summaryrefslogtreecommitdiffstats
path: root/openbsd-compat/arc4random_uniform.c
diff options
context:
space:
mode:
authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 14:40:04 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 14:40:04 +0000
commit25505898530a333011f4fd5cbc841ad6b26c089c (patch)
tree333a33fdd60930bcccc3f177ed9467d535e9bac6 /openbsd-compat/arc4random_uniform.c
parentInitial commit. (diff)
downloadopenssh-upstream.tar.xz
openssh-upstream.zip
Adding upstream version 1:9.2p1.upstream/1%9.2p1upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'openbsd-compat/arc4random_uniform.c')
-rw-r--r--openbsd-compat/arc4random_uniform.c64
1 files changed, 64 insertions, 0 deletions
diff --git a/openbsd-compat/arc4random_uniform.c b/openbsd-compat/arc4random_uniform.c
new file mode 100644
index 0000000..591f92d
--- /dev/null
+++ b/openbsd-compat/arc4random_uniform.c
@@ -0,0 +1,64 @@
+/* $OpenBSD: arc4random_uniform.c,v 1.3 2019/01/20 02:59:07 bcook Exp $ */
+
+/*
+ * Copyright (c) 2008, Damien Miller <djm@openbsd.org>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+/* OPENBSD ORIGINAL: lib/libc/crypto/arc4random_uniform.c */
+
+#include "includes.h"
+
+#ifdef HAVE_STDINT_H
+# include <stdint.h>
+#endif
+#include <stdlib.h>
+
+#ifndef HAVE_ARC4RANDOM_UNIFORM
+/*
+ * Calculate a uniformly distributed random number less than upper_bound
+ * avoiding "modulo bias".
+ *
+ * Uniformity is achieved by generating new random numbers until the one
+ * returned is outside the range [0, 2**32 % upper_bound). This
+ * guarantees the selected random number will be inside
+ * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound)
+ * after reduction modulo upper_bound.
+ */
+uint32_t
+arc4random_uniform(uint32_t upper_bound)
+{
+ uint32_t r, min;
+
+ if (upper_bound < 2)
+ return 0;
+
+ /* 2**32 % x == (2**32 - x) % x */
+ min = -upper_bound % upper_bound;
+
+ /*
+ * This could theoretically loop forever but each retry has
+ * p > 0.5 (worst case, usually far better) of selecting a
+ * number inside the range we need, so it should rarely need
+ * to re-roll.
+ */
+ for (;;) {
+ r = arc4random();
+ if (r >= min)
+ break;
+ }
+
+ return r % upper_bound;
+}
+#endif /* !HAVE_ARC4RANDOM_UNIFORM */