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Merge #13451: rpc: expose CBlockIndex::nTx in getblock(header)

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86edf4a2a5 expose CBlockIndex::nTx in getblock(header) (Gregory Sanders)

Pull request description:

  Recent publication of a weakness in Bitcoin's merkle tree construction demonstrates many SPV applications vulnerable to an expensive to pull off yet still plausible attack: https://bitslog.wordpress.com/2018/06/09/leaf-node-weakness-in-bitcoin-merkle-tree-design/

  Including the coinbase in the txoutproof seems the most effective fix, however results in a significant efficiency downgrade. Transactors will not even know a priori what the size of their proof will be within a couple orders of magnitude, unless they use the mid-state of SHA2 as detailed in the blog post.

  Some applications, like Elements blockchain platform that take SPV-style proofs have optional access to a bitcoind to verify these proofs of inclusion and check depth in the chain. Returning `CBlockIndex::nTx` would allow an extremely easy and compact way of checking the depth of the tree, with no additional overhead to the codebase, and works with pruned nodes.

  `getblockheader` is arguably not the place for it, but as mentioned before, is a natural workflow for us checking depth of a block in a possibly pruned node.

  We should also ensure that `verifytxoutproof` ends up validating this depth fact as well, but left this for another PR.

Tree-SHA512: af4cf48e704c6088f8da06a477fda1aaa6f8770cee9b876c4465d1075966d6a95831a88817673fe5a0d6bbcdc1ffcbc1892e2be0d838c60fc6958d33eacdcc14
This commit is contained in:
Wladimir J. van der Laan 2018-06-14 19:38:19 +02:00
commit cc7cbd756a
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GPG key ID: 1E4AED62986CD25D
3 changed files with 12 additions and 0 deletions
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4
src/rpc/blockchain.cpp
View file

@ -95,6 +95,7 @@ UniValue blockheaderToJSON(const CBlockIndex* blockindex)
result.pushKV("bits", strprintf("%08x", blockindex->nBits));
result.pushKV("difficulty", GetDifficulty(blockindex));
result.pushKV("chainwork", blockindex->nChainWork.GetHex());
result.pushKV("nTx", (uint64_t)blockindex->nTx);
if (blockindex->pprev)
result.pushKV("previousblockhash", blockindex->pprev->GetBlockHash().GetHex());
@ -140,6 +141,7 @@ UniValue blockToJSON(const CBlock& block, const CBlockIndex* blockindex, bool tx
result.pushKV("bits", strprintf("%08x", block.nBits));
result.pushKV("difficulty", GetDifficulty(blockindex));
result.pushKV("chainwork", blockindex->nChainWork.GetHex());
result.pushKV("nTx", (uint64_t)blockindex->nTx);
if (blockindex->pprev)
result.pushKV("previousblockhash", blockindex->pprev->GetBlockHash().GetHex());
@ -694,6 +696,7 @@ static UniValue getblockheader(const JSONRPCRequest& request)
" \"bits\" : \"1d00ffff\", (string) The bits\n"
" \"difficulty\" : x.xxx, (numeric) The difficulty\n"
" \"chainwork\" : \"0000...1f3\" (string) Expected number of hashes required to produce the current chain (in hex)\n"
" \"nTx\" : n, (numeric) The number of transactions in the block.\n"
" \"previousblockhash\" : \"hash\", (string) The hash of the previous block\n"
" \"nextblockhash\" : \"hash\", (string) The hash of the next block\n"
"}\n"
@ -782,6 +785,7 @@ static UniValue getblock(const JSONRPCRequest& request)
" \"bits\" : \"1d00ffff\", (string) The bits\n"
" \"difficulty\" : x.xxx, (numeric) The difficulty\n"
" \"chainwork\" : \"xxxx\", (string) Expected number of hashes required to produce the chain up to this block (in hex)\n"
" \"nTx\" : n, (numeric) The number of transactions in the block.\n"
" \"previousblockhash\" : \"hash\", (string) The hash of the previous block\n"
" \"nextblockhash\" : \"hash\" (string) The hash of the next block\n"
"}\n"

7
test/functional/feature_pruning.py
View file

@ -260,10 +260,17 @@ class PruneTest(BitcoinTestFramework):
# should not prune because chain tip of node 3 (995) < PruneAfterHeight (1000)
assert_raises_rpc_error(-1, "Blockchain is too short for pruning", node.pruneblockchain, height(500))
# Save block transaction count before pruning, assert value
block1_details = node.getblock(node.getblockhash(1))
assert_equal(block1_details["nTx"], len(block1_details["tx"]))
# mine 6 blocks so we are at height 1001 (i.e., above PruneAfterHeight)
node.generate(6)
assert_equal(node.getblockchaininfo()["blocks"], 1001)
# Pruned block should still know the number of transactions
assert_equal(node.getblockheader(node.getblockhash(1))["nTx"], block1_details["nTx"])
# negative heights should raise an exception
assert_raises_rpc_error(-8, "Negative", node.pruneblockchain, -10)

1
test/functional/rpc_blockchain.py
View file

@ -217,6 +217,7 @@ class BlockchainTest(BitcoinTestFramework):
assert_equal(header['confirmations'], 1)
assert_equal(header['previousblockhash'], secondbesthash)
assert_is_hex_string(header['chainwork'])
assert_equal(header['nTx'], 1)
assert_is_hash_string(header['hash'])
assert_is_hash_string(header['previousblockhash'])
assert_is_hash_string(header['merkleroot'])