kevacoin/doc/litecoin-release-notes/release-notes-0.13.2.md

Kevacoin Core version 0.13.2 is now available from:

https://download.kevacoin.org/kevacoin-0.13.2.1/

This is a new major version release, including new features, various bugfixes and performance improvements, as well as updated translations. It is recommended to upgrade to this version.

Please report bugs using the issue tracker at github:

https://github.com/kevacoin-project/kevacoin/issues

Compatibility

Microsoft ended support for Windows XP on April 8th, 2014, an OS initially released in 2001. This means that not even critical security updates will be released anymore. Without security updates, using a kevacoin wallet on a XP machine is irresponsible at least.

In addition to that, with 0.12.x there have been varied reports of Bitcoin Core randomly crashing on Windows XP. It is not clear what the source of these crashes is, but it is likely that upstream libraries such as Qt are no longer being tested on XP.

We do not have time nor resources to provide support for an OS that is end-of-life. From 0.13.0 on, Windows XP is no longer supported. Users are suggested to upgrade to a newer version of Windows, or install an alternative OS that is supported.

No attempt is made to prevent installing or running the software on Windows XP, you can still do so at your own risk, but do not expect it to work: do not report issues about Windows XP to the issue tracker.

From 0.13.1 onwards OS X 10.7 is no longer supported. 0.13.0 was intended to work on 10.7+, but severe issues with the libc++ version on 10.7.x keep it from running reliably. 0.13.1 now requires 10.8+, and will communicate that to 10.7 users, rather than crashing unexpectedly.

Notable changes

Signature validation using libsecp256k1

ECDSA signatures inside Kevacoin transactions now use validation using libsecp256k1 instead of OpenSSL.

Depending on the platform, this means a significant speedup for raw signature validation speed. The advantage is largest on x86_64, where validation is over five times faster. In practice, this translates to a raw reindexing and new block validation times that are less than half of what it was before.

Libsecp256k1 has undergone very extensive testing and validation.

A side effect of this change is that libconsensus no longer depends on OpenSSL.

Reduce upload traffic

A major part of the outbound traffic is caused by serving historic blocks to other nodes in initial block download state.

It is now possible to reduce the total upload traffic via the -maxuploadtarget parameter. This is not a hard limit but a threshold to minimize the outbound traffic. When the limit is about to be reached, the uploaded data is cut by not serving historic blocks (blocks older than one week). Moreover, any SPV peer is disconnected when they request a filtered block.

This option can be specified in MiB per day and is turned off by default (-maxuploadtarget=0). The recommended minimum is 144 * MAX_BLOCK_SIZE (currently 144MB) per day.

Whitelisted peers will never be disconnected, although their traffic counts for calculating the target.

A more detailed documentation about keeping traffic low can be found in /doc/reduce-traffic.md.

Direct headers announcement (BIP 130)

Between compatible peers, [BIP 130] (https://github.com/bitcoin/bips/blob/master/bip-0130.mediawiki) direct headers announcement is used. This means that blocks are advertised by announcing their headers directly, instead of just announcing the hash. In a reorganization, all new headers are sent, instead of just the new tip. This can often prevent an extra roundtrip before the actual block is downloaded.

Memory pool limiting

Previous versions of Kevacoin Core had their mempool limited by checking a transaction's fees against the node's minimum relay fee. There was no upper bound on the size of the mempool and attackers could send a large number of transactions paying just slighly more than the default minimum relay fee to crash nodes with relatively low RAM. A temporary workaround for previous versions of Kevacoin Core was to raise the default minimum relay fee.

Kevacoin Core 0.13.2 will have a strict maximum size on the mempool. The default value is 300 MB and can be configured with the -maxmempool parameter. Whenever a transaction would cause the mempool to exceed its maximum size, the transaction that (along with in-mempool descendants) has the lowest total feerate (as a package) will be evicted and the node's effective minimum relay feerate will be increased to match this feerate plus the initial minimum relay feerate. The initial minimum relay feerate is set to 1000 satoshis per kB.

Kevacoin Core 0.13.2 also introduces new default policy limits on the length and size of unconfirmed transaction chains that are allowed in the mempool (generally limiting the length of unconfirmed chains to 25 transactions, with a total size of 101 KB). These limits can be overriden using command line arguments; see the extended help (--help -help-debug) for more information.

RPC: Random-cookie RPC authentication

When no -rpcpassword is specified, the daemon now uses a special 'cookie' file for authentication. This file is generated with random content when the daemon starts, and deleted when it exits. Its contents are used as authentication token. Read access to this file controls who can access through RPC. By default it is stored in the data directory but its location can be overridden with the option -rpccookiefile.

