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/* vi: set sw=4 ts=4:
*
* Copyright (C) 2015 Christian Hohnstaedt.
*
* All rights reserved.
*/
#include <stdio.h>
#include <QtGlobal>
#if !defined(Q_OS_WIN32)
#include <unistd.h>
#include <fcntl.h>
#endif
#include <QDir>
#include <QDebug>
#include <openssl/rand.h>
#include "func.h"
#include "xfile.h"
#include "entropy.h"
/* Entropy sources for XCA
*
* Entropy is a very important topic for key generation.
*
* XCA uses the following sources for entropy:
*
* 1) During startup
* RAND_poll()
* The OpenSSL seeding mechanism.
* It uses /dev/urandom where possible and the
* Screen content on Windows.
*
* If "/dev/random" exists, it will be used for additional
* 256bit entropy. Same is true for "/dev/hwrng"
*
* 2) Before any key or parameter generation a "reseeding"
* is done. Some say reseeding is not necessary, but
* all say it does not harm.
*
* Entropy by Mouse and keyboard events
* main.cpp: bool XcaApplication::eventFilter()
* 256bit from /dev/urandom (unix/Mac)
*
* 3) A .rnd state file in the XCA application directory
* is written on exit and read on startup.
* After reading it, the file will be erased to avoid replays.
*
* 4) When managing a token that supports C_GenerateRandom
* and C_SeedRandom, XCA will seed the token and in return
* seed himself from the token.
*/
#undef DEBUG_ENTROPY
#define pool_siz (sizeof(pool)/sizeof(pool[0]))
unsigned char Entropy::pool[512];
unsigned Entropy::pool_pos = 0;
QElapsedTimer Entropy::timer;
unsigned Entropy::seed_strength = 0;
QString Entropy::makeSalt(void)
{
QString s = "T";
unsigned char rand[8];
Entropy::get(rand, sizeof rand);
for (unsigned i=0; i< sizeof rand; i++)
s += QString("%1").arg(rand[i], 2, 16, QChar('0'));
return s;
}
void Entropy::add(int rand)
{
unsigned char entropy = (rand ^ timer.elapsed()) & 0xff;
pool[pool_pos++ % pool_siz] = entropy;
}
void Entropy::add_buf(const unsigned char *buf, int buflen)
{
RAND_seed(buf, buflen);
seed_strength += buflen;
}
int Entropy::get(unsigned char *buf, int num)
{
seed_rng();
return RAND_bytes(buf, num);
}
void Entropy::seed_rng()
{
if (pool_pos > pool_siz)
pool_pos = pool_siz;
RAND_seed(pool, pool_pos);
seed_strength += pool_pos;
random_from_file("/dev/urandom", 32);
#ifdef DEBUG_ENTROPY
{
QDebug dbg = qDebug();
dbg << QString("Seeding %1 bytes:").arg(pool_pos);
for (unsigned i=0; i<pool_pos; i++)
dbg << pool[i];
}
qDebug("Entropy strength: %d", seed_strength);
#endif
pool_pos = 0;
}
int Entropy::random_from_file(QString fname, unsigned amount, int weakness)
{
#if !defined(Q_OS_WIN32)
char buf[256];
int fd, sum;
/* OpenSSL: RAND_load_file() is blocking
* and does not support wchar_t */
XFile file(fname);
try {
file.open_read();
} catch (errorEx &e) {
qDebug() << "random_from_file" << fname << e.getString();
return 0;
}
fd = file.handle();
if (fd == -1)
return 0;
if (fcntl(fd, F_SETFL, O_NONBLOCK) == -1)
return 0;
for (sum=0; amount > 0;) {
int len = read(fd, buf, amount > sizeof buf ?
sizeof buf : amount);
if (len > 0) {
RAND_seed(buf, len);
seed_strength += len / weakness;
amount -= len;
sum += len;
}
if (len == -1) {
if (errno != EWOULDBLOCK)
qWarning("Error '%s' while reading '%s'\n",
strerror(errno), CCHAR(fname));
len = 0;
}
if (len == 0)
break;
}
#ifdef DEBUG_ENTROPY
qDebug("Entropy from file '%s' = %d bytes", CCHAR(fname), sum);
#endif
return sum;
#else
(void)fname;
(void)amount;
(void)weakness;
return 0;
#endif
}
unsigned Entropy::strength()
{
return seed_strength;
}
Entropy::Entropy()
{
timer.start();
rnd = getUserSettingsDir() + "/.rnd";
random_from_file(rnd, 1024, 128);
QFile::remove(rnd); // don't use it again
RAND_poll();
seed_strength += 8;
random_from_file("/dev/random", 32);
random_from_file("/dev/hwrng", 32);
}
Entropy::~Entropy()
{
unsigned char buf[1024];
if (RAND_bytes(buf, sizeof buf) == 1) {
XFile file(rnd);
try {
file.open_key();
file.write((char*)buf, sizeof buf);
} catch (errorEx &e) {
qDebug() << "random_from_file" << rnd
<< e.getString();
}
file.close();
}
memset(buf, 0, sizeof buf);
#ifdef DEBUG_ENTROPY
qDebug("Seed strength: %d", seed_strength);
#endif
}
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