Certificate Transparency: Code for unpacking EV cert hashes whitelist

net/cert/ct_ev_whitelist.h

Index: net/cert/ct_ev_whitelist.h
diff --git a/net/cert/ct_ev_whitelist.h b/net/cert/ct_ev_whitelist.h
new file mode 100644
index 0000000000000000000000000000000000000000..6e4476129547449ed5ae5bda0778282f22d0b9f8
--- /dev/null
+++ b/net/cert/ct_ev_whitelist.h
@@ -0,0 +1,90 @@
+// Copyright 2014 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.
+
+#ifndef NET_CERT_CT_EV_WHITELIST_H_
+#define NET_CERT_CT_EV_WHITELIST_H_
+
+#include <set>
+#include <string>
+
+#include "base/files/file_path.h"
+#include "net/base/net_export.h"
+
+namespace net {
+
+namespace ct {
+
+namespace internal {
+
+/**

[wtc, 2014/09/02 23:03:02]

Unless you are using a tool like javadoc or doxygen to generate documentation
from comments, we should just use C++ style comments ( // ...).

[Eran Messeri, 2014/09/03 09:38:50]

Done.

+ * Abstraction over a stream of bits, to be read independently
+ * of the bytes they're packed into. Bits are read MSB-first from the stream.
+ * It is limited to 64-bit reads and is inefficient as a design choice - Since
+ * it is used infrequently to unpack the Golomb-coded EV certificate hashes
+ * whitelist in a blocking thread.
+ *
+ * This class is declared here so it can be tested.
+ */
+class NET_EXPORT_PRIVATE BitStreamReader {
+ public:
+  BitStreamReader(const char* source, size_t length);
+
+  // Reads unary-encoded number into |out|. Returns true if
+  // there was at least one bit to read, false otherwise.
+  bool ReadUnaryEncoding(uint64* out);
+  // Reads |num_bits| (up to 64) into |out|. |out| is filled from the MSB to the
+  // LSB. If |num_bits| is less than 64, the most significant |64 - num_bits|
+  // bits are left unused. Returns true if the stream had the requested

[wtc, 2014/09/02 23:03:02]

Nit: "left unused" doesn't say what values those bits have. You can say "unused
and left as zeros" or "set to zeros", for example.

[Eran Messeri, 2014/09/03 09:38:51]

Done.

+  // |num_bits|, false otherwise.
+  bool ReadBits(uint8 num_bits, uint64* out);
+  // Returns the number of bits left in the stream.
+  uint64 BitsLeft() const;
+
+ private:
+  // Reads a single bit. Within a byte, the bits are read from the MSB to the
+  // LSB.
+  uint8 ReadBit();
+
+  const char* const source_;
+  const size_t length_;
+
+  // Index of the byte currently being read from.
+  uint64 current_byte_;
+  // Index of the last bit read within |current_byte_|. Since bits are read
+  // from the MSB to the LSB, this value is initialized to 7 and decreases

[wtc, 2014/09/02 23:03:02]

Nit: decreases => decremented

[Eran Messeri, 2014/09/03 09:38:50]

Done.

+  // after each read.
+  int8 current_bit_;
+};
+
+// Given a Golomb-coded list of hashes in |compressed_whitelist|, unpack into
+// |uncompressed_list|. Returns true if the format of the compressed whitelist
+// is valid, false otherwise.
+NET_EXPORT_PRIVATE bool UncompressEVWhitelist(
+    const std::string& compressed_whitelist,
+    std::set<std::string>* uncompressed_list);
+
+// Sets the given |ev_whitelist| into the global context.
+// Note that |ev_whitelist| will contain the old EV whitelist data after this
+// call as the implementation is using set::swap() to efficiently switch the
+// sets.
+NET_EXPORT_PRIVATE void SetEVWhitelistData(std::set<std::string>& ev_whitelist);

[wtc, 2014/09/02 23:03:02]

IMPORTANT: a non-const reference is usually disallowed by our Style Guide. I
think this is probably OK.

[Eran Messeri, 2014/09/03 09:38:50]

Acknowledged - Since this code is not performance-critical, I could change it to
copy the set, but copying ~1MB of data around just to adhere to the Style Guide
seems wasteful.
If you come to the conclusion that copying the data is better, I can change in a
follow-up CL, but IMHO this is one of the cases where an exception to the rules
is acceptable (especially since this API is only expected to be used in one
place).

+}  // namespace internal

[wtc, 2014/09/02 23:03:02]

Please add a blank line before this line.

[Eran Messeri, 2014/09/03 09:38:50]

Done.

+
+// Sets the global EV certificate hashes whitelist from
+// |compressed_whitelist_file| in the global context, after uncompressing it.
+// If the data in |compressed_whitelist_file| is not a valid compressed
+// whitelist, does nothing.
+NET_EXPORT void SetEVWhitelistFromFile(
+    const base::FilePath& compressed_whitelist_file);
+
+// Returns true if the |certificate_hash| appears in the EV certificate hashes
+// whitelist.
+NET_EXPORT bool IsCertificateHashInWhitelist(
+    const std::string& certificate_hash);
+
+}  // namespace ct
+
+}  // namespace net
+
+#endif  // NET_CERT_CT_EV_WHITELIST_H_