FreeBSD/Linux Kernel Cross Reference
sys/drivers/char/random.c

     /*
      * random.c -- A strong random number generator
      *
      * Version 1.89, last modified 19-Sep-99
      * 
      * Copyright Theodore Ts'o, 1994, 1995, 1996, 1997, 1998, 1999.  All
      * rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, and the entire permission notice in its entirety,
     *    including the disclaimer of warranties.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. The name of the author may not be used to endorse or promote
     *    products derived from this software without specific prior
     *    written permission.
     * 
     * ALTERNATIVELY, this product may be distributed under the terms of
     * the GNU General Public License, in which case the provisions of the GPL are
     * required INSTEAD OF the above restrictions.  (This clause is
     * necessary due to a potential bad interaction between the GPL and
     * the restrictions contained in a BSD-style copyright.)
     * 
     * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
     * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
     * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
     * WHICH ARE HEREBY DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE
     * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
     * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
     * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
     * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
     * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH
     * DAMAGE.
     */
    
    /*
     * (now, with legal B.S. out of the way.....) 
     * 
     * This routine gathers environmental noise from device drivers, etc.,
     * and returns good random numbers, suitable for cryptographic use.
     * Besides the obvious cryptographic uses, these numbers are also good
     * for seeding TCP sequence numbers, and other places where it is
     * desirable to have numbers which are not only random, but hard to
     * predict by an attacker.
     *
     * Theory of operation
     * ===================
     * 
     * Computers are very predictable devices.  Hence it is extremely hard
     * to produce truly random numbers on a computer --- as opposed to
     * pseudo-random numbers, which can easily generated by using a
     * algorithm.  Unfortunately, it is very easy for attackers to guess
     * the sequence of pseudo-random number generators, and for some
     * applications this is not acceptable.  So instead, we must try to
     * gather "environmental noise" from the computer's environment, which
     * must be hard for outside attackers to observe, and use that to
     * generate random numbers.  In a Unix environment, this is best done
     * from inside the kernel.
     * 
     * Sources of randomness from the environment include inter-keyboard
     * timings, inter-interrupt timings from some interrupts, and other
     * events which are both (a) non-deterministic and (b) hard for an
     * outside observer to measure.  Randomness from these sources are
     * added to an "entropy pool", which is mixed using a CRC-like function.
     * This is not cryptographically strong, but it is adequate assuming
     * the randomness is not chosen maliciously, and it is fast enough that
     * the overhead of doing it on every interrupt is very reasonable.
     * As random bytes are mixed into the entropy pool, the routines keep
     * an *estimate* of how many bits of randomness have been stored into
     * the random number generator's internal state.
     * 
     * When random bytes are desired, they are obtained by taking the SHA
     * hash of the contents of the "entropy pool".  The SHA hash avoids
     * exposing the internal state of the entropy pool.  It is believed to
     * be computationally infeasible to derive any useful information
     * about the input of SHA from its output.  Even if it is possible to
     * analyze SHA in some clever way, as long as the amount of data
     * returned from the generator is less than the inherent entropy in
     * the pool, the output data is totally unpredictable.  For this
     * reason, the routine decreases its internal estimate of how many
     * bits of "true randomness" are contained in the entropy pool as it
     * outputs random numbers.
     * 
     * If this estimate goes to zero, the routine can still generate
     * random numbers; however, an attacker may (at least in theory) be
     * able to infer the future output of the generator from prior
     * outputs.  This requires successful cryptanalysis of SHA, which is
     * not believed to be feasible, but there is a remote possibility.
     * Nonetheless, these numbers should be useful for the vast majority
     * of purposes.
     * 
     * Exported interfaces ---- output
     * ===============================
    * 
    * There are three exported interfaces; the first is one designed to
    * be used from within the kernel:
    *
    *      void get_random_bytes(void *buf, int nbytes);
    *
    * This interface will return the requested number of random bytes,
    * and place it in the requested buffer.
    * 
    * The two other interfaces are two character devices /dev/random and
    * /dev/urandom.  /dev/random is suitable for use when very high
    * quality randomness is desired (for example, for key generation or
    * one-time pads), as it will only return a maximum of the number of
    * bits of randomness (as estimated by the random number generator)
    * contained in the entropy pool.
    * 
    * The /dev/urandom device does not have this limit, and will return
    * as many bytes as are requested.  As more and more random bytes are
    * requested without giving time for the entropy pool to recharge,
    * this will result in random numbers that are merely cryptographically
    * strong.  For many applications, however, this is acceptable.
    *
    * Exported interfaces ---- input
    * ==============================
    * 
    * The current exported interfaces for gathering environmental noise
    * from the devices are:
    * 
    *      void add_keyboard_randomness(unsigned char scancode);
    *      void add_mouse_randomness(__u32 mouse_data);
    *      void add_interrupt_randomness(int irq);
    *      void add_blkdev_randomness(int irq);
    * 
    * add_keyboard_randomness() uses the inter-keypress timing, as well as the
    * scancode as random inputs into the "entropy pool".
    * 
    * add_mouse_randomness() uses the mouse interrupt timing, as well as
    * the reported position of the mouse from the hardware.
    *
    * add_interrupt_randomness() uses the inter-interrupt timing as random
    * inputs to the entropy pool.  Note that not all interrupts are good
    * sources of randomness!  For example, the timer interrupts is not a
    * good choice, because the periodicity of the interrupts is too
    * regular, and hence predictable to an attacker.  Disk interrupts are
    * a better measure, since the timing of the disk interrupts are more
    * unpredictable.
    * 
    * add_blkdev_randomness() times the finishing time of block requests.
    * 
    * All of these routines try to estimate how many bits of randomness a
    * particular randomness source.  They do this by keeping track of the
    * first and second order deltas of the event timings.
    *
    * Ensuring unpredictability at system startup
    * ============================================
    * 
    * When any operating system starts up, it will go through a sequence
    * of actions that are fairly predictable by an adversary, especially
    * if the start-up does not involve interaction with a human operator.
    * This reduces the actual number of bits of unpredictability in the
    * entropy pool below the value in entropy_count.  In order to
    * counteract this effect, it helps to carry information in the
    * entropy pool across shut-downs and start-ups.  To do this, put the
    * following lines an appropriate script which is run during the boot
    * sequence: 
    *
    *      echo "Initializing random number generator..."
    *      random_seed=/var/run/random-seed
    *      # Carry a random seed from start-up to start-up
    *      # Load and then save the whole entropy pool
    *      if [ -f $random_seed ]; then
    *              cat $random_seed >/dev/urandom
    *      else
    *              touch $random_seed
    *      fi
    *      chmod 600 $random_seed
    *      poolfile=/proc/sys/kernel/random/poolsize
    *      [ -r $poolfile ] && bytes=`cat $poolfile` || bytes=512
    *      dd if=/dev/urandom of=$random_seed count=1 bs=$bytes
    *
    * and the following lines in an appropriate script which is run as
    * the system is shutdown:
    *
    *      # Carry a random seed from shut-down to start-up
    *      # Save the whole entropy pool
    *      echo "Saving random seed..."
    *      random_seed=/var/run/random-seed
    *      touch $random_seed
    *      chmod 600 $random_seed
    *      poolfile=/proc/sys/kernel/random/poolsize
    *      [ -r $poolfile ] && bytes=`cat $poolfile` || bytes=512
    *      dd if=/dev/urandom of=$random_seed count=1 bs=$bytes
    *
    * For example, on most modern systems using the System V init
    * scripts, such code fragments would be found in
    * /etc/rc.d/init.d/random.  On older Linux systems, the correct script
    * location might be in /etc/rcb.d/rc.local or /etc/rc.d/rc.0.
    * 
    * Effectively, these commands cause the contents of the entropy pool
    * to be saved at shut-down time and reloaded into the entropy pool at
    * start-up.  (The 'dd' in the addition to the bootup script is to
    * make sure that /etc/random-seed is different for every start-up,
    * even if the system crashes without executing rc.0.)  Even with
    * complete knowledge of the start-up activities, predicting the state
    * of the entropy pool requires knowledge of the previous history of
    * the system.
    *
    * Configuring the /dev/random driver under Linux
    * ==============================================
    *
    * The /dev/random driver under Linux uses minor numbers 8 and 9 of
    * the /dev/mem major number (#1).  So if your system does not have
    * /dev/random and /dev/urandom created already, they can be created
    * by using the commands:
    *
    *      mknod /dev/random c 1 8
    *      mknod /dev/urandom c 1 9
    * 
    * Acknowledgements:
    * =================
    *
    * Ideas for constructing this random number generator were derived
    * from Pretty Good Privacy's random number generator, and from private
    * discussions with Phil Karn.  Colin Plumb provided a faster random
    * number generator, which speed up the mixing function of the entropy
    * pool, taken from PGPfone.  Dale Worley has also contributed many
    * useful ideas and suggestions to improve this driver.
    * 
    * Any flaws in the design are solely my responsibility, and should
    * not be attributed to the Phil, Colin, or any of authors of PGP.
    * 
    * The code for SHA transform was taken from Peter Gutmann's
    * implementation, which has been placed in the public domain.
    * The code for MD5 transform was taken from Colin Plumb's
    * implementation, which has been placed in the public domain.
    * The MD5 cryptographic checksum was devised by Ronald Rivest, and is
    * documented in RFC 1321, "The MD5 Message Digest Algorithm".
    * 
    * Further background information on this topic may be obtained from
    * RFC 1750, "Randomness Recommendations for Security", by Donald
    * Eastlake, Steve Crocker, and Jeff Schiller.
    */
   
   #include <linux/utsname.h>
   #include <linux/config.h>
   #include <linux/module.h>
   #include <linux/kernel.h>
   #include <linux/major.h>
   #include <linux/string.h>
   #include <linux/fcntl.h>
   #include <linux/slab.h>
   #include <linux/random.h>
   #include <linux/poll.h>
   #include <linux/init.h>
   #include <linux/interrupt.h>
   #include <linux/spinlock.h>
   
   #include <asm/processor.h>
   #include <asm/uaccess.h>
   #include <asm/irq.h>
   #include <asm/io.h>
   
   /*
    * Configuration information
    */
   #define DEFAULT_POOL_SIZE 512
   #define SECONDARY_POOL_SIZE 128
   #define BATCH_ENTROPY_SIZE 256
   #define USE_SHA
   
   /*
    * The minimum number of bits of entropy before we wake up a read on
    * /dev/random.  Should always be at least 8, or at least 1 byte.
    */
   static int random_read_wakeup_thresh = 8;
   
   /*
    * If the entropy count falls under this number of bits, then we
    * should wake up processes which are selecting or polling on write
    * access to /dev/random.
    */
   static int random_write_wakeup_thresh = 128;
   
   /*
    * A pool of size .poolwords is stirred with a primitive polynomial
    * of degree .poolwords over GF(2).  The taps for various sizes are
    * defined below.  They are chosen to be evenly spaced (minimum RMS
    * distance from evenly spaced; the numbers in the comments are a
    * scaled squared error sum) except for the last tap, which is 1 to
    * get the twisting happening as fast as possible.
    */
   static struct poolinfo {
           int     poolwords;
           int     tap1, tap2, tap3, tap4, tap5;
   } poolinfo_table[] = {
           /* x^2048 + x^1638 + x^1231 + x^819 + x^411 + x + 1  -- 115 */
           { 2048, 1638,   1231,   819,    411,    1 },
   
