From 9602ffc30b29e48544c3d947367e118ad8c61c92 Mon Sep 17 00:00:00 2001
From: Corinna Vinschen <corinna@vinschen.de>
Date: Mon, 24 Jul 2000 11:33:02 +0000
Subject:         * fhandler.h (class fhandler_dev_random): Add members for
 managing         pseudo randomness.         * fhandler_random.cc: Rearrange.
 Use pseudo random number generator         as entropy source if system
 entropy isn't available and if device is         used as /dev/urandom. Allow
 initializing device by calling write().

---
 winsup/cygwin/fhandler_random.cc | 93 +++++++++++++++++++++++++++++++++++-----
 1 file changed, 82 insertions(+), 11 deletions(-)

(limited to 'winsup/cygwin/fhandler_random.cc')

diff --git a/winsup/cygwin/fhandler_random.cc b/winsup/cygwin/fhandler_random.cc
index 9b784a853..9991c3b7e 100644
--- a/winsup/cygwin/fhandler_random.cc
+++ b/winsup/cygwin/fhandler_random.cc
@@ -1,4 +1,4 @@
-/* fhandler_dev_random.cc: code to access /dev/random
+/* fhandler_dev_random.cc: code to access /dev/random and /dev/urandom
 
    Copyright 2000 Cygnus Solutions.
 
@@ -11,11 +11,15 @@ Cygwin license.  Please consult the file "CYGWIN_LICENSE" for
 details. */
 
 #include <errno.h>
+#include <limits.h>
 #include "winsup.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),
@@ -31,35 +35,102 @@ fhandler_dev_random::open (const char *, int flags, mode_t)
   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::write (const void *, size_t len)
+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::read (void *ptr, size_t len)
+fhandler_dev_random::write (const void *ptr, size_t len)
 {
   if (!len)
     return 0;
-  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 ))
+  if (!ptr)
     {
-      __seterrno ();
+      set_errno (EINVAL);
       return -1;
     }
-  if (!CryptGenRandom (crypt_prov, len, (BYTE *)ptr))
+
+  /* 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)
 {
-- 
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