Fix MS-Windows build broken by a botched merge from emacs-25

* src/w32.c (w32_crypto_hprov): New static variable.
(globals_of_w32): Initialize w32_crypto_hprov.
(w32_init_crypt_random, w32_init_random): New functions.
Include wincrypt.h.
* src/w32.h (w32_init_random): Add prototype.

2 files changed, 35 insertions, 0 deletions

diff --git a/src/w32.c b/src/w32.c
index 183a4e7e9d9..6f1d5fd1698 100644
--- a/src/w32.c
+++ b/src/w32.c
@@ -224,6 +224,8 @@ typedef struct _REPARSE_DATA_BUFFER {
 
 #include <iphlpapi.h>   /* should be after winsock2.h */
 
+#include <wincrypt.h>
+
 #include <c-strcase.h>
 
 #include "w32.h"
@@ -2094,6 +2096,34 @@ init_user_info (void)
     CloseHandle (token);
 }
 
+static HCRYPTPROV w32_crypto_hprov;
+static int
+w32_init_crypt_random (void)
+{
+  if (!CryptAcquireContext (&w32_crypto_hprov, NULL, NULL, PROV_RSA_FULL,
+                            CRYPT_VERIFYCONTEXT | CRYPT_SILENT))
+    {
+      DebPrint (("CryptAcquireContext failed with error %x\n",
+                 GetLastError ()));
+      w32_crypto_hprov = 0;
+      return -1;
+    }
+  return 0;
+}
+
+int
+w32_init_random (void *buf, ptrdiff_t buflen)
+{
+  if (!w32_crypto_hprov)
+    w32_init_crypt_random ();
+  if (w32_crypto_hprov)
+    {
+      if (CryptGenRandom (w32_crypto_hprov, buflen, (BYTE *)buf))
+        return 0;
+    }
+  return -1;
+}
+
 int
 random (void)
 {
@@ -9417,6 +9447,8 @@ globals_of_w32 (void)
   extern void dynlib_reset_last_error (void);
   dynlib_reset_last_error ();
 #endif
+
+  w32_crypto_hprov = (HCRYPTPROV)0;
 }
 
 /* For make-serial-process  */
diff --git a/src/w32.h b/src/w32.h
index 097241b1b8f..fde3803c739 100644
--- a/src/w32.h
+++ b/src/w32.h
@@ -223,6 +223,9 @@ extern int w32_memory_info (unsigned long long *, unsigned long long *,
 /* Compare 2 UTF-8 strings in locale-dependent fashion.  */
 extern int w32_compare_strings (const char *, const char *, char *, int);
 
+/* Return a cryptographically secure seed for PRNG.  */
+extern int w32_init_random (void *, ptrdiff_t);
+
 #ifdef HAVE_GNUTLS
 #include <gnutls/gnutls.h>