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// Copyright (c) 2014-2019, The Monero Project
//
// 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, this list of
// conditions and the following disclaimer.
//
// 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. Neither the name of the copyright holder nor the names of its contributors may be
// used to endorse or promote products derived from this software without specific
// prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "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 COPYRIGHT HOLDER OR CONTRIBUTORS 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.
//
// Parts of this file are originally copyright (c) 2012-2013 The Cryptonote developers
#include <assert.h>
#include <stddef.h>
#include <string.h>
#include "hash-ops.h"
/***
* Round to power of two, for count>=3 and for count being not too large (as reasonable for tree hash calculations)
*/
size_t tree_hash_cnt(size_t count) {
// This algo has some bad history but all we are doing is 1 << floor(log2(count))
// There are _many_ ways to do log2, for some reason the one selected was the most obscure one,
// and fixing it made it even more obscure.
//
// Iterative method implemented below aims for clarity over speed, if performance is needed
// then my advice is to use the BSR instruction on x86
//
// All the paranoid asserts have been removed since it is trivial to mathematically prove that
// the return will always be a power of 2.
// Problem space has been defined as 3 <= count <= 2^28. Of course quarter of a billion transactions
// is not a sane upper limit for a block, so there will be tighter limits in other parts of the code
assert( count >= 3 ); // cases for 0,1,2 are handled elsewhere
assert( count <= 0x10000000 ); // sanity limit to 2^28, MSB=1 will cause an inf loop
size_t pow = 2;
while(pow < count) pow <<= 1;
return pow >> 1;
}
void tree_hash(const char (*hashes)[HASH_SIZE], size_t count, char *root_hash) {
// The blockchain block at height 202612 https://moneroblocks.info/block/202612
// contained 514 transactions, that triggered bad calculation of variable "cnt" in the original version of this function
// as from CryptoNote code.
//
// This bug applies to all CN altcoins.
//
// Mathematical bug here was first published on 14:45:34 (GMT+2) 2014-09-04 by Rafal Freeman <rfree>
// https://github.com/rfree2monero/bitmonero/commit/b417abfb7a297d09f1bbb6de29030f8de9952ac8
// and soon also applied to CryptoNote (15:10 GMT+2), and BoolBerry used not fully correct work around:
// the work around of sizeof(size_t)*8 or <<3 as used before in 2 coins and in BBL later was blocking
// exploitation on normal platforms, how ever we strongly recommend the following fix because it removes
// mistake in mathematical formula.
assert(count > 0);
if (count == 1) {
memcpy(root_hash, hashes, HASH_SIZE);
} else if (count == 2) {
cn_fast_hash(hashes, 2 * HASH_SIZE, root_hash);
} else {
size_t i, j;
size_t cnt = tree_hash_cnt( count );
char ints[cnt][HASH_SIZE];
memset(ints, 0 , sizeof(ints)); // zero out as extra protection for using uninitialized mem
memcpy(ints, hashes, (2 * cnt - count) * HASH_SIZE);
for (i = 2 * cnt - count, j = 2 * cnt - count; j < cnt; i += 2, ++j) {
cn_fast_hash(hashes[i], 64, ints[j]);
}
assert(i == count);
while (cnt > 2) {
cnt >>= 1;
for (i = 0, j = 0; j < cnt; i += 2, ++j) {
cn_fast_hash(ints[i], 64, ints[j]);
}
}
cn_fast_hash(ints[0], 64, root_hash);
}
}
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