remoting/protocol/auth_util.cc

// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "remoting/protocol/auth_util.h"

#include "base/base64.h"
#include "base/compiler_specific.h"
#include "base/logging.h"
#include "base/strings/string_util.h"
#include "base/strings/string_view_util.h"
#include "crypto/hmac.h"
#include "net/base/net_errors.h"
#include "net/socket/ssl_socket.h"

namespace remoting::protocol {

const char kClientAuthSslExporterLabel[] =
    "EXPORTER-remoting-channel-auth-client";
const char kHostAuthSslExporterLabel[] = "EXPORTER-remoting-channel-auth-host";

const char kSslFakeHostName[] = "chromoting";

std::string GetSharedSecretHash(const std::string& tag,
                                const std::string& shared_secret) {
  // Note that the use of these parameters is backward from what you might
  // expect - a more usual construction would be to use the existing shared
  // secret as the key and the tag as the message, since here we're using the
  // hash as a key derivation function (but not using HKDF).
  base::span<const uint8_t> key = base::as_byte_span(tag);
  base::span<const uint8_t> message = base::as_byte_span(shared_secret);

  const auto hmac = crypto::hmac::SignSha256(key, message);
  return std::string(base::as_string_view(hmac));
}

// static
std::string GetAuthBytes(net::SSLSocket* socket,
                         const std::string_view& label,
                         const std::string_view& shared_secret) {
  // Get keying material from SSL.
  std::array<uint8_t, kAuthDigestLength> key;
  int export_result = socket->ExportKeyingMaterial(label, std::nullopt, key);
  if (export_result != net::OK) {
    LOG(ERROR) << "Error fetching keying material: " << export_result;
    return std::string();
  }

  // Generate auth digest based on the keying material and shared secret.
  base::span<const uint8_t> message = base::as_byte_span(shared_secret);
  const auto out = crypto::hmac::SignSha256(key, message);
  return std::string(base::as_string_view(out));
}

}  // namespace remoting::protocol