Monthly Archives: June 2017

Offchain Transactions In Ethereum/RSK (2)

Previous Post

Each contract in Ethereum/RSK has an associated storage. This storage has addresses and content. The addresses are 32-bytes values, and the content is 32-bytes values (notably, RSK has support for storing arbitrary byte arrays in an storage cell, topic for another post). Then, an onchain storage looks like:

(simplified addresses and contents). Each missing address has a default value (zero in Ethereum for numeric storage cells). When the contract is running OFFCHAIN, the storage state is kept in the designated running node, not shared with the rest of the network. The offchain storage state is only known by the running node, and it can be altered sending offchain transactions to the contract, and invoking offchain calls to the contract/running node.

An offchain contract have code (written by the contract programmer) that commits the contract. If the commit operation is invoked (an special new opcode in Ethereum Virtual Machine, to be mapped by a modified solidity compiler, or using the assembly keyword in a solidity program), then the contract emits an onchain transaction, the so called delta transaction. Is a transaction that when mined and added to the winning blockchain, alters the onchain storage to the current offline storage state:

Some details to decide: the cost of such transactions, who pays the cost (my first guess: the sender of the invoke that raise the commit in the contract method code).

The delta transaction start to have more sense if its size is shorter than the size of all the offchain transaction that were processed by the running node, when the contract was in offchain state. Maybe, it could be the case for token contracts, where the state is usually the token balance by account, independently of the number of token transfer that were executed.

Although these ideas could be difficult to implement in the existing Ethereum implementations, RSK is a new implementation still under development, and then, this proposal could be implemented without disrupt existing behavior.

Next post topics: the offline transfer of value, cost of offchain transactions.

Stay tuned!

Angel “Java” Lopez



Alternative Proposal for Remasc Contract in Ethereum/RSK

Since the release of public RSK testnet, the source code was published. And now, I can write about implementation details.

Ethereum platform supports the concept of precompiled contracts: contracts that are already implemented in the node code. In the case of RSK, we have two additional precompiled contracts: the Bridge contract, and the Remasc contract. In this post, I will propose an alternative implementation for Remasc contract (not yet with source code, there is no published official description for Remasc contract).

What is Remasc contract? AFAIK (remember, there is no public description yet), it is a contract that assign rewards to miners, examining the recent blockchain story. In order to calculate and assign rewards, it should have state related to the past blocks in the blockchain. This is the current state class. Also, there is a special Remasc transaction ADDED to EACH mined block, at the end of the list of transactions. And the target account is the Remasc contract. So, at the end of execution, that transaction is executed.

According to Ethereum Yellow Paper, there is a block finalization step:

11. Block Finalisation
The process of finalising a block involves four stages:
(1) Validate (or, if mining, determine) ommers;
(2) validate (or, if mining, determine) transactions;
(3) apply rewards;
(4) verify (or, if mining, compute a valid) state and nonce.

So, my first proposal is to remove the “compulsive added” transaction, and use the block finalization to invoke the contract. In this way, I could get rid off the nonce calculation, signing of transaction, block validation (a block SHOULD have that transaction), transaction serialization, transaction receipt storage, block transactions storage, etc….  To me, it is clear that having the reward process in the block finalization step instead of into an explicit transaction, is a simpler way. And you know, simplicity pays 🙂

The other proposal, to be explored, is to simplify the use of storage. The calculation of the next state could be performed with the blockchain information, already available. So, the current storage use is only a performance hack, that could be replaced, if needed, by an in-memory cache, removing the use of public blockchain storage. Ethereum storage is costly, and RSK is not an exception: in the current implementation, after more than 100000 blocks in testnet, running a local node in my machine, the Remasc storage takes 1/3 (one third) of total local storage. The Remasc should be deterministic, as any other contract. If for some reason it needs storage (to be reviewed when the specification is published)t, my first guess is that it needs less space than current implementation.

Stay tuned!

Angel “Java” Lopez


Offchain Transactions in Ethereum/RSK (1)

Next Post

In Ethereum/RSK, a contract has a lifecycle like:

A contract is an account, it has an address and balance like any other account. But additionally, it has code and storage. The transactions it received, can have value and invocation data. And each transaction has a cost, as it is saved in the blockchain.

In this post series, I will describe a possible implementation of support for offchain transactions and state. The idea is that a contract could be in another states, others than normal one:

When a contract is at offline state, it is executed in a designated running node, only ONE node, not in EVERY node of the network. The transactions it receives are execute only in the RUNNING NODE, and they are not added to the blockchain. So, the cost of the transactions could be free or near to free. Only when the contract decided to commit the new storage state, the state is published in the blockchain using a delta onchain transaction.

