12/05 02:45:57]

Done.

+  if (!key_data)
+    return false;
+  DCHECK(key_data->data);

[eroman, 2013/12/05 01:47:53]

Would it ever be possible for key_data->len to be 0?

[padolph, 2013/12/05 02:45:57]

Yes. Empty symmetric keys are possible and already part of the unit tests.

+
+  *buffer = webcrypto::CreateArrayBuffer(key_data->data, key_data->len);
+
+  return true;
+}
+
 typedef scoped_ptr<CERTSubjectPublicKeyInfo,
                    crypto::NSSDestroyer<CERTSubjectPublicKeyInfo,
                                         SECKEY_DestroySubjectPublicKeyInfo> >
@@ -424,8 +449,7 @@ bool ExportKeyInternalSpki(
   DCHECK(spki_der->data);
   DCHECK(spki_der->len);
 
-  *buffer = blink::WebArrayBuffer::create(spki_der->len, 1);
-  memcpy(buffer->data(), spki_der->data, spki_der->len);
+  *buffer = webcrypto::CreateArrayBuffer(spki_der->data, spki_der->len);
 
   return true;
 }
@@ -827,8 +851,7 @@ bool WebCryptoImpl::ExportKeyInternal(
     blink::WebArrayBuffer* buffer) {
   switch (format) {
     case blink::WebCryptoKeyFormatRaw:
-      // TODO(padolph): Implement raw export
-      return false;
+      return ExportKeyInternalRaw(key, buffer);
     case blink::WebCryptoKeyFormatSpki:
       return ExportKeyInternalSpki(key, buffer);
     case blink::WebCryptoKeyFormatPkcs8: