/*
 * random.c -- A strong random number generator
 *
 * Version 1.01, last modified 13-Feb-97
 * 
 * Copyright Theodore Ts'o, 1994, 1995, 1996, 1997.  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 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 ARE
 * 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 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 MD5
 * hash of the contents of the "entropy pool".  The MD5 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 MD5 from its output.  Even if it is possible to
 * analyze MD5 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 MD5, 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 to
 * 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..."
 *	# Carry a random seed from start-up to start-up
 *	# Load and then save 512 bytes, which is the size of the entropy pool
 * 	if [ -f /etc/random-seed ]; then
 *		cat /etc/random-seed >/dev/urandom
 * 	fi
 *	dd if=/dev/urandom of=/etc/random-seed count=1
 *
 * 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 512 bytes, which is the size of the entropy pool
 *	echo "Saving random seed..."
 *	dd if=/dev/urandom of=/etc/random-seed count=1
 * 
 * For example, on many Linux systems, the appropriate scripts are
 * usually /etc/rc.d/rc.local and /etc/rc.d/rc.0, respectively.
 * 
 * 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 the 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 PGP 3.0 (under development).  It has since
 * been modified by myself to provide better mixing in the case where
 * the input values to add_entropy_word() are mostly small numbers.
 * 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 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/kernel.h>
#include <linux/major.h>
#include <linux/string.h>
#include <linux/fcntl.h>
#include <linux/malloc.h>
#include <linux/random.h>
#include <linux/poll.h>

#include <asm/uaccess.h>
#include <asm/irq.h>
#include <asm/io.h>

/*
 * Configuration information
 */
#undef RANDOM_BENCHMARK
#undef BENCHMARK_NOINT

/*
 * The pool is stirred with a primitive polynomial of degree 128
 * over GF(2), namely x^128 + x^99 + x^59 + x^31 + x^9 + x^7 + 1.
 * For a pool of size 64, try x^64+x^62+x^38+x^10+x^6+x+1.
 */
#define POOLWORDS 128    /* Power of 2 - note that this is 32-bit words */
#define POOLBITS (POOLWORDS*32)
#if POOLWORDS == 128
#define TAP1    99     /* The polynomial taps */
#define TAP2    59
#define TAP3    31
#define TAP4    9
#define TAP5    7
#elif POOLWORDS == 64
#define TAP1    62      /* The polynomial taps */
#define TAP2    38
#define TAP3    10
#define TAP4    6
#define TAP5    1
#else
#error No primitive polynomial available for chosen POOLWORDS
#endif

/*
 * 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.  (Note that the behavior
 * of the 1.0 version of the driver was equivalent to using a second
 * element of 0x80000000).
 */
static __u32 twist_table[2] = { 0, 0xEDB88320 };

/*
 * The minimum number of bits to release a "wait on input".  Should
 * probably always be 8, since a /dev/random read can return a single
 * byte.
 */
#define WAIT_INPUT_BITS 8
/* 
 * The limit number of bits under which to release a "wait on
 * output".  Should probably always be the same as WAIT_INPUT_BITS, so
 * that an output wait releases when and only when a wait on input
 * would block.
 */
#define WAIT_OUTPUT_BITS WAIT_INPUT_BITS

/* There is actually only one of these, globally. */
struct random_bucket {
	unsigned add_ptr;
	unsigned entropy_count;
	int input_rotate;
	__u32 pool[POOLWORDS];
};

#ifdef RANDOM_BENCHMARK
/* For benchmarking only */
struct random_benchmark {
	unsigned long long 	start_time;
	int			times;		/* # of samples */
	unsigned long		min;
	unsigned long		max;
	unsigned long		accum;		/* accumulator for average */
	const char		*descr;
	int			unit;
	unsigned long		flags;
};

