Allow empty keys in hmac_openssl.cc.

crypto/hmac_openssl.cc

Index: crypto/hmac_openssl.cc
diff --git a/crypto/hmac_openssl.cc b/crypto/hmac_openssl.cc
index f7010c81bc651a562996b788645352b6cb2a3e1b..2f9218387092c15fe76df9b67d86359c674de042 100644
--- a/crypto/hmac_openssl.cc
+++ b/crypto/hmac_openssl.cc
@@ -31,6 +31,12 @@ bool HMAC::Init(const unsigned char* key, size_t key_length) {
   DCHECK(plat_->key.empty());
 
   plat_->key.assign(key, key + key_length);
+  if (key_length == 0) {
+    // Special-case: if the key is empty, use a key with one zero byte. OpenSSL
+    // does not like NULL keys, but keys are padded with zeros, so they're
+    // equivalent.

[wtc, 2014/04/09 21:30:58]

It would be nice to note what a NULL key means to OpenSSL.

I confirm that an empty key and a key of one zero byte are equivalent.

[davidben, 2014/04/09 21:44:29]

Done.

+    plat_->key.push_back(0);
+  }
   return true;
 }