Fix numerous problems with Tor's weak RNG.

We need a weak RNG in a couple of places where the strong RNG is
both needless and too slow.  We had been using the weak RNG from our
platform's libc implementation, but that was problematic (because
many platforms have exceptionally horrible weak RNGs -- like, ones
that only return values between 0 and SHORT_MAX) and because we were
using it in a way that was wrong for LCG-based weak RNGs.  (We were
counting on the low bits of the LCG output to be as random as the
high ones, which isn't true.)

This patch adds a separate type for a weak RNG, adds an LCG
implementation for it, and uses that exclusively where we had been
using the platform weak RNG.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/common/crypto.h b/src/common/crypto.h
index 08efc801d..12fcfae27 100644
--- a/src/common/crypto.h
+++ b/src/common/crypto.h
@@ -256,6 +256,8 @@ int crypto_strongest_rand(uint8_t *out, size_t out_len);
 int crypto_rand_int(unsigned int max);
 uint64_t crypto_rand_uint64(uint64_t max);
 double crypto_rand_double(void);
+struct tor_weak_rng_t;
+void crypto_seed_weak_rng(struct tor_weak_rng_t *rng);
 
 char *crypto_random_hostname(int min_rand_len, int max_rand_len,
                              const char *prefix, const char *suffix);