getentropy on Windows. It compiles but has not been thoroughly tested yet.

OK: beck@

src/lib/libcrypto/arc4random/getentropy_win.c

@@ -0,0 +1,56 @@
+/*	$OpenBSD: getentropy_win.c,v 1.1 2014/07/12 20:54:49 wouter Exp $	*/
+
+/*
+ * Copyright (c) 2014, Theo de Raadt <deraadt@openbsd.org> 
+ * Copyright (c) 2014, Bob Beck <beck@obtuse.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <windows.h>
+#include <errno.h>
+#include <stdint.h>
+#include <sys/types.h>
+#include <wincrypt.h>
+#include <process.h>
+
+int	getentropy(void *buf, size_t len);
+
+/*
+ * On Windows, CryptGenRandom is supposed to be a well-seeded
+ * cryptographically strong random number generator.
+ */
+int
+getentropy(void *buf, size_t len)
+{
+	HCRYPTPROV provider;
+
+	if (len > 256) {
+		errno = EIO;
+		return -1;
+	}
+
+	if (CryptAcquireContext(&provider, NULL, NULL, PROV_RSA_FULL,
+	    CRYPT_VERIFYCONTEXT) != 0)
+		goto fail;
+	if (CryptGenRandom(provider, len, buf) != 0) {
+		CryptReleaseContext(provider, 0);
+		goto fail;
+	}
+	CryptReleaseContext(provider, 0);
+	return (0);
+
+fail:
+	errno = EIO;
+	return (-1);
+}

src/lib/libcrypto/crypto/getentropy_win.c

@@ -0,0 +1,56 @@
+/*	$OpenBSD: getentropy_win.c,v 1.1 2014/07/12 20:54:49 wouter Exp $	*/
+
+/*
+ * Copyright (c) 2014, Theo de Raadt <deraadt@openbsd.org> 
+ * Copyright (c) 2014, Bob Beck <beck@obtuse.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <windows.h>
+#include <errno.h>
+#include <stdint.h>
+#include <sys/types.h>
+#include <wincrypt.h>
+#include <process.h>
+
+int	getentropy(void *buf, size_t len);
+
+/*
+ * On Windows, CryptGenRandom is supposed to be a well-seeded
+ * cryptographically strong random number generator.
+ */
+int
+getentropy(void *buf, size_t len)
+{
+	HCRYPTPROV provider;
+
+	if (len > 256) {
+		errno = EIO;
+		return -1;
+	}
+
+	if (CryptAcquireContext(&provider, NULL, NULL, PROV_RSA_FULL,
+	    CRYPT_VERIFYCONTEXT) != 0)
+		goto fail;
+	if (CryptGenRandom(provider, len, buf) != 0) {
+		CryptReleaseContext(provider, 0);
+		goto fail;
+	}
+	CryptReleaseContext(provider, 0);
+	return (0);
+
+fail:
+	errno = EIO;
+	return (-1);
+}