This is similar to Tor's CookieAuthentication: see https://www.torproject.org/docs/tor-manual.html.en

This allows running kevacoind without having to do any manual configuration.

Relay: Any sequence of pushdatas in OP_RETURN outputs now allowed

Previously OP_RETURN outputs with a payload were only relayed and mined if they had a single pushdata. This restriction has been lifted to allow any combination of data pushes and numeric constant opcodes (OP_1 to OP_16) after the OP_RETURN. The limit on OP_RETURN output size is now applied to the entire serialized scriptPubKey, 83 bytes by default. (the previous 80 byte default plus three bytes overhead)

Relay: New and only new blocks relayed when pruning

When running in pruned mode, the client will now relay new blocks. When responding to the getblocks message, only hashes of blocks that are on disk and are likely to remain there for some reasonable time window (1 hour) will be returned (previously all relevant hashes were returned).

Relay and Mining: Priority transactions

Kevacoin Core has a heuristic 'priority' based on coin value and age. This calculation is used for relaying of transactions which do not pay the minimum relay fee, and can be used as an alternative way of sorting transactions for mined blocks. Kevacoin Core will relay transactions with insufficient fees depending on the setting of -limitfreerelay=<r> (default: r=15 kB per minute) and -blockprioritysize=<s>.

In Bitcoin Core 0.12, when mempool limit has been reached a higher minimum relay fee takes effect to limit memory usage. Transactions which do not meet this higher effective minimum relay fee will not be relayed or mined even if they rank highly according to the priority heuristic.

The mining of transactions based on their priority is also now disabled by default. To re-enable it, simply set -blockprioritysize=<n> where is the size in bytes of your blocks to reserve for these transactions. The old default was 50k, so to retain approximately the same policy, you would set -blockprioritysize=50000.

Additionally, as a result of computational simplifications, the priority value used for transactions received with unconfirmed inputs is lower than in prior versions due to avoiding recomputing the amounts as input transactions confirm.

External miner policy set via the prioritisetransaction RPC to rank transactions already in the mempool continues to work as it has previously. Note, however, that if mining priority transactions is left disabled, the priority delta will be ignored and only the fee metric will be effective.

This internal automatic prioritization handling is being considered for removal entirely in Kevacoin Core 0.13, and it is at this time undecided whether the more accurate priority calculation for chained unconfirmed transactions will be restored. Community direction on this topic is particularly requested to help set project priorities.

Automatically use Tor hidden services

Starting with Tor version 0.2.7.1 it is possible, through Tor's control socket API, to create and destroy 'ephemeral' hidden services programmatically. Kevacoin Core has been updated to make use of this.

This means that if Tor is running (and proper authorization is available), Kevacoin Core automatically creates a hidden service to listen on, without manual configuration. Kevacoin Core will also use Tor automatically to connect to other .onion nodes if the control socket can be successfully opened. This will positively affect the number of available .onion nodes and their usage.

This new feature is enabled by default if Kevacoin Core is listening, and a connection to Tor can be made. It can be configured with the -listenonion, -torcontrol and -torpassword settings. To show verbose debugging information, pass -debug=tor.

Notifications through ZMQ

Litecoind can now (optionally) asynchronously notify clients through a ZMQ-based PUB socket of the arrival of new transactions and blocks. This feature requires installation of the ZMQ C API library 4.x and configuring its use through the command line or configuration file. Please see docs/zmq.md for details of operation.

Wallet: Transaction fees

Various improvements have been made to how the wallet calculates transaction fees.

Users can decide to pay a predefined fee rate by setting -paytxfee=<n> (or settxfee <n> rpc during runtime). A value of n=0 signals Kevacoin Core to use floating fees. By default, Kevacoin Core will use floating fees.

Based on past transaction data, floating fees approximate the fees required to get into the mth block from now. This is configurable with -txconfirmtarget=<m> (default: 2).

Sometimes, it is not possible to give good estimates, or an estimate at all. Therefore, a fallback value can be set with -fallbackfee=<f> (default: 0.0002 LTC/kB).

At all times, Kevacoin Core will cap fees at -maxtxfee=<x> (default: 0.10) LTC. Furthermore, Kevacoin Core will never create transactions paying less than the current minimum relay fee. Finally, a user can set the minimum fee rate for all transactions with -mintxfee=<i>, which defaults to 1000 satoshis per kB.