#define BENCHMARK_INTERVAL 500

static void initialize_benchmark(struct random_benchmark *bench,
				 const char *descr, int unit);
static void begin_benchmark(struct random_benchmark *bench);
static void end_benchmark(struct random_benchmark *bench);

struct random_benchmark timer_benchmark;
#endif

/* There is one of these per entropy source */
struct timer_rand_state {
	unsigned long	last_time;
	int 		last_delta,last_delta2;
	int		dont_count_entropy:1;
};

static struct random_bucket random_state;
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];
static struct wait_queue *random_read_wait;
static struct wait_queue *random_write_wait;

static long random_read(struct inode * inode, struct file * file,
		       char * buf, unsigned long nbytes);
static long random_read_unlimited(struct inode * inode, struct file * file,
				 char * buf, unsigned long nbytes);
static unsigned int random_poll(struct file *file, poll_table * wait);
static long random_write(struct inode * inode, struct file * file,
			const char * buffer, unsigned long count);
static int random_ioctl(struct inode * inode, struct file * file,
			unsigned int cmd, unsigned long arg);

static inline void fast_add_entropy_word(struct random_bucket *r,
					 const __u32 input);

static void add_entropy_word(struct random_bucket *r,
				    const __u32 input);

#ifndef MIN
#define MIN(a,b) (((a) < (b)) ? (a) : (b))
#endif

/*
 * 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__))
extern inline __u32 rotate_left(int i, __u32 word)
{
	return (word << i) | (word >> (32 - i));
	
}
#else
extern inline __u32 rotate_left(int i, __u32 word)
{
	__asm__("roll %%cl,%0"
		:"=r" (word)
		:"0" (word),"c" (i));
	return word;
}
#endif

/*
 * More asm magic....
 * 
 * For entropy estimation, we need to do an integral base 2
 * logarithm.  By default, use an open-coded C version, although we do
 * have a version which takes advantage of the Intel's x86's "bsr"
 * instruction.
 */
#if (!defined (__i386__))
static inline __u32 int_ln(__u32 word)
{
	__u32 nbits = 0;
	
	while (1) {
		word >>= 1;
		if (!word)
			break;
		nbits++;
	}
	return nbits;
}
#else
static inline __u32 int_ln(__u32 word)
{
	__asm__("bsrl %1,%0\n\t"
		"jnz 1f\n\t"
		"movl $0,%0\n"
		"1:"
		:"=r" (word)
		:"r" (word));
	return word;
}
#endif

	
/*
 * Initialize the random pool with standard stuff.
 *
 * NOTE: This is an OS-dependent function.
 */
static void init_std_data(struct random_bucket *r)
{
	__u32 word, *p;
	int i;
	struct timeval 	tv;

	do_gettimeofday(&tv);
	add_entropy_word(r, tv.tv_sec);
	add_entropy_word(r, tv.tv_usec);

	for (p = (__u32 *) &system_utsname,
	     i = sizeof(system_utsname) / sizeof(__u32);
	     i ; i--, p++) {
		memcpy(&word, p, sizeof(__u32));
		add_entropy_word(r, word);
	}
	
}

/* Clear the entropy pool and associated counters. */
static void rand_clear_pool(void)
{
	memset(&random_state, 0, sizeof(random_state));
	init_std_data(&random_state);
}

void rand_initialize(void)
{
	int i;

	rand_clear_pool();
	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));
#ifdef RANDOM_BENCHMARK
	initialize_benchmark(&timer_benchmark, "timer", 0);
#endif
	extract_timer_state.dont_count_entropy = 1;
	random_read_wait = NULL;
	random_write_wait = NULL;
}

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) {
		irq_timer_state[irq] = state;
		memset(state, 0, sizeof(struct timer_rand_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) {
		blkdev_timer_state[major] = state;
		memset(state, 0, sizeof(struct timer_rand_state));
	}
}

/*
 * This function adds a byte into the entropy "pool".  It does not
 * update the entropy estimate.  The caller must do this if appropriate.
 *
 * The pool is stirred with a primitive polynomial of degree 128
 * over GF(2), namely x^128 + x^99 + x^59 + x^31 + x^9 + x^7 + 1.
 * For a pool of size 64, try x^64+x^62+x^38+x^10+x^6+x+1.
 * 
 * We rotate the input word by a changing number of bits, to help
 * assure that all bits in the entropy get toggled.  Otherwise, if we
 * consistently feed the entropy pool small numbers (like jiffies and
 * scancodes, for example), the upper bits of the entropy pool don't
 * get affected. --- TYT, 10/11/95
 */
static inline void fast_add_entropy_word(struct random_bucket *r,
					 const __u32 input)
{
	unsigned i;
	int new_rotate;
	__u32 w;

	/*
	 * 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 = r->add_ptr--))
		new_rotate -= 7;
	r->input_rotate = new_rotate & 31;

	w = rotate_left(r->input_rotate, input);
	