The change of state from normal to offchain is triggered by the contract itself. In its code, there is a new instruction (translated to new Ethereum VM opcode), to switch to offchain status. Then, all onchain transaction are rejected for this contract, no miner could add those transactions. But new offchain transactions should be routed to the running node (the only node that is running the offchain contract instance). An offchain transaction could be identified, ie, by a nonce of -1 (it is an implementation detail: the users can send onchain and offchain transactions: the former are processed only when the target contract is in normal state; the later only when it is in offchain state),

Again, the contract code could decide, when being in offchain state, to commit its state to the blockchain, or to rollback to the previous published state. If it decides to commit, then it switch to a temporary frozen state, until a delta onchain transaction is mined and accepted by the rest of the network. The delta transaction has the mission to update the published state to the new one, hosted by the running node.

In the next posts, I will describe the delta transaction with more detail, and I will discuss also the value transfer in case of offchain transactions. Maybe, now the RSK main code is public, I would publish a light implementation of these ideas.

Stay tuned!

Angel “Java” Lopez

Multi-Blockchains in Ethereum/RSK (1)

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The implementation of a blockchain includes the creation, distribution, and manage of blocks:

A block, in Bitcoin and Ethereum, has:

  • An unique hash
  • A parent block, identified by hash
  • A block number (one plus parent block number)
  • A list of transactions

In the case of Ethereum and RSK, a transaction has:

  • A sender account
  • A receiver account
  • A value to transfer
  • Additional data (used if the receiver account is a smart contract)

A list of chained valid blocks form a blockchain:

In Ethereum/RSK, a block has also:

  • Uncle blocks
  • Associated Block Difficulty (difficulty of proof of work plus the sum of uncles difficulties)

So, the presence of uncles contributes to the block difficulty. And this number adds to the TOTAL difficulty of the blockchain. Many nodes in the network, called miners, could generate blocks to be added to the current blockchain, but the consensus algorithm  choose the blockchain with the greater total difficulty:

(in Bitcoin, the longest blockchain wins; in Ethereum/RSK a shorter blockchain could win if it has greater total cummulative associated difficulty).

One problem is to keep the state of all accounts and contracts in the system. Each transaction also has

  • State Root Hash

the hash of the world state AFTER the execution of the transaction. This hash is verified by every node in the network, so all the working nodes agrees on the resulting world state. A world state is saved in a trie, that can be identified by such root hash (see my previous work on tries Building a Blockchain (5) Building a Blockchain (12))

The block itself also has a State Root Hash, representing the world state AFTER the execution of the block. It could be different than the last transaction state root hash: the execution of block could assign rewards and alter account balances, if the protocol specifies the changes. This block root is also checked by the running nodes in the network, in order to validate the block state and consensus.

One problem is that the build of a block could be a bottlenect if the system should process many transactions (maybe hunders or thousands per second). This is the principal use case that guides the proposal of this post series. It could be interesting to have MANY blockchains:

Then, one blockchain could be dedicated to the process of a popular token/contract, or other blockchain could be dedicated to the transfer in a particular country. Only in few cases could be needed a transfer between blockchains. And this schema is not limited to TWO blockchains, we could have many blockchains. And the state storage and status could be maintaned by MANY nodes, sometimes, a node is dedicated to keep only ONE or TWO blockchains. So the scale of the operation does not hurt the system.

In the next post, I will describe the modification to apply to Ethereum/RSK so we can  manage multiple blockchains in the network.

Stay tuned!

Angel “Java” Lopez

Blockchain: Links And Resources (44)

Previous Post
Next Post

Visualizing Where Major US Banks Have Invested in Fintech

A Blockchain in 200 Lines of Code

Gartner’s Cool Vendors In Blockchain Platforms

eth Interactive Console

All cases when Solidity compiles to invalid jump destination

RSK’s Ginger: New step for bitcoin community

Dos proyectos argentinos ganaron una competencia global para combatir la corrupción

Ethereum – Distributed Consensus (A Concise Ethereum History Book)

Ethereum flavored WebAssembly (eWASM) Design

How Etheroll and other Dapps will kill Ethereum

Ethereum Ecosystem

My Links

Stay tuned!

