SecureRandom should try /dev/urandom first [Bug #9569]

	* random.c (InitVM_Random): rename Random.raw_seed to
	  Random.urandom.  A quick search seems there are no practical use
	  of this method than securerandom.rb so I think it's OK to rename
	  but if there are users of it, this hunk is subject to revert.

	* test/ruby/test_rand.rb (TestRand#test_urandom): test for it.

	* lib/securerandom.rb (SecureRandom.gen_random): Prefer OS-
	  provided CSPRNG if available. Otherwise falls back to OpenSSL.
	  Current preference is:

	  1. CSPRNG routine that the OS has; one of
	     - getrandom(2),
	     - arc4random(3), or
	     - CryptGenRandom()
	  2. /dev/urandom device
	  3. OpenSSL's RAND_bytes(3)

	  If none of above random number generators are available, you
	  cannot use this module.  An exception is raised that case.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57384 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 11 insertions, 4 deletions

diff --git a/random.c b/random.c
index ddbbeedf92..6555cc54ad 100644
--- a/random.c
+++ b/random.c
@@ -603,11 +603,18 @@ random_seed(void)
 }
 
 /*
- * call-seq: Random.raw_seed(size) -> string
+ * call-seq: Random.urandom(size) -> string
  *
- * Returns a raw seed string, using platform providing features.
+ * Returns a string, using platform providing features.
+ * Returned value expected to be a cryptographically secure
+ * pseudo-random number in binary form.
  *
- *   Random.raw_seed(8)  #=> "\x78\x41\xBA\xAF\x7D\xEA\xD8\xEA"
+ * In 2017, Linux manpage random(7) writes that "no cryptographic
+ * primitive available today can hope to promise more than 256 bits of
+ * security".  So it might be questionable to pass size > 32 to this
+ * method.
+ *
+ *   Random.urandom(8)  #=> "\x78\x41\xBA\xAF\x7D\xEA\xD8\xEA"
  */
 static VALUE
 random_raw_seed(VALUE self, VALUE size)
@@ -1616,7 +1623,7 @@ InitVM_Random(void)
     rb_define_singleton_method(rb_cRandom, "srand", rb_f_srand, -1);
     rb_define_singleton_method(rb_cRandom, "rand", random_s_rand, -1);
     rb_define_singleton_method(rb_cRandom, "new_seed", random_seed, 0);
-    rb_define_singleton_method(rb_cRandom, "raw_seed", random_raw_seed, 1);
+    rb_define_singleton_method(rb_cRandom, "urandom", random_raw_seed, 1);
     rb_define_private_method(CLASS_OF(rb_cRandom), "state", random_s_state, 0);
     rb_define_private_method(CLASS_OF(rb_cRandom), "left", random_s_left, 0);