	/* XOR in the various taps */
	w ^= r->pool[(i+TAP1)&(POOLWORDS-1)];
	w ^= r->pool[(i+TAP2)&(POOLWORDS-1)];
	w ^= r->pool[(i+TAP3)&(POOLWORDS-1)];
	w ^= r->pool[(i+TAP4)&(POOLWORDS-1)];
	w ^= r->pool[(i+TAP5)&(POOLWORDS-1)];
	w ^= r->pool[i&(POOLWORDS-1)];
	/* Use a twisted GFSR for the mixing operation */
	r->pool[i&(POOLWORDS-1)] = (w >> 1) ^ twist_table[w & 1];
}

/*
 * For places where we don't need the inlined version
 */
static void add_entropy_word(struct random_bucket *r,
				    const __u32 input)
{
	fast_add_entropy_word(r, input);
}

/*
 * 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 random_bucket *r,
				 struct timer_rand_state *state, unsigned num)
{
	int	delta, delta2, delta3;
	__u32		time;

#ifdef RANDOM_BENCHMARK
	begin_benchmark(&timer_benchmark);
#endif
#if defined (__i386__)
	if (x86_capability & 16) {
		unsigned long low, high;
		__asm__(".byte 0x0f,0x31"
			:"=a" (low), "=d" (high));
		time = (__u32) low;
		num ^= (__u32) high;
	} else {
		time = jiffies;
	}
#else
	time = jiffies;
#endif

	fast_add_entropy_word(r, (__u32) num);
	fast_add_entropy_word(r, time);
	
	/*
	 * Calculate number of bits of randomness we probably
	 * added.  We take into account the first and second order
	 * deltas in order to make our estimate.
	 */
	if (!state->dont_count_entropy &&
	    (r->entropy_count < POOLBITS)) {
		delta = time - state->last_time;
		state->last_time = time;
		if (delta < 0) delta = -delta;

		delta2 = delta - state->last_delta;
		state->last_delta = delta;
		if (delta2 < 0) delta2 = -delta2;

		delta3 = delta2 - state->last_delta2;
		state->last_delta2 = delta2;
		if (delta3 < 0) delta3 = -delta3;

		delta = MIN(MIN(delta, delta2), delta3) >> 1;
		/* Limit entropy estimate to 12 bits */
		delta &= (1 << 12) - 1;

		r->entropy_count += int_ln(delta);

		/* Prevent overflow */
		if (r->entropy_count > POOLBITS)
			r->entropy_count = POOLBITS;
	}
		
	/* Wake up waiting processes, if we have enough entropy. */
	if (r->entropy_count >= WAIT_INPUT_BITS)
		wake_up_interruptible(&random_read_wait);
#ifdef RANDOM_BENCHMARK
	end_benchmark(&timer_benchmark);
#endif
}

void add_keyboard_randomness(unsigned char scancode)
{
	add_timer_randomness(&random_state, &keyboard_timer_state, scancode);
}

void add_mouse_randomness(__u32 mouse_data)
{
	add_timer_randomness(&random_state, &mouse_timer_state, mouse_data);
}

void add_interrupt_randomness(int irq)
{
	if (irq >= NR_IRQS || irq_timer_state[irq] == 0)
		return;

	add_timer_randomness(&random_state, 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(&random_state, blkdev_timer_state[major],
			     0x200+major);
}

#define USE_SHA

#ifdef USE_SHA

#define SMALL_VERSION		/* Optimize for space over time */

#define HASH_BUFFER_SIZE 5
#define HASH_TRANSFORM SHATransform

/*
 * SHA transform algorithm, taken from code written by Peter Gutman,
 * and apparently in the public domain.
 */

/* The SHA f()-functions.  */

#define f1(x,y,z)   ( z ^ ( x & ( y ^ z ) ) )           /* Rounds  0-19 */
#define f2(x,y,z)   ( x ^ y ^ z )                       /* Rounds 20-39 */
#define f3(x,y,z)   ( ( x & y ) | ( z & ( x | y ) ) )   /* Rounds 40-59 */
#define f4(x,y,z)   ( x ^ y ^ z )                       /* Rounds 60-79 */

