Add a new facility that handles entropy abstraction

2 files changed, 72 insertions, 0 deletions

diff --git a/ot_random.c b/ot_random.c
new file mode 100644
index 0000000..3fae876
--- /dev/null
+++ b/ot_random.c
@@ -0,0 +1,53 @@
+/* This software was written by Dirk Engling <erdgeist@erdgeist.org>
+   It is considered beerware. Prost. Skol. Cheers or whatever.
+
+   $id$ */
+
+/* System */
+#include <stdint.h>
+#include <stdlib.h>
+
+/* Opentracker */
+#include "ot_random.h"
+
+#ifdef WANT_INSECURE_RANDOM_FALLBACK
+
+#warning WANT_INSECURE_RANDOM_FALLBACK builds without arc4random. UDP connection ids become predictable and announces can be forged. Do not ship this.
+
+#include <time.h>
+
+void random_init(void) {
+#ifdef WANT_DEV_RANDOM
+  srandomdev();
+#else
+  srandom(time(NULL));
+#endif
+}
+
+/* random() yields 31 bits, so one draw can never set the top bit. Combine
+   two of them rather than hand out a value that is quietly half as wide as
+   its type claims. */
+uint32_t random_uint32(void) { return ((uint32_t)random() << 16) ^ (uint32_t)random(); }
+
+void     random_bytes(void *buf, size_t len) {
+  uint8_t *out = buf;
+  /* random() leaves the top bit clear and its lowest bits are the weakest,
+     so take a byte from the middle of each draw */
+  while (len--)
+       *out++ = (uint8_t)(random() >> 8);
+}
+
+#else
+
+#if !defined(__FreeBSD__) && !defined(__OpenBSD__) && !defined(__NetBSD__) && !defined(__DragonFly__) && !defined(__APPLE__) &&                                     \
+    !(defined(__GLIBC__) && (__GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 36)))
+#include <bsd/stdlib.h>
+#endif
+
+void     random_init(void) {}
+
+uint32_t random_uint32(void) { return arc4random(); }
+
+void     random_bytes(void *buf, size_t len) { arc4random_buf(buf, len); }
+
+#endif
diff --git a/ot_random.h b/ot_random.h
new file mode 100644
index 0000000..5200dbc
--- /dev/null
+++ b/ot_random.h
@@ -0,0 +1,19 @@
+/* This software was written by Dirk Engling <erdgeist@erdgeist.org>
+   It is considered beerware. Prost. Skol. Cheers or whatever.
+
+   $id$ */
+
+#ifndef OT_RANDOM_H__
+#define OT_RANDOM_H__
+
+#include <stddef.h>
+#include <stdint.h>
+
+/* Seed whatever generator the build settled on. A no-op when backed by
+   arc4random, which seeds itself from the kernel. */
+void     random_init(void);
+
+uint32_t random_uint32(void);
+void     random_bytes(void *buf, size_t len);
+
+#endif