Been meaning to get round to this for a while: use CryptGenRandom to

gather extra entropy at Windows PuTTY startup time. (It's only used as
one of the inputs to PuTTY's internal entropy pool, so nobody is
required to trust it.)

git-svn-id: svn://svn.tartarus.org/sgt/putty@9941 cda61777-01e9-0310-a592-d414129be87e

diff --git a/windows/winnoise.c b/windows/winnoise.c
index affb1a5..3136454 100644 (file)
--- a/windows/winnoise.c
+++ b/windows/winnoise.c
@@ -9,10 +9,18 @@
 #include "ssh.h"
 #include "storage.h"
 
+#include <wincrypt.h>
+
+DECL_WINDOWS_FUNCTION(static, BOOL, CryptAcquireContextA,
+                      (HCRYPTPROV *, LPCTSTR, LPCTSTR, DWORD, DWORD));
+DECL_WINDOWS_FUNCTION(static, BOOL, CryptGenRandom,
+                      (HCRYPTPROV, DWORD, BYTE *));
+DECL_WINDOWS_FUNCTION(static, BOOL, CryptReleaseContext,
+                      (HCRYPTPROV, DWORD));
+static HMODULE wincrypt_module = NULL;
+
 /*
- * This function is called once, at PuTTY startup, and will do some
- * seriously silly things like listing directories and getting disk
- * free space and a process snapshot.
+ * This function is called once, at PuTTY startup.
  */
 
 void noise_get_heavy(void (*func) (void *, int))
@@ -20,6 +28,7 @@ void noise_get_heavy(void (*func) (void *, int))
     HANDLE srch;
     WIN32_FIND_DATA finddata;
     DWORD pid;
+    HCRYPTPROV crypt_provider;
     char winpath[MAX_PATH + 3];
 
     GetWindowsDirectory(winpath, sizeof(winpath));
@@ -35,6 +44,24 @@ void noise_get_heavy(void (*func) (void *, int))
     pid = GetCurrentProcessId();
     func(&pid, sizeof(pid));
 
+    if (!wincrypt_module) {
+        wincrypt_module = load_system32_dll("advapi32.dll");
+        GET_WINDOWS_FUNCTION(wincrypt_module, CryptAcquireContextA);
+        GET_WINDOWS_FUNCTION(wincrypt_module, CryptGenRandom);
+        GET_WINDOWS_FUNCTION(wincrypt_module, CryptReleaseContext);
+    }
+
+    if (wincrypt_module && p_CryptAcquireContextA &&
+        p_CryptGenRandom && p_CryptReleaseContext &&
+        p_CryptAcquireContextA(&crypt_provider, NULL, NULL, PROV_RSA_FULL,
+                               CRYPT_VERIFYCONTEXT)) {
+        BYTE buf[32];
+        if (p_CryptGenRandom(crypt_provider, 32, buf)) {
+            func(buf, sizeof(buf));
+        }
+        p_CryptReleaseContext(crypt_provider, 0);
+    }
+
     read_random_seed(func);
     /* Update the seed immediately, in case another instance uses it. */
     random_save_seed();