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Zendoo is Horizen’s revolutionary sidechain and scaling solution, and it is the first completely decentralized and fully customizable sidechain protocol on the market. The Zendoo sidechain platform enables businesses and developers to affordably and quickly create real-world blockchain applications on Horizen’s fully distributed, secure, and privacy-preserving architecture.

Sidechains are an elegant innovation devised to overcome current limitations regarding scalability and extensibility in blockchain. Sidechains are parallel platforms and application layers with desired features that supplement the capabilities of the mainchain without imposing a significant burden.

Zendoo extends the Horizen network from a cryptocurrency to a privacy-preserving platform that scales for commercial applications.

What makes Zendoo Different

Differently from many other sidechain solutions, Zendoo is designed to be completely decentralized without the need to rely on pre-defined trusted parties - it solves the biggest problems in applying blockchain solutions to real-world use cases:

Zendoo SDK

Each sidechain is a full blockchain application that requires the implementation of Consensus, network layer, wallet, history, and many other pieces. Most sidechains, beyond their specific logic and data, can be based on the same implementation.

Zendoo comes with an SDK that addresses most of these aspects and includes all necessary components required for building a blockchain in a single toolbox. This allows developers to focus only on the specific features of their blockchain instead of low-level tasks, making the deployment of a complete blockchain much easier and faster.

Zendoo Beta SDK is live on testnet

Zendoo to mainnet in Q4 2021

Zendoo Facts

Zendoo includes: 1,130 files & 114,000 lines of code

Mainchain changes to support sidechains (ZEND)
  • 211 files changed
  • 25,000 lines added
Sidechain SDK
  • 538 files
  • 50,000 lines
Privacy tool: Ginger-lib
  • 302 files
  • 30,000 lines
  • 22 files
  • 3,000 lines
  • 57 files
  • 6,000 lines

Decoupled Consensus Between Chains
A novel sidechain construction

Zendoo is designed with a novel sidechain construction tailored to be compatible with the Horizen blockchain but it can also be adopted for other blockchain systems. It is designed for conducting secure and decentralized cross-chain transfers without requiring the mainchain nodes to track a sidechain to verify them. The Zendoo construction requires modifications in the mainchain core consensus protocol to enable cross-chain transfers but once implemented, it will allow deploying many sidechains in a reliable way.

Cross-Chain Transfer Protocol (CCTP)

CCTP determines how assets can be transferred between mainchain and sidechain. All sidechains employ the same unified CCTP, which is known by the mainchain.


Even though the participants of the CCTP will be different for different sidechains, the procedure will be specified by the mainchain consensus protocol. Such unification will allow the system to deploy many sidechains without the need to modify the mainchain consensus protocol for each of them separately.

The CCTP defines the structure of the 2-way peg, so it consists of two sub-protocols. The first defines a forward transfer procedure and the other a backward transfer procedure. A forward transfer transmits coins from the mainchain (MC) to the sidechain (SC). A backward transfer transmits coins back from SC to MC.

The most important part of the sidechain construction is the CCTP itself since it defines the overall structure of the communications between MC and SC. The backward transfers are especially important because the MC, for scalability reasons, does not keep track of the sidechain so is not able to directly verify the validity of an SC to MC transfer.

Privacy for your sidechains

Ginger-lib is a new zk-SNARK library and a general-purpose toolkit that enables developers to build scalable privacy solutions into their applications while maintaining the speed and security of the network. Ginger-lib is Horizen’s first original contribution to the Zero-Knowledge Proof base and the global zk-SNARK movement.

Ginger-lib introduces several new cryptographic primitives and gadgets that can be used by developers based on their needs. It allows developers to implement zk-SNARKs supporting full recursive proof composition.

Some of the key additions to the library are the MNT4-753 and MNT6-753 elliptic curve cycles with all the fields, groups, primitives, and gadgets necessary to implement recursive SNARKs. For example, Ginger-lib includes a specific implementation of the POSEIDON hash, the Schnorr signature, a VRF, and a Merkle tree implementation based on POSEIDON.

Sidechain role in the Horizen ecosystem

dApps, Products & Services

Bringing blockchain benefits to life through real-world utility


A revolutionary scaling solution with an open-sourced SDK

Horizen Public Mainchain

A powerful infrastructure fueled by its native cryptocurrency ZEN and a massive node network

Horizen Node Network

The largest and most distributed multi-tiered node networks with over 40000 active nodes

The latest updates

Horizen Academy

Learn all about sidechains