/* The SHA Mysterious Constants */

#define K1  0x5A827999L                                 /* Rounds  0-19 */
#define K2  0x6ED9EBA1L                                 /* Rounds 20-39 */
#define K3  0x8F1BBCDCL                                 /* Rounds 40-59 */
#define K4  0xCA62C1D6L                                 /* Rounds 60-79 */

#define ROTL(n,X)  ( ( ( X ) << n ) | ( ( X ) >> ( 32 - n ) ) )

#define expand(W,i) ( W[ i & 15 ] = \
		     ROTL( 1, ( W[ i & 15 ] ^ W[ (i - 14) & 15 ] ^ \
			        W[ (i - 8) & 15 ] ^ W[ (i - 3) & 15 ] ) ) )

#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, __u32 *data)
    {
    __u32 A, B, C, D, E;     /* Local vars */
    __u32 eData[ 16 ];       /* Expanded data */
#ifdef SMALL_VERSION
    int	i;
    __u32 TEMP;
#endif

    /* Set up first buffer and local data buffer */
    A = digest[ 0 ];
    B = digest[ 1 ];
    C = digest[ 2 ];
    D = digest[ 3 ];
    E = digest[ 4 ];
    memcpy( eData, data, 16*sizeof(__u32));

#ifdef SMALL_VERSION
    /*
     * Approximately 50% of the speed of the optimized version, but
     * takes up 1/16 the space.  Saves about 6k on an i386 kernel.
     */
    for (i=0; i < 80; i++) {
	    if (i < 20)
		    TEMP = f1(B, C, D) + K1;
	    else if (i < 40)
		    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 +
		    ((i > 15) ? expand(eData, i) : eData[i]);
	    E = D; D = C; C = ROTL(30, B); B = A; A = TEMP;
    }
#else
    /* Heavy mangling, in 4 sub-rounds of 20 iterations each. */
    subRound( A, B, C, D, E, f1, K1, eData[  0 ] );
    subRound( E, A, B, C, D, f1, K1, eData[  1 ] );
    subRound( D, E, A, B, C, f1, K1, eData[  2 ] );
    subRound( C, D, E, A, B, f1, K1, eData[  3 ] );
    subRound( B, C, D, E, A, f1, K1, eData[  4 ] );
    subRound( A, B, C, D, E, f1, K1, eData[  5 ] );
    subRound( E, A, B, C, D, f1, K1, eData[  6 ] );
    subRound( D, E, A, B, C, f1, K1, eData[  7 ] );
    subRound( C, D, E, A, B, f1, K1, eData[  8 ] );
    subRound( B, C, D, E, A, f1, K1, eData[  9 ] );
    subRound( A, B, C, D, E, f1, K1, eData[ 10 ] );
    subRound( E, A, B, C, D, f1, K1, eData[ 11 ] );
    subRound( D, E, A, B, C, f1, K1, eData[ 12 ] );
    subRound( C, D, E, A, B, f1, K1, eData[ 13 ] );
    subRound( B, C, D, E, A, f1, K1, eData[ 14 ] );
    subRound( A, B, C, D, E, f1, K1, eData[ 15 ] );
    subRound( E, A, B, C, D, f1, K1, expand( eData, 16 ) );
    subRound( D, E, A, B, C, f1, K1, expand( eData, 17 ) );
    subRound( C, D, E, A, B, f1, K1, expand( eData, 18 ) );
    subRound( B, C, D, E, A, f1, K1, expand( eData, 19 ) );

    subRound( A, B, C, D, E, f2, K2, expand( eData, 20 ) );
    subRound( E, A, B, C, D, f2, K2, expand( eData, 21 ) );
    subRound( D, E, A, B, C, f2, K2, expand( eData, 22 ) );
    subRound( C, D, E, A, B, f2, K2, expand( eData, 23 ) );
    subRound( B, C, D, E, A, f2, K2, expand( eData, 24 ) );
    subRound( A, B, C, D, E, f2, K2, expand( eData, 25 ) );
    subRound( E, A, B, C, D, f2, K2, expand( eData, 26 ) );
    subRound( D, E, A, B, C, f2, K2, expand( eData, 27 ) );
    subRound( C, D, E, A, B, f2, K2, expand( eData, 28 ) );
    subRound( B, C, D, E, A, f2, K2, expand( eData, 29 ) );
    subRound( A, B, C, D, E, f2, K2, expand( eData, 30 ) );
    subRound( E, A, B, C, D, f2, K2, expand( eData, 31 ) );
    subRound( D, E, A, B, C, f2, K2, expand( eData, 32 ) );
    subRound( C, D, E, A, B, f2, K2, expand( eData, 33 ) );
    subRound( B, C, D, E, A, f2, K2, expand( eData, 34 ) );
    subRound( A, B, C, D, E, f2, K2, expand( eData, 35 ) );
    subRound( E, A, B, C, D, f2, K2, expand( eData, 36 ) );
    subRound( D, E, A, B, C, f2, K2, expand( eData, 37 ) );
    subRound( C, D, E, A, B, f2, K2, expand( eData, 38 ) );
    subRound( B, C, D, E, A, f2, K2, expand( eData, 39 ) );

