Implement and test probability distributions used by WTF-PAD.

This project introduces the prob_distr.c subsystem which implements all the
probability distributions that WTF-PAD needs. It also adds unittests for all of
them.

Code and tests courtesy of Riastradh.

Co-authored-by: Taylor R Campbell <campbell+tor@mumble.net>
Co-authored-by: Mike Perry <mikeperry-git@torproject.org>

2 files changed, 12 insertions, 0 deletions

diff --git a/src/lib/crypt_ops/crypto_rand.c b/src/lib/crypt_ops/crypto_rand.c
index cffd0610f3..7a2c417e5a 100644
--- a/src/lib/crypt_ops/crypto_rand.c
+++ b/src/lib/crypt_ops/crypto_rand.c
@@ -529,6 +529,17 @@ crypto_rand_unmocked(char *to, size_t n)
 }
 
 /**
+ * Draw an unsigned 32-bit integer uniformly at random.
+ */
+uint32_t
+crypto_rand_uint32(void)
+{
+  uint32_t rand;
+  crypto_rand((void*)&rand, sizeof(rand));
+  return rand;
+}
+
+/**
  * Return a pseudorandom integer, chosen uniformly from the values
  * between 0 and <b>max</b>-1 inclusive.  <b>max</b> must be between 1 and
  * INT_MAX+1, inclusive.
diff --git a/src/lib/crypt_ops/crypto_rand.h b/src/lib/crypt_ops/crypto_rand.h
index 0c538d81ac..61fd82c806 100644
--- a/src/lib/crypt_ops/crypto_rand.h
+++ b/src/lib/crypt_ops/crypto_rand.h
@@ -27,6 +27,7 @@ int crypto_rand_int(unsigned int max);
 int crypto_rand_int_range(unsigned int min, unsigned int max);
 uint64_t crypto_rand_uint64_range(uint64_t min, uint64_t max);
 time_t crypto_rand_time_range(time_t min, time_t max);
+uint32_t crypto_rand_uint32(void);
 uint64_t crypto_rand_uint64(uint64_t max);
 double crypto_rand_double(void);
 struct tor_weak_rng_t;