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/* fhandler_random.cc: code to access /dev/random and /dev/urandom
Copyright 2000, 2001 Red Hat, Inc.
Written by Corinna Vinschen (vinschen@cygnus.com)
This file is part of Cygwin.
This software is a copyrighted work licensed under the terms of the
Cygwin license. Please consult the file "CYGWIN_LICENSE" for
details. */
#include "winsup.h"
#include <errno.h>
#include <limits.h>
#include "cygerrno.h"
#include "security.h"
#include "fhandler.h"
#define RANDOM 8
#define URANDOM 9
#define PSEUDO_MULTIPLIER (6364136223846793005LL)
#define PSEUDO_SHIFTVAL (21)
fhandler_dev_random::fhandler_dev_random (const char *name, int nunit)
: fhandler_base (FH_RANDOM, name),
unit(nunit),
crypt_prov((HCRYPTPROV)NULL)
{
set_cb (sizeof *this);
}
int
fhandler_dev_random::open (path_conv *, int flags, mode_t)
{
set_flags (flags);
set_open_status ();
return 1;
}
BOOL
fhandler_dev_random::crypt_gen_random (void *ptr, size_t len)
{
if (!crypt_prov
&& !CryptAcquireContext (&crypt_prov, NULL, MS_DEF_PROV, PROV_RSA_FULL,
CRYPT_VERIFYCONTEXT | CRYPT_MACHINE_KEYSET)
&& !CryptAcquireContext (&crypt_prov, NULL, MS_DEF_PROV, PROV_RSA_FULL,
CRYPT_VERIFYCONTEXT | CRYPT_MACHINE_KEYSET
| CRYPT_NEWKEYSET))
{
debug_printf ("%E = CryptAquireContext()");
return FALSE;
}
if (!CryptGenRandom (crypt_prov, len, (BYTE *)ptr))
{
debug_printf ("%E = CryptGenRandom()");
return FALSE;
}
return TRUE;
}
int
fhandler_dev_random::pseudo_write (const void *ptr, size_t len)
{
/* Use buffer to mess up the pseudo random number generator. */
for (size_t i = 0; i < len; ++i)
pseudo = (pseudo + ((unsigned char *)ptr)[i]) * PSEUDO_MULTIPLIER + 1;
return len;
}
int
fhandler_dev_random::write (const void *ptr, size_t len)
{
if (!len)
return 0;
if (!ptr)
{
set_errno (EINVAL);
return -1;
}
/* Limit len to a value <= 512 since we don't want to overact.
Copy to local buffer because CryptGenRandom violates const. */
unsigned char buf[512];
size_t limited_len = len <= 512 ? len : 512;
memcpy (buf, ptr, limited_len);
/* Mess up system entropy source. Return error if device is /dev/random. */
if (!crypt_gen_random (buf, limited_len) && unit == RANDOM)
{
__seterrno ();
return -1;
}
/* Mess up the pseudo random number generator. */
pseudo_write (buf, limited_len);
return len;
}
int
fhandler_dev_random::pseudo_read (void *ptr, size_t len)
{
/* Use pseudo random number generator as fallback entropy source.
This multiplier was obtained from Knuth, D.E., "The Art of
Computer Programming," Vol 2, Seminumerical Algorithms, Third
Edition, Addison-Wesley, 1998, p. 106 (line 26) & p. 108 */
for (size_t i = 0; i < len; ++i)
{
pseudo = pseudo * PSEUDO_MULTIPLIER + 1;
((unsigned char *)ptr)[i] = (pseudo >> PSEUDO_SHIFTVAL) & UCHAR_MAX;
}
return len;
}
int
fhandler_dev_random::read (void *ptr, size_t len)
{
if (!len)
return 0;
if (!ptr)
{
set_errno (EINVAL);
return -1;
}
if (crypt_gen_random (ptr, len))
return len;
/* If device is /dev/urandom, use pseudo number generator as fallback.
Don't do this for /dev/random since it's intended for uses that need
very high quality randomness. */
if (unit == URANDOM)
return pseudo_read (ptr, len);
__seterrno ();
return -1;
}
off_t
fhandler_dev_random::lseek (off_t, int)
{
return 0;
}
int
fhandler_dev_random::close (void)
{
if (crypt_prov)
while (!CryptReleaseContext (crypt_prov, 0)
&& GetLastError () == ERROR_BUSY)
Sleep(10);
return 0;
}
int
fhandler_dev_random::dup (fhandler_base *child)
{
fhandler_dev_random *fhr = (fhandler_dev_random *) child;
fhr->unit = unit;
fhr->crypt_prov = (HCRYPTPROV)NULL;
return 0;
}
void
fhandler_dev_random::dump ()
{
paranoid_printf("here, fhandler_dev_random");
}
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