zcashd/doc/release-notes/release-notes-2.1.0-rc1.md

Notable changes

DoS Mitigation: Mempool Size Limit and Random Drop

This release adds a mechanism for preventing nodes from running out of memory in the situation where an attacker is trying to overwhelm the network with transactions. This is achieved by keeping track of and limiting the total cost and evictionWeight of all transactions in the mempool. The cost of a transaction is determined by its size in bytes, and its evictionWeight is a function of the transaction's cost and its fee. The maximum total cost is configurable via the parameter mempooltxcostlimit which defaults to 80,000,000 (up to 20,000 txs). If a node's total mempool cost exceeds this limit the node will evict a random transaction, preferentially picking larger transactions and ones with below the standard fee. To prevent a node from re-accepting evicted transactions, it keeps track of ones that it has evicted recently. By default, a transaction will be considered recently evicted for 60 minutes, but this can be configured with the parameter mempoolevictionmemoryminutes.

For full details see ZIP 401.

Fake chain detection during initial block download

One of the mechanisms that zcashd uses to detect whether it is in "initial block download" (IBD) mode is to compare the active chain's cumulative work against a hard-coded "minimum chain work" value. This mechanism (inherited from Bitcoin Core) means that once a node exits IBD mode, it is either on the main chain, or a fake alternate chain with similar amounts of work. In the latter case, the node has most likely become the victim of a 50% + 1 adversary.

Starting from this release, zcashd additionally hard-codes the block hashes for the activation blocks of each past network upgrade (NU). During initial chain synchronization, and after the active chain has reached "minimum chain work", the node checks the blocks at each NU activation height against the hard-coded hashes. If any of them do not match, the node will immediately alert the user and shut down for safety.

Disabling old Sprout proofs

As part of our ongoing work to clean up the codebase and minimise the security surface of zcashd, we are removing libsnark from the codebase, and dropping support for creating and verifying old Sprout proofs. Funds stored in Sprout addresses are not affected, as they are spent using the hybrid Sprout circuit (built using bellman) that was deployed during the Sapling network upgrade.

This change has several implications:

• zcashd no longer verifies old Sprout proofs, and will instead assume they are valid. This has a minor implication for nodes: during initial block download, an adversary could feed the node fake blocks containing invalid old Sprout proofs, and the node would accept the fake chain as valid. However, as soon as the active chain contains at least as much work as the hard-coded "minimum chain work" value, the node will detect this situation and shut down.

• Shielded transactions can no longer be created before Sapling has activated. This does not affect Zcash itself, but will affect downstream codebases that have not yet activated Sapling (or that start a new chain after this point and do not activate Sapling from launch). Note that the old Sprout circuit is vulnerable to counterfeiting and should not be used in current deployments.

• Starting from this release, the circuit parameters from the original Sprout MPC are no longer required to start zcashd, and will not be downloaded by fetch-params.sh. They are not being automatically deleted at this time.

We would like to take a moment to thank the libsnark authors and contributors. It was vital to the success of Zcash, and the development of zero-knowledge proofs in general, to have this code available and usable.

Changelog

Bryant Eisenbach (2): doc: Change Debian package description doc: Move text prior to "This package provides..."

Daira Hopwood (4): Remove copyright entries for Autoconf macros that have been deleted. Remove copyright entry for libsnark. Test setting an expiry height of 0. Fix setting an expiry height of 0. fixes #4132

Eirik Ogilvie-Wigley (33): Wrap metrics message in strprintf DoS protection: Weighted random drop of txs if mempool full Rebuild weighted list on removal and fix size calculation Grammatical fixes Remove transactions when ensuring size limit Help message cleanup and add lock Performance: Store weighted transactions in a tree Fix naming conventions No need to activate Overwinter/Sapling in rpc test Fix recently evicted list size Put size increment and decrement on their own lines Prevent adding duplicate transactions Move duplicate macro to reusable location mempool_limit rpc test cleanup Represent tx costs as signed integers Fix comments Rename variables for consistency Use tx cost rather than evictionWeight when checking mempool capacity Log rather than return error if a transaction is recently evicted Represent recently evicted list as a deque Rename files Update release notes Add test minor rpc test clean up Add explanatory comments Wording and grammatical fixes Update parameter names to match ZIP Clarify the difference between cost and evictionWeight Fix test cases: default mempool limiters Remove dots and underscores from parameter names Use same type when calling max make-release.py: Versioning changes for 2.1.0-rc1. make-release.py: Updated manpages for 2.1.0-rc1.

Gareth Davies (1): Updating IPFS link for chunking

Jack Grigg (39): depends: Add FreeBSD to hosts and builders depends: Explicitly set Boost toolchain during configuration depends: Add FreeBSD support to OpenSSL depends: Patch libevent to detect arch4random_addrandom depends: Add FreeBSD Rust binaries depends: Explicitly call Rust install script using bash depends: Use project-config.jam to configure Boost instead of user-config.jam depends: Set PIC flags for FreeBSD Always skip verification for old Sprout proofs Remove ability to create non-Groth16 Sprout JSDescriptions Use Sapling JSDescriptions in Boost tests Remove non-Groth16 Sprout proofs from joinsplit gtests Migrate test utilities to generate Sapling-type Sprout proofs Use Sapling JSDescriptions in gtests Revert "Allow user to ask server to save the Sprout R1CS out during startup." Remove libsnark code for pre-Sapling Sprout proofs Remove pre-Sapling Sprout circuit Revert "configure: Guess -march for libsnark OPTFLAGS instead of hard-coding" Revert "Check if OpenMP is available before using it" Remove libsnark from build system Remove libsnark Remove libgmp Remove libsnark unit tests from full test suite test: Require minimum of Sapling for all RPC tests test: Add Sapling v4 transactions to mininode framework test: Add hashFinalSaplingProxy to create_block test: Update RPC tests to use a minimum of Sapling rpc: Use Sapling transactions in zc_raw_joinsplit depends: Fix crate vendoring path depends: Helper for vendoring new crates depends: Add flag for building with a local librustzcash repo tests: Clean up use of repr() in mininode Remove makeGrothProof argument from JoinSplit::prove Stop fetching old Sprout parameters Add libsnark removal to notable changes Move AbortNode to the top of main.cpp Abort node if NU activations have unexpected hashes Add block hashes for Overwinter, Sapling, and testnet Blossom Update release notes with node abort behaviour

Larry Ruane (4): insightexplorer: formatting, pyflakes cleanups precompute empty merkle roots update unit tests to compute empty roots access array element using at()

jeff-liang (1): Display which network the node is running on.

Benjamin Winston (1): Removed stale seeder, fixing #4153