Here's an 'mcookie' implementation for toybox.

mcookie simply prints out 16 bytes of entropy in hexadecimal; it is typically
used as the source for the "MIT magic cookies" that X11 uses for "secure"
connections.
The only implementation I know of is in util-linux; the problems with its
documented behavior motivated me to write an alternate implementation.
Specifically, getting 128 bytes from the kernel and finding the MD5 sum is
not a sane PRNG, especially when only 16 bytes are needed.

1 files changed, 47 insertions, 0 deletions

diff --git a/toys/pending/mcookie.c b/toys/pending/mcookie.c
new file mode 100644
index 00000000..83cf0a91
--- /dev/null
+++ b/toys/pending/mcookie.c
@@ -0,0 +1,47 @@
+/* mcookie - generate a 128-bit random number (used for X "magic cookies")
+ *
+ * Copyright 2019 AD Isaac Dunham <ibid.ag@gmail.com>
+ *
+ * No standard.
+ * util-linux mcookie originally found the md5sum of several files in /proc
+ * and reported that; more recent versions use the best random number source
+ * and find the md5sum, thus wasting entropy.
+ * We just ask the system for 128 bits and print it.
+ *
+ *
+USE_MCOOKIE(NEWTOY(mcookie, "v(verbose)V(version)", TOYFLAG_USR|TOYFLAG_BIN))
+
+config MCOOKIE
+  bool "mcookie"
+  default n
+  help
+    usage: mcookie [-v | -V]
+
+    Generate a 128-bit random number from system sources.
+    -f and -m are not supported; md5 sums of arbitrary files are not a
+        good source of entropy
+    -h  show help
+    -v  show entropy source (verbose)
+    -V  show version
+*/
+
+#define FOR_mcookie
+#include "toys.h"
+
+void mcookie_main(void)
+{
+  int i;
+  if (toys.optflags & FLAG_V) {
+    puts("mcookie from toybox");
+    return;
+  }
+  xgetrandom(toybuf, 16, 0);
+  if (toys.optflags & FLAG_v) {
+    fputs("Got 16 bytes from xgetrandom()\n", stderr);
+  }
+  for (i = 0; i < 16; i++) {
+    sprintf(toybuf+16+2*i,"%02x", toybuf[i]);
+  }
+  toybuf[48] = '\0';
+  puts(toybuf + 16);
+}