           /* x^1024 + x^817 + x^615 + x^412 + x^204 + x + 1 -- 290 */
           { 1024, 817,    615,    412,    204,    1 },
   #if 0                           /* Alternate polynomial */
           /* x^1024 + x^819 + x^616 + x^410 + x^207 + x^2 + 1 -- 115 */
           { 1024, 819,    616,    410,    207,    2 },
   #endif
   
           /* x^512 + x^411 + x^308 + x^208 + x^104 + x + 1 -- 225 */
           { 512,  411,    308,    208,    104,    1 },
   #if 0                           /* Alternates */
           /* x^512 + x^409 + x^307 + x^206 + x^102 + x^2 + 1 -- 95 */
           { 512,  409,    307,    206,    102,    2 },
           /* x^512 + x^409 + x^309 + x^205 + x^103 + x^2 + 1 -- 95 */
           { 512,  409,    309,    205,    103,    2 },
   #endif
   
           /* x^256 + x^205 + x^155 + x^101 + x^52 + x + 1 -- 125 */
           { 256,  205,    155,    101,    52,     1 },
   
           /* x^128 + x^103 + x^76 + x^51 +x^25 + x + 1 -- 105 */
           { 128,  103,    76,     51,     25,     1 },
   #if 0   /* Alternate polynomial */
           /* x^128 + x^103 + x^78 + x^51 + x^27 + x^2 + 1 -- 70 */
           { 128,  103,    78,     51,     27,     2 },
   #endif
   
           /* x^64 + x^52 + x^39 + x^26 + x^14 + x + 1 -- 15 */
           { 64,   52,     39,     26,     14,     1 },
   
           /* x^32 + x^26 + x^20 + x^14 + x^7 + x + 1 -- 15 */
           { 32,   26,     20,     14,     7,      1 },
   
           { 0,    0,      0,      0,      0,      0 },
   };
   
   #define POOLBITS        poolwords*32
   #define POOLBYTES       poolwords*4
   
   /*
    * For the purposes of better mixing, we use the CRC-32 polynomial as
    * well to make a twisted Generalized Feedback Shift Reigster
    *
    * (See M. Matsumoto & Y. Kurita, 1992.  Twisted GFSR generators.  ACM
    * Transactions on Modeling and Computer Simulation 2(3):179-194.
    * Also see M. Matsumoto & Y. Kurita, 1994.  Twisted GFSR generators
    * II.  ACM Transactions on Mdeling and Computer Simulation 4:254-266)
    *
    * Thanks to Colin Plumb for suggesting this.
    * 
    * We have not analyzed the resultant polynomial to prove it primitive;
    * in fact it almost certainly isn't.  Nonetheless, the irreducible factors
    * of a random large-degree polynomial over GF(2) are more than large enough
    * that periodicity is not a concern.
    * 
    * The input hash is much less sensitive than the output hash.  All
    * that we want of it is that it be a good non-cryptographic hash;
    * i.e. it not produce collisions when fed "random" data of the sort
    * we expect to see.  As long as the pool state differs for different
    * inputs, we have preserved the input entropy and done a good job.
    * The fact that an intelligent attacker can construct inputs that
    * will produce controlled alterations to the pool's state is not
    * important because we don't consider such inputs to contribute any
    * randomness.  The only property we need with respect to them is that
    * the attacker can't increase his/her knowledge of the pool's state.
    * Since all additions are reversible (knowing the final state and the
    * input, you can reconstruct the initial state), if an attacker has
    * any uncertainty about the initial state, he/she can only shuffle
    * that uncertainty about, but never cause any collisions (which would
    * decrease the uncertainty).
    *
    * The chosen system lets the state of the pool be (essentially) the input
    * modulo the generator polymnomial.  Now, for random primitive polynomials,
    * this is a universal class of hash functions, meaning that the chance
    * of a collision is limited by the attacker's knowledge of the generator
    * polynomail, so if it is chosen at random, an attacker can never force
    * a collision.  Here, we use a fixed polynomial, but we *can* assume that
    * ###--> it is unknown to the processes generating the input entropy. <-###
    * Because of this important property, this is a good, collision-resistant
    * hash; hash collisions will occur no more often than chance.
    */
   
   /*
    * Linux 2.2 compatibility
    */
   #ifndef DECLARE_WAITQUEUE
   #define DECLARE_WAITQUEUE(WAIT, PTR)    struct wait_queue WAIT = { PTR, NULL }
   #endif
   #ifndef DECLARE_WAIT_QUEUE_HEAD
   #define DECLARE_WAIT_QUEUE_HEAD(WAIT) struct wait_queue *WAIT
   #endif
   
   /*
    * Static global variables
    */
   static struct entropy_store *random_state; /* The default global store */
   static struct entropy_store *sec_random_state; /* secondary store */
   static DECLARE_WAIT_QUEUE_HEAD(random_read_wait);
   static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
   
   /*
    * Forward procedure declarations
    */
   #ifdef CONFIG_SYSCTL
   static void sysctl_init_random(struct entropy_store *random_state);
   #endif
   
   /*****************************************************************
    *
    * Utility functions, with some ASM defined functions for speed
    * purposes
    * 
    *****************************************************************/
   
   /*
    * Unfortunately, while the GCC optimizer for the i386 understands how
    * to optimize a static rotate left of x bits, it doesn't know how to
    * deal with a variable rotate of x bits.  So we use a bit of asm magic.
    */
   #if (!defined (__i386__))
   static inline __u32 rotate_left(int i, __u32 word)
   {
           return (word << i) | (word >> (32 - i));
           
   }
   #else
   static inline __u32 rotate_left(int i, __u32 word)
   {
           __asm__("roll %%cl,%0"
                   :"=r" (word)
                   :"" (word),"c" (i));
           return word;
   }
   #endif
   
   /*
    * More asm magic....
    * 
    * For entropy estimation, we need to do an integral base 2
    * logarithm.  
    *
    * Note the "12bits" suffix - this is used for numbers between
    * 0 and 4095 only.  This allows a few shortcuts.
    */
   #if 0   /* Slow but clear version */
   static inline __u32 int_ln_12bits(__u32 word)
   {
           __u32 nbits = 0;
           
           while (word >>= 1)
                   nbits++;
           return nbits;
   }
   #else   /* Faster (more clever) version, courtesy Colin Plumb */
   static inline __u32 int_ln_12bits(__u32 word)
   {
           /* Smear msbit right to make an n-bit mask */
           word |= word >> 8;
           word |= word >> 4;
           word |= word >> 2;
           word |= word >> 1;
           /* Remove one bit to make this a logarithm */
           word >>= 1;
           /* Count the bits set in the word */
           word -= (word >> 1) & 0x555;
           word = (word & 0x333) + ((word >> 2) & 0x333);
           word += (word >> 4);
           word += (word >> 8);
           return word & 15;
   }
   #endif
   
   #if 0
   #define DEBUG_ENT(fmt, arg...) printk(KERN_DEBUG "random: " fmt, ## arg)
   #else
   #define DEBUG_ENT(fmt, arg...) do {} while (0)
   #endif
   
   /**********************************************************************
    *
    * OS independent entropy store.   Here are the functions which handle
    * storing entropy in an entropy pool.
    * 
    **********************************************************************/
   
   struct entropy_store {
           unsigned        add_ptr;
           int             entropy_count;
           int             input_rotate;
           int             extract_count;
           struct poolinfo poolinfo;
           __u32           *pool;
   };
   
   /*
    * Initialize the entropy store.  The input argument is the size of
    * the random pool.
    *
    * Returns an negative error if there is a problem.
    */
   static int create_entropy_store(int size, struct entropy_store **ret_bucket)
   {
           struct  entropy_store   *r;
           struct  poolinfo        *p;
           int     poolwords;
   
           poolwords = (size + 3) / 4; /* Convert bytes->words */
           /* The pool size must be a multiple of 16 32-bit words */
           poolwords = ((poolwords + 15) / 16) * 16; 
   
           for (p = poolinfo_table; p->poolwords; p++) {
                   if (poolwords == p->poolwords)
                           break;
           }
           if (p->poolwords == 0)
                   return -EINVAL;
   
           r = kmalloc(sizeof(struct entropy_store), GFP_KERNEL);
           if (!r)
                   return -ENOMEM;
   
           memset (r, 0, sizeof(struct entropy_store));
           r->poolinfo = *p;
   
           r->pool = kmalloc(POOLBYTES, GFP_KERNEL);
           if (!r->pool) {
                   kfree(r);
                   return -ENOMEM;
           }
           memset(r->pool, 0, POOLBYTES);
           *ret_bucket = r;
           return 0;
   }
   
   /* Clear the entropy pool and associated counters. */
   static void clear_entropy_store(struct entropy_store *r)
   {
           r->add_ptr = 0;
           r->entropy_count = 0;
           r->input_rotate = 0;
           r->extract_count = 0;
           memset(r->pool, 0, r->poolinfo.POOLBYTES);
   }
   
   static void free_entropy_store(struct entropy_store *r)
   {
           if (r->pool)
                   kfree(r->pool);
           kfree(r);
   }
   
   /*
    * This function adds a byte into the entropy "pool".  It does not
    * update the entropy estimate.  The caller should call
    * credit_entropy_store if this is appropriate.
    * 
    * The pool is stirred with a primitive polynomial of the appropriate
    * degree, and then twisted.  We twist by three bits at a time because
    * it's cheap to do so and helps slightly in the expected case where
    * the entropy is concentrated in the low-order bits.
    */
   static void add_entropy_words(struct entropy_store *r, const __u32 *in,
                                 int nwords)
   {
           static __u32 const twist_table[8] = {
                            0, 0x3b6e20c8, 0x76dc4190, 0x4db26158,
                   0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278 };
           unsigned i;
           int new_rotate;
           int wordmask = r->poolinfo.poolwords - 1;
           __u32 w;
   
           while (nwords--) {
                   w = rotate_left(r->input_rotate, *in++);
                   i = r->add_ptr = (r->add_ptr - 1) & wordmask;
                   /*
                    * Normally, we add 7 bits of rotation to the pool.
                    * At the beginning of the pool, add an extra 7 bits
                    * rotation, so that successive passes spread the
                    * input bits across the pool evenly.
                    */
                   new_rotate = r->input_rotate + 14;
                   if (i)
                           new_rotate = r->input_rotate + 7;
                   r->input_rotate = new_rotate & 31;
   
                   /* XOR in the various taps */
                   w ^= r->pool[(i + r->poolinfo.tap1) & wordmask];
                   w ^= r->pool[(i + r->poolinfo.tap2) & wordmask];
                   w ^= r->pool[(i + r->poolinfo.tap3) & wordmask];
                   w ^= r->pool[(i + r->poolinfo.tap4) & wordmask];
                   w ^= r->pool[(i + r->poolinfo.tap5) & wordmask];
                   w ^= r->pool[i];
                   r->pool[i] = (w >> 3) ^ twist_table[w & 7];
           }
   }
   
   /*
    * Credit (or debit) the entropy store with n bits of entropy
    */
   static void credit_entropy_store(struct entropy_store *r, int nbits)
   {
           if (r->entropy_count + nbits < 0) {
                   DEBUG_ENT("negative entropy/overflow (%d+%d)\n",
                             r->entropy_count, nbits);
                   r->entropy_count = 0;
           } else if (r->entropy_count + nbits > r->poolinfo.POOLBITS) {
                   r->entropy_count = r->poolinfo.POOLBITS;
           } else {
                   r->entropy_count += nbits;
                   if (nbits)
                           DEBUG_ENT("%s added %d bits, now %d\n",
                                     r == sec_random_state ? "secondary" :
                                     r == random_state ? "primary" : "unknown",
                                     nbits, r->entropy_count);
           }
   }
   