    subRound( A, B, C, D, E, f3, K3, expand( eData, 40 ) );
    subRound( E, A, B, C, D, f3, K3, expand( eData, 41 ) );
    subRound( D, E, A, B, C, f3, K3, expand( eData, 42 ) );
    subRound( C, D, E, A, B, f3, K3, expand( eData, 43 ) );
    subRound( B, C, D, E, A, f3, K3, expand( eData, 44 ) );
    subRound( A, B, C, D, E, f3, K3, expand( eData, 45 ) );
    subRound( E, A, B, C, D, f3, K3, expand( eData, 46 ) );
    subRound( D, E, A, B, C, f3, K3, expand( eData, 47 ) );
    subRound( C, D, E, A, B, f3, K3, expand( eData, 48 ) );
    subRound( B, C, D, E, A, f3, K3, expand( eData, 49 ) );
    subRound( A, B, C, D, E, f3, K3, expand( eData, 50 ) );
    subRound( E, A, B, C, D, f3, K3, expand( eData, 51 ) );
    subRound( D, E, A, B, C, f3, K3, expand( eData, 52 ) );
    subRound( C, D, E, A, B, f3, K3, expand( eData, 53 ) );
    subRound( B, C, D, E, A, f3, K3, expand( eData, 54 ) );
    subRound( A, B, C, D, E, f3, K3, expand( eData, 55 ) );
    subRound( E, A, B, C, D, f3, K3, expand( eData, 56 ) );
    subRound( D, E, A, B, C, f3, K3, expand( eData, 57 ) );
    subRound( C, D, E, A, B, f3, K3, expand( eData, 58 ) );
    subRound( B, C, D, E, A, f3, K3, expand( eData, 59 ) );

    subRound( A, B, C, D, E, f4, K4, expand( eData, 60 ) );
    subRound( E, A, B, C, D, f4, K4, expand( eData, 61 ) );
    subRound( D, E, A, B, C, f4, K4, expand( eData, 62 ) );
    subRound( C, D, E, A, B, f4, K4, expand( eData, 63 ) );
    subRound( B, C, D, E, A, f4, K4, expand( eData, 64 ) );
    subRound( A, B, C, D, E, f4, K4, expand( eData, 65 ) );
    subRound( E, A, B, C, D, f4, K4, expand( eData, 66 ) );
    subRound( D, E, A, B, C, f4, K4, expand( eData, 67 ) );
    subRound( C, D, E, A, B, f4, K4, expand( eData, 68 ) );
    subRound( B, C, D, E, A, f4, K4, expand( eData, 69 ) );
    subRound( A, B, C, D, E, f4, K4, expand( eData, 70 ) );
    subRound( E, A, B, C, D, f4, K4, expand( eData, 71 ) );
    subRound( D, E, A, B, C, f4, K4, expand( eData, 72 ) );
    subRound( C, D, E, A, B, f4, K4, expand( eData, 73 ) );
    subRound( B, C, D, E, A, f4, K4, expand( eData, 74 ) );
    subRound( A, B, C, D, E, f4, K4, expand( eData, 75 ) );
    subRound( E, A, B, C, D, f4, K4, expand( eData, 76 ) );
    subRound( D, E, A, B, C, f4, K4, expand( eData, 77 ) );
    subRound( C, D, E, A, B, f4, K4, expand( eData, 78 ) );
    subRound( B, C, D, E, A, f4, K4, expand( eData, 79 ) );
#endif /* SMALL_VERSION */

    /* Build message digest */
    digest[ 0 ] += A;
    digest[ 1 ] += B;
    digest[ 2 ] += C;
    digest[ 3 ] += D;
    digest[ 4 ] += E;
    }

