85 lines
2.8 KiB
C++
85 lines
2.8 KiB
C++
/* $OpenBSD: arc4random_uniform.c,v 1.2 2015/09/13 08:31:47 guenther Exp $ */
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/*
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* Copyright (c) 2008, Damien Miller <djm@openbsd.org>
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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// This is arc4random_uniform.c from OpenBSD's source tree at
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// $OPENBSD_ROOT/lib/libc/crypt/arc4random_uniform.c.
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//
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// Mumble-specific changes:
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//
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// - Change file extension to .cpp and rename to mumble_arc4random_uniform.cpp.
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// - Add CryptographicRandom.h include.
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// - Remove <sys/types.h> and <stdlib.h> includes, include <stdint.h> for uint32_t.
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// - Added an implementation of arc4random called mumble_arc4random.
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// - Rename arc4random_uniform to mumble_arc4random_uniform.
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// - Change call to arc4random in mumble_arc4random_uniform to call
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// mumble_arc4random instead of arc4random.
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// - Remove DEF_WEAK for arc4random_uniform.
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// - Disable MSVC warning 4146.
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#include <stdint.h>
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#include "crypto/CryptographicRandom.h"
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#if defined(_MSC_VER)
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// Disable "unary minus operator applied to unsigned type, result still unsigned"
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// warning. The unary minus operator used in arc4random_uniform is perfectly valid.
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# pragma warning(disable: 4146)
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#endif
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// Call through to CryptographicRandom::uint32()
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uint32_t
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mumble_arc4random(void)
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{
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return CryptographicRandom::uint32();
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}
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/*
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* Calculate a uniformly distributed random number less than upper_bound
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* avoiding "modulo bias".
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*
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* Uniformity is achieved by generating new random numbers until the one
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* returned is outside the range [0, 2**32 % upper_bound). This
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* guarantees the selected random number will be inside
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* [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound)
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* after reduction modulo upper_bound.
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*/
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uint32_t
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mumble_arc4random_uniform(uint32_t upper_bound)
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{
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uint32_t r, min;
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if (upper_bound < 2)
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return 0;
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/* 2**32 % x == (2**32 - x) % x */
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min = -upper_bound % upper_bound;
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/*
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* This could theoretically loop forever but each retry has
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* p > 0.5 (worst case, usually far better) of selecting a
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* number inside the range we need, so it should rarely need
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* to re-roll.
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*/
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for (;;) {
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r = mumble_arc4random();
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if (r >= min)
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break;
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}
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return r % upper_bound;
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}
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