   /**********************************************************************
    *
    * Entropy batch input management
    *
    * We batch entropy to be added to avoid increasing interrupt latency
    *
    **********************************************************************/
   
   static __u32    *batch_entropy_pool;
   static int      *batch_entropy_credit;
   static int      batch_max;
   static int      batch_head, batch_tail;
   static struct tq_struct batch_tqueue;
   static void batch_entropy_process(void *private_);
   
   /* note: the size must be a power of 2 */
   static int __init batch_entropy_init(int size, struct entropy_store *r)
   {
           batch_entropy_pool = kmalloc(2*size*sizeof(__u32), GFP_KERNEL);
           if (!batch_entropy_pool)
                   return -1;
           batch_entropy_credit =kmalloc(size*sizeof(int), GFP_KERNEL);
           if (!batch_entropy_credit) {
                   kfree(batch_entropy_pool);
                   return -1;
           }
           batch_head = batch_tail = 0;
           batch_max = size;
           batch_tqueue.routine = batch_entropy_process;
           batch_tqueue.data = r;
           return 0;
   }
   
   /*
    * Changes to the entropy data is put into a queue rather than being added to
    * the entropy counts directly.  This is presumably to avoid doing heavy
    * hashing calculations during an interrupt in add_timer_randomness().
    * Instead, the entropy is only added to the pool once per timer tick.
    */
   void batch_entropy_store(u32 a, u32 b, int num)
   {
           int     new;
   
           if (!batch_max)
                   return;
           
           batch_entropy_pool[2*batch_head] = a;
           batch_entropy_pool[(2*batch_head) + 1] = b;
           batch_entropy_credit[batch_head] = num;
   
           new = (batch_head+1) & (batch_max-1);
           if (new != batch_tail) {
                   queue_task(&batch_tqueue, &tq_timer);
                   batch_head = new;
           } else {
                   DEBUG_ENT("batch entropy buffer full\n");
           }
   }
   
   /*
    * Flush out the accumulated entropy operations, adding entropy to the passed
    * store (normally random_state).  If that store has enough entropy, alternate
    * between randomizing the data of the primary and secondary stores.
    */
   static void batch_entropy_process(void *private_)
   {
           struct entropy_store *r = (struct entropy_store *) private_, *p;
           int max_entropy = r->poolinfo.POOLBITS;
   
           if (!batch_max)
                   return;
   
           p = r;
           while (batch_head != batch_tail) {
                   if (r->entropy_count >= max_entropy) {
                           r = (r == sec_random_state) ?   random_state :
                                                           sec_random_state;
                           max_entropy = r->poolinfo.POOLBITS;
                   }
                   add_entropy_words(r, batch_entropy_pool + 2*batch_tail, 2);
                   credit_entropy_store(r, batch_entropy_credit[batch_tail]);
                   batch_tail = (batch_tail+1) & (batch_max-1);
           }
           if (p->entropy_count >= random_read_wakeup_thresh)
                   wake_up_interruptible(&random_read_wait);
   }
   
   /*********************************************************************
    *
    * Entropy input management
    *
    *********************************************************************/
   
   /* There is one of these per entropy source */
   struct timer_rand_state {
           __u32           last_time;
           __s32           last_delta,last_delta2;
           int             dont_count_entropy:1;
   };
   
   static struct timer_rand_state keyboard_timer_state;
   static struct timer_rand_state mouse_timer_state;
   static struct timer_rand_state extract_timer_state;
   static struct timer_rand_state *irq_timer_state[NR_IRQS];
   static struct timer_rand_state *blkdev_timer_state[MAX_BLKDEV];
   
   /*
    * This function adds entropy to the entropy "pool" by using timing
    * delays.  It uses the timer_rand_state structure to make an estimate
    * of how many bits of entropy this call has added to the pool.
    *
    * The number "num" is also added to the pool - it should somehow describe
    * the type of event which just happened.  This is currently 0-255 for
    * keyboard scan codes, and 256 upwards for interrupts.
    * On the i386, this is assumed to be at most 16 bits, and the high bits
    * are used for a high-resolution timer.
    *
    */
   static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
   {
           __u32           time;
           __s32           delta, delta2, delta3;
           int             entropy = 0;
   
   #if defined (__i386__)
           if (cpu_has_tsc) {
                   __u32 high;
                   rdtsc(time, high);
                   num ^= high;
           } else {
                   time = jiffies;
           }
   #elif defined (__x86_64__)
           __u32 high;
           rdtsc(time, high);
           num ^= high;
   #else
           time = jiffies;
   #endif
   
           /*
            * Calculate number of bits of randomness we probably added.
            * We take into account the first, second and third-order deltas
            * in order to make our estimate.
            */
           if (!state->dont_count_entropy) {
                   delta = time - state->last_time;
                   state->last_time = time;
   
                   delta2 = delta - state->last_delta;
                   state->last_delta = delta;
   
                   delta3 = delta2 - state->last_delta2;
                   state->last_delta2 = delta2;
   
                   if (delta < 0)
                           delta = -delta;
                   if (delta2 < 0)
                           delta2 = -delta2;
                   if (delta3 < 0)
                           delta3 = -delta3;
                   if (delta > delta2)
                           delta = delta2;
                   if (delta > delta3)
                           delta = delta3;
   
                   /*
                    * delta is now minimum absolute delta.
                    * Round down by 1 bit on general principles,
                    * and limit entropy entimate to 12 bits.
                    */
                   delta >>= 1;
                   delta &= (1 << 12) - 1;
   
                   entropy = int_ln_12bits(delta);
           }
           batch_entropy_store(num, time, entropy);
   }
   
   void add_keyboard_randomness(unsigned char scancode)
   {
           static unsigned char last_scancode;
           /* ignore autorepeat (multiple key down w/o key up) */
           if (scancode != last_scancode) {
                   last_scancode = scancode;
                   add_timer_randomness(&keyboard_timer_state, scancode);
           }
   }
   
   void add_mouse_randomness(__u32 mouse_data)
   {
           add_timer_randomness(&mouse_timer_state, mouse_data);
   }
   
   void add_interrupt_randomness(int irq)
   {
           if (irq >= NR_IRQS || irq_timer_state[irq] == 0)
                   return;
   
           add_timer_randomness(irq_timer_state[irq], 0x100+irq);
   }
   
   void add_blkdev_randomness(int major)
   {
           if (major >= MAX_BLKDEV)
                   return;
   
           if (blkdev_timer_state[major] == 0) {
                   rand_initialize_blkdev(major, GFP_ATOMIC);
                   if (blkdev_timer_state[major] == 0)
                           return;
           }
                   
           add_timer_randomness(blkdev_timer_state[major], 0x200+major);
   }
   
   /******************************************************************
    *
    * Hash function definition
    *
    *******************************************************************/
   
   /*
    * This chunk of code defines a function
    * void HASH_TRANSFORM(__u32 digest[HASH_BUFFER_SIZE + HASH_EXTRA_SIZE],
    *              __u32 const data[16])
    * 
    * The function hashes the input data to produce a digest in the first
    * HASH_BUFFER_SIZE words of the digest[] array, and uses HASH_EXTRA_SIZE
    * more words for internal purposes.  (This buffer is exported so the
    * caller can wipe it once rather than this code doing it each call,
    * and tacking it onto the end of the digest[] array is the quick and
    * dirty way of doing it.)
    *
    * It so happens that MD5 and SHA share most of the initial vector
    * used to initialize the digest[] array before the first call:
    * 1) 0x67452301
    * 2) 0xefcdab89
    * 3) 0x98badcfe
    * 4) 0x10325476
    * 5) 0xc3d2e1f0 (SHA only)
    * 
    * For /dev/random purposes, the length of the data being hashed is
    * fixed in length, so appending a bit count in the usual way is not
    * cryptographically necessary.
    */
   
   #ifdef USE_SHA
   
   #define HASH_BUFFER_SIZE 5
   #define HASH_EXTRA_SIZE 80
   #define HASH_TRANSFORM SHATransform
   
   /* Various size/speed tradeoffs are available.  Choose 0..3. */
   #define SHA_CODE_SIZE 0
   
   /*
    * SHA transform algorithm, taken from code written by Peter Gutmann,
    * and placed in the public domain.
    */
   
   /* The SHA f()-functions.  */
   
   #define f1(x,y,z)   ( z ^ (x & (y^z)) )         /* Rounds  0-19: x ? y : z */
   #define f2(x,y,z)   (x ^ y ^ z)                 /* Rounds 20-39: XOR */
   #define f3(x,y,z)   ( (x & y) + (z & (x ^ y)) ) /* Rounds 40-59: majority */
   #define f4(x,y,z)   (x ^ y ^ z)                 /* Rounds 60-79: XOR */
   
   /* The SHA Mysterious Constants */
   
   #define K1  0x5A827999L                 /* Rounds  0-19: sqrt(2) * 2^30 */
   #define K2  0x6ED9EBA1L                 /* Rounds 20-39: sqrt(3) * 2^30 */
   #define K3  0x8F1BBCDCL                 /* Rounds 40-59: sqrt(5) * 2^30 */
   #define K4  0xCA62C1D6L                 /* Rounds 60-79: sqrt(10) * 2^30 */
   
   #define ROTL(n,X)  ( ( ( X ) << n ) | ( ( X ) >> ( 32 - n ) ) )
   
   #define subRound(a, b, c, d, e, f, k, data) \
       ( e += ROTL( 5, a ) + f( b, c, d ) + k + data, b = ROTL( 30, b ) )
   
   
   static void SHATransform(__u32 digest[85], __u32 const data[16])
   {
       __u32 A, B, C, D, E;     /* Local vars */
       __u32 TEMP;
       int i;
   #define W (digest + HASH_BUFFER_SIZE)   /* Expanded data array */
   
       /*
        * Do the preliminary expansion of 16 to 80 words.  Doing it
        * out-of-line line this is faster than doing it in-line on
        * register-starved machines like the x86, and not really any
        * slower on real processors.
        */
       memcpy(W, data, 16*sizeof(__u32));
       for (i = 0; i < 64; i++) {
               TEMP = W[i] ^ W[i+2] ^ W[i+8] ^ W[i+13];
               W[i+16] = ROTL(1, TEMP);
       }
   
       /* Set up first buffer and local data buffer */
       A = digest[ 0 ];
       B = digest[ 1 ];
       C = digest[ 2 ];
       D = digest[ 3 ];
       E = digest[ 4 ];
   
