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random.c
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#include "Python.h"
#ifdef MS_WINDOWS
#include <windows.h>
#else
#include <fcntl.h>
#endif
#ifdef Py_DEBUG
int _Py_HashSecret_Initialized = 0;
#else
static int _Py_HashSecret_Initialized = 0;
#endif
#ifdef MS_WINDOWS
typedef BOOL (WINAPI *CRYPTACQUIRECONTEXTA)(HCRYPTPROV *phProv,\
LPCSTR pszContainer, LPCSTR pszProvider, DWORD dwProvType,\
DWORD dwFlags );
typedef BOOL (WINAPI *CRYPTGENRANDOM)(HCRYPTPROV hProv, DWORD dwLen,\
BYTE *pbBuffer );
static CRYPTGENRANDOM pCryptGenRandom = NULL;
/* This handle is never explicitly released. Instead, the operating
system will release it when the process terminates. */
static HCRYPTPROV hCryptProv = 0;
static int
win32_urandom_init(int raise)
{
HINSTANCE hAdvAPI32 = NULL;
CRYPTACQUIRECONTEXTA pCryptAcquireContext = NULL;
/* Obtain handle to the DLL containing CryptoAPI. This should not fail. */
hAdvAPI32 = GetModuleHandle("advapi32.dll");
if(hAdvAPI32 == NULL)
goto error;
/* Obtain pointers to the CryptoAPI functions. This will fail on some early
versions of Win95. */
pCryptAcquireContext = (CRYPTACQUIRECONTEXTA)GetProcAddress(
hAdvAPI32, "CryptAcquireContextA");
if (pCryptAcquireContext == NULL)
goto error;
pCryptGenRandom = (CRYPTGENRANDOM)GetProcAddress(hAdvAPI32,
"CryptGenRandom");
if (pCryptGenRandom == NULL)
goto error;
/* Acquire context */
if (! pCryptAcquireContext(&hCryptProv, NULL, NULL,
PROV_RSA_FULL, CRYPT_VERIFYCONTEXT))
goto error;
return 0;
error:
if (raise)
PyErr_SetFromWindowsErr(0);
else
Py_FatalError("Failed to initialize Windows random API (CryptoGen)");
return -1;
}
/* Fill buffer with size pseudo-random bytes generated by the Windows CryptoGen
API. Return 0 on success, or -1 on error. */
static int
win32_urandom(unsigned char *buffer, Py_ssize_t size, int raise)
{
Py_ssize_t chunk;
if (hCryptProv == 0)
{
if (win32_urandom_init(raise) == -1)
return -1;
}
while (size > 0)
{
chunk = size > INT_MAX ? INT_MAX : size;
if (!pCryptGenRandom(hCryptProv, chunk, buffer))
{
/* CryptGenRandom() failed */
if (raise)
PyErr_SetFromWindowsErr(0);
else
Py_FatalError("Failed to initialized the randomized hash "
"secret using CryptoGen)");
return -1;
}
buffer += chunk;
size -= chunk;
}
return 0;
}
#endif /* MS_WINDOWS */
#ifdef __VMS
/* Use openssl random routine */
#include <openssl/rand.h>
static int
vms_urandom(unsigned char *buffer, Py_ssize_t size, int raise)
{
if (RAND_pseudo_bytes(buffer, size) < 0) {
if (raise) {
PyErr_Format(PyExc_ValueError,
"RAND_pseudo_bytes");
} else {
Py_FatalError("Failed to initialize the randomized hash "
"secret using RAND_pseudo_bytes");
}
return -1;
}
return 0;
}
#endif /* __VMS */
#if !defined(MS_WINDOWS) && !defined(__VMS)
/* Read size bytes from /dev/urandom into buffer.
Call Py_FatalError() on error. */
static void
dev_urandom_noraise(char *buffer, Py_ssize_t size)
{
int fd;
Py_ssize_t n;
assert (0 < size);
fd = open("/dev/urandom", O_RDONLY);
if (fd < 0)
Py_FatalError("Failed to open /dev/urandom");
while (0 < size)
{
do {
n = read(fd, buffer, (size_t)size);
} while (n < 0 && errno == EINTR);
if (n <= 0)
{
/* stop on error or if read(size) returned 0 */
Py_FatalError("Failed to read bytes from /dev/urandom");
break;
}
buffer += n;
size -= (Py_ssize_t)n;
}
close(fd);
}
/* Read size bytes from /dev/urandom into buffer.