Wallet: Negative confirmations and conflict detection

The wallet will now report a negative number for confirmations that indicates how deep in the block chain the conflict is found. For example, if a transaction A has 5 confirmations and spends the same input as a wallet transaction B, B will be reported as having -5 confirmations. If another wallet transaction C spends an output from B, it will also be reported as having -5 confirmations. To detect conflicts with historical transactions in the chain a one-time -rescan may be needed.

Unlike earlier versions, unconfirmed but non-conflicting transactions will never get a negative confirmation count. They are not treated as spendable unless they're coming from ourself (change) and accepted into our local mempool, however. The new "trusted" field in the listtransactions RPC output indicates whether outputs of an unconfirmed transaction are considered spendable.

Wallet: Merkle branches removed

Previously, every wallet transaction stored a Merkle branch to prove its presence in blocks. This wasn't being used for more than an expensive sanity check. Since 0.13.2, these are no longer stored. When loading a 0.13.2 wallet into an older version, it will automatically rescan to avoid failed checks.

Wallet: Pruning

With 0.13.2 it is possible to use wallet functionality in pruned mode. This can reduce the disk usage from currently around 6 GB to around 0.2 GB.

However, rescans as well as the RPCs importwallet, importaddress, importprivkey are disabled.

To enable block pruning set prune=<N> on the command line or in kevacoin.conf, where N is the number of MiB to allot for raw block & undo data.

A value of 0 disables pruning. The minimal value above 0 is 550. Your wallet is as secure with high values as it is with low ones. Higher values merely ensure that your node will not shut down upon blockchain reorganizations of more than 2 days - which are unlikely to happen in practice. In future releases, a higher value may also help the network as a whole: stored blocks could be served to other nodes.

For further information about pruning, you may also consult the release notes of Bitcoin Core v0.11.0.

NODE_BLOOM service bit

Support for the NODE_BLOOM service bit, as described in BIP 111, has been added to the P2P protocol code.

BIP 111 defines a service bit to allow peers to advertise that they support bloom filters (such as used by SPV clients) explicitly. It also bumps the protocol version to allow peers to identify old nodes which allow bloom filtering of the connection despite lacking the new service bit.

In this version, it is only enforced for peers that send protocol versions >=70011. For the next major version it is planned that this restriction will be removed. It is recommended to update SPV clients to check for the NODE_BLOOM service bit for nodes that report versions newer than 70011.

Option parsing behavior

Command line options are now parsed strictly in the order in which they are specified. It used to be the case that -X -noX ends up, unintuitively, with X set, as -X had precedence over -noX. This is no longer the case. Like for other software, the last specified value for an option will hold.

RPC: Low-level API changes

• Monetary amounts can be provided as strings. This means that for example the argument to sendtoaddress can be "0.0001" instead of 0.0001. This can be an advantage if a JSON library insists on using a lossy floating point type for numbers, which would be dangerous for monetary amounts.

• The asm property of each scriptSig now contains the decoded signature hash type for each signature that provides a valid defined hash type.

• OP_NOP2 has been renamed to OP_CHECKLOCKTIMEVERIFY by BIP 65

The following items contain assembly representations of scriptSig signatures and are affected by this change:

• RPC getrawtransaction
• RPC decoderawtransaction
• RPC decodescript
• REST /rest/tx/ (JSON format)
• REST /rest/block/ (JSON format when including extended tx details)
• kevacoin-tx -json

For example, the scriptSig.asm property of a transaction input that previously showed an assembly representation of:

304502207fa7a6d1e0ee81132a269ad84e68d695483745cde8b541e3bf630749894e342a022100c1f7ab20e13e22fb95281a870f3dcf38d782e53023ee313d741ad0cfbc0c509001 400000 OP_NOP2

now shows as:

304502207fa7a6d1e0ee81132a269ad84e68d695483745cde8b541e3bf630749894e342a022100c1f7ab20e13e22fb95281a870f3dcf38d782e53023ee313d741ad0cfbc0c5090[ALL] 400000 OP_CHECKLOCKTIMEVERIFY

Note that the output of the RPC decodescript did not change because it is configured specifically to process scriptPubKey and not scriptSig scripts.

RPC: SSL support dropped

SSL support for RPC, previously enabled by the option rpcssl has been dropped from both the client and the server. This was done in preparation for removing the dependency on OpenSSL for the daemon completely.

Trying to use rpcssl will result in an error:

Error: SSL mode for RPC (-rpcssl) is no longer supported.