       /* Heavy mangling, in 4 sub-rounds of 20 iterations each. */
   #if SHA_CODE_SIZE == 0
       /*
        * Approximately 50% of the speed of the largest version, but
        * takes up 1/16 the space.  Saves about 6k on an i386 kernel.
        */
       for (i = 0; i < 80; i++) {
           if (i < 40) {
               if (i < 20)
                   TEMP = f1(B, C, D) + K1;
               else
                   TEMP = f2(B, C, D) + K2;
           } else {
               if (i < 60)
                   TEMP = f3(B, C, D) + K3;
               else
                   TEMP = f4(B, C, D) + K4;
           }
           TEMP += ROTL(5, A) + E + W[i];
           E = D; D = C; C = ROTL(30, B); B = A; A = TEMP;
       }
   #elif SHA_CODE_SIZE == 1
       for (i = 0; i < 20; i++) {
           TEMP = f1(B, C, D) + K1 + ROTL(5, A) + E + W[i];
           E = D; D = C; C = ROTL(30, B); B = A; A = TEMP;
       }
       for (; i < 40; i++) {
           TEMP = f2(B, C, D) + K2 + ROTL(5, A) + E + W[i];
           E = D; D = C; C = ROTL(30, B); B = A; A = TEMP;
       }
       for (; i < 60; i++) {
           TEMP = f3(B, C, D) + K3 + ROTL(5, A) + E + W[i];
           E = D; D = C; C = ROTL(30, B); B = A; A = TEMP;
       }
       for (; i < 80; i++) {
           TEMP = f4(B, C, D) + K4 + ROTL(5, A) + E + W[i];
           E = D; D = C; C = ROTL(30, B); B = A; A = TEMP;
       }
   #elif SHA_CODE_SIZE == 2
       for (i = 0; i < 20; i += 5) {
           subRound( A, B, C, D, E, f1, K1, W[ i   ] );
           subRound( E, A, B, C, D, f1, K1, W[ i+1 ] );
           subRound( D, E, A, B, C, f1, K1, W[ i+2 ] );
           subRound( C, D, E, A, B, f1, K1, W[ i+3 ] );
           subRound( B, C, D, E, A, f1, K1, W[ i+4 ] );
       }
       for (; i < 40; i += 5) {
           subRound( A, B, C, D, E, f2, K2, W[ i   ] );
           subRound( E, A, B, C, D, f2, K2, W[ i+1 ] );
           subRound( D, E, A, B, C, f2, K2, W[ i+2 ] );
           subRound( C, D, E, A, B, f2, K2, W[ i+3 ] );
           subRound( B, C, D, E, A, f2, K2, W[ i+4 ] );
       }
       for (; i < 60; i += 5) {
           subRound( A, B, C, D, E, f3, K3, W[ i   ] );
           subRound( E, A, B, C, D, f3, K3, W[ i+1 ] );
           subRound( D, E, A, B, C, f3, K3, W[ i+2 ] );
           subRound( C, D, E, A, B, f3, K3, W[ i+3 ] );
           subRound( B, C, D, E, A, f3, K3, W[ i+4 ] );
       }
       for (; i < 80; i += 5) {
           subRound( A, B, C, D, E, f4, K4, W[ i   ] );
           subRound( E, A, B, C, D, f4, K4, W[ i+1 ] );
           subRound( D, E, A, B, C, f4, K4, W[ i+2 ] );
           subRound( C, D, E, A, B, f4, K4, W[ i+3 ] );
           subRound( B, C, D, E, A, f4, K4, W[ i+4 ] );
       }
   #elif SHA_CODE_SIZE == 3 /* Really large version */
       subRound( A, B, C, D, E, f1, K1, W[  0 ] );
       subRound( E, A, B, C, D, f1, K1, W[  1 ] );
       subRound( D, E, A, B, C, f1, K1, W[  2 ] );
       subRound( C, D, E, A, B, f1, K1, W[  3 ] );
       subRound( B, C, D, E, A, f1, K1, W[  4 ] );
       subRound( A, B, C, D, E, f1, K1, W[  5 ] );
       subRound( E, A, B, C, D, f1, K1, W[  6 ] );
       subRound( D, E, A, B, C, f1, K1, W[  7 ] );
       subRound( C, D, E, A, B, f1, K1, W[  8 ] );
       subRound( B, C, D, E, A, f1, K1, W[  9 ] );
      subRound( A, B, C, D, E, f1, K1, W[ 10 ] );
      subRound( E, A, B, C, D, f1, K1, W[ 11 ] );
      subRound( D, E, A, B, C, f1, K1, W[ 12 ] );
      subRound( C, D, E, A, B, f1, K1, W[ 13 ] );
      subRound( B, C, D, E, A, f1, K1, W[ 14 ] );
      subRound( A, B, C, D, E, f1, K1, W[ 15 ] );
      subRound( E, A, B, C, D, f1, K1, W[ 16 ] );
      subRound( D, E, A, B, C, f1, K1, W[ 17 ] );
      subRound( C, D, E, A, B, f1, K1, W[ 18 ] );
      subRound( B, C, D, E, A, f1, K1, W[ 19 ] );
  
      subRound( A, B, C, D, E, f2, K2, W[ 20 ] );
      subRound( E, A, B, C, D, f2, K2, W[ 21 ] );
      subRound( D, E, A, B, C, f2, K2, W[ 22 ] );
      subRound( C, D, E, A, B, f2, K2, W[ 23 ] );
      subRound( B, C, D, E, A, f2, K2, W[ 24 ] );
      subRound( A, B, C, D, E, f2, K2, W[ 25 ] );
      subRound( E, A, B, C, D, f2, K2, W[ 26 ] );
      subRound( D, E, A, B, C, f2, K2, W[ 27 ] );
      subRound( C, D, E, A, B, f2, K2, W[ 28 ] );
      subRound( B, C, D, E, A, f2, K2, W[ 29 ] );
      subRound( A, B, C, D, E, f2, K2, W[ 30 ] );
      subRound( E, A, B, C, D, f2, K2, W[ 31 ] );
      subRound( D, E, A, B, C, f2, K2, W[ 32 ] );
      subRound( C, D, E, A, B, f2, K2, W[ 33 ] );
      subRound( B, C, D, E, A, f2, K2, W[ 34 ] );
      subRound( A, B, C, D, E, f2, K2, W[ 35 ] );
      subRound( E, A, B, C, D, f2, K2, W[ 36 ] );
      subRound( D, E, A, B, C, f2, K2, W[ 37 ] );
      subRound( C, D, E, A, B, f2, K2, W[ 38 ] );
      subRound( B, C, D, E, A, f2, K2, W[ 39 ] );
      
      subRound( A, B, C, D, E, f3, K3, W[ 40 ] );
      subRound( E, A, B, C, D, f3, K3, W[ 41 ] );
      subRound( D, E, A, B, C, f3, K3, W[ 42 ] );
      subRound( C, D, E, A, B, f3, K3, W[ 43 ] );
      subRound( B, C, D, E, A, f3, K3, W[ 44 ] );
      subRound( A, B, C, D, E, f3, K3, W[ 45 ] );
      subRound( E, A, B, C, D, f3, K3, W[ 46 ] );
      subRound( D, E, A, B, C, f3, K3, W[ 47 ] );
      subRound( C, D, E, A, B, f3, K3, W[ 48 ] );
      subRound( B, C, D, E, A, f3, K3, W[ 49 ] );
      subRound( A, B, C, D, E, f3, K3, W[ 50 ] );
      subRound( E, A, B, C, D, f3, K3, W[ 51 ] );
      subRound( D, E, A, B, C, f3, K3, W[ 52 ] );
      subRound( C, D, E, A, B, f3, K3, W[ 53 ] );
      subRound( B, C, D, E, A, f3, K3, W[ 54 ] );
      subRound( A, B, C, D, E, f3, K3, W[ 55 ] );
      subRound( E, A, B, C, D, f3, K3, W[ 56 ] );
      subRound( D, E, A, B, C, f3, K3, W[ 57 ] );
      subRound( C, D, E, A, B, f3, K3, W[ 58 ] );
      subRound( B, C, D, E, A, f3, K3, W[ 59 ] );
  
      subRound( A, B, C, D, E, f4, K4, W[ 60 ] );
      subRound( E, A, B, C, D, f4, K4, W[ 61 ] );
      subRound( D, E, A, B, C, f4, K4, W[ 62 ] );
      subRound( C, D, E, A, B, f4, K4, W[ 63 ] );
      subRound( B, C, D, E, A, f4, K4, W[ 64 ] );
      subRound( A, B, C, D, E, f4, K4, W[ 65 ] );
      subRound( E, A, B, C, D, f4, K4, W[ 66 ] );
      subRound( D, E, A, B, C, f4, K4, W[ 67 ] );
      subRound( C, D, E, A, B, f4, K4, W[ 68 ] );
      subRound( B, C, D, E, A, f4, K4, W[ 69 ] );
      subRound( A, B, C, D, E, f4, K4, W[ 70 ] );
      subRound( E, A, B, C, D, f4, K4, W[ 71 ] );
      subRound( D, E, A, B, C, f4, K4, W[ 72 ] );
      subRound( C, D, E, A, B, f4, K4, W[ 73 ] );
      subRound( B, C, D, E, A, f4, K4, W[ 74 ] );
      subRound( A, B, C, D, E, f4, K4, W[ 75 ] );
      subRound( E, A, B, C, D, f4, K4, W[ 76 ] );
      subRound( D, E, A, B, C, f4, K4, W[ 77 ] );
      subRound( C, D, E, A, B, f4, K4, W[ 78 ] );
      subRound( B, C, D, E, A, f4, K4, W[ 79 ] );
  #else
  #error Illegal SHA_CODE_SIZE
  #endif
  
      /* Build message digest */
      digest[ 0 ] += A;
      digest[ 1 ] += B;
      digest[ 2 ] += C;
      digest[ 3 ] += D;
      digest[ 4 ] += E;
  
          /* W is wiped by the caller */
  #undef W
  }
  
  #undef ROTL
  #undef f1
  #undef f2
  #undef f3
  #undef f4
  #undef K1       
  #undef K2
  #undef K3       
  #undef K4       
  #undef subRound
          
  #else /* !USE_SHA - Use MD5 */
  
  #define HASH_BUFFER_SIZE 4
  #define HASH_EXTRA_SIZE 0
  #define HASH_TRANSFORM MD5Transform
          
  /*
   * MD5 transform algorithm, taken from code written by Colin Plumb,
   * and put into the public domain
   */
  
  /* The four core functions - F1 is optimized somewhat */
  
  /* #define F1(x, y, z) (x & y | ~x & z) */
  #define F1(x, y, z) (z ^ (x & (y ^ z)))
  #define F2(x, y, z) F1(z, x, y)
  #define F3(x, y, z) (x ^ y ^ z)
  #define F4(x, y, z) (y ^ (x | ~z))
  
  /* This is the central step in the MD5 algorithm. */
  #define MD5STEP(f, w, x, y, z, data, s) \
          ( w += f(x, y, z) + data,  w = w<<s | w>>(32-s),  w += x )
  
  /*
   * The core of the MD5 algorithm, this alters an existing MD5 hash to
   * reflect the addition of 16 longwords of new data.  MD5Update blocks
   * the data and converts bytes into longwords for this routine.
   */
  static void MD5Transform(__u32 buf[HASH_BUFFER_SIZE], __u32 const in[16])
  {
          __u32 a, b, c, d;
  
          a = buf[0];
          b = buf[1];
          c = buf[2];
          d = buf[3];
  
