What is Horizen?
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🟢 The simple version
Plain English — no jargon. Start here.
Horizen is a blockchain platform that evolved from a privacy coin into a sidechain infrastructure system — using zk-SNARKs not just for transaction privacy but to allow custom application-specific blockchains (sidechains) to be created and verified by the main Horizen chain without the main chain needing to know the sidechain's rules.
Horizen's origin — ZClassic fork
Horizen (originally named ZenCash) launched in May 2017 as a fork of ZClassic — itself a fork of Zcash. ZenCash removed the "Founders' Reward" that directed a percentage of block rewards to Zcash's founding team, distributing all rewards to miners instead. The original focus was privacy-preserving transactions using Zcash's zk-SNARK technology.
Horizen then evolved significantly beyond its privacy coin origins. The team pivoted toward building blockchain infrastructure — specifically a sidechain platform where any developer could deploy their own blockchain that inherits security from the Horizen mainchain. This pivot distinguished Horizen from other Zcash forks and positioned it as infrastructure rather than just a currency.
Zendoo — the sidechain protocol
Zendoo is Horizen's cross-chain transfer protocol — a system that allows sidechains to communicate with the Horizen mainchain using zk-SNARKs for verification. The key insight: instead of requiring the mainchain to understand the rules of each sidechain (which would require mainchain upgrades for every new sidechain), Zendoo uses zk-SNARK proofs to allow any sidechain to prove to the mainchain that withdrawals are valid, without the mainchain knowing anything about the sidechain's logic.
Node tiers and the SuperNodes
Horizen operates a multi-tier node system. Regular nodes relay transactions. Secure Nodes require 42 ZEN collateral and provide encrypted communication. SuperNodes require 500 ZEN collateral and support the sidechain infrastructure. Node operators earn ZEN rewards: 10% of block rewards to Secure Nodes, 10% to SuperNodes, 20% to the Horizen DAO treasury, 60% to miners.
Is it legal in India?
Yes. ZEN is a VDA under Indian law. 30% tax and 1% TDS apply. See India regulation.
🟡 A bit more detail
For when you want to go a little deeper.
Zendoo's cross-chain verification model
The Zendoo protocol's innovation is "proof of absence of knowledge" — the mainchain verifier does not need to know the sidechain's state machine rules to verify that a withdrawal proof is valid. Each sidechain generates a backward transfer certificate (a zk-SNARK proof) proving that the withdrawal request is valid according to that sidechain's own rules. The mainchain verifier contract checks the SNARK proof's validity using the sidechain's verification key (registered at sidechain creation) — but never processes the sidechain's actual state transitions.
Horizen's sidechain infrastructure has been used by several blockchain projects as a deployment platform. Cobalt (by Horizen Labs) is a permissioned sidechain framework for enterprise blockchain applications. The EON (EVM-compatible) sidechain launched in 2023 as a public Ethereum-compatible smart contract platform on Horizen's sidechain infrastructure — allowing Solidity developers to deploy on an EVM chain that settles to the Horizen mainchain. The Horizen DAO (previously Horizen Foundation) funds ecosystem development through its 20% treasury allocation.
EON — the EVM sidechain
EON is Horizen's EVM-compatible sidechain launched in 2023. It is a full Ethereum Virtual Machine implementation that runs as a Zendoo sidechain — meaning Solidity contracts deploy normally, MetaMask connects to it, and it is secured by the Horizen mainchain's zk-SNARK verification. ZEN is the native gas token. EON positions Horizen as accessible to the Ethereum developer ecosystem while maintaining the unique security model of Zendoo's trustless cross-chain verification.
Key Horizen metrics: number of deployed sidechains, EON daily transactions, ZEN node count (Secure + SuperNodes), and treasury DAO activity. Horizen's pivot from privacy coin to sidechain infrastructure is the key development to understand — the coin's value is increasingly tied to infrastructure utility rather than privacy-coin demand. Live data: CoinGecko · Horizen Explorer.
🟣 The full technical picture
For the technically curious.
Zendoo technical architecture
The Zendoo paper (Garoffolo et al., 2020) formalises the cross-chain transfer protocol. Each sidechain declares a verification key at registration — a cryptographic commitment to the SNARK circuit that the sidechain will use to prove withdrawal validity. When the sidechain submits a backward transfer certificate, it includes: (1) the list of withdrawal outputs, (2) a SNARK proof that these withdrawals are valid according to the sidechain's circuit, and (3) a reference to the relevant sidechain epoch. The mainchain verifies the SNARK proof against the registered verification key — a constant-time operation regardless of sidechain complexity.
Source: Garoffolo, A. et al. (2020). Zendoo: A Zk-SNARK Verifiable Cross-Chain Transfer Protocol Enabling Decoupled and Decentralised Sidechains. horizen.io/research/sidechains · Horizen docs: docs.horizen.io
The 51% attack and the enhanced difficulty adjustment
In June 2018, ZenCash (before rebranding to Horizen) suffered a 51% attack — an attacker rented hashrate, reorganised the chain, and double-spent approximately $550,000 in ZEN across three exchanges. In response, Horizen developed an enhanced delayed block penalty (EDPB) algorithm — a modified proof-of-work difficulty adjustment that imposes severe penalties on blockchain reorganisations extending more than a few blocks. The penalty makes deep reorganisations exponentially more expensive in terms of hashrate required, substantially reducing the profitability of 51% attacks without changing the fundamental PoW consensus model.
Horizen's node incentive tiers are secured by IP address tracking and challenge-response authentication to prevent sybil attacks (one operator claiming to run many nodes). Each Secure Node or SuperNode must respond to a cryptographic challenge from its registered IP address within a time limit, proving it is actually operated rather than being a paper node. Node tier eligibility is determined by ZEN balance and uptime percentage tracked over a rolling period. This system ensures the node collateral requirements correspond to real operational commitments rather than just locked tokens.
Key facts
- Origin: ZClassic → ZenCash → Horizen (2017)
- Sidechain protocol: Zendoo (zk-SNARK verified cross-chain transfers)
- EVM sidechain: EON (launched 2023, Solidity-compatible)
- Node tiers: Miners / Secure Nodes (42 ZEN) / SuperNodes (500 ZEN)
- Block reward split: 60% miners / 10% Secure Nodes / 10% SuperNodes / 20% DAO
- ZEN supply: ~21 million (fixed)
- 51% attack history: June 2018 (addressed via EDPB)