If you are one of the few people that relies on this feature, a flexible migration path is to use stunnel. This is an utility that can tunnel arbitrary TCP connections inside SSL. On e.g. Ubuntu it can be installed with:

sudo apt-get install stunnel4

Then, to tunnel a SSL connection on 29332 to a RPC server bound on localhost on port 19334 do:

stunnel -d 29332 -r 127.0.0.1:19334 -p stunnel.pem -P ''

It can also be set up system-wide in inetd style.

Another way to re-attain SSL would be to setup a httpd reverse proxy. This solution would allow the use of different authentication, loadbalancing, on-the-fly compression and caching. A sample config for apache2 could look like:

Listen 443

NameVirtualHost *:443
<VirtualHost *:443>

SSLEngine On
SSLCertificateFile /etc/apache2/ssl/server.crt
SSLCertificateKeyFile /etc/apache2/ssl/server.key

<Location /litecoinrpc>
    ProxyPass http://127.0.0.1:9332/
    ProxyPassReverse http://127.0.0.1:9332/
    # optional enable digest auth
    # AuthType Digest
    # ...

    # optional bypass kevacoind rpc basic auth
    # RequestHeader set Authorization "Basic <hash>"
    # get the <hash> from the shell with: base64 <<< litecoinrpc:<password>
</Location>

# Or, balance the load:
# ProxyPass / balancer://balancer_cluster_name

</VirtualHost>

Other P2P Changes

The list of banned peers is now stored on disk rather than in memory. Restarting kevacoind will no longer clear out the list of banned peers; instead a new RPC call (clearbanned) can be used to manually clear the list. The new setban RPC call can also be used to manually ban or unban a peer.

Database cache memory increased

As a result of growth of the UTXO set, performance with the prior default database cache of 100 MiB has suffered. For this reason the default was changed to 300 MiB in this release.

For nodes on low-memory systems, the database cache can be changed back to 100 MiB (or to another value) by either:

• Adding dbcache=100 in kevacoin.conf
• Changing it in the GUI under Options → Size of database cache

Note that the database cache setting has the most performance impact during initial sync of a node, and when catching up after downtime.

kevacoin-cli: arguments privacy

The RPC command line client gained a new argument, -stdin to read extra arguments from standard input, one per line until EOF/Ctrl-D. For example:

$ src/kevacoin-cli -stdin walletpassphrase
mysecretcode
120
..... press Ctrl-D here to end input
$

It is recommended to use this for sensitive information such as wallet passphrases, as command-line arguments can usually be read from the process table by any user on the system.

C++11 and Python 3

Various code modernizations have been done. The Kevacoin Core code base has started using C++11. This means that a C++11-capable compiler is now needed for building. Effectively this means GCC 4.7 or higher, or Clang 3.3 or higher.

When cross-compiling for a target that doesn't have C++11 libraries, configure with ./configure --enable-glibc-back-compat ... LDFLAGS=-static-libstdc++.

For running the functional tests in qa/rpc-tests, Python3.4 or higher is now required.

Linux ARM builds

Due to popular request, Linux ARM builds have been added to the uploaded executables.

The following extra files can be found in the download directory or torrent:

• kevacoin-${VERSION}-arm-linux-gnueabihf.tar.gz: Linux binaries for the most common 32-bit ARM architecture.
• kevacoin-${VERSION}-aarch64-linux-gnu.tar.gz: Linux binaries for the most common 64-bit ARM architecture.

ARM builds are still experimental. If you have problems on a certain device or Linux distribution combination please report them on the bug tracker, it may be possible to resolve them.

Note that Android is not considered ARM Linux in this context. The executables are not expected to work out of the box on Android.

BIP68 soft fork to enforce sequence locks for relative locktime

[BIP68][] introduces relative lock-time consensus-enforced semantics of the sequence number field to enable a signed transaction input to remain invalid for a defined period of time after confirmation of its corresponding outpoint.

For more information about the implementation, see https://github.com/bitcoin/bitcoin/pull/7184

BIP112 soft fork to enforce OP_CHECKSEQUENCEVERIFY

[BIP112][] redefines the existing OP_NOP3 as OP_CHECKSEQUENCEVERIFY (CSV) for a new opcode in the Kevacoin scripting system that in combination with [BIP68][] allows execution pathways of a script to be restricted based on the age of the output being spent.

For more information about the implementation, see https://github.com/bitcoin/bitcoin/pull/7524

BIP113 locktime enforcement soft fork

This release seeks to make mempool-only locktime enforcement using GetMedianTimePast() a consensus rule.

Kevacoin transactions currently may specify a locktime indicating when they may be added to a valid block. Current consensus rules require that blocks have a block header time greater than the locktime specified in any transaction in that block.