          MD5STEP(F1, a, b, c, d, in[ 0]+0xd76aa478,  7);
          MD5STEP(F1, d, a, b, c, in[ 1]+0xe8c7b756, 12);
          MD5STEP(F1, c, d, a, b, in[ 2]+0x242070db, 17);
          MD5STEP(F1, b, c, d, a, in[ 3]+0xc1bdceee, 22);
          MD5STEP(F1, a, b, c, d, in[ 4]+0xf57c0faf,  7);
          MD5STEP(F1, d, a, b, c, in[ 5]+0x4787c62a, 12);
          MD5STEP(F1, c, d, a, b, in[ 6]+0xa8304613, 17);
          MD5STEP(F1, b, c, d, a, in[ 7]+0xfd469501, 22);
          MD5STEP(F1, a, b, c, d, in[ 8]+0x698098d8,  7);
          MD5STEP(F1, d, a, b, c, in[ 9]+0x8b44f7af, 12);
          MD5STEP(F1, c, d, a, b, in[10]+0xffff5bb1, 17);
          MD5STEP(F1, b, c, d, a, in[11]+0x895cd7be, 22);
          MD5STEP(F1, a, b, c, d, in[12]+0x6b901122,  7);
          MD5STEP(F1, d, a, b, c, in[13]+0xfd987193, 12);
          MD5STEP(F1, c, d, a, b, in[14]+0xa679438e, 17);
          MD5STEP(F1, b, c, d, a, in[15]+0x49b40821, 22);
  
          MD5STEP(F2, a, b, c, d, in[ 1]+0xf61e2562,  5);
          MD5STEP(F2, d, a, b, c, in[ 6]+0xc040b340,  9);
          MD5STEP(F2, c, d, a, b, in[11]+0x265e5a51, 14);
          MD5STEP(F2, b, c, d, a, in[ 0]+0xe9b6c7aa, 20);
          MD5STEP(F2, a, b, c, d, in[ 5]+0xd62f105d,  5);
          MD5STEP(F2, d, a, b, c, in[10]+0x02441453,  9);
          MD5STEP(F2, c, d, a, b, in[15]+0xd8a1e681, 14);
          MD5STEP(F2, b, c, d, a, in[ 4]+0xe7d3fbc8, 20);
          MD5STEP(F2, a, b, c, d, in[ 9]+0x21e1cde6,  5);
          MD5STEP(F2, d, a, b, c, in[14]+0xc33707d6,  9);
          MD5STEP(F2, c, d, a, b, in[ 3]+0xf4d50d87, 14);
          MD5STEP(F2, b, c, d, a, in[ 8]+0x455a14ed, 20);
          MD5STEP(F2, a, b, c, d, in[13]+0xa9e3e905,  5);
          MD5STEP(F2, d, a, b, c, in[ 2]+0xfcefa3f8,  9);
          MD5STEP(F2, c, d, a, b, in[ 7]+0x676f02d9, 14);
          MD5STEP(F2, b, c, d, a, in[12]+0x8d2a4c8a, 20);
  
          MD5STEP(F3, a, b, c, d, in[ 5]+0xfffa3942,  4);
          MD5STEP(F3, d, a, b, c, in[ 8]+0x8771f681, 11);
          MD5STEP(F3, c, d, a, b, in[11]+0x6d9d6122, 16);
          MD5STEP(F3, b, c, d, a, in[14]+0xfde5380c, 23);
          MD5STEP(F3, a, b, c, d, in[ 1]+0xa4beea44,  4);
          MD5STEP(F3, d, a, b, c, in[ 4]+0x4bdecfa9, 11);
          MD5STEP(F3, c, d, a, b, in[ 7]+0xf6bb4b60, 16);
          MD5STEP(F3, b, c, d, a, in[10]+0xbebfbc70, 23);
          MD5STEP(F3, a, b, c, d, in[13]+0x289b7ec6,  4);
          MD5STEP(F3, d, a, b, c, in[ 0]+0xeaa127fa, 11);
          MD5STEP(F3, c, d, a, b, in[ 3]+0xd4ef3085, 16);
          MD5STEP(F3, b, c, d, a, in[ 6]+0x04881d05, 23);
          MD5STEP(F3, a, b, c, d, in[ 9]+0xd9d4d039,  4);
          MD5STEP(F3, d, a, b, c, in[12]+0xe6db99e5, 11);
          MD5STEP(F3, c, d, a, b, in[15]+0x1fa27cf8, 16);
          MD5STEP(F3, b, c, d, a, in[ 2]+0xc4ac5665, 23);
  
          MD5STEP(F4, a, b, c, d, in[ 0]+0xf4292244,  6);
          MD5STEP(F4, d, a, b, c, in[ 7]+0x432aff97, 10);
          MD5STEP(F4, c, d, a, b, in[14]+0xab9423a7, 15);
          MD5STEP(F4, b, c, d, a, in[ 5]+0xfc93a039, 21);
          MD5STEP(F4, a, b, c, d, in[12]+0x655b59c3,  6);
          MD5STEP(F4, d, a, b, c, in[ 3]+0x8f0ccc92, 10);
          MD5STEP(F4, c, d, a, b, in[10]+0xffeff47d, 15);
          MD5STEP(F4, b, c, d, a, in[ 1]+0x85845dd1, 21);
          MD5STEP(F4, a, b, c, d, in[ 8]+0x6fa87e4f,  6);
          MD5STEP(F4, d, a, b, c, in[15]+0xfe2ce6e0, 10);
          MD5STEP(F4, c, d, a, b, in[ 6]+0xa3014314, 15);
          MD5STEP(F4, b, c, d, a, in[13]+0x4e0811a1, 21);
          MD5STEP(F4, a, b, c, d, in[ 4]+0xf7537e82,  6);
          MD5STEP(F4, d, a, b, c, in[11]+0xbd3af235, 10);
          MD5STEP(F4, c, d, a, b, in[ 2]+0x2ad7d2bb, 15);
          MD5STEP(F4, b, c, d, a, in[ 9]+0xeb86d391, 21);
  
          buf[0] += a;
          buf[1] += b;
          buf[2] += c;
          buf[3] += d;
  }
  
  #undef F1
  #undef F2
  #undef F3
  #undef F4
  #undef MD5STEP
  
  #endif /* !USE_SHA */
  
  /*********************************************************************
   *
   * Entropy extraction routines
   *
   *********************************************************************/
  
  #define EXTRACT_ENTROPY_USER            1
  #define EXTRACT_ENTROPY_SECONDARY       2
  #define TMP_BUF_SIZE                    (HASH_BUFFER_SIZE + HASH_EXTRA_SIZE)
  #define SEC_XFER_SIZE                   (TMP_BUF_SIZE*4)
  
  static ssize_t extract_entropy(struct entropy_store *r, void * buf,
                                 size_t nbytes, int flags);
  
  /*
   * This utility inline function is responsible for transfering entropy
   * from the primary pool to the secondary extraction pool.  We pull
   * randomness under two conditions; one is if there isn't enough entropy
   * in the secondary pool.  The other is after we have extracted 1024 bytes,
   * at which point we do a "catastrophic reseeding".
   */
  static inline void xfer_secondary_pool(struct entropy_store *r,
                                         size_t nbytes, __u32 *tmp)
  {
          if (r->entropy_count < nbytes * 8 &&
              r->entropy_count < r->poolinfo.POOLBITS) {
                  int nwords = min_t(int,
                                     r->poolinfo.poolwords - r->entropy_count/32,
                                     sizeof(tmp) / 4);
  
                  DEBUG_ENT("xfer %d from primary to %s (have %d, need %d)\n",
                            nwords * 32,
                            r == sec_random_state ? "secondary" : "unknown",
                            r->entropy_count, nbytes * 8);
  
                  extract_entropy(random_state, tmp, nwords * 4, 0);
                  add_entropy_words(r, tmp, nwords);
                  credit_entropy_store(r, nwords * 32);
          }
          if (r->extract_count > 1024) {
                  DEBUG_ENT("reseeding %s with %d from primary\n",
                            r == sec_random_state ? "secondary" : "unknown",
                            sizeof(tmp) * 8);
                  extract_entropy(random_state, tmp, sizeof(tmp), 0);
                  add_entropy_words(r, tmp, sizeof(tmp) / 4);
                  r->extract_count = 0;
          }
  }
  
  /*
   * This function extracts randomness from the "entropy pool", and
   * returns it in a buffer.  This function computes how many remaining
   * bits of entropy are left in the pool, but it does not restrict the
   * number of bytes that are actually obtained.  If the EXTRACT_ENTROPY_USER
   * flag is given, then the buf pointer is assumed to be in user space.
   *
   * If the EXTRACT_ENTROPY_SECONDARY flag is given, then we are actually
   * extracting entropy from the secondary pool, and can refill from the
   * primary pool if needed.
   *
   * Note: extract_entropy() assumes that .poolwords is a multiple of 16 words.
   */
  static ssize_t extract_entropy(struct entropy_store *r, void * buf,
                                 size_t nbytes, int flags)
  {
          ssize_t ret, i;
          __u32 tmp[TMP_BUF_SIZE];
          __u32 x;
  
          add_timer_randomness(&extract_timer_state, nbytes);
  
          /* Redundant, but just in case... */
          if (r->entropy_count > r->poolinfo.POOLBITS)
                  r->entropy_count = r->poolinfo.POOLBITS;
  
          if (flags & EXTRACT_ENTROPY_SECONDARY)
                  xfer_secondary_pool(r, nbytes, tmp);
  
          DEBUG_ENT("%s has %d bits, want %d bits\n",
                    r == sec_random_state ? "secondary" :
                    r == random_state ? "primary" : "unknown",
                    r->entropy_count, nbytes * 8);
  
          if (r->entropy_count / 8 >= nbytes)
                  r->entropy_count -= nbytes*8;
          else
                  r->entropy_count = 0;
  
          if (r->entropy_count < random_write_wakeup_thresh)
                  wake_up_interruptible(&random_write_wait);
  
          r->extract_count += nbytes;
          
          ret = 0;
          while (nbytes) {
                  /*
                   * Check if we need to break out or reschedule....
                   */
                  if ((flags & EXTRACT_ENTROPY_USER) && current->need_resched) {
                          if (signal_pending(current)) {
                                  if (ret == 0)
                                          ret = -ERESTARTSYS;
                                  break;
                          }
                          schedule();
                  }
  
                  /* Hash the pool to get the output */
                  tmp[0] = 0x67452301;
                  tmp[1] = 0xefcdab89;
                  tmp[2] = 0x98badcfe;
                  tmp[3] = 0x10325476;
  #ifdef USE_SHA
                  tmp[4] = 0xc3d2e1f0;
  #endif
                  /*
                   * As we hash the pool, we mix intermediate values of
                   * the hash back into the pool.  This eliminates
                   * backtracking attacks (where the attacker knows
                   * the state of the pool plus the current outputs, and
                   * attempts to find previous ouputs), unless the hash
                   * function can be inverted.
                   */
                  for (i = 0, x = 0; i < r->poolinfo.poolwords; i += 16, x+=2) {
                          HASH_TRANSFORM(tmp, r->pool+i);
                          add_entropy_words(r, &tmp[x%HASH_BUFFER_SIZE], 1);
                  }
                  
                  /*
                   * In case the hash function has some recognizable
                   * output pattern, we fold it in half.
                   */
                  for (i = 0; i <  HASH_BUFFER_SIZE/2; i++)
                          tmp[i] ^= tmp[i + (HASH_BUFFER_SIZE+1)/2];
  #if HASH_BUFFER_SIZE & 1        /* There's a middle word to deal with */
                  x = tmp[HASH_BUFFER_SIZE/2];
                  x ^= (x >> 16);         /* Fold it in half */
                  ((__u16 *)tmp)[HASH_BUFFER_SIZE-1] = (__u16)x;
  #endif
                  
