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/*
* Copyright (c) 1996, David Mazieres <dm@uun.org>
* Copyright (c) 2008, Damien Miller <djm@openbsd.org>
*
* 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 "CryptographicallyRandomNumber.h"
#include "NeverDestroyed.h"
#include "OSRandomSource.h"
#include "ThreadingPrimitives.h"
namespace WTF {
namespace {
class ARC4Stream {
public:
ARC4Stream();
uint8_t i;
uint8_t j;
uint8_t s[256];
};
class ARC4RandomNumberGenerator {
WTF_MAKE_FAST_ALLOCATED;
public:
ARC4RandomNumberGenerator();
uint32_t randomNumber();
void randomValues(void* buffer, size_t length);
private:
inline void addRandomData(unsigned char *data, int length);
void stir();
void stirIfNeeded();
inline uint8_t getByte();
inline uint32_t getWord();
ARC4Stream m_stream;
int m_count;
Mutex m_mutex;
};
ARC4Stream::ARC4Stream()
{
for (int n = 0; n < 256; n++)
s[n] = n;
i = 0;
j = 0;
}
ARC4RandomNumberGenerator::ARC4RandomNumberGenerator()
: m_count(0)
{
}
void ARC4RandomNumberGenerator::addRandomData(unsigned char* data, int length)
{
m_stream.i--;
for (int n = 0; n < 256; n++) {
m_stream.i++;
uint8_t si = m_stream.s[m_stream.i];
m_stream.j += si + data[n % length];
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()
{
unsigned char randomness[128];
size_t length = sizeof(randomness);
cryptographicallyRandomValuesFromOS(randomness, length);
addRandomData(randomness, length);
// Discard early keystream, as per recommendations in:
// http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps
for (int 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]);
}
uint32_t ARC4RandomNumberGenerator::getWord()
{
uint32_t val;
val = getByte() << 24;
val |= getByte() << 16;
val |= getByte() << 8;
val |= getByte();
return val;
}
uint32_t ARC4RandomNumberGenerator::randomNumber()
{
MutexLocker locker(m_mutex);
m_count -= 4;
stirIfNeeded();
return getWord();
}
void ARC4RandomNumberGenerator::randomValues(void* buffer, size_t length)
{
MutexLocker locker(m_mutex);
unsigned char* result = reinterpret_cast<unsigned char*>(buffer);
stirIfNeeded();
while (length--) {
m_count--;
stirIfNeeded();
result[length] = getByte();
}
}
ARC4RandomNumberGenerator& sharedRandomNumberGenerator()
{
static NeverDestroyed<ARC4RandomNumberGenerator> randomNumberGenerator;
return randomNumberGenerator;
}
}
uint32_t cryptographicallyRandomNumber()
{
return sharedRandomNumberGenerator().randomNumber();
}
void cryptographicallyRandomValues(void* buffer, size_t length)
{
sharedRandomNumberGenerator().randomValues(buffer, length);
}
}
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