Miners get to choose what time they use for their header time, with the consensus rule being that no node will accept a block whose time is more than two hours in the future. This creates a incentive for miners to set their header times to future values in order to include locktimed transactions which weren't supposed to be included for up to two more hours.

The consensus rules also specify that valid blocks may have a header time greater than that of the median of the 11 previous blocks. This GetMedianTimePast() time has a key feature we generally associate with time: it can't go backwards.

[BIP113][] specifies a soft fork enforced in this release that weakens this perverse incentive for individual miners to use a future time by requiring that valid blocks have a computed GetMedianTimePast() greater than the locktime specified in any transaction in that block.

Mempool inclusion rules currently require transactions to be valid for immediate inclusion in a block in order to be accepted into the mempool. This release begins applying the BIP113 rule to received transactions, so transaction whose time is greater than the GetMedianTimePast() will no longer be accepted into the mempool.

Implication for miners: you will begin rejecting transactions that would not be valid under BIP113, which will prevent you from producing invalid blocks when BIP113 is enforced on the network. Any transactions which are valid under the current rules but not yet valid under the BIP113 rules will either be mined by other miners or delayed until they are valid under BIP113. Note, however, that time-based locktime transactions are more or less unseen on the network currently.

Implication for users: GetMedianTimePast() always trails behind the current time, so a transaction locktime set to the present time will be rejected by nodes running this release until the median time moves forward. To compensate, subtract one hour (3,600 seconds) from your locktimes to allow those transactions to be included in mempools at approximately the expected time.

For more information about the implementation, see https://github.com/bitcoin/bitcoin/pull/6566

Compact Block support (BIP 152)

Support for block relay using the Compact Blocks protocol has been implemented in PR 8068.

The primary goal is reducing the bandwidth spikes at relay time, though in many cases it also reduces propagation delay. It is automatically enabled between compatible peers. BIP 152

As a side-effect, ordinary non-mining nodes will download and upload blocks faster if those blocks were produced by miners using similar transaction filtering policies. This means that a miner who produces a block with many transactions discouraged by your node will be relayed slower than one with only transactions already in your memory pool. The overall effect of such relay differences on the network may result in blocks which include widely- discouraged transactions losing a stale block race, and therefore miners may wish to configure their node to take common relay policies into consideration.

Hierarchical Deterministic Key Generation

Newly created wallets will use hierarchical deterministic key generation according to BIP32 (keypath m/0'/0'/k'). Existing wallets will still use traditional key generation.

Backups of HD wallets, regardless of when they have been created, can therefore be used to re-generate all possible private keys, even the ones which haven't already been generated during the time of the backup. Attention: Encrypting the wallet will create a new seed which requires a new backup!

Wallet dumps (created using the dumpwallet RPC) will contain the deterministic seed. This is expected to allow future versions to import the seed and all associated funds, but this is not yet implemented.

HD key generation for new wallets can be disabled by -usehd=0. Keep in mind that this flag only has affect on newly created wallets. You can't disable HD key generation once you have created a HD wallet.

There is no distinction between internal (change) and external keys.

HD wallets are incompatible with older versions of Kevacoin Core.

Pull request, BIP 32

Mining transaction selection ("Child Pays For Parent")

The mining transaction selection algorithm has been replaced with an algorithm that selects transactions based on their feerate inclusive of unconfirmed ancestor transactions. This means that a low-fee transaction can become more likely to be selected if a high-fee transaction that spends its outputs is relayed.

With this change, the -blockminsize command line option has been removed.

The command line option -blockmaxsize remains an option to specify the maximum number of serialized bytes in a generated block. In addition, the new command line option -blockmaxweight has been added, which specifies the maximum "block weight" of a generated block, as defined by [BIP 141 (Segregated Witness)] (https://github.com/bitcoin/bips/blob/master/bip-0141.mediawiki).

In preparation for Segregated Witness, the mining algorithm has been modified to optimize transaction selection for a given block weight, rather than a given number of serialized bytes in a block. In this release, transaction selection is unaffected by this distinction (as BIP 141 activation is not supported on mainnet in this release, see above), but in future releases and after BIP 141 activation, these calculations would be expected to differ.

For optimal runtime performance, miners using this release should specify -blockmaxweight on the command line, and not specify -blockmaxsize. Additionally (or only) specifying -blockmaxsize, or relying on default settings for both, may result in performance degradation, as the logic to support -blockmaxsize performs additional computation to ensure that constraint is met. (Note that for mainnet, in this release, the equivalent parameter for -blockmaxweight would be four times the desired -blockmaxsize. See [BIP 141] (https://github.com/bitcoin/bips/blob/master/bip-0141.mediawiki) for additional details.)