                  /* Copy data to destination buffer */
                  i = min(nbytes, HASH_BUFFER_SIZE*sizeof(__u32)/2);
                  if (flags & EXTRACT_ENTROPY_USER) {
                          i -= copy_to_user(buf, (__u8 const *)tmp, i);
                          if (!i) {
                                  ret = -EFAULT;
                                  break;
                          }
                  } else
                          memcpy(buf, (__u8 const *)tmp, i);
                  nbytes -= i;
                  buf += i;
                  ret += i;
                  add_timer_randomness(&extract_timer_state, nbytes);
          }
  
          /* Wipe data just returned from memory */
          memset(tmp, 0, sizeof(tmp));
          
          return ret;
  }
  
  /*
   * This function is the exported kernel interface.  It returns some
   * number of good random numbers, suitable for seeding TCP sequence
   * numbers, etc.
   */
  void get_random_bytes(void *buf, int nbytes)
  {
          if (sec_random_state)  
                  extract_entropy(sec_random_state, (char *) buf, nbytes, 
                                  EXTRACT_ENTROPY_SECONDARY);
          else if (random_state)
                  extract_entropy(random_state, (char *) buf, nbytes, 0);
          else
                  printk(KERN_NOTICE "get_random_bytes called before "
                                     "random driver initialization\n");
  }
  
  /*********************************************************************
   *
   * Functions to interface with Linux
   *
   *********************************************************************/
  
  /*
   * Initialize the random pool with standard stuff.
   *
   * NOTE: This is an OS-dependent function.
   */
  static void init_std_data(struct entropy_store *r)
  {
          struct timeval  tv;
          __u32           words[2];
          char            *p;
          int             i;
  
          do_gettimeofday(&tv);
          words[0] = tv.tv_sec;
          words[1] = tv.tv_usec;
          add_entropy_words(r, words, 2);
  
          /*
           *      This doesn't lock system.utsname. However, we are generating
           *      entropy so a race with a name set here is fine.
           */
          p = (char *) &system_utsname;
          for (i = sizeof(system_utsname) / sizeof(words); i; i--) {
                  memcpy(words, p, sizeof(words));
                  add_entropy_words(r, words, sizeof(words)/4);
                  p += sizeof(words);
          }
  }
  
  void __init rand_initialize(void)
  {
          int i;
  
          if (create_entropy_store(DEFAULT_POOL_SIZE, &random_state))
                  return;         /* Error, return */
          if (batch_entropy_init(BATCH_ENTROPY_SIZE, random_state))
                  return;         /* Error, return */
          if (create_entropy_store(SECONDARY_POOL_SIZE, &sec_random_state))
                  return;         /* Error, return */
          clear_entropy_store(random_state);
          clear_entropy_store(sec_random_state);
          init_std_data(random_state);
  #ifdef CONFIG_SYSCTL
          sysctl_init_random(random_state);
  #endif
          for (i = 0; i < NR_IRQS; i++)
                  irq_timer_state[i] = NULL;
          for (i = 0; i < MAX_BLKDEV; i++)
                  blkdev_timer_state[i] = NULL;
          memset(&keyboard_timer_state, 0, sizeof(struct timer_rand_state));
          memset(&mouse_timer_state, 0, sizeof(struct timer_rand_state));
          memset(&extract_timer_state, 0, sizeof(struct timer_rand_state));
          extract_timer_state.dont_count_entropy = 1;
  }
  
  void rand_initialize_irq(int irq)
  {
          struct timer_rand_state *state;
          
          if (irq >= NR_IRQS || irq_timer_state[irq])
                  return;
  
          /*
           * If kmalloc returns null, we just won't use that entropy
           * source.
           */
          state = kmalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
          if (state) {
                  memset(state, 0, sizeof(struct timer_rand_state));
                  irq_timer_state[irq] = state;
          }
  }
  
  void rand_initialize_blkdev(int major, int mode)
  {
          struct timer_rand_state *state;
          
          if (major >= MAX_BLKDEV || blkdev_timer_state[major])
                  return;
  
          /*
           * If kmalloc returns null, we just won't use that entropy
           * source.
           */
          state = kmalloc(sizeof(struct timer_rand_state), mode);
          if (state) {
                  memset(state, 0, sizeof(struct timer_rand_state));
                  blkdev_timer_state[major] = state;
          }
  }
  
  
  static ssize_t
  random_read(struct file * file, char * buf, size_t nbytes, loff_t *ppos)
  {
          DECLARE_WAITQUEUE(wait, current);
          ssize_t                 n, retval = 0, count = 0;
          
          if (nbytes == 0)
                  return 0;
  
          add_wait_queue(&random_read_wait, &wait);
          while (nbytes > 0) {
                  set_current_state(TASK_INTERRUPTIBLE);
                  
                  n = nbytes;
                  if (n > SEC_XFER_SIZE)
                          n = SEC_XFER_SIZE;
                  if (n > random_state->entropy_count / 8)
                          n = random_state->entropy_count / 8;
                  if (n == 0) {
                          if (file->f_flags & O_NONBLOCK) {
                                  retval = -EAGAIN;
                                  break;
                          }
                          if (signal_pending(current)) {
                                  retval = -ERESTARTSYS;
                                  break;
                          }
                          schedule();
                          continue;
                  }
                  n = extract_entropy(sec_random_state, buf, n,
                                      EXTRACT_ENTROPY_USER |
                                      EXTRACT_ENTROPY_SECONDARY);
                  if (n < 0) {
                          retval = n;
                          break;
                  }
                  count += n;
                  buf += n;
                  nbytes -= n;
                  break;          /* This break makes the device work */
                                  /* like a named pipe */
          }
          current->state = TASK_RUNNING;
          remove_wait_queue(&random_read_wait, &wait);
  
          /*
           * If we gave the user some bytes, update the access time.
           */
          if (count != 0) {
                  UPDATE_ATIME(file->f_dentry->d_inode);
          }
          
          return (count ? count : retval);
  }
  
  static ssize_t
  urandom_read(struct file * file, char * buf,
                        size_t nbytes, loff_t *ppos)
  {
          return extract_entropy(sec_random_state, buf, nbytes,
                                 EXTRACT_ENTROPY_USER |
                                 EXTRACT_ENTROPY_SECONDARY);
  }
  
  static unsigned int
  random_poll(struct file *file, poll_table * wait)
  {
          unsigned int mask;
  
          poll_wait(file, &random_read_wait, wait);
          poll_wait(file, &random_write_wait, wait);
          mask = 0;
          if (random_state->entropy_count >= random_read_wakeup_thresh)
                  mask |= POLLIN | POLLRDNORM;
          if (random_state->entropy_count < random_write_wakeup_thresh)
                  mask |= POLLOUT | POLLWRNORM;
          return mask;
  }
  
  static ssize_t
  random_write(struct file * file, const char * buffer,
               size_t count, loff_t *ppos)
  {
          int             ret = 0;
          size_t          bytes;
          __u32           buf[16];
          const char      *p = buffer;
          size_t          c = count;
  
          while (c > 0) {
                  bytes = min(c, sizeof(buf));
  
                  bytes -= copy_from_user(&buf, p, bytes);
                  if (!bytes) {
                          ret = -EFAULT;
                          break;
                  }
                  c -= bytes;
                  p += bytes;
  
                  add_entropy_words(random_state, buf, (bytes + 3) / 4);
          }
          if (p == buffer) {
                  return (ssize_t)ret;
          } else {
                  file->f_dentry->d_inode->i_mtime = CURRENT_TIME;
                  mark_inode_dirty(file->f_dentry->d_inode);
                  return (ssize_t)(p - buffer);
          }
  }
  
  static int
  random_ioctl(struct inode * inode, struct file * file,
               unsigned int cmd, unsigned long arg)
  {
          int *p, size, ent_count;
          int retval;
          
          switch (cmd) {
          case RNDGETENTCNT:
                  ent_count = random_state->entropy_count;
                  if (put_user(ent_count, (int *) arg))
                          return -EFAULT;
                  return 0;
          case RNDADDTOENTCNT:
                  if (!capable(CAP_SYS_ADMIN))
                          return -EPERM;
                  if (get_user(ent_count, (int *) arg))
                          return -EFAULT;
                  credit_entropy_store(random_state, ent_count);
                  /*
                   * Wake up waiting processes if we have enough
                   * entropy.
                   */
                  if (random_state->entropy_count >= random_read_wakeup_thresh)
                          wake_up_interruptible(&random_read_wait);
                  return 0;
          case RNDGETPOOL:
                  if (!capable(CAP_SYS_ADMIN))
                          return -EPERM;
                  p = (int *) arg;
                  ent_count = random_state->entropy_count;
                  if (put_user(ent_count, p++) ||
                      get_user(size, p) ||
                      put_user(random_state->poolinfo.poolwords, p++))
                          return -EFAULT;
                  if (size < 0)
                          return -EINVAL;
                  if (size > random_state->poolinfo.poolwords)
                          size = random_state->poolinfo.poolwords;
                  if (copy_to_user(p, random_state->pool, size * sizeof(__u32)))
                          return -EFAULT;
                  return 0;
          case RNDADDENTROPY:
                  if (!capable(CAP_SYS_ADMIN))
                          return -EPERM;
                  p = (int *) arg;
                  if (get_user(ent_count, p++))
                          return -EFAULT;
                  if (ent_count < 0)
                          return -EINVAL;
                  if (get_user(size, p++))
                          return -EFAULT;
                  retval = random_write(file, (const char *) p,
                                        size, &file->f_pos);
                  if (retval < 0)
                          return retval;
                  credit_entropy_store(random_state, ent_count);
                  /*
                   * Wake up waiting processes if we have enough
                   * entropy.
                   */
                  if (random_state->entropy_count >= random_read_wakeup_thresh)
                          wake_up_interruptible(&random_read_wait);
                  return 0;
          case RNDZAPENTCNT:
                  if (!capable(CAP_SYS_ADMIN))
                          return -EPERM;
                  random_state->entropy_count = 0;
                  return 0;
          case RNDCLEARPOOL:
                  /* Clear the entropy pool and associated counters. */
                  if (!capable(CAP_SYS_ADMIN))
                          return -EPERM;
                  clear_entropy_store(random_state);
                  init_std_data(random_state);
                  return 0;
          default:
                  return -EINVAL;
          }
  }
  
  struct file_operations random_fops = {
          read:           random_read,
          write:          random_write,
          poll:           random_poll,
          ioctl:          random_ioctl,
  };
  
  struct file_operations urandom_fops = {
          read:           urandom_read,
          write:          random_write,
          ioctl:          random_ioctl,
  };
  
  /***************************************************************
   * Random UUID interface
   * 
   * Used here for a Boot ID, but can be useful for other kernel 
   * drivers.
   ***************************************************************/
  
  /*
   * Generate random UUID
   */
  void generate_random_uuid(unsigned char uuid_out[16])
  {
          get_random_bytes(uuid_out, 16);
          /* Set UUID version to 4 --- truely random generation */
          uuid_out[6] = (uuid_out[6] & 0x0F) | 0x40;
          /* Set the UUID variant to DCE */
          uuid_out[8] = (uuid_out[8] & 0x3F) | 0x80;
  }
  
  /********************************************************************
   *
   * Sysctl interface
   *
   ********************************************************************/
  
  #ifdef CONFIG_SYSCTL
  
  #include <linux/sysctl.h>
  
  static int sysctl_poolsize;
  static int min_read_thresh, max_read_thresh;
  static int min_write_thresh, max_write_thresh;
  static char sysctl_bootid[16];
  
