Chain-Agnostic Authorization Mode

• Chain-agnostic authorization is a blockchain paradigm using tokens validated across multiple chains to enable uniform access control and delegation.
• It employs cryptographic techniques like ECDSA signatures, hash/time-locks, and RLP-based message hashing to securely construct and verify authorization artifacts.
• While enhancing flexibility and cross-chain interoperability, this model raises risks of replay-like exploits, necessitating strict per-chain scoping and robust security mitigations.

Chain-agnostic authorization mode refers to a blockchain-based authorization paradigm in which an authorization artifact, such as a cryptographically signed tuple or token, is intentionally constructed or interpreted so that it is accepted as valid authorization on multiple independent blockchain networks. This mode can be realized via explicit protocol design, as with the “cid = 0” (chain identifier zero) convention in EIP-7702, or through cross-ledger smart contract and hash/time-lock techniques in interledger systems. Chain-agnostic authorization enables uniform access control, delegation, and transaction capabilities across heterogeneous blockchain domains, but exposes unique operational and security properties—including replay-like multi-chain exploits, policy abstraction, and atomic settlement primitives (Qi et al., 13 Dec 2025, Siris et al., 2019).

1. Formal Definition and Protocol Mechanics

In EIP-7702, the chain-agnostic mode is defined at the tuple level: for an externally owned account (EOA), authorization is enabled by submission of a signed tuple $$a_i = (\mathrm{cid}_i, \mathrm{addr}_i, \nu_i, y_i, r_i, s_i)$$, with each component representing the chain identifier ($\mathrm{cid}_i$), the delegate contract address ($\mathrm{addr}_i$), the nonce ($\nu_i$), and the ECDSA signature ($y_i, r_i, s_i$). The signed message is

$$\mathrm{msg}(\mathrm{cid},\mathrm{addr},\nu) = H(\mathrm{MAGIC} \parallel \mathrm{RLP}([\mathrm{cid}, \mathrm{addr}, \nu]))$$

where $\mathrm{MAGIC}$ is a 1-byte EIP-7702 domain separator.

A tuple is accepted by a client on chain $CH$ if:

1. $\mathrm{cid} = CH$ or $\mathrm{cid} = 0$ (i.e., chain-agnostic),
2. $$\mathrm{ecrecover}(\mathrm{msg}, y, r, s) = \text{victim EOA}$$,
3. $\text{victim.nonce} = \nu$,
4. The signature is canonical.

Upon acceptance and after preprocessing, the EOA’s code field is replaced: $$\text{code}(\text{victim}) \leftarrow 0xef0100 \mathbin\Vert \mathrm{addr}$$ granting code delegation privileges to $\mathrm{addr}$ on all chains where this tuple is accepted (Qi et al., 13 Dec 2025).

In interledger smart contract systems targeting resource-constrained IoT, chain-agnosticism is modeled via multi-ledger state transitions and atomic lock/reveal flows. Hash-time-lock contracts (HTLCs) with deterministic pre-images, policy abstraction, and salted identifiers allow policies and authorizations to be securely and portably instantiated on multiple blockchains (Siris et al., 2019).

2. Stepwise Construction and Execution of Chain-Agnostic Authorization

For EIP-7702, the construction and exploitation of the chain-agnostic tuple proceeds as follows (Qi et al., 13 Dec 2025):

1. Delegate Contract Preparation: The attacker deploys a malicious delegate contract $T$ (with a fallback handler to drain assets).
2. Tuple Creation:
   • $n \leftarrow \mathrm{nonce}(\text{victim})$
   • $$\mathrm{msg} \leftarrow \mathrm{keccak}(\mathrm{MAGIC} \parallel \mathrm{RLP}([0, T, n]))$$
   • $$(y, r, s) \leftarrow \mathrm{sign}(\text{victim.SK}, \mathrm{msg})$$
   • $a \leftarrow (0, T, n, y, r, s)$
3. Transaction Submission: Construct and broadcast a type 0x04 transaction with the tuple included.
4. Client Authorization Preprocessing:
   • Extract and verify the tuple under chain-agnostic rules.
   • Write $$\text{code}(\text{victim}) = 0xef0100 \mathbin\Vert T$$.
5. Delegated Execution:
   • Any call to the EOA routes execution to $T$, which then drains ETH, ERC-20, and ERC-721 assets.

In interledger settings for IoT, chain-agnostic authorization is achieved by:

• Enforcing interface abstraction (e.g., lockAsset, revealSecret, claim) mirrored across participating ledgers.
• Relying on strong hash/time-lock primitives and uniform event notification to guarantee atomic settlement and cross-chain policy enforcement (Siris et al., 2019).

3. Replay-Like and Multi-Chain Exploitation

Chain-agnostic EIP-7702 authorizations enable a novel replay-like attack. A tuple with $\mathrm{cid}=0$ can be (re)broadcast on any number of independent EVM-compatible chains (L1, L2, rollups, testnets), provided the EOA nonce is freshly unused on that chain. Each chain independently verifies and accepts the same signature, updating the EOA’s code to delegate to the attacker's contract $T$ (Qi et al., 13 Dec 2025). This enables the attacker to compromise all corresponding EOAs on all networks where the user has not yet spent the nonce.

