crypto: Refactor (P)RNG functionality into new crypto_rand module.

* ADD new /src/common/crypto_rand.[ch] module.
 * ADD new /src/common/crypto_util.[ch] module (contains the memwipe()
   function, since all crypto_* modules need this).
 * FIXES part of #24658: https://bugs.torproject.org/24658

src/ext/ed25519/donna/ed25519-randombytes-custom.h

@@ -8,7 +8,7 @@
 */
 
 /* Tor: Instead of calling OpenSSL's CSPRNG directly, call the wrapper. */
-#include "crypto.h"
+#include "crypto_rand.h"
 
 static void
 ED25519_FN(ed25519_randombytes_unsafe) (void *p, size_t len)

src/ext/ed25519/donna/ed25519_tor.c

@@ -40,6 +40,8 @@
 #include "ed25519-randombytes.h"
 #include "ed25519-hash.h"
 
+#include "crypto_util.h"
+
 typedef unsigned char ed25519_signature[64];
 typedef unsigned char ed25519_public_key[32];
 typedef unsigned char ed25519_secret_key[32];

src/ext/ed25519/ref10/blinding.c

@@ -7,7 +7,7 @@
 #include "ed25519_ref10.h"
 
 #include <string.h>
-#include "crypto.h"
+#include "crypto_util.h"
 
 static void
 ed25519_ref10_gettweak(unsigned char *out, const unsigned char *param)

src/ext/ed25519/ref10/keypair.c

@@ -6,6 +6,9 @@
 #include "crypto_hash_sha512.h"
 #include "ge.h"
 
+#include "crypto_rand.h"
+#include "crypto_util.h"
+
 int
 crypto_sign_seckey(unsigned char *sk)
 {

src/ext/keccak-tiny/keccak-tiny-unrolled.c

@@ -9,7 +9,7 @@
 #include "keccak-tiny.h"
 
 #include <string.h>
-#include "crypto.h"
+#include "crypto_util.h"
 #include "byteorder.h"
 
 /******** Endianness conversion helpers ********/