Implement HKDF for WebCrypto (blink-side)

Source/platform/exported/WebCryptoKeyAlgorithm.cpp

Index: Source/platform/exported/WebCryptoKeyAlgorithm.cpp
diff --git a/Source/platform/exported/WebCryptoKeyAlgorithm.cpp b/Source/platform/exported/WebCryptoKeyAlgorithm.cpp
index bef587d0d25dbd6e796cacba6688ed7e2bc256b6..b69acc47db2df33ad11dc6e762850801b62b4955 100644
--- a/Source/platform/exported/WebCryptoKeyAlgorithm.cpp
+++ b/Source/platform/exported/WebCryptoKeyAlgorithm.cpp
@@ -93,6 +93,11 @@ WebCryptoKeyAlgorithm WebCryptoKeyAlgorithm::createEc(WebCryptoAlgorithmId id, W
     return WebCryptoKeyAlgorithm(id, adoptPtr(new WebCryptoEcKeyAlgorithmParams(namedCurve)));
 }
 
+WebCryptoKeyAlgorithm WebCryptoKeyAlgorithm::create(WebCryptoAlgorithmId id)

[eroman, 2014/12/23 20:58:24]

Call this createHkdf() instead and omit the ID parameter. (There is no other
valid ID that can be passed).

[nharper, 2014/12/23 22:46:59]

Done.

+{
+    return WebCryptoKeyAlgorithm(id, nullptr);

[eroman, 2014/12/23 20:58:24]

We should find out from the working group if this is likely to stick. It seems
like at a minimum there should be a "length" attribute for the key to match how
HMAC and AES keys work.

The reason this is important, is once we support these keys and allow
serializing them, if all the properties aren't there and are added later we will
have to monkey that in, which is not great.

[eroman, 2014/12/23 22:03:53]

Actually I am fairly confident a "length" attribute isn't a good idea. But would
still be good to confirm with Ryan before this becomes set in stone.

[nharper, 2014/12/23 22:46:59]

PBKDF2 and CONCAT both have no extra params for KeyAlgorithm, like HKDF here.
The only reason I can find for HMAC having a length attribute is for
generateKey, a method which HKDF does not support.

[eroman, 2014/12/23 23:34:29]

The other reason HMAC needs it, is HMAC keys are not necessarily byte-lengthed,
so without reflecting the key length there would be information loss when
exporting / re-importing.

(Even though algorithmically HMAC internally sets that stuff to zero...)

+}
+
 bool WebCryptoKeyAlgorithm::isNull() const
 {
     return m_private.isNull();
@@ -148,7 +153,8 @@ void WebCryptoKeyAlgorithm::writeToDictionary(WebCryptoKeyAlgorithmDictionary* d
 {
     ASSERT(!isNull());
     dict->setString("name", WebCryptoAlgorithm::lookupAlgorithmInfo(id())->name);
-    m_private->params.get()->writeToDictionary(dict);
+    if (m_private->params.get())
+        m_private->params.get()->writeToDictionary(dict);
 }
 
 void WebCryptoKeyAlgorithm::assign(const WebCryptoKeyAlgorithm& other)