[PATCH] API for true Random Number Generators to add entropy (2.4.29)

David McCullough
2005-03-24T04:30:45Z

Hi all,

Here is a small patch for 2.4.29 that adds a routine:

add_true_randomness(__u32 *buf, int nwords);

so that true random number generator device drivers can add a entropy
to the system. Drivers that use this can be found in the latest release
of ocf-linux, an asynchronous crypto implementation for linux based on
the *BSD Cryptographic Framework.

http://ocf-linux.sourceforge.net/

Adding this can dramatically improve the performance of /dev/random on
small embedded systems which do not generate much entropy.

Cheers,
Davidm

Signed-off-by: David McCullough <davidm@snapgear.com>

Index: linux-2.4.29/include/linux/random.h
===================================================================
RCS file: /cvs/sw/linux-2.4.29/include/linux/random.h,v
retrieving revision 1.1.1.1
retrieving revision 1.3
diff -u -r1.1.1.1 -r1.3
--- linux-2.4.29/include/linux/random.h 9 Jul 2001 00:39:16 -0000 1.1.1.1
+++ linux-2.4.29/include/linux/random.h 18 Mar 2005 04:33:35 -0000 1.3
@@ -52,6 +52,7 @@
extern void add_mouse_randomness(__u32 mouse_data);
extern void add_interrupt_randomness(int irq);
extern void add_blkdev_randomness(int major);
+extern void add_true_randomness(__u32 *buf, int nwords);

extern void get_random_bytes(void *buf, int nbytes);
void generate_random_uuid(unsigned char uuid_out[16]);
Index: linux-2.4.29/drivers/char/random.c
===================================================================
RCS file: /cvs/sw/linux-2.4.29/drivers/char/random.c,v
retrieving revision 1.1.1.9
retrieving revision 1.11
diff -u -r1.1.1.9 -r1.11
--- linux-2.4.29/drivers/char/random.c 4 Feb 2005 00:28:36 -0000 1.1.1.9
+++ linux-2.4.29/drivers/char/random.c 18 Mar 2005 04:33:35 -0000 1.11
@@ -842,6 +837,39 @@
add_timer_randomness(blkdev_timer_state[major], 0x200+major);
}

+/*
+ * provide a mechanism for HW RNG's to add entropy that is of
+ * very good quality.
+ */
+void add_true_randomness(__u32 *buf, int nwords)
+{
+ struct entropy_store *r;
+ int wakeup_check = 0;
+
+
+ if (!random_state || !sec_random_state)
+ return;
+
+ /*
+ * if we have too much entropy, put some in the secondary pool
+ */
+ r = random_state;
+ if (r->entropy_count >= r->poolinfo.POOLBITS)
+ r = sec_random_state;
+ else
+ wakeup_check = (r->entropy_count < random_read_wakeup_thresh);
+
+ add_entropy_words(r, buf, nwords);
+ credit_entropy_store(r, nwords * 32);
+
+ /*
+ * wakeup if we added enough entropy to cross the threshold
+ */
+ if (wakeup_check && r->entropy_count >= random_read_wakeup_thresh)
+ wake_up_interruptible(&random_read_wait);
+}
+EXPORT_SYMBOL(add_true_randomness);
+
/******************************************************************
*
* Hash function definition

--
David McCullough, davidm@snapgear.com Ph:+61 7 34352815 http://www.SnapGear.com
Custom Embedded Solutions + Security Fx:+61 7 38913630 http://www.uCdot.org