328 lines
8.2 KiB
C
328 lines
8.2 KiB
C
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/* $NetBSD: arc4random.c,v 1.29 2011/11/29 13:16:27 drochner Exp $ */
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/*-
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* Copyright (c) 2002, 2011 The NetBSD Foundation, Inc.
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* All rights reserved.
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*
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* This code is derived from software contributed to The NetBSD Foundation
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* by Thor Lancelot Simon.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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/*-
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* THE BEER-WARE LICENSE
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*
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* <dan@FreeBSD.ORG> wrote this file. As long as you retain this notice you
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* can do whatever you want with this stuff. If we meet some day, and you
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* think this stuff is worth it, you can buy me a beer in return.
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*
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* Dan Moschuk
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*
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* $FreeBSD: src/sys/libkern/arc4random.c,v 1.9 2001/08/30 12:30:58 bde Exp $
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*/
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#include <sys/cdefs.h>
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#ifdef _KERNEL
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#include "rnd.h"
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#else
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#define NRND 0
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#endif
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#include <sys/types.h>
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#include <sys/time.h>
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#include <sys/param.h>
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#ifdef _KERNEL
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#include <sys/kernel.h>
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#endif
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#include <sys/systm.h>
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#ifdef _KERNEL
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#include <sys/mutex.h>
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#include <sys/rngtest.h>
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#else
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#define mutex_spin_enter(x) ;
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#define mutex_spin_exit(x) ;
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#define mutex_init(x, y, z) ;
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#endif
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#include <lib/libkern/libkern.h>
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#if NRND > 0
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#include <sys/rnd.h>
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#include <dev/rnd_private.h>
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static rndsink_t rs;
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#endif
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/*
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* The best known attack that distinguishes RC4 output from a random
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* bitstream requires 2^25 bytes. (see Paul and Preneel, Analysis of
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* Non-fortuitous Predictive States of the RC4 Keystream Generator.
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* INDOCRYPT 2003, pp52 – 67).
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*
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* However, we discard the first 1024 bytes of output, avoiding the
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* biases detected in this paper. The best current attack that
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* can distinguish this "RC4[drop]" output seems to be Fleuhrer &
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* McGrew's attack which requires 2^30.6 bytes of output:
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* Fluhrer and McGrew, Statistical Analysis of the Alleged RC4
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* Keystream Generator. FSE 2000, pp19 – 30
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*
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* We begin trying to rekey at 2^24 bytes, and forcibly rekey at 2^29 bytes
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* even if the resulting key cannot be guaranteed to have full entropy.
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*/
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#define ARC4_MAXBYTES (16 * 1024 * 1024)
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#define ARC4_HARDMAX (512 * 1024 * 1024)
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#define ARC4_RESEED_SECONDS 300
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#define ARC4_KEYBYTES 16 /* 128 bit key */
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#ifdef _STANDALONE
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#define time_uptime 1 /* XXX ugly! */
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#endif /* _STANDALONE */
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static u_int8_t arc4_i, arc4_j;
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static int arc4_initialized = 0;
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static int arc4_numbytes = 0;
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static u_int8_t arc4_sbox[256];
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static time_t arc4_nextreseed;
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#ifdef _KERNEL
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kmutex_t arc4_mtx;
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#endif
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static inline u_int8_t arc4_randbyte(void);
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static inline void arc4randbytes_unlocked(void *, size_t);
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void _arc4randbytes(void *, size_t);
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uint32_t _arc4random(void);
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static inline void
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arc4_swap(u_int8_t *a, u_int8_t *b)
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{
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u_int8_t c;
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c = *a;
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*a = *b;
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*b = c;
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}
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/*
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* Stir our S-box.
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*/
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static void
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arc4_randrekey(void *arg)
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{
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u_int8_t key[256];
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int n, ask_for_more = 0;
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#ifdef _KERNEL
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#ifdef DIAGNOSTIC
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#if 0 /* XXX rngtest_t is too large and could cause stack overflow */
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rngtest_t rt;
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#endif
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#endif
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#endif
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#if NRND > 0
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static int callback_pending;
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int r;
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#endif
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/*
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* The first time through, we must take what we can get,
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* so schedule ourselves for callback no matter what.