  /*
   * This function handles a request from the user to change the pool size 
   * of the primary entropy store.
   */
  static int change_poolsize(int poolsize)
  {
          struct entropy_store    *new_store, *old_store;
          int                     ret;
          
          if ((ret = create_entropy_store(poolsize, &new_store)))
                  return ret;
  
          add_entropy_words(new_store, random_state->pool,
                            random_state->poolinfo.poolwords);
          credit_entropy_store(new_store, random_state->entropy_count);
  
          sysctl_init_random(new_store);
          old_store = random_state;
          random_state = batch_tqueue.data = new_store;
          free_entropy_store(old_store);
          return 0;
  }
  
  static int proc_do_poolsize(ctl_table *table, int write, struct file *filp,
                              void *buffer, size_t *lenp)
  {
          int     ret;
  
          sysctl_poolsize = random_state->poolinfo.POOLBYTES;
  
          ret = proc_dointvec(table, write, filp, buffer, lenp);
          if (ret || !write ||
              (sysctl_poolsize == random_state->poolinfo.POOLBYTES))
                  return ret;
  
          return change_poolsize(sysctl_poolsize);
  }
  
  static int poolsize_strategy(ctl_table *table, int *name, int nlen,
                               void *oldval, size_t *oldlenp,
                               void *newval, size_t newlen, void **context)
  {
          int     len;
          
          sysctl_poolsize = random_state->poolinfo.POOLBYTES;
  
          /*
           * We only handle the write case, since the read case gets
           * handled by the default handler (and we don't care if the
           * write case happens twice; it's harmless).
           */
          if (newval && newlen) {
                  len = newlen;
                  if (len > table->maxlen)
                          len = table->maxlen;
                  if (copy_from_user(table->data, newval, len))
                          return -EFAULT;
          }
  
          if (sysctl_poolsize != random_state->poolinfo.POOLBYTES)
                  return change_poolsize(sysctl_poolsize);
  
          return 0;
  }
  
  /*
   * These functions is used to return both the bootid UUID, and random
   * UUID.  The difference is in whether table->data is NULL; if it is,
   * then a new UUID is generated and returned to the user.
   * 
   * If the user accesses this via the proc interface, it will be returned
   * as an ASCII string in the standard UUID format.  If accesses via the 
   * sysctl system call, it is returned as 16 bytes of binary data.
   */
  static int proc_do_uuid(ctl_table *table, int write, struct file *filp,
                          void *buffer, size_t *lenp)
  {
          ctl_table       fake_table;
          unsigned char   buf[64], tmp_uuid[16], *uuid;
  
          uuid = table->data;
          if (!uuid) {
                  uuid = tmp_uuid;
                  uuid[8] = 0;
          }
          if (uuid[8] == 0)
                  generate_random_uuid(uuid);
  
          sprintf(buf, "%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-"
                  "%02x%02x%02x%02x%02x%02x",
                  uuid[0],  uuid[1],  uuid[2],  uuid[3],
                  uuid[4],  uuid[5],  uuid[6],  uuid[7],
                  uuid[8],  uuid[9],  uuid[10], uuid[11],
                  uuid[12], uuid[13], uuid[14], uuid[15]);
          fake_table.data = buf;
          fake_table.maxlen = sizeof(buf);
  
          return proc_dostring(&fake_table, write, filp, buffer, lenp);
  }
  
  static int uuid_strategy(ctl_table *table, int *name, int nlen,
                           void *oldval, size_t *oldlenp,
                           void *newval, size_t newlen, void **context)
  {
          unsigned char   tmp_uuid[16], *uuid;
          unsigned int    len;
  
          if (!oldval || !oldlenp)
                  return 1;
  
          uuid = table->data;
          if (!uuid) {
                  uuid = tmp_uuid;
                  uuid[8] = 0;
          }
          if (uuid[8] == 0)
                  generate_random_uuid(uuid);
  
          if (get_user(len, oldlenp))
                  return -EFAULT;
          if (len) {
                  if (len > 16)
                          len = 16;
                  if (copy_to_user(oldval, uuid, len) ||
                      put_user(len, oldlenp))
                          return -EFAULT;
          }
          return 1;
  }
  
  ctl_table random_table[] = {
          {RANDOM_POOLSIZE, "poolsize",
           &sysctl_poolsize, sizeof(int), 0644, NULL,
           &proc_do_poolsize, &poolsize_strategy},
          {RANDOM_ENTROPY_COUNT, "entropy_avail",
           NULL, sizeof(int), 0444, NULL,
           &proc_dointvec},
          {RANDOM_READ_THRESH, "read_wakeup_threshold",
           &random_read_wakeup_thresh, sizeof(int), 0644, NULL,
           &proc_dointvec_minmax, &sysctl_intvec, 0,
           &min_read_thresh, &max_read_thresh},
          {RANDOM_WRITE_THRESH, "write_wakeup_threshold",
           &random_write_wakeup_thresh, sizeof(int), 0644, NULL,
           &proc_dointvec_minmax, &sysctl_intvec, 0,
           &min_write_thresh, &max_write_thresh},
          {RANDOM_BOOT_ID, "boot_id",
           &sysctl_bootid, 16, 0444, NULL,
           &proc_do_uuid, &uuid_strategy},
          {RANDOM_UUID, "uuid",
           NULL, 16, 0444, NULL,
           &proc_do_uuid, &uuid_strategy},
          {0}
  };
  
  static void sysctl_init_random(struct entropy_store *random_state)
  {
          min_read_thresh = 8;
          min_write_thresh = 0;
          max_read_thresh = max_write_thresh = random_state->poolinfo.POOLBITS;
          random_table[1].data = &random_state->entropy_count;
  }
  #endif  /* CONFIG_SYSCTL */
  
  /********************************************************************
   *
   * Random funtions for networking
   *
   ********************************************************************/
  
  /*
   * TCP initial sequence number picking.  This uses the random number
   * generator to pick an initial secret value.  This value is hashed
   * along with the TCP endpoint information to provide a unique
   * starting point for each pair of TCP endpoints.  This defeats
   * attacks which rely on guessing the initial TCP sequence number.
   * This algorithm was suggested by Steve Bellovin.
   *
   * Using a very strong hash was taking an appreciable amount of the total
   * TCP connection establishment time, so this is a weaker hash,
   * compensated for by changing the secret periodically.
   */
  
  /* F, G and H are basic MD4 functions: selection, majority, parity */
  #define F(x, y, z) ((z) ^ ((x) & ((y) ^ (z))))
  #define G(x, y, z) (((x) & (y)) + (((x) ^ (y)) & (z)))
  #define H(x, y, z) ((x) ^ (y) ^ (z))
  
  /*
   * The generic round function.  The application is so specific that
   * we don't bother protecting all the arguments with parens, as is generally
   * good macro practice, in favor of extra legibility.
   * Rotation is separate from addition to prevent recomputation
   */
  #define ROUND(f, a, b, c, d, x, s)      \
          (a += f(b, c, d) + x, a = (a << s) | (a >> (32-s)))
  #define K1 0
  #define K2 013240474631UL
  #define K3 015666365641UL
  
  /*
   * Basic cut-down MD4 transform.  Returns only 32 bits of result.
   */
  static __u32 halfMD4Transform (__u32 const buf[4], __u32 const in[8])
  {
          __u32   a = buf[0], b = buf[1], c = buf[2], d = buf[3];
  
          /* Round 1 */
          ROUND(F, a, b, c, d, in[0] + K1,  3);
          ROUND(F, d, a, b, c, in[1] + K1,  7);
          ROUND(F, c, d, a, b, in[2] + K1, 11);
          ROUND(F, b, c, d, a, in[3] + K1, 19);
          ROUND(F, a, b, c, d, in[4] + K1,  3);
          ROUND(F, d, a, b, c, in[5] + K1,  7);
          ROUND(F, c, d, a, b, in[6] + K1, 11);
          ROUND(F, b, c, d, a, in[7] + K1, 19);
  
          /* Round 2 */
          ROUND(G, a, b, c, d, in[1] + K2,  3);
          ROUND(G, d, a, b, c, in[3] + K2,  5);
          ROUND(G, c, d, a, b, in[5] + K2,  9);
          ROUND(G, b, c, d, a, in[7] + K2, 13);
          ROUND(G, a, b, c, d, in[0] + K2,  3);
          ROUND(G, d, a, b, c, in[2] + K2,  5);
          ROUND(G, c, d, a, b, in[4] + K2,  9);
          ROUND(G, b, c, d, a, in[6] + K2, 13);
  
          /* Round 3 */
          ROUND(H, a, b, c, d, in[3] + K3,  3);
          ROUND(H, d, a, b, c, in[7] + K3,  9);
          ROUND(H, c, d, a, b, in[2] + K3, 11);
          ROUND(H, b, c, d, a, in[6] + K3, 15);
          ROUND(H, a, b, c, d, in[1] + K3,  3);
          ROUND(H, d, a, b, c, in[5] + K3,  9);
          ROUND(H, c, d, a, b, in[0] + K3, 11);
          ROUND(H, b, c, d, a, in[4] + K3, 15);
  
          return buf[1] + b;      /* "most hashed" word */
          /* Alternative: return sum of all words? */
  }
  
  #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
  
  static __u32 twothirdsMD4Transform (__u32 const buf[4], __u32 const in[12])
  {
          __u32   a = buf[0], b = buf[1], c = buf[2], d = buf[3];
  
          /* Round 1 */
          ROUND(F, a, b, c, d, in[ 0] + K1,  3);
          ROUND(F, d, a, b, c, in[ 1] + K1,  7);
          ROUND(F, c, d, a, b, in[ 2] + K1, 11);
          ROUND(F, b, c, d, a, in[ 3] + K1, 19);
          ROUND(F, a, b, c, d, in[ 4] + K1,  3);
          ROUND(F, d, a, b, c, in[ 5] + K1,  7);
          ROUND(F, c, d, a, b, in[ 6] + K1, 11);
          ROUND(F, b, c, d, a, in[ 7] + K1, 19);
          ROUND(F, a, b, c, d, in[ 8] + K1,  3);
          ROUND(F, d, a, b, c, in[ 9] + K1,  7);
          ROUND(F, c, d, a, b, in[10] + K1, 11);
          ROUND(F, b, c, d, a, in[11] + K1, 19);
  
          /* Round 2 */
          ROUND(G, a, b, c, d, in[ 1] + K2,  3);
          ROUND(G, d, a, b, c, in[ 3] + K2,  5);
          ROUND(G, c, d, a, b, in[ 5] + K2,  9);
          ROUND(G, b, c, d, a, in[ 7] + K2, 13);
          ROUND(G, a, b, c, d, in[ 9] + K2,  3);
          ROUND(G, d, a, b, c, in[11] + K2,  5);
          ROUND(G, c, d, a, b, in[ 0] + K2,  9);
          ROUND(G, b, c, d, a, in[ 2] + K2, 13);
          ROUND(G, a, b, c, d, in[ 4] + K2,  3);
          ROUND(G, d, a, b, c, in[ 6] + K2,  5);
          ROUND(G, c, d, a, b, in[ 8] + K2,  9);
          ROUND(G, b, c, d, a, in[10] + K2, 13);
  
