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/*
* Copyright (c) 1996, David Mazieres <dm@uun.org>
* Copyright (c) 2008, Damien Miller <djm@openbsd.org>
* Copyright (C) 2022 Apple Inc. All rights reserved.
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
/*
* Arc4 random number generator for OpenBSD.
*
* This code is derived from section 17.1 of Applied Cryptography,
* second edition, which describes a stream cipher allegedly
* compatible with RSA Labs "RC4" cipher (the actual description of
* which is a trade secret). The same algorithm is used as a stream
* cipher called "arcfour" in Tatu Ylonen's ssh package.
*
* RC4 is a registered trademark of RSA Laboratories.
*/
#include "config.h"
#include <wtf/CryptographicallyRandomNumber.h>
#include <array>
#include <mutex>
#include <wtf/IteratorRange.h>
#include <wtf/Lock.h>
#include <wtf/NeverDestroyed.h>
#include <wtf/OSRandomSource.h>
namespace WTF {
namespace {
class ARC4Stream {
WTF_MAKE_FAST_ALLOCATED;
public:
ARC4Stream();
uint8_t i { 0 };
uint8_t j { 0 };
std::array<uint8_t, 256> s;
};
class ARC4RandomNumberGenerator {
WTF_MAKE_FAST_ALLOCATED;
public:
ARC4RandomNumberGenerator() = default;
template<typename IntegerType>
IntegerType randomNumber();
void randomValues(std::span<uint8_t>);
private:
inline void addRandomData(std::span<const uint8_t, 128>);
void stir() WTF_REQUIRES_LOCK(m_lock);
void stirIfNeeded() WTF_REQUIRES_LOCK(m_lock);
inline uint8_t getByte() WTF_REQUIRES_LOCK(m_lock);
Lock m_lock;
ARC4Stream m_stream;
int m_count { 0 };
};
ARC4Stream::ARC4Stream()
{
for (unsigned n = 0; n < 256; ++n)
s[n] = n;
}
void ARC4RandomNumberGenerator::addRandomData(std::span<const uint8_t, 128> data)
{
--m_stream.i;
for (unsigned n = 0; n < 256; ++n) {
++m_stream.i;
uint8_t si = m_stream.s[m_stream.i];
m_stream.j += si + data[n % data.size()];
m_stream.s[m_stream.i] = m_stream.s[m_stream.j];
m_stream.s[m_stream.j] = si;
}
m_stream.j = m_stream.i;
}
void ARC4RandomNumberGenerator::stir()
{
std::array<uint8_t, 128> randomness;
cryptographicallyRandomValuesFromOS(randomness);
addRandomData(randomness);
// Discard early keystream, as per recommendations in:
// http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps
for (unsigned i = 0; i < 256; ++i)
getByte();
m_count = 1600000;
}
void ARC4RandomNumberGenerator::stirIfNeeded()
{
if (m_count <= 0)
stir();
}
uint8_t ARC4RandomNumberGenerator::getByte()
{
m_stream.i++;
uint8_t si = m_stream.s[m_stream.i];
m_stream.j += si;
uint8_t sj = m_stream.s[m_stream.j];
m_stream.s[m_stream.i] = sj;
m_stream.s[m_stream.j] = si;
return (m_stream.s[(si + sj) & 0xff]);
}
template<typename IntegerType>
IntegerType ARC4RandomNumberGenerator::randomNumber()
{
Locker locker { m_lock };
IntegerType val = 0;
for (unsigned i = 0; i < sizeof(IntegerType); ++i) {
m_count--;
stirIfNeeded();
val = (val << 8) | getByte();
}
return val;
}
void ARC4RandomNumberGenerator::randomValues(std::span<uint8_t> buffer)
{
Locker locker { m_lock };
for (auto& byte : WTF::makeReversedRange(buffer)) {
m_count--;
stirIfNeeded();
byte = getByte();
}
}
ARC4RandomNumberGenerator& sharedRandomNumberGenerator()
{
static LazyNeverDestroyed<ARC4RandomNumberGenerator> randomNumberGenerator;
static std::once_flag onceFlag;
std::call_once(
onceFlag,
[] {
randomNumberGenerator.construct();
});
return randomNumberGenerator;
}
}
template<> uint8_t cryptographicallyRandomNumber<uint8_t>()
{
return sharedRandomNumberGenerator().randomNumber<uint8_t>();
}
template<> unsigned cryptographicallyRandomNumber<unsigned>()
{
return sharedRandomNumberGenerator().randomNumber<unsigned>();
}
void cryptographicallyRandomValues(std::span<uint8_t> buffer)
{
sharedRandomNumberGenerator().randomValues(buffer);
}
template<> uint64_t cryptographicallyRandomNumber<uint64_t>()
{
return sharedRandomNumberGenerator().randomNumber<uint64_t>();
}
double cryptographicallyRandomUnitInterval()
{
return cryptographicallyRandomNumber<unsigned>() / (std::numeric_limits<unsigned>::max() + 1.0);
}
}
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