In the future, the -blockmaxsize option may be removed, as block creation is no longer optimized for this metric. Feedback is requested on whether to deprecate or keep this command line option in future releases.

Reindexing changes

In earlier versions, reindexing did validation while reading through the block files on disk. These two have now been split up, so that all blocks are known before validation starts. This was necessary to make certain optimizations that are available during normal synchronizations also available during reindexing.

The two phases are distinct in the Kevacoin-Qt GUI. During the first one, "Reindexing blocks on disk" is shown. During the second (slower) one, "Processing blocks on disk" is shown.

It is possible to only redo validation now, without rebuilding the block index, using the command line option -reindex-chainstate (in addition to -reindex which does both). This new option is useful when the blocks on disk are assumed to be fine, but the chainstate is still corrupted. It is also useful for benchmarks.

Removal of internal miner

As CPU mining has been useless for a long time, the internal miner has been removed in this release, and replaced with a simpler implementation for the test framework.

The overall result of this is that setgenerate RPC call has been removed, as well as the -gen and -genproclimit command-line options.

For testing, the generate call can still be used to mine a block, and a new RPC call generatetoaddress has been added to mine to a specific address. This works with wallet disabled.

New bytespersigop implementation

The former implementation of the bytespersigop filter accidentally broke bare multisig (which is meant to be controlled by the permitbaremultisig option), since the consensus protocol always counts these older transaction forms as 20 sigops for backwards compatibility. Simply fixing this bug by counting more accurately would have reintroduced a vulnerability. It has therefore been replaced with a new implementation that rather than filter such transactions, instead treats them (for fee purposes only) as if they were in fact the size of a transaction actually using all 20 sigops.

Low-level P2P changes

• The optional new p2p message "feefilter" is implemented and the protocol version is bumped to 70013. Upon receiving a feefilter message from a peer, a node will not send invs for any transactions which do not meet the filter feerate. BIP 133

• The P2P alert system has been removed in PR #7692 and the alert P2P message is no longer supported.

• The transaction relay mechanism used to relay one quarter of all transactions instantly, while queueing up the rest and sending them out in batch. As this resulted in chains of dependent transactions being reordered, it systematically hurt transaction relay. The relay code was redesigned in PRs #7840 and #8082, and now always batches transactions announcements while also sorting them according to dependency order. This significantly reduces orphan transactions. To compensate for the removal of instant relay, the frequency of batch sending was doubled for outgoing peers.

• Since PR #7840 the BIP35 mempool command is also subject to batch processing. Also the mempool message is no longer handled for non-whitelisted peers when NODE_BLOOM is disabled through -peerbloomfilters=0.

• The maximum size of orphan transactions that are kept in memory until their ancestors arrive has been raised in PR #8179 from 5000 to 99999 bytes. They are now also removed from memory when they are included in a block, conflict with a block, and time out after 20 minutes.

• We respond at most once to a getaddr request during the lifetime of a connection since PR #7856.

• Connections to peers who have recently been the first one to give us a valid new block or transaction are protected from disconnections since PR #8084.

Low-level RPC changes

• RPC calls have been added to output detailed statistics for individual mempool entries, as well as to calculate the in-mempool ancestors or descendants of a transaction: see getmempoolentry, getmempoolancestors, getmempooldescendants.

• gettxoutsetinfo UTXO hash (hash_serialized) has changed. There was a divergence between 32-bit and 64-bit platforms, and the txids were missing in the hashed data. This has been fixed, but this means that the output will be different than from previous versions.

• Full UTF-8 support in the RPC API. Non-ASCII characters in, for example, wallet labels have always been malformed because they weren't taken into account properly in JSON RPC processing. This is no longer the case. This also affects the GUI debug console.

• Asm script outputs replacements for OP_NOP2 and OP_NOP3

  • OP_NOP2 has been renamed to OP_CHECKLOCKTIMEVERIFY by BIP 65

  • OP_NOP3 has been renamed to OP_CHECKSEQUENCEVERIFY by BIP 112

  • The following outputs are affected by this change:

    • RPC getrawtransaction (in verbose mode)
    • RPC decoderawtransaction
    • RPC decodescript
    • REST /rest/tx/ (JSON format)
    • REST /rest/block/ (JSON format when including extended tx details)
    • kevacoin-tx -json

• The sorting of the output of the getrawmempool output has changed.