          /* Round 3 */
          ROUND(H, a, b, c, d, in[ 3] + K3,  3);
          ROUND(H, d, a, b, c, in[ 7] + K3,  9);
          ROUND(H, c, d, a, b, in[11] + K3, 11);
          ROUND(H, b, c, d, a, in[ 2] + K3, 15);
          ROUND(H, a, b, c, d, in[ 6] + K3,  3);
          ROUND(H, d, a, b, c, in[10] + K3,  9);
          ROUND(H, c, d, a, b, in[ 1] + K3, 11);
          ROUND(H, b, c, d, a, in[ 5] + K3, 15);
          ROUND(H, a, b, c, d, in[ 9] + K3,  3);
          ROUND(H, d, a, b, c, in[ 0] + K3,  9);
          ROUND(H, c, d, a, b, in[ 4] + K3, 11);
          ROUND(H, b, c, d, a, in[ 8] + K3, 15);
  
          return buf[1] + b;      /* "most hashed" word */
          /* Alternative: return sum of all words? */
  }
  #endif
  
  #undef ROUND
  #undef F
  #undef G
  #undef H
  #undef K1
  #undef K2
  #undef K3
  
  /* This should not be decreased so low that ISNs wrap too fast. */
  #define REKEY_INTERVAL  300
  /*
   * Bit layout of the tcp sequence numbers (before adding current time):
   * bit 24-31: increased after every key exchange
   * bit 0-23: hash(source,dest)
   *
   * The implementation is similar to the algorithm described
   * in the Appendix of RFC 1185, except that
   * - it uses a 1 MHz clock instead of a 250 kHz clock
   * - it performs a rekey every 5 minutes, which is equivalent
   *      to a (source,dest) tulple dependent forward jump of the
   *      clock by 0..2^(HASH_BITS+1)
   *
   * Thus the average ISN wraparound time is 68 minutes instead of
   * 4.55 hours.
   *
   * SMP cleanup and lock avoidance with poor man's RCU.
   *                      Manfred Spraul <manfred@colorfullife.com>
   *              
   */
  #define COUNT_BITS      8
  #define COUNT_MASK      ( (1<<COUNT_BITS)-1)
  #define HASH_BITS       24
  #define HASH_MASK       ( (1<<HASH_BITS)-1 )
  
  static struct keydata {
          time_t rekey_time;
          __u32   count;          // already shifted to the final position
          __u32   secret[12];
  } ____cacheline_aligned ip_keydata[2];
  
  static spinlock_t ip_lock = SPIN_LOCK_UNLOCKED;
  static unsigned int ip_cnt;
  
  static struct keydata *__check_and_rekey(time_t time)
  {
          struct keydata *keyptr;
          spin_lock_bh(&ip_lock);
          keyptr = &ip_keydata[ip_cnt&1];
          if (!keyptr->rekey_time || (time - keyptr->rekey_time) > REKEY_INTERVAL) {
                  keyptr = &ip_keydata[1^(ip_cnt&1)];
                  keyptr->rekey_time = time;
                  get_random_bytes(keyptr->secret, sizeof(keyptr->secret));
                  keyptr->count = (ip_cnt&COUNT_MASK)<<HASH_BITS;
                  mb();
                  ip_cnt++;
          }
          spin_unlock_bh(&ip_lock);
          return keyptr;
  }
  
  static inline struct keydata *check_and_rekey(time_t time)
  {
          struct keydata *keyptr = &ip_keydata[ip_cnt&1];
  
          rmb();
          if (!keyptr->rekey_time || (time - keyptr->rekey_time) > REKEY_INTERVAL) {
                  keyptr = __check_and_rekey(time);
          }
  
          return keyptr;
  }
  
  #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
  __u32 secure_tcpv6_sequence_number(__u32 *saddr, __u32 *daddr,
                                     __u16 sport, __u16 dport)
  {
          struct timeval  tv;
          __u32           seq;
          __u32           hash[12];
          struct keydata *keyptr;
  
          /* The procedure is the same as for IPv4, but addresses are longer.
           * Thus we must use twothirdsMD4Transform.
           */
  
          do_gettimeofday(&tv);   /* We need the usecs below... */
          keyptr = check_and_rekey(tv.tv_sec);
  
          memcpy(hash, saddr, 16);
          hash[4]=(sport << 16) + dport;
          memcpy(&hash[5],keyptr->secret,sizeof(__u32)*7);
  
          seq = twothirdsMD4Transform(daddr, hash) & HASH_MASK;
          seq += keyptr->count;
          seq += tv.tv_usec + tv.tv_sec*1000000;
  
          return seq;
  }
  
  __u32 secure_ipv6_id(__u32 *daddr)
  {
          struct keydata *keyptr;
  
          keyptr = check_and_rekey(CURRENT_TIME);
  
          return halfMD4Transform(daddr, keyptr->secret);
  }
  
  #endif
  
  
  __u32 secure_tcp_sequence_number(__u32 saddr, __u32 daddr,
                                   __u16 sport, __u16 dport)
  {
          struct timeval  tv;
          __u32           seq;
          __u32   hash[4];
          struct keydata *keyptr;
  
          /*
           * Pick a random secret every REKEY_INTERVAL seconds.
           */
          do_gettimeofday(&tv);   /* We need the usecs below... */
          keyptr = check_and_rekey(tv.tv_sec);
  
          /*
           *  Pick a unique starting offset for each TCP connection endpoints
           *  (saddr, daddr, sport, dport).
           *  Note that the words are placed into the starting vector, which is 
           *  then mixed with a partial MD4 over random data.
           */
          hash[0]=saddr;
          hash[1]=daddr;
          hash[2]=(sport << 16) + dport;
          hash[3]=keyptr->secret[11];
  
          seq = halfMD4Transform(hash, keyptr->secret) & HASH_MASK;
          seq += keyptr->count;
          /*
           *      As close as possible to RFC 793, which
           *      suggests using a 250 kHz clock.
           *      Further reading shows this assumes 2 Mb/s networks.
           *      For 10 Mb/s Ethernet, a 1 MHz clock is appropriate.
           *      That's funny, Linux has one built in!  Use it!
           *      (Networks are faster now - should this be increased?)
           */
          seq += tv.tv_usec + tv.tv_sec*1000000;
  #if 0
          printk("init_seq(%lx, %lx, %d, %d) = %d\n",
                 saddr, daddr, sport, dport, seq);
  #endif
          return seq;
  }
  
  /*  The code below is shamelessly stolen from secure_tcp_sequence_number().
   *  All blames to Andrey V. Savochkin <saw@msu.ru>.
   */
  __u32 secure_ip_id(__u32 daddr)
  {
          struct keydata *keyptr;
          __u32 hash[4];
  
          keyptr = check_and_rekey(CURRENT_TIME);
  
          /*
           *  Pick a unique starting offset for each IP destination.
           *  The dest ip address is placed in the starting vector,
           *  which is then hashed with random data.
           */
          hash[0] = daddr;
          hash[1] = keyptr->secret[9];
          hash[2] = keyptr->secret[10];
          hash[3] = keyptr->secret[11];
  
          return halfMD4Transform(hash, keyptr->secret);
  }
  
  #ifdef CONFIG_SYN_COOKIES
  /*
   * Secure SYN cookie computation. This is the algorithm worked out by
   * Dan Bernstein and Eric Schenk.
   *
   * For linux I implement the 1 minute counter by looking at the jiffies clock.
   * The count is passed in as a parameter, so this code doesn't much care.
   */
  
  #define COOKIEBITS 24   /* Upper bits store count */
  #define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
  
  static int      syncookie_init;
  static __u32    syncookie_secret[2][16-3+HASH_BUFFER_SIZE];
  
  __u32 secure_tcp_syn_cookie(__u32 saddr, __u32 daddr, __u16 sport,
                  __u16 dport, __u32 sseq, __u32 count, __u32 data)
  {
          __u32   tmp[16 + HASH_BUFFER_SIZE + HASH_EXTRA_SIZE];
          __u32   seq;
  
          /*
           * Pick two random secrets the first time we need a cookie.
           */
          if (syncookie_init == 0) {
                  get_random_bytes(syncookie_secret, sizeof(syncookie_secret));
                  syncookie_init = 1;
          }
  
          /*
           * Compute the secure sequence number.
           * The output should be:
           *   HASH(sec1,saddr,sport,daddr,dport,sec1) + sseq + (count * 2^24)
           *      + (HASH(sec2,saddr,sport,daddr,dport,count,sec2) % 2^24).
           * Where sseq is their sequence number and count increases every
           * minute by 1.
           * As an extra hack, we add a small "data" value that encodes the
           * MSS into the second hash value.
           */
  
          memcpy(tmp+3, syncookie_secret[0], sizeof(syncookie_secret[0]));
          tmp[0]=saddr;
          tmp[1]=daddr;
          tmp[2]=(sport << 16) + dport;
          HASH_TRANSFORM(tmp+16, tmp);
          seq = tmp[17] + sseq + (count << COOKIEBITS);
  
          memcpy(tmp+3, syncookie_secret[1], sizeof(syncookie_secret[1]));
          tmp[0]=saddr;
          tmp[1]=daddr;
          tmp[2]=(sport << 16) + dport;
          tmp[3] = count; /* minute counter */
          HASH_TRANSFORM(tmp+16, tmp);
  
          /* Add in the second hash and the data */
          return seq + ((tmp[17] + data) & COOKIEMASK);
  }
  
  /*
   * This retrieves the small "data" value from the syncookie.
   * If the syncookie is bad, the data returned will be out of
   * range.  This must be checked by the caller.
   *
   * The count value used to generate the cookie must be within
   * "maxdiff" if the current (passed-in) "count".  The return value
   * is (__u32)-1 if this test fails.
   */
  __u32 check_tcp_syn_cookie(__u32 cookie, __u32 saddr, __u32 daddr, __u16 sport,
                  __u16 dport, __u32 sseq, __u32 count, __u32 maxdiff)
  {
          __u32   tmp[16 + HASH_BUFFER_SIZE + HASH_EXTRA_SIZE];
          __u32   diff;
  
          if (syncookie_init == 0)
                  return (__u32)-1;       /* Well, duh! */
  
          /* Strip away the layers from the cookie */
          memcpy(tmp+3, syncookie_secret[0], sizeof(syncookie_secret[0]));
          tmp[0]=saddr;
          tmp[1]=daddr;
          tmp[2]=(sport << 16) + dport;
          HASH_TRANSFORM(tmp+16, tmp);
          cookie -= tmp[17] + sseq;
          /* Cookie is now reduced to (count * 2^24) ^ (hash % 2^24) */
  
          diff = (count - (cookie >> COOKIEBITS)) & ((__u32)-1 >> COOKIEBITS);
          if (diff >= maxdiff)
                  return (__u32)-1;
  
          memcpy(tmp+3, syncookie_secret[1], sizeof(syncookie_secret[1]));
          tmp[0] = saddr;
          tmp[1] = daddr;
          tmp[2] = (sport << 16) + dport;
          tmp[3] = count - diff;  /* minute counter */
          HASH_TRANSFORM(tmp+16, tmp);
  
          return (cookie - tmp[17]) & COOKIEMASK; /* Leaving the data behind */
  }
  #endif
  
  
  
  EXPORT_SYMBOL(add_keyboard_randomness);
  EXPORT_SYMBOL(add_mouse_randomness);
  EXPORT_SYMBOL(add_interrupt_randomness);
  EXPORT_SYMBOL(add_blkdev_randomness);
  EXPORT_SYMBOL(batch_entropy_store);
  EXPORT_SYMBOL(generate_random_uuid);
  

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