This behavior is distinct from classical transaction replay, which attempts to reuse a transaction; here, the authorization signature is the replay vector, enabling creation of new, chain-native transactions that are independently validated everywhere.

In interledger authorization for IoT, the equivalent property is established by forming protocol interactions (requests, locks, secret reveals) such that their cryptographic commitments (e.g., hash pre-images $x$ in HTLCs) are portable across chains with deterministic hash functions and time parameters (Siris et al., 2019). This guarantees that authorization and settlement is realized on all ledgers where a policy is instantiated, up to $n$-of-$m$ reveal conditions for decentralized authorities.

4. Empirical Multi-Chain Attack and Chain-Agnostic Generalization

A controlled experiment on three Hardhat EVM networks (chain IDs 1337, 2337, 3337) demonstrates practical cross-chain compromise using a single cid = 0 tuple (Qi et al., 13 Dec 2025):

Chain (ID)	ETH before	ETH after	ERC-20 before	ERC-20 after
1337	10,000.0	0.000432931	2,000.0	0.0
2337	10,000.0	0.000432931	2,000.0	0.0
3337	10,000.0	0.000432931	2,000.0	0.0

Total losses: approximately 30,000 ETH, 6,000 ERC-20 tokens.

This empirically confirms that a chain-agnostic signature enables compromise of the user's EOA and total fund drainage on all chains with the same EOA/private key. The chain-agnostic model thus presents a cross-network threat surface unparalleled in classical replay behavior.

For interledger IoT systems, chain-agnostic generalization is implemented by designing standard interfaces (e.g., lockAsset, revealSecret, claim/refund) and ensuring they are surface-compatible across ledgers—requiring support for scripting with hash/time-locks, event notification, and synchronized, monotonic block/time counters. Portability is contingent upon pinned hash algorithms and compatible timing semantics. Atomicity is formally guaranteed when paired HTLC settlement windows are correctly parameterized and relay delays bounded (Siris et al., 2019).

5. Security Analysis and Protocol-Level Mitigations

Security analysis shows that chain-agnostic authorization greatly amplifies the risk of multi-chain compromise. A single victim signature can be weaponized on every chain, causing systemic replay-like theft.

For EIP-7702, the following protocol-level mitigations are recommended (Qi et al., 13 Dec 2025):

• Forbid chain-agnostic tuples by default: Enforce $\text{cid} = \text{currentChainId}$ in client verification logic, explicitly rejecting $\text{cid}=0$.
• Explicit per-chain context binding: If cross-chain migration is required, include unique per-chain salts in the signed message (e.g., $$\mathrm{msg} = H(MAGIC \parallel \mathrm{RLP}[\mathrm{cid}, \mathrm{addr}, \nu, \text{context\_salt}])$$).
• Pre-flight wallet checks: UI/SDK mechanisms should warn or block on ambiguous $\text{cid}$ usage, particularly if $\text{cid}=0$.
• Scoped authorizations: Authorizations should include expiry or single-use constraints (such as an $expiryBlock$ field), with clients required to reject tuples that are expired or used.

In interledger/IoT systems, security best practices for chain-agnostic authorization involve:

• Enforcing time-locks, hash-locks, and atomic cross-ledger pre-image exposure.
• Parameterizing settlement and reveal windows to account for relay unpredictability.
• Salting policies and commitments per chain to prevent unwanted transferability.
• Pinning hash function selection and formalizing policy IDs to maintain determinism (Siris et al., 2019).

6. Cross-Domain Applications and Implementation Considerations

Chain-agnostic authorization models are relevant beyond EVM chains, extending to IoT device management and decentralized interledger protocols. Key implementation considerations are:

• Authorization policy storage and evaluation: Off-chain hashed policy descriptions ($h_P = \Hash(P)$), on-chain enforcement of $m$-of-$n$ authority revelations, and linkage to payment flows.
• Performance metrics: On Ethereum testnets, public chain gas for basic flows is $\sim$60–200 kgas, with delays from 42–60 seconds; IoT data overhead can be reduced by 18–32% via MAC aggregation and field deduplication (Siris et al., 2019).
• Interoperability requirements: Deployment on arbitrary ledgers necessitates: i) scripting for time/hashlocks, ii) event logs, iii) deterministic hash compatibility, and iv) synchronization of settlement timing windows.
• Connector incentives and safety: Encouraging relayers via fee mechanisms, enforcing reveal windows, synchronizing block/time, and parameterizing fee rates by chain. Eventual interoperability and atomicity depend on these connective guarantees.

This suggests that chain-agnostic authorization, while enabling flexible multi-chain delegation and atomic settlement, introduces systemic security exposure in the absence of robust per-chain scoping, and thus demands explicit design constraints to avoid exploitability.

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References

• "EIP-7702 Phishing Attack" (Qi et al., 13 Dec 2025)
• "Interledger Smart Contracts for Decentralized Authorization to Constrained Things" (Siris et al., 2019)