• New RPC commands: generatetoaddress, importprunedfunds, removeprunedfunds, signmessagewithprivkey, getmempoolancestors, getmempooldescendants, getmempoolentry, createwitnessaddress, addwitnessaddress.

• Removed RPC commands: setgenerate, getgenerate.

• New options were added to fundrawtransaction: includeWatching, changeAddress, changePosition and feeRate.

Low-level ZMQ changes

• Each ZMQ notification now contains an up-counting sequence number that allows listeners to detect lost notifications. The sequence number is always the last element in a multi-part ZMQ notification and therefore backward compatible. Each message type has its own counter. PR #7762.

Segregated witness soft fork

Segregated witness (segwit) is a soft fork that, if activated, will allow transaction-producing software to separate (segregate) transaction signatures (witnesses) from the part of the data in a transaction that is covered by the txid. This provides several immediate benefits:

• Elimination of unwanted transaction malleability: Segregating the witness allows both existing and upgraded software to calculate the transaction identifier (txid) of transactions without referencing the witness, which can sometimes be changed by third-parties (such as miners) or by co-signers in a multisig spend. This solves all known cases of unwanted transaction malleability, which is a problem that makes programming Kevacoin wallet software more difficult and which seriously complicates the design of smart contracts for Kevacoin.

• Capacity increase: Segwit transactions contain new fields that are not part of the data currently used to calculate the size of a block, which allows a block containing segwit transactions to hold more data than allowed by the current maximum block size. Estimates based on the transactions currently found in blocks indicate that if all wallets switch to using segwit, the network will be able to support about 70% more transactions. The network will also be able to support more of the advanced-style payments (such as multisig) than it can support now because of the different weighting given to different parts of a transaction after segwit activates (see the following section for details).

• Weighting data based on how it affects node performance: Some parts of each Kevacoin block need to be stored by nodes in order to validate future blocks; other parts of a block can be immediately forgotten (pruned) or used only for helping other nodes sync their copy of the block chain. One large part of the immediately prunable data are transaction signatures (witnesses), and segwit makes it possible to give a different "weight" to segregated witnesses to correspond with the lower demands they place on node resources. Specifically, each byte of a segregated witness is given a weight of 1, each other byte in a block is given a weight of 4, and the maximum allowed weight of a block is 4 million. Weighting the data this way better aligns the most profitable strategy for creating blocks with the long-term costs of block validation.

• Signature covers value: A simple improvement in the way signatures are generated in segwit simplifies the design of secure signature generators (such as hardware wallets), reduces the amount of data the signature generator needs to download, and allows the signature generator to operate more quickly. This is made possible by having the generator sign the amount of litecoins they think they are spending, and by having full nodes refuse to accept those signatures unless the amount of litecoins being spent is exactly the same as was signed. For non-segwit transactions, wallets instead had to download the complete previous transactions being spent for every payment they made, which could be a slow operation on hardware wallets and in other situations where bandwidth or computation speed was constrained.

• Linear scaling of sighash operations: In 2015 a block was produced that required about 25 seconds to validate on modern hardware because of the way transaction signature hashes are performed. Other similar blocks, or blocks that could take even longer to validate, can still be produced today. The problem that caused this can't be fixed in a soft fork without unwanted side-effects, but transactions that opt-in to using segwit will now use a different signature method that doesn't suffer from this problem and doesn't have any unwanted side-effects.

• Increased security for multisig: Kevacoin addresses (both P2PKH addresses that start with a '1' and P2SH addresses that start with a '3' or 'M') use a hash function known as RIPEMD-160. For P2PKH addresses, this provides about 160 bits of security---which is beyond what cryptographers believe can be broken today. But because P2SH is more flexible, only about 80 bits of security is provided per address. Although 80 bits is very strong security, it is within the realm of possibility that it can be broken by a powerful adversary. Segwit allows advanced transactions to use the SHA256 hash function instead, which provides about 128 bits of security (that is 281 trillion times as much security as 80 bits and is equivalent to the maximum bits of security believed to be provided by Kevacoin's choice of parameters for its Elliptic Curve Digital Security Algorithm [ECDSA].)

• More efficient almost-full-node security Satoshi Nakamoto's original Bitcoin paper describes a method for allowing newly-started full nodes to skip downloading and validating some data from historic blocks that are protected by large amounts of proof of work. Unfortunately, Nakamoto's method can't guarantee that a newly-started node using this method will produce an accurate copy of Kevacoin's current ledger (called the UTXO set), making the node vulnerable to falling out of consensus with other nodes. Although the problems with Nakamoto's method can't be fixed in a soft fork, Segwit accomplishes something similar to his original proposal: it makes it possible for a node to optionally skip downloading some blockchain data (specifically, the segregated witnesses) while still ensuring that the node can build an accurate copy of the UTXO set for the block chain with the most proof of work. Segwit enables this capability at the consensus layer, but note that Kevacoin Core does not provide an option to use this capability as of this 0.13.2 release.

