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A USDC deposit address can be generated without a private key when a contract predicts the address of code that will be deployed there later. In Edy Cu’s Pigeonhole demonstration on Arc, a second dependency proved just as important: the app inferred invoice status from blockchain logs, and a public RPC endpoint rejected log queries spanning 10,000 blocks. A full-history scan could therefore fail and leave a paid invoice displayed as UNPAID.
How can a USDC deposit address have no private key?
In Edy Cu’s account of Pigeonhole, each invoice gets a deterministic deposit address derived from its invoice ID. A factory hashes that ID into a CREATE2 salt and predicts where a small contract would be created. The predicted address can be shared before that contract exists; in the author’s description, it initially has no private key, code, or nonce.
The factory uses an immutable treasury address and the init code for a 22-byte throwaway contract. Its runtime behavior is PUSH20 treasury; SELFDESTRUCT. When someone calls the sweep function, the factory deploys the contract at the predicted address using CREATE2. The constructor immediately executes SELFDESTRUCT, transferring the address’s native balance to the treasury.
Cu invokes EIP-6780 to explain why the account created and self-destructed in the same transaction is deleted again. The article says the address can then be reused. These are implementation details and protocol claims reported by the project’s author, not an independent contract audit.
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Why the chain’s asset behavior matters
The pattern relies on Cu’s description of Arc: USDC is the native balance used for gas and can be sent through an ordinary native-value transfer. That makes it possible for the throwaway contract to sweep the balance with SELFDESTRUCT. Cu cautions that ordinary ERC-20 USDC on other EVM chains cannot be swept this way: an ERC-20 token balance is held by the token contract, not as the address’s native balance. Do not assume the same design works on another chain merely because it is EVM-compatible.
Why a paid invoice could appear as UNPAID
Pigeonhole has no database, according to Cu’s article. Its page reconstructs invoice state from Arc transfer logs: an incoming Transfer log from Arc’s system emitter to the deposit address indicates PAID, while an outgoing transfer from that address that takes its balance to zero indicates SWEPT.
That makes log retrieval part of the product’s correctness, not just a convenient read. The first version requested the full relevant history in one eth_getLogs call. If the RPC rejected that request, the page could not see the payment log and could continue to label the invoice UNPAID. Cu’s concise diagnosis was: “The mental model that was wrong: ‘a view call is free, so ask for everything.’ Log queries are not views.”
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What the 9,999-block RPC cap means
Cu reports measuring a public Arc RPC endpoint on 2026-09-17: a query spanning 9,999 blocks succeeded, while one spanning 10,000