Move crypto_helpers from sync to base

crypto/random.h

+// Copyright (c) 2011 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 CRYPTO_RANDOM_H_
+#define CRYPTO_RANDOM_H_
+#pragma once
+
+#include <string>
+
+// GetRandomBytes fills |output_length| bytes of |output| with
+// cryptographically strong random data.
+void GetRandomBytes(void* output, size_t output_length);

[Ryan Sleevi, 2011/04/27 02:32:24]

This makes the third implementation to get random bytes. Perhaps these should be
consolidated.

1: this
2: src/ppapi/shared_impl/crypto_impl.cc (brettw@)
3: src/webkit/glue/webkitclient_impl.cc (abarth@)

Prior to agl@'s comments, all three implementations were exactly the same -
iterate through a series of uint64s, copying into the target buffer - with #2
and #3 being straight up line for line the same.

All three make the claim of "cryptographically strong", although as agl@ pointed
out, it's not the case for RandUint64 on Windows.

[wtc, 2011/04/28 19:42:22]

GetRandomBytes should be moved to base/rand_util.h.
It is closely related to the functions in base/rand_util.h.

+
+// Generate128BitRandomBase64String returns a string of length 22 containing
+// cryptographically strong random data encoded in base64.
+std::string Generate128BitRandomBase64String();

[wtc, 2011/04/28 19:42:22]

API design issue: this function is not generally useful.
It should ideally be moved back to where its callers are
(chrome/browser/sync/util).

[abarth-chromium, 2011/04/29 07:47:11]

http://codereview.chromium.org/6904118/ contains a function that generates
a random string of arbitrary length, which is generally useful.  :)

[wtc, 2011/04/29 18:07:08]

abarth: yes.  Your RandString function is equivalent to
the GetRandomBytes function above.  The Generate128BitRandomBase64String
function also encodes the output in base64 so that it is
truly a "text" string.

+
+#endif  // CRYPTO_RANDOM_H_