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// Copyright (c) 2016 Ryan Prichard
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to
// deal in the Software without restriction, including without limitation the
// rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
// sell copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
// IN THE SOFTWARE.
#include "GenRandom.h"
#include <stdint.h>
#include <string.h>
#include "DebugClient.h"
#include "StringBuilder.h"
static volatile LONG g_pipeCounter;
GenRandom::GenRandom() : m_advapi32(L"advapi32.dll") {
// First try to use the pseudo-documented RtlGenRandom function from
// advapi32.dll. Creating a CryptoAPI context is slow, and RtlGenRandom
// avoids the overhead. It's documented in this blog post[1] and on
// MSDN[2] with a disclaimer about future breakage. This technique is
// apparently built-in into the MSVC CRT, though, for the rand_s function,
// so perhaps it is stable enough.
//
// [1] http://blogs.msdn.com/b/michael_howard/archive/2005/01/14/353379.aspx
// [2] https://msdn.microsoft.com/en-us/library/windows/desktop/aa387694(v=vs.85).aspx
//
// Both RtlGenRandom and the Crypto API functions exist in XP and up.
m_rtlGenRandom = reinterpret_cast<RtlGenRandom_t*>(
m_advapi32.proc("SystemFunction036"));
// The OsModule class logs an error message if the proc is nullptr.
if (m_rtlGenRandom != nullptr) {
return;
}
// Fall back to the crypto API.
m_cryptProvIsValid =
CryptAcquireContext(&m_cryptProv, nullptr, nullptr,
PROV_RSA_FULL, CRYPT_VERIFYCONTEXT) != 0;
if (!m_cryptProvIsValid) {
trace("GenRandom: CryptAcquireContext failed: %u",
static_cast<unsigned>(GetLastError()));
}
}
GenRandom::~GenRandom() {
if (m_cryptProvIsValid) {
CryptReleaseContext(m_cryptProv, 0);
}
}
// Returns false if the context is invalid or the generation fails.
bool GenRandom::fillBuffer(void *buffer, size_t size) {
memset(buffer, 0, size);
bool success = false;
if (m_rtlGenRandom != nullptr) {
success = m_rtlGenRandom(buffer, size) != 0;
if (!success) {
trace("GenRandom: RtlGenRandom/SystemFunction036 failed: %u",
static_cast<unsigned>(GetLastError()));
}
} else if (m_cryptProvIsValid) {
success =
CryptGenRandom(m_cryptProv, size,
reinterpret_cast<BYTE*>(buffer)) != 0;
if (!success) {
trace("GenRandom: CryptGenRandom failed, size=%d, lasterror=%u",
static_cast<int>(size),
static_cast<unsigned>(GetLastError()));
}
}
return success;
}
// Returns an empty string if either of CryptAcquireContext or CryptGenRandom
// fail.
std::string GenRandom::randomBytes(size_t numBytes) {
std::string ret(numBytes, '\0');
if (!fillBuffer(&ret[0], numBytes)) {
return std::string();
}
return ret;
}
std::wstring GenRandom::randomHexString(size_t numBytes) {
const std::string bytes = randomBytes(numBytes);
std::wstring ret(bytes.size() * 2, L'\0');
for (size_t i = 0; i < bytes.size(); ++i) {
static const wchar_t hex[] = L"0123456789abcdef";
ret[i * 2] = hex[static_cast<uint8_t>(bytes[i]) >> 4];
ret[i * 2 + 1] = hex[static_cast<uint8_t>(bytes[i]) & 0xF];
}
return ret;
}
// Returns a 64-bit value representing the number of 100-nanosecond intervals
// since January 1, 1601.
static uint64_t systemTimeAsUInt64() {
FILETIME monotonicTime = {};
GetSystemTimeAsFileTime(&monotonicTime);
return (static_cast<uint64_t>(monotonicTime.dwHighDateTime) << 32) |
static_cast<uint64_t>(monotonicTime.dwLowDateTime);
}
// Generates a unique and hard-to-guess case-insensitive string suitable for
// use in a pipe filename or a Windows object name.
std::wstring GenRandom::uniqueName() {
// First include enough information to avoid collisions assuming
// cooperative software. This code assumes that a process won't die and
// be replaced with a recycled PID within a single GetSystemTimeAsFileTime
// interval.
WStringBuilder sb(64);
sb << GetCurrentProcessId()
<< L'-' << InterlockedIncrement(&g_pipeCounter)
<< L'-' << whexOfInt(systemTimeAsUInt64());
// It isn't clear to me how the crypto APIs would fail. It *probably*
// doesn't matter that much anyway? In principle, a predictable pipe name
// is subject to a local denial-of-service attack.
auto random = randomHexString(16);
if (!random.empty()) {
sb << L'-' << random;
}
return sb.str_moved();
}
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