#else
#define HASH_BUFFER_SIZE 4
#define HASH_TRANSFORM MD5Transform
	
/*
 * MD5 transform algorithm, taken from code written by Colin Plumb,
 * and put into the public domain
 *
 * QUESTION: Replace this with SHA, which as generally received better
 * reviews from the cryptographic community?
 */

/* 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[4],
			 __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


#if POOLWORDS % 16
#error extract_entropy() assumes that POOLWORDS is a multiple of 16 words.
#endif
/*
 * 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.
 */
static int extract_entropy(struct random_bucket *r, char * buf,
				  int nbytes, int to_user)
{
	int ret, i;
	__u32 tmp[HASH_BUFFER_SIZE];
	char *cp,*dp;

	add_timer_randomness(r, &extract_timer_state, nbytes);
	
	/* Redundant, but just in case... */
	if (r->entropy_count > POOLBITS) 
		r->entropy_count = POOLBITS;

	ret = nbytes;
	if (r->entropy_count / 8 >= nbytes)
		r->entropy_count -= nbytes*8;
	else
		r->entropy_count = 0;

	if (r->entropy_count < WAIT_OUTPUT_BITS)
		wake_up_interruptible(&random_write_wait);
	
	while (nbytes) {
		/* 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
		for (i = 0; i < POOLWORDS; i += 16)
			HASH_TRANSFORM(tmp, r->pool+i);
		/* Modify pool so next hash will produce different results */
		add_entropy_word(r, tmp[0]);
		add_entropy_word(r, tmp[1]);
		add_entropy_word(r, tmp[2]);
		add_entropy_word(r, tmp[3]);
#ifdef USE_SHA
		add_entropy_word(r, tmp[4]);
#endif
		/*
		 * Run the hash transform one more time, since we want
		 * to add at least minimal obscuring of the inputs to
		 * add_entropy_word().
		 */
		HASH_TRANSFORM(tmp, r->pool);

		/*
		 * In case the hash function has some recognizable
		 * output pattern, we fold it in half.
		 */
		cp = (char *) tmp;
		dp = cp + (HASH_BUFFER_SIZE*sizeof(__u32)) - 1;
		for (i=0; i <  HASH_BUFFER_SIZE*sizeof(__u32)/2; i++) {
			*cp ^= *dp;
			cp++;  dp--;
		}
		
		/* Copy data to destination buffer */
		i = MIN(nbytes, HASH_BUFFER_SIZE*sizeof(__u32)/2);
		if (to_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;
		add_timer_randomness(r, &extract_timer_state, nbytes);
		if (to_user && need_resched)
			schedule();
	}

	/* Wipe data 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)
{
	extract_entropy(&random_state, (char *) buf, nbytes, 0);
}

static long
random_read(struct inode * inode, struct file * file, char * buf, unsigned long nbytes)
{
	struct wait_queue 	wait = { current, NULL };
	int			n;
	int			retval = 0;
	int			count = 0;
	
	if (nbytes == 0)
		return 0;

	add_wait_queue(&random_read_wait, &wait);
	while (nbytes > 0) {
		current->state = TASK_INTERRUPTIBLE;
		
		n = nbytes;
		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 (current->signal & ~current->blocked) {
				retval = -ERESTARTSYS;
				break;
			}
			schedule();
			continue;
		}
		n = extract_entropy(&random_state, buf, n, 1);
		if (n < 0) {
			if (count == 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 and we have an inode pointer,
	 * update the access time.
	 */
	if (inode && count != 0) {
		inode->i_atime = CURRENT_TIME;
		inode->i_dirt = 1;
	}
	
	return (count ? count : retval);
}

static long
random_read_unlimited(struct inode * inode, struct file * file,
		      char * buf, unsigned long nbytes)
{
	return extract_entropy(&random_state, buf, nbytes, 1);
}

static unsigned int
random_poll(struct file *file, poll_table * wait)
{
	unsigned int mask;

	poll_wait(&random_read_wait, wait);
	poll_wait(&random_write_wait, wait);
	mask = 0;
	if (random_state.entropy_count >= WAIT_INPUT_BITS)
		mask |= POLLIN | POLLRDNORM;
	if (random_state.entropy_count < WAIT_OUTPUT_BITS)
		mask |= POLLOUT | POLLWRNORM;
	return mask;
}