Return 0 on success, raise an exception and return -1 on error. */
static int
dev_urandom_python(char *buffer, Py_ssize_t size)
{
int fd;
Py_ssize_t n;
if (size <= 0)
return 0;
Py_BEGIN_ALLOW_THREADS
fd = open("/dev/urandom", O_RDONLY);
Py_END_ALLOW_THREADS
if (fd < 0)
{
if (errno == ENOENT || errno == ENXIO ||
errno == ENODEV || errno == EACCES)
PyErr_SetString(PyExc_NotImplementedError,
"/dev/urandom (or equivalent) not found");
else
PyErr_SetFromErrno(PyExc_OSError);
return -1;
}
Py_BEGIN_ALLOW_THREADS
do {
do {
n = read(fd, buffer, (size_t)size);
} while (n < 0 && errno == EINTR);
if (n <= 0)
break;
buffer += n;
size -= (Py_ssize_t)n;
} while (0 < size);
Py_END_ALLOW_THREADS
if (n <= 0)
{
/* stop on error or if read(size) returned 0 */
if (n < 0)
PyErr_SetFromErrno(PyExc_OSError);
else
PyErr_Format(PyExc_RuntimeError,
"Failed to read %zi bytes from /dev/urandom",
size);
close(fd);
return -1;
}
close(fd);
return 0;
}
#endif /* !defined(MS_WINDOWS) && !defined(__VMS) */
/* Fill buffer with pseudo-random bytes generated by a linear congruent
generator (LCG):
x(n+1) = (x(n) * 214013 + 2531011) % 2^32
Use bits 23..16 of x(n) to generate a byte. */
static void
lcg_urandom(unsigned int x0, unsigned char *buffer, size_t size)
{
size_t index;
unsigned int x;
x = x0;
for (index=0; index < size; index++) {
x *= 214013;
x += 2531011;
/* modulo 2 ^ (8 * sizeof(int)) */
buffer[index] = (x >> 16) & 0xff;
}
}
/* Fill buffer with size pseudo-random bytes from the operating system random
number generator (RNG). It is suitable for for most cryptographic purposes
except long living private keys for asymmetric encryption.
Return 0 on success, raise an exception and return -1 on error. */
int
_PyOS_URandom(void *buffer, Py_ssize_t size)
{
if (size < 0) {
PyErr_Format(PyExc_ValueError,
"negative argument not allowed");
return -1;
}
if (size == 0)
return 0;
#ifdef MS_WINDOWS
return win32_urandom((unsigned char *)buffer, size, 1);
#else
# ifdef __VMS
return vms_urandom((unsigned char *)buffer, size, 1);
# else
return dev_urandom_python((char*)buffer, size);
# endif
#endif
}
void
_PyRandom_Init(void)
{
char *env;
void *secret = &_Py_HashSecret;
Py_ssize_t secret_size = sizeof(_Py_HashSecret_t);
if (_Py_HashSecret_Initialized)
return;
_Py_HashSecret_Initialized = 1;
/*
Hash randomization is enabled. Generate a per-process secret,
using PYTHONHASHSEED if provided.
*/
env = Py_GETENV("PYTHONHASHSEED");
if (env && *env != '\0' && strcmp(env, "random") != 0) {
char *endptr = env;
unsigned long seed;
seed = strtoul(env, &endptr, 10);
if (*endptr != '\0'
|| seed > 4294967295UL
|| (errno == ERANGE && seed == ULONG_MAX))
{
Py_FatalError("PYTHONHASHSEED must be \"random\" or an integer "
"in range [0; 4294967295]");
}
if (seed == 0) {
/* disable the randomized hash */
memset(secret, 0, secret_size);
}
else {
lcg_urandom(seed, (unsigned char*)secret, secret_size);
}
}
else {
#ifdef MS_WINDOWS
(void)win32_urandom((unsigned char *)secret, secret_size, 0);
#else /* #ifdef MS_WINDOWS */
# ifdef __VMS
vms_urandom((unsigned char *)secret, secret_size, 0);
# else
dev_urandom_noraise((char*)secret, secret_size);
# endif
#endif
}
}