• Script versioning: Segwit makes it easy for future soft forks to allow Kevacoin users to individually opt-in to almost any change in the Kevacoin Script language when those users receive new transactions. Features currently being researched by Bitcoin and Kevacoin Core contributors that may use this capability include support for Schnorr signatures, which can improve the privacy and efficiency of multisig transactions (or transactions with multiple inputs), and Merklized Abstract Syntax Trees (MAST), which can improve the privacy and efficiency of scripts with two or more conditions. Other Bitcoin community members are studying several other improvements that can be made using script versioning.

Activation for the segwit soft fork is being managed using BIP9. At the beginning of the first retarget period after segwit's start date of 1 January 2017 miners can update the Kevacoin client to Kevacoin Core 0.13.2 to signal for segwit support. When a super-majority of 75% is reached segwit is activated by optional, and if 75% of blocks within a 8,064-block retarget period (about 3.5 days) signal support for segwit, after another 8,064 blocks, segwit will be required.

For more information about segwit, please see the segwit FAQ, the segwit wallet developers guide or BIPs 141, 143, 144, and 145.

Null dummy soft fork

Combined with the segwit soft fork is an additional change that turns a long-existing network relay policy into a consensus rule. The OP_CHECKMULTISIG and OP_CHECKMULTISIGVERIFY opcodes consume an extra stack element ("dummy element") after signature validation. The dummy element is not inspected in any manner, and could be replaced by any value without invalidating the script.

Because any value can be used for this dummy element, it's possible for a third-party to insert data into other people's transactions, changing the transaction's txid (called transaction malleability) and possibly causing other problems.

Since Kevacoin Core 0.10.0, nodes have defaulted to only relaying and mining transactions whose dummy element was a null value (0x00, also called OP_0). The null dummy soft fork turns this relay rule into a consensus rule both for non-segwit transactions and segwit transactions, so that this method of mutating transactions is permanently eliminated from the network.

Signaling for the null dummy soft fork is done by signaling support for segwit, and the null dummy soft fork will activate at the same time as segwit.

For more information, please see BIP147.

Low-level RPC changes

• importprunedfunds only accepts two required arguments. Some versions accept an optional third arg, which was always ignored. Make sure to never pass more than two arguments.

Linux ARM builds

Pre-built Linux ARM binaries have been added to the set of uploaded executables. Additional detail on the ARM architecture targeted by each is provided below.

The following extra files can be found in the download directory or torrent:

• kevacoin-${VERSION}-arm-linux-gnueabihf.tar.gz: Linux binaries targeting the 32-bit ARMv7-A architecture.
• kevacoin-${VERSION}-aarch64-linux-gnu.tar.gz: Linux binaries targeting the 64-bit ARMv8-A architecture.

ARM builds are still experimental. If you have problems on a certain device or Linux distribution combination please report them on the bug tracker, it may be possible to resolve them. Note that the device you use must be (backward) compatible with the architecture targeted by the binary that you use. For example, a Raspberry Pi 2 Model B or Raspberry Pi 3 Model B (in its 32-bit execution state) device, can run the 32-bit ARMv7-A targeted binary. However, no model of Raspberry Pi 1 device can run either binary because they are all ARMv6 architecture devices that are not compatible with ARMv7-A or ARMv8-A.

Note that Android is not considered ARM Linux in this context. The executables are not expected to work out of the box on Android.

Change to wallet handling of mempool rejection

When a newly created transaction failed to enter the mempool due to the limits on chains of unconfirmed transactions the sending RPC calls would return an error. The transaction would still be queued in the wallet and, once some of the parent transactions were confirmed, broadcast after the software was restarted.

This behavior has been changed to return success and to reattempt mempool insertion at the same time transaction rebroadcast is attempted, avoiding a need for a restart.

Transactions in the wallet which cannot be accepted into the mempool can be abandoned with the previously existing abandontransaction RPC (or in the GUI via a context menu on the transaction).

Credits

Thanks to everyone who directly contributed to this release:

• The Bitcoin Core Developers
• Charles Lee
• Adrian Gallagher
• shaolinfry
• Xinxi Wang
• Xinrong Guo
• Fan Yang
• Peng Sun
• Loshan T