Adds function for generating MerkleTreeLeaf hash.

net/cert/merkle_tree_leaf.cc

 // Copyright 2016 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 "net/cert/merkle_tree_leaf.h"
 
+#include "crypto/sha2.h"
 #include "net/cert/ct_objects_extractor.h"
+#include "net/cert/ct_serialization.h"
 #include "net/cert/x509_certificate.h"
 
 namespace net {
 
 namespace ct {
 
 MerkleTreeLeaf::MerkleTreeLeaf() {}
 
 MerkleTreeLeaf::~MerkleTreeLeaf() {}
 
+bool Hash(const MerkleTreeLeaf& tree_leaf, std::string* out) {
+  std::string leaf_in_tls_format;
+  if (!EncodeTreeLeaf(tree_leaf, &leaf_in_tls_format))
+    return false;
+
+  // Prepend 0 byte as per RFC 6962, section-2.1
+  *out = crypto::SHA256HashString('\0' + leaf_in_tls_format);

[eroman, 2016/05/09 19:01:22]

Note: since EncodeTreeLeaf() already does an append, you could avoid this
concatenation. i.e something like:

leaf_in_tls_format.push_back('\0');
if (!EncodeTreeLeaf(tree_leaf, &leaf_in_tls_format))
  return false;

*out = crypto::SHA256HashString(leaf_in_tls_format);

[Rob Percival, 2016/05/09 19:55:50]

Done.

+  return true;
+}
+
 bool GetMerkleTreeLeaf(const X509Certificate* cert,
                        const SignedCertificateTimestamp* sct,
                        MerkleTreeLeaf* merkle_tree_leaf) {
   if (sct->origin == SignedCertificateTimestamp::SCT_EMBEDDED) {
     if (cert->GetIntermediateCertificates().empty() ||
         !GetPrecertLogEntry(cert->os_cert_handle(),
                             cert->GetIntermediateCertificates().front(),
                             &merkle_tree_leaf->log_entry)) {
       return false;
     }
   } else {
     if (!GetX509LogEntry(cert->os_cert_handle(),
                          &merkle_tree_leaf->log_entry)) {
       return false;
     }
   }
 
   merkle_tree_leaf->log_id = sct->log_id;
   merkle_tree_leaf->timestamp = sct->timestamp;
   merkle_tree_leaf->extensions = sct->extensions;
   return true;
 }
 
 }  // namespace ct
 
 }  // namespace net