Move weakrng into lib/intmath

4 files changed, 81 insertions, 2 deletions

diff --git a/src/lib/crypt_ops/crypto_rand.c b/src/lib/crypt_ops/crypto_rand.c
index 247a502241..8ac7d3bfe8 100644
--- a/src/lib/crypt_ops/crypto_rand.c
+++ b/src/lib/crypt_ops/crypto_rand.c
@@ -30,6 +30,7 @@
 #include "lib/log/torlog.h"
 #include "common/util.h"
 #include "lib/encoding/binascii.h"
+#include "lib/intmath/weakrng.h"
 
 DISABLE_GCC_WARNING(redundant-decls)
 #include <openssl/rand.h>
diff --git a/src/lib/intmath/include.am b/src/lib/intmath/include.am
index 40459d106d..1ae5d618d4 100644
--- a/src/lib/intmath/include.am
+++ b/src/lib/intmath/include.am
@@ -8,7 +8,8 @@ endif
 src_lib_libtor_intmath_a_SOURCES =			\
 	src/lib/intmath/addsub.c			\
 	src/lib/intmath/bits.c				\
-	src/lib/intmath/muldiv.c
+	src/lib/intmath/muldiv.c			\
+	src/lib/intmath/weakrng.c
 
 src_lib_libtor_intmath_testing_a_SOURCES = \
 	$(src_lib_libtor_intmath_a_SOURCES)
@@ -19,4 +20,5 @@ noinst_HEADERS +=					\
 	src/lib/intmath/addsub.h			\
 	src/lib/intmath/cmp.h				\
 	src/lib/intmath/bits.h				\
-	src/lib/intmath/muldiv.h
+	src/lib/intmath/muldiv.h			\
+	src/lib/intmath/weakrng.h
diff --git a/src/lib/intmath/weakrng.c b/src/lib/intmath/weakrng.c
new file mode 100644
index 0000000000..2ecab97cc1
--- /dev/null
+++ b/src/lib/intmath/weakrng.c
@@ -0,0 +1,51 @@
+/* Copyright (c) 2003, Roger Dingledine
+ * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
+ * Copyright (c) 2007-2018, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+#include "lib/intmath/weakrng.h"
+#include "lib/err/torerr.h"
+
+#include <stdlib.h>
+
+/** Initialize the insecure RNG <b>rng</b> from a seed value <b>seed</b>. */
+void
+tor_init_weak_random(tor_weak_rng_t *rng, unsigned seed)
+{
+  rng->state = (uint32_t)(seed & 0x7fffffff);
+}
+
+/** Return a randomly chosen value in the range 0..TOR_WEAK_RANDOM_MAX based
+ * on the RNG state of <b>rng</b>.  This entropy will not be cryptographically
+ * strong; do not rely on it for anything an adversary should not be able to
+ * predict. */
+int32_t
+tor_weak_random(tor_weak_rng_t *rng)
+{
+  /* Here's a linear congruential generator. OpenBSD and glibc use these
+   * parameters; they aren't too bad, and should have maximal period over the
+   * range 0..INT32_MAX. We don't want to use the platform rand() or random(),
+   * since some platforms have bad weak RNGs that only return values in the
+   * range 0..INT16_MAX, which just isn't enough. */
+  rng->state = (rng->state * 1103515245 + 12345) & 0x7fffffff;
+  return (int32_t) rng->state;
+}
+
+/** Return a random number in the range [0 , <b>top</b>). {That is, the range
+ * of integers i such that 0 <= i < top.}  Chooses uniformly.  Requires that
+ * top is greater than 0. This randomness is not cryptographically strong; do
+ * not rely on it for anything an adversary should not be able to predict. */
+int32_t
+tor_weak_random_range(tor_weak_rng_t *rng, int32_t top)
+{
+  /* We don't want to just do tor_weak_random() % top, since random() is often
+   * implemented with an LCG whose modulus is a power of 2, and those are
+   * cyclic in their low-order bits. */
+  int divisor, result;
+  raw_assert(top > 0);
+  divisor = TOR_WEAK_RANDOM_MAX / top;
+  do {
+    result = (int32_t)(tor_weak_random(rng) / divisor);
+  } while (result >= top);
+  return result;
+}
diff --git a/src/lib/intmath/weakrng.h b/src/lib/intmath/weakrng.h
new file mode 100644
index 0000000000..e5a88b30fe
--- /dev/null
+++ b/src/lib/intmath/weakrng.h
@@ -0,0 +1,25 @@
+/* Copyright (c) 2003, Roger Dingledine
+ * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
+ * Copyright (c) 2007-2018, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+#ifndef TOR_WEAKRNG_H
+#define TOR_WEAKRNG_H
+
+#include "lib/cc/torint.h"
+
+/* ===== Insecure rng */
+typedef struct tor_weak_rng_t {
+  uint32_t state;
+} tor_weak_rng_t;
+
+#define TOR_WEAK_RNG_INIT {383745623}
+#define TOR_WEAK_RANDOM_MAX (INT_MAX)
+void tor_init_weak_random(tor_weak_rng_t *weak_rng, unsigned seed);
+int32_t tor_weak_random(tor_weak_rng_t *weak_rng);
+int32_t tor_weak_random_range(tor_weak_rng_t *rng, int32_t top);
+/** Randomly return true according to <b>rng</b> with probability 1 in
+ * <b>n</b> */
+#define tor_weak_random_one_in_n(rng, n) (0==tor_weak_random_range((rng),(n)))
+
+#endif