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*/
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if (__predict_true(arc4_initialized)) {
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mutex_spin_enter(&arc4_mtx);
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}
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#if NRND > 0 /* XXX without rnd, we will key from the stack, ouch! */
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else {
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ask_for_more = 1;
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r = rnd_extract_data(key, ARC4_KEYBYTES, RND_EXTRACT_ANY);
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goto got_entropy;
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}
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if (arg == NULL) {
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if (callback_pending) {
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if (arc4_numbytes > ARC4_HARDMAX) {
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printf("arc4random: WARNING, hit 2^29 bytes, "
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"forcibly rekeying.\n");
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r = rnd_extract_data(key, ARC4_KEYBYTES,
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RND_EXTRACT_ANY);
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rndsink_detach(&rs);
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callback_pending = 0;
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goto got_entropy;
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} else {
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mutex_spin_exit(&arc4_mtx);
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return;
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}
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}
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r = rnd_extract_data(key, ARC4_KEYBYTES, RND_EXTRACT_GOOD);
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if (r < ARC4_KEYBYTES) {
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ask_for_more = 1;
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}
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} else {
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ask_for_more = 0;
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callback_pending = 0;
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if (rs.len != ARC4_KEYBYTES) {
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panic("arc4_randrekey: rekey callback bad length");
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}
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memcpy(key, rs.data, rs.len);
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memset(rs.data, 0, rs.len);
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}
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got_entropy:
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if (!ask_for_more) {
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callback_pending = 0;
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} else if (!callback_pending) {
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callback_pending = 1;
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strlcpy(rs.name, "arc4random", sizeof(rs.name));
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rs.cb = arc4_randrekey;
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rs.arg = &rs;
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rs.len = ARC4_KEYBYTES;
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rndsink_attach(&rs);
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}
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#endif
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/*
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* If it's the first time, or we got a good key, actually rekey.
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*/
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if (!ask_for_more || !arc4_initialized) {
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for (n = ARC4_KEYBYTES; n < sizeof(key); n++)
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key[n] = key[n % ARC4_KEYBYTES];
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for (n = 0; n < 256; n++) {
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arc4_j = (arc4_j + arc4_sbox[n] + key[n]) % 256;
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arc4_swap(&arc4_sbox[n], &arc4_sbox[arc4_j]);
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}
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arc4_i = arc4_j;
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memset(key, 0, sizeof(key));
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/*
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* Throw away the first N words of output, as suggested in the
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* paper "Weaknesses in the Key Scheduling Algorithm of RC4"
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* by Fluher, Mantin, and Shamir. (N = 256 in our case.)
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*/
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for (n = 0; n < 256 * 4; n++)
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arc4_randbyte();
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/* Reset for next reseed cycle. */
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arc4_nextreseed = time_uptime + ARC4_RESEED_SECONDS;
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arc4_numbytes = 0;
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#ifdef _KERNEL
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#ifdef DIAGNOSTIC
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#if 0 /* XXX rngtest_t is too large and could cause stack overflow */
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/*
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* Perform the FIPS 140-2 statistical RNG test; warn if our
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* output has such poor quality as to fail the test.
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*/
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arc4randbytes_unlocked(rt.rt_b, sizeof(rt.rt_b));
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strlcpy(rt.rt_name, "arc4random", sizeof(rt.rt_name));
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if (rngtest(&rt)) {
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/* rngtest will scream to the console. */
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arc4_nextreseed = time_uptime;
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arc4_numbytes = ARC4_MAXBYTES;
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/* XXX should keep old context around, *NOT* use new */
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}
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#endif
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#endif
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#endif
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}
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if (__predict_true(arc4_initialized)) {
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mutex_spin_exit(&arc4_mtx);
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}
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}
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/*
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* Initialize our S-box to its beginning defaults.
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*/
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static void
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arc4_init(void)
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{
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int n;
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mutex_init(&arc4_mtx, MUTEX_DEFAULT, IPL_VM);
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arc4_i = arc4_j = 0;
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for (n = 0; n < 256; n++)
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arc4_sbox[n] = (u_int8_t) n;
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arc4_randrekey(NULL);
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arc4_initialized = 1;
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}
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/*
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* Generate a random byte.
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*/
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static inline u_int8_t
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arc4_randbyte(void)
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{
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u_int8_t arc4_t;
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arc4_i = (arc4_i + 1) % 256;
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arc4_j = (arc4_j + arc4_sbox[arc4_i]) % 256;
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arc4_swap(&arc4_sbox[arc4_i], &arc4_sbox[arc4_j]);
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arc4_t = (arc4_sbox[arc4_i] + arc4_sbox[arc4_j]) % 256;
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return arc4_sbox[arc4_t];
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}
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static inline void
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arc4randbytes_unlocked(void *p, size_t len)
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{
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u_int8_t *buf = (u_int8_t *)p;
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size_t i;
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for (i = 0; i < len; buf[i] = arc4_randbyte(), i++)
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continue;
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}
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void
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_arc4randbytes(void *p, size_t len)
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{
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/* Initialize array if needed. */
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if (!arc4_initialized) {
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arc4_init();
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/* avoid conditionalizing locking */
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return arc4randbytes_unlocked(p, len);
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}
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mutex_spin_enter(&arc4_mtx);
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arc4randbytes_unlocked(p, len);
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arc4_numbytes += len;
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mutex_spin_exit(&arc4_mtx);
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if ((arc4_numbytes > ARC4_MAXBYTES) ||
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(time_uptime > arc4_nextreseed)) {
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arc4_randrekey(NULL);
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}
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}
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u_int32_t
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_arc4random(void)
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{
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u_int32_t ret;
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u_int8_t *retc;
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retc = (u_int8_t *)&ret;
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_arc4randbytes(retc, sizeof(u_int32_t));
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return ret;
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}
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