static long
random_write(struct inode * inode, struct file * file,
	     const char * buffer, unsigned long count)
{
	int 		i, bytes, ret = 0;
	__u32 		buf[16];
	const char 	*p = buffer;
	int		c = count;

	while (c > 0) {
		bytes = MIN(c, sizeof(buf));

		bytes -= copy_from_user(&buf, p, bytes);
		if (!bytes) {
			if (!ret)
				ret = -EFAULT;
			break;
		}
		c -= bytes;
		p += bytes;
		ret += bytes;
		
		i = (bytes+sizeof(__u32)-1) / sizeof(__u32);
		while (i--)
			add_entropy_word(&random_state, buf[i]);
	}
	if ((ret > 0) && inode) {
		inode->i_mtime = CURRENT_TIME;
		inode->i_dirt = 1;
	}
	return ret;
}

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:
		retval = verify_area(VERIFY_WRITE, (void *) arg, sizeof(int));
		if (retval)
			return(retval);
		ent_count = random_state.entropy_count;
		put_user(ent_count, (int *) arg);
		return 0;
	case RNDADDTOENTCNT:
		if (!suser())
			return -EPERM;
		retval = verify_area(VERIFY_READ, (void *) arg, sizeof(int));
		if (retval)
			return(retval);
		get_user(ent_count, (int *) arg);
		/*
		 * Add i to entropy_count, limiting the result to be
		 * between 0 and POOLBITS.
		 */
		if (ent_count < -random_state.entropy_count)
			random_state.entropy_count = 0;
		else if (ent_count > POOLBITS)
			random_state.entropy_count = POOLBITS;
		else {
			random_state.entropy_count += ent_count;
			if (random_state.entropy_count > POOLBITS)
				random_state.entropy_count = POOLBITS;
			if (random_state.entropy_count < 0)
				random_state.entropy_count = 0;
		}
		/*
		 * Wake up waiting processes if we have enough
		 * entropy.
		 */
		if (random_state.entropy_count >= WAIT_INPUT_BITS)
			wake_up_interruptible(&random_read_wait);
		return 0;
	case RNDGETPOOL:
		if (!suser())
			return -EPERM;
		p = (int *) arg;
		retval = verify_area(VERIFY_WRITE, (void *) p, sizeof(int));
		if (retval)
			return(retval);
		ent_count = random_state.entropy_count;
		put_user(ent_count, p++);
		retval = verify_area(VERIFY_WRITE, (void *) p, sizeof(int));
		if (retval)
			return(retval);
		get_user(size, p);
		put_user(POOLWORDS, p++);
		if (size < 0)
			return -EINVAL;
		if (size > POOLWORDS)
			size = POOLWORDS;
		if (copy_to_user(p, random_state.pool, size*sizeof(__u32)))
			return -EFAULT;
		return 0;
	case RNDADDENTROPY:
		if (!suser())
			return -EPERM;
		p = (int *) arg;
		retval = verify_area(VERIFY_READ, (void *) p, 2*sizeof(int));
		if (retval)
			return(retval);
		get_user(ent_count, p++);
		if (ent_count < 0)
			return -EINVAL;
		get_user(size, p++);
		retval = verify_area(VERIFY_READ, (void *) p, size);
		if (retval)
			return retval;
		retval = random_write(0, file, (const char *) p, size);
		if (retval < 0)
			return retval;
		/*
		 * Add ent_count to entropy_count, limiting the result to be
		 * between 0 and POOLBITS.
		 */
		if (ent_count > POOLBITS)
			random_state.entropy_count = POOLBITS;
		else {
			random_state.entropy_count += ent_count;
			if (random_state.entropy_count > POOLBITS)
				random_state.entropy_count = POOLBITS;
			if (random_state.entropy_count < 0)
				random_state.entropy_count = 0;
		}
		/*
		 * Wake up waiting processes if we have enough
		 * entropy.
		 */
		if (random_state.entropy_count >= WAIT_INPUT_BITS)
			wake_up_interruptible(&random_read_wait);
		return 0;
	case RNDZAPENTCNT:
		if (!suser())
			return -EPERM;
		random_state.entropy_count = 0;
		return 0;
	case RNDCLEARPOOL:
		/* Clear the entropy pool and associated counters. */
		if (!suser())
			return -EPERM;
		rand_clear_pool();
		return 0;
	default:
		return -EINVAL;
	}
}

