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/*-------------------------------------------------------------------------
*
* pg_strong_random.c
* pg_strong_random() function to return a strong random number
*
* Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
*
*
* IDENTIFICATION
* src/port/pg_strong_random.c
*
*-------------------------------------------------------------------------
*/
#ifndef FRONTEND
#include "postgres.h"
#else
#include "postgres_fe.h"
#endif
#include <fcntl.h>
#include <unistd.h>
#ifdef USE_SSL
#include <openssl/rand.h>
#endif
#ifdef WIN32
#include <Wincrypt.h>
#endif
static bool random_from_file(char *filename, void *buf, size_t len);
#ifdef WIN32
/*
* Cache a global crypto provider that only gets freed when the process
* exits, in case we need random numbers more than once.
*/
static HCRYPTPROV hProvider = 0;
#endif
/*
* Read (random) bytes from a file.
*/
static bool
random_from_file(char *filename, void *buf, size_t len)
{
int f;
char *p = buf;
ssize_t res;
f = open(filename, O_RDONLY, 0);
if (f == -1)
return false;
while (len)
{
res = read(f, p, len);
if (res <= 0)
{
if (errno == EINTR)
continue; /* interrupted by signal, just retry */
close(f);
return false;
}
p += res;
len -= res;
}
close(f);
return true;
}
/*
* pg_strong_random
*
* Generate requested number of random bytes. The bytes are
* cryptographically strong random, suitable for use e.g. in key
* generation.
*
* The bytes can be acquired from a number of sources, depending
* on what's available. We try the following, in this order:
*
* 1. OpenSSL's RAND_bytes()
* 2. Windows' CryptGenRandom() function
* 3. /dev/urandom
* 4. /dev/random
*
* Returns true on success, and false if none of the sources
* were available. NB: It is important to check the return value!
* Proceeding with key generation when no random data was available
* would lead to predictable keys and security issues.
*/
bool
pg_strong_random(void *buf, size_t len)
{
#ifdef USE_SSL
/*
* When built with OpenSSL, first try the random generation function from
* there.
*/
if (RAND_bytes(buf, len) == 1)
return true;
#endif
#ifdef WIN32
/*
* Windows has CryptoAPI for strong cryptographic numbers.
*/
if (hProvider == 0)
{
if (!CryptAcquireContext(&hProvider,
NULL,
MS_DEF_PROV,
PROV_RSA_FULL,
CRYPT_VERIFYCONTEXT | CRYPT_SILENT))
{
/*
* On failure, set back to 0 in case the value was for some reason
* modified.
*/
hProvider = 0;
}
}
/* Re-check in case we just retrieved the provider */
if (hProvider != 0)
{
if (CryptGenRandom(hProvider, len, buf))
return true;
}
#endif
/*
* If there is no OpenSSL and no CryptoAPI (or they didn't work), then
* fall back on reading /dev/urandom or even /dev/random.
*/
if (random_from_file("/dev/urandom", buf, len))
return true;
if (random_from_file("/dev/random", buf, len))
return true;
/* None of the sources were available. */
return false;
}
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