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107 lines
4.5 KiB
C
107 lines
4.5 KiB
C
// Copyright (c) 2014-2019, The Monero Project
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//
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// All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without modification, are
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// permitted provided that the following conditions are met:
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//
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// 1. Redistributions of source code must retain the above copyright notice, this list of
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// conditions and the following disclaimer.
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//
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// 2. Redistributions in binary form must reproduce the above copyright notice, this list
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// of conditions and the following disclaimer in the documentation and/or other
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// materials provided with the distribution.
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//
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// 3. Neither the name of the copyright holder nor the names of its contributors may be
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// used to endorse or promote products derived from this software without specific
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// prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
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// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
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// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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// PROCUREMENT OF 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 CONTRACT,
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// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
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// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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//
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// Parts of this file are originally copyright (c) 2012-2013 The Cryptonote developers
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#include <assert.h>
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#include <stddef.h>
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#include <stdlib.h>
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#include <string.h>
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#include "hash-ops.h"
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/***
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* Round to power of two, for count>=3 and for count being not too large (as reasonable for tree hash calculations)
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*/
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size_t tree_hash_cnt(size_t count) {
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// This algo has some bad history but all we are doing is 1 << floor(log2(count))
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// There are _many_ ways to do log2, for some reason the one selected was the most obscure one,
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// and fixing it made it even more obscure.
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//
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// Iterative method implemented below aims for clarity over speed, if performance is needed
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// then my advice is to use the BSR instruction on x86
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//
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// All the paranoid asserts have been removed since it is trivial to mathematically prove that
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// the return will always be a power of 2.
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// Problem space has been defined as 3 <= count <= 2^28. Of course quarter of a billion transactions
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// is not a sane upper limit for a block, so there will be tighter limits in other parts of the code
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assert( count >= 3 ); // cases for 0,1,2 are handled elsewhere
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assert( count <= 0x10000000 ); // sanity limit to 2^28, MSB=1 will cause an inf loop
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size_t pow = 2;
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while(pow < count) pow <<= 1;
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return pow >> 1;
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}
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void tree_hash(const char (*hashes)[HASH_SIZE], size_t count, char *root_hash) {
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// The blockchain block at height 202612 https://moneroblocks.info/block/202612
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// contained 514 transactions, that triggered bad calculation of variable "cnt" in the original version of this function
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// as from CryptoNote code.
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//
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// This bug applies to all CN altcoins.
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//
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// Mathematical bug here was first published on 14:45:34 (GMT+2) 2014-09-04 by Rafal Freeman <rfree>
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// https://github.com/rfree2monero/bitmonero/commit/b417abfb7a297d09f1bbb6de29030f8de9952ac8
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// and soon also applied to CryptoNote (15:10 GMT+2), and BoolBerry used not fully correct work around:
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// the work around of sizeof(size_t)*8 or <<3 as used before in 2 coins and in BBL later was blocking
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// exploitation on normal platforms, how ever we strongly recommend the following fix because it removes
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// mistake in mathematical formula.
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assert(count > 0);
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if (count == 1) {
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memcpy(root_hash, hashes, HASH_SIZE);
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} else if (count == 2) {
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cn_fast_hash(hashes, 2 * HASH_SIZE, root_hash);
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} else {
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size_t i, j;
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size_t cnt = tree_hash_cnt( count );
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char *ints = calloc(cnt, HASH_SIZE); // zero out as extra protection for using uninitialized mem
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assert(ints);
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memcpy(ints, hashes, (2 * cnt - count) * HASH_SIZE);
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for (i = 2 * cnt - count, j = 2 * cnt - count; j < cnt; i += 2, ++j) {
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cn_fast_hash(hashes[i], 64, ints + j * HASH_SIZE);
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}
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assert(i == count);
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while (cnt > 2) {
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cnt >>= 1;
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for (i = 0, j = 0; j < cnt; i += 2, ++j) {
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cn_fast_hash(ints + i * HASH_SIZE, 64, ints + j * HASH_SIZE);
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}
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}
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cn_fast_hash(ints, 64, root_hash);
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free(ints);
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}
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}
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