Angel “Java” Lopez

Running an Ethereum/RSK Node

The RSK public testnet was launched, and the core source was opened. If don’t know what RSK is, please visit:

Technically, it is a fork of Ethereum (Java source), with a 2-way peg with Bitcoin, and merge-mining capabilities. You can run your own node, alone, in your own network, or join it to the public testnet. There are instructions at thecore project github wiki:

In this post, I want to describe my usual workflow, to run experiments with RSK implementation and ideas (disclaimer:I’m a member of RSK development team, but this is a description of my personal experiments). First, you have to downloadthe source code from:

Currently, the most updated published version is at branch Ginger:

Also, you can clone the repository into your own one. Once you have the source code, you can compile using IntelliJ  deaCommunity Edition, or use the command line:

.\gradlew build shadow -x testnet

(I’m usually work with Windows, in Linux, Mac, you must use the normal /). More details at:

The shadow option is to build a jar with all the dependencies. The -x test skips the run of test from build step. The command generates a .jar file in one subdirectory. Then, you can execute

cd rskj-core\build\libs
java -Drsk.conf.file=<path> -cp rskj-core-0.2.0-GINGER-all.jar co.rsk.Start

What config file to use and to configure it? More info at:

An initial config file at:

You must set a unique nodeId for your instance. You can generate a nodeId using the command line:

java -cp rskj-core-0.2.0-GINGER-all.jar co.rsk.GenNodeKeyId

It dumps a JSON file to console. You must copy the private key and the node id, to your config file:

# Private key of the peer
nodeId = 66cf57...
privateKey = 46f850...

You only need to copy the privateKey to run the node, but you can include the nodeId also for your own reference. The other line to configure is the coinbase secret:

# this string is computed
# to be eventually the address
# that get the miner reward
coinbase.secret = mytreasure

You must put an arbitrary string here.

To allow the CORS (Cross-Origin Resource Sharing) for your JSON RPC (Remote Procedure Call), set the cors property:

rpc {
    enabled = true		# you can disable rpc
    port = 4444
    cors = "*"    # you can put "localhost here"

The RPC capability is only used to query the node, and disabling it does not interfere with the normalwork of the node. How the node knows how to connect to the public Testnet? There is a list of bootstrap nodes:

peer {
	discovery = {
        # if peer discovery is off
        # the peer window will show
        # only what retrieved by active
        # peer [true/false]
        enabled = true

        # List of the peers to start
        # the search of the online peers
        # values: [ip:port]
        ip.list = [

to use in what is call the “peer discovery” process. You can disable them if you want only to use your own node in your network.

If you want to run MANY local nodes, you must have MANY configuration file. In these files, adjust also the properties:

    # Peer for server to listen for incoming connections
    # 50505 for testnet
    listen.port = 50505 # ie to 50506

and the already mentioned:

rpc {
    enabled = true
    port = 4444		# ie to 4445

Additionally, you can set your own network id, so your local o networked nodes only work for this network:

    # Network id
    networkId = 777  # ie to 42

You can also specify in each of your nodes the active nodes to connect, instead of using peer discovery and bootstrap public nodes:

    # Boot node list
    # Use to connect to specific nodes
    active = [    
        #    ip =
        #    port = 50505
        #    nodeId = e437a483...

As usual, you can set the machine name instead of IP number, using the same property ip.

If you want your node mine new blocks, change these properties to true:

# miner options
miner {
    server.enabled = false  # change to true
    client.enabled = false	# change to true

If you change only the server.enabled property to true, you can expose the new block to merge mining process, but this feature is beyond the scope of this post.

Any other question? You can visit the RSKJ gitter channel:


RSK is hiring! Interested?

Stay tuned!

Angel “Java” Lopez


New Month’s Resolutions: June 2017

A new month begins, time to write down the monthly resolutions. But first, a review of the past ones:

– Continue RskSharp [pending]
– Continue SimpleBlockchain [complete] see repo
– Continue BlockchainSharp [pending]
– Continue ChineseP [pending]
– Continue TensorSharp [pending
– Continue RSharp [complete] see repo

I also worked on:

– Improve AjDrawJS [complete] see repo
– Improve AjTalkJS [complete] see repo
– Improve SimpleForth [complete] see repo
– Improve ClojJS Clojure in JavaScript [complete] see repo
– Additional sample for SimpleGA, genetic algorithms [complete] see repo
– Experiments on RSKJ form [complete] see repo
– Create wordie, literate programming language [complete] see repo
– Create domie, a DOM-like for JavaScript testing [complete] see repo
– Create vyu, a vue.js-like framework [complete] see repo

My new resolutions:

– Continue RskSharp
– Continue SimpleBlockchain
– Continue BlockchainSharp
– Continue ChineseP
– Continue TensorSharp
– Continue RSharp
– Experiments with RSKJ fork
– Continue Vyu
– Continue Domie
– Continue Wordie

Stay tuned!

Angel “Java” Lopez