struct file_operations random_fops = {
	NULL,		/* random_lseek */
	random_read,
	random_write,
	NULL,		/* random_readdir */
	random_poll,	/* random_poll */
	random_ioctl,
	NULL,		/* random_mmap */
	NULL,		/* no special open code */
	NULL		/* no special release code */
};

struct file_operations urandom_fops = {
	NULL,		/* unrandom_lseek */
	random_read_unlimited,
	random_write,
	NULL,		/* urandom_readdir */
	NULL,		/* urandom_poll */
	random_ioctl,
	NULL,		/* urandom_mmap */
	NULL,		/* no special open code */
	NULL		/* no special release code */
};

/*
 * 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.
 */
__u32 secure_tcp_sequence_number(__u32 saddr, __u32 daddr,
				 __u16 sport, __u16 dport)
{
	static int	is_init = 0;
	static __u32	secret[16];
	struct timeval 	tv;
	__u32 		tmp[16];
	__u32		seq;

	/*
	 * Pick a random secret the first time we open a TCP
	 * connection.
	 */
	if (is_init == 0) {
		get_random_bytes(&secret, sizeof(secret));
		is_init = 1;
	}

	memcpy(tmp, secret, sizeof(tmp));
	/*
	 * Pick a unique starting offset for each
	 * TCP connection endpoints (saddr, daddr, sport, dport)
	 */
	tmp[8]=saddr;
	tmp[9]=daddr;
	tmp[10]=(sport << 16) + dport;
	HASH_TRANSFORM(tmp, tmp);
	
	/*
	 *	As close as possible to RFC 793, which
	 *	suggests using a 250kHz clock.
	 *	Further reading shows this assumes 2MB/s networks.
	 *	For 10MB/s ethernet, a 1MHz clock is appropriate.
	 *	That's funny, Linux has one built in!  Use it!
	 */
	do_gettimeofday(&tv);
	seq = tmp[1] + 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);
}

#ifdef RANDOM_BENCHMARK
/*
 * This is so we can do some benchmarking of the random driver, to see
 * how much overhead add_timer_randomness really takes.  This only
 * works on a Pentium, since it depends on the timer clock...
 *
 * Note: the results of this benchmark as of this writing (5/27/96)
 *
 * On a Pentium, add_timer_randomness() takes between 150 and 1000
 * clock cycles, with an average of around 600 clock cycles.  On a 75
 * MHz Pentium, this translates to 2 to 13 microseconds, with an
 * average time of 8 microseconds.  This should be fast enough so we
 * can use add_timer_randomness() even with the fastest of interrupts...
 */
static inline unsigned long long get_clock_cnt(void)
{
	unsigned long low, high;
	__asm__(".byte 0x0f,0x31" :"=a" (low), "=d" (high));
	return (((unsigned long long) high << 31) | low); 
}

static void initialize_benchmark(struct random_benchmark *bench,
				 const char *descr, int unit)
{
	bench->times = 0;
	bench->accum = 0;
	bench->max = 0;
	bench->min = 1 << 31;
	bench->descr = descr;
	bench->unit = unit;
}

static void begin_benchmark(struct random_benchmark *bench)
{
#ifdef BENCHMARK_NOINT
	save_flags(bench->flags); cli();
#endif
	bench->start_time = get_clock_cnt();
}

static void end_benchmark(struct random_benchmark *bench)
{
	unsigned long ticks;
	
	ticks = (unsigned long) (get_clock_cnt() - bench->start_time);
#ifdef BENCHMARK_NOINT
	restore_flags(bench->flags);
#endif
	if (ticks < bench->min)
		bench->min = ticks;
	if (ticks > bench->max)
		bench->max = ticks;
	bench->accum += ticks;
	bench->times++;
	if (bench->times == BENCHMARK_INTERVAL) {
		printk("Random benchmark: %s %d: %lu min, %lu avg, "
		       "%lu max\n", bench->descr, bench->unit, bench->min,
		       bench->accum / BENCHMARK_INTERVAL, bench->max);
		bench->times = 0;
		bench->accum = 0;
		bench->max = 0;
		bench->min = 1 << 31;
	}
}	
#endif /* RANDOM_BENCHMARK */
