From: Scott Ellis <scott@jumpnowtek.com>
Date: Fri, 7 Dec 2018 13:50:13 +0000 (-0500)
Subject: Initial commit
X-Git-Tag: hippotat/1.0.0~303^2~2
X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ian/git?a=commitdiff_plain;h=5790bda0c5667b151a2b9c8fd9526d25746b751c;p=hippotat.git

Initial commit
---

5790bda0c5667b151a2b9c8fd9526d25746b751c
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..a997b67
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+rndaddtoentcnt
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..3c24ce5
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,2 @@
+rndaddtoentcnt: rndaddtoentcnt.c
+	$(CC) rndaddtoentcnt.c -o rndaddtoentcnt
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..9f85b29
--- /dev/null
+++ b/README.md
@@ -0,0 +1,15 @@
+### rndaddtoentcnt
+
+Seeding the random number generator by writing to /dev/urandom does not update the entropy count.
+
+This utility makes the RNDADDTOENTCNT ioctl call needed to do this.
+
+Used in startup scripts after initializing /dev/urandom with a presaved seed.
+
+Example:
+
+    dd if=/path/to/some/random-seed-file of=/dev/urandom bs=512 count=1
+
+    /path/to/rdnaddtoentcnt <entropy-bit-count>
+
+where entropy-bit-count is a number between 1 and (8 * 512) depending on how much you trust the seed file.
diff --git a/rndaddtoentcnt.c b/rndaddtoentcnt.c
new file mode 100644
index 0000000..929bf4d
--- /dev/null
+++ b/rndaddtoentcnt.c
@@ -0,0 +1,46 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/ioctl.h>
+#include <fcntl.h>
+
+#include <linux/random.h>
+
+
+int main(int argc, char **argv)
+{
+    int count, fd;
+
+    if (argc != 2) {
+        printf("Usage: rndaddtoentcnt <entropy-bit-count>\n");
+        exit(1);
+    }
+
+    count = strtoul(argv[1], NULL, 0);
+
+    if (count < 1 || count > 4096) {
+        printf("Count range is 1 to 4096\n");
+        exit(1);
+    }
+
+    fd = open("/dev/urandom", O_WRONLY);
+
+    if (fd < 0) {
+        perror("open(/dev/urandom)");
+        exit(1);
+    }
+
+
+    if (ioctl(fd, RNDADDTOENTCNT, &count) < 0) {
+        perror("ioctl(RNDADDTOENTCNT)");
+        close(fd);
+        exit(1);
+    }
+
+    close(fd);
+
+    return 0;
+}