“Axelar: Interoperable Smart Contracts” is the 2021 whitepaper by Axelar Network (co-founded by Sergey Gorbunov and Georgios Vlachos, former Algorand team members) describing a decentralized network for general-purpose cross-chain messaging — enabling smart contracts on any connected chain to send messages and call functions on contracts on any other chain.

Unlike bridges that focus solely on token transfers, Axelar enables General Message Passing (GMP): arbitrary smart contract calls and state changes across chain boundaries, opening up cross-chain DeFi composability, cross-chain NFT operations, and interoperable dApp logic.

> Whitepaper: Available at axelar.network/wp-content/uploads/2021/07/axelar_whitepaper.pdf.

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Publication and Context

In 2021, the multi-chain universe had expanded significantly: Ethereum, Binance Smart Chain, Avalanche, Polygon, Terra, Solana, and Cosmos were all live with active DeFi ecosystems. Users wanting to move assets between chains faced a fragmented landscape of manual bridges — many of which used insecure multisig designs that later resulted in >$2 billion in bridge hacks.

Axelar proposed a decentralized validator-secured approach to cross-chain messaging, combining Cosmos SDK infrastructure with threshold cryptography for multi-chain key management.

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Architecture: Gateway + Validator Network

Two-layer architecture:

1. Gateway Smart Contracts (per connected chain):

• A Gateway contract is deployed on each supported chain (e.g., Ethereum, Avalanche, Polygon)
• Users/dApps initiate cross-chain calls by calling the Gateway’s callContract function with the destination chain, destination address, and payload
• The Gateway emits an event that Axelar validators observe
• On the destination chain, the Gateway executes the incoming validated message by calling the target contract

2. Axelar Validator Network:

• Axelar is itself a Cosmos SDK-based blockchain with its own validator set secured by AXL token staking
• Validators observe Gateway events on all connected chains
• When 2/3+ of validators confirm an event (Vote → Approve → Execute), the message is relayed
• Validators sign messages using threshold ECDSA (each chain’s private key is a distributed secret held by the validator set)

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Threshold ECDSA for Multi-Chain Keys

Every connected EVM chain has an associated private key — a single key that the Axelar validators collectively control and whose public key is registered in each chain’s Gateway contract.

Instead of one party holding this key (a centralized bridge multisig), Axelar uses threshold ECDSA (via Multi-Party Computation):

• The private key is never assembled in one place
• Validators hold secret shares; any 2/3+ can collaboratively produce a valid ECDSA signature
• The signature can be verified against the registered public key on the destination chain

This means the Axelar validator set can authorize cross-chain messages without any single validator (or even a group of <1/3 validators) being able to forge a message.

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General Message Passing (GMP)

GMP is Axelar’s key differentiator from simple token bridges:

Token bridge: Transfer 100 USDC from Ethereum to Avalanche.

GMP example: On Ethereum, call a smart contract function that:

1. Sends 100 USDC to an Avalanche address AND
2. Calls depositAndFarm(address, uint256) on an Avalanche yield farming contract with the received USDC as an argument

This enables cross-chain contract composability: a single user transaction on Chain A can trigger a multi-step action on Chain B.

squid (now Squid Router) is the most prominent consumer of Axelar GMP, enabling one-click cross-chain token swaps that involve multiple chains and protocols.

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Trust Model

Axelar’s security depends on its validator set:

• Safety: If <1/3 of AXL stake is Byzantine, cross-chain messages cannot be forged
• Liveness: If <2/3 of AXL stake goes offline, message processing halts
• Validators are slashed for equivocation (signing conflicting messages)
• AXL staking rewards incentivize honest participation

Comparison to other bridges:

• More decentralized than multisig bridges (Ronin: 9 of 9 keys stolen → $625M hack)
• More centralized than light-client bridges (IBC on Cosmos) that provide cryptographic proof rather than validator consensus

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Reality Check

Axelar is one of the most widely deployed cross-chain messaging protocols (supporting 50+ chains as of 2024). Its GMP capability is genuinely novel. However:

• Security depends on AXL market cap: Validator stake security is proportional to AXL’s value. A significant AXL price decline reduces the cost of attacking the validator set.
• Bridge hacks context: No major Axelar funds loss as of 2024, but cross-chain bridges as a category have lost >$2.5B in hacks. Users must trust the validator set continuously.
• Message latency: Cross-chain messages require validator consensus (~15–30 seconds typical), plus source and destination chain block times. Not suitable for latency-sensitive applications.

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Legacy

Axelar popularized the hub-and-spoke interoperability model — a single decentralized network connecting all chains — as an alternative to point-to-point bridges. The GMP concept influenced LayerZero and Wormhole’s evolution toward general cross-chain contract calls. Axelar’s Cosmos SDK architecture enables governance-driven chain support additions without protocol upgrades.

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Related Terms

• Cross-Chain Bridge
• LayerZero Whitepaper
• Wormhole Whitepaper
• Threshold Signature

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Research

• Bharathan, P., Kamath, S., et al. (2021). Axelar: Interoperable Smart Contracts. Axelar Network.

— Primary whitepaper. Section 3 defines gateway contracts; Section 4 covers threshold ECDSA.

• Gennaro, R., Goldfeder, S., & Narayanan, A. (2016). Threshold-Optimal DSA/ECDSA Signatures and an Application to Cryptocurrency Hardware Wallets. IACR ePrint 2016/013.

— Threshold ECDSA construction; the cryptographic primitive used by Axelar validators for distributed key signing.

• Mackinga, T., Nadahalli, T., & Wattenhofer, R. (2022). TWAP Oracle Attacks: Easier Done than Said? IEEE Blockchain 2022.

— Cross-chain bridge security analysis; context for Axelar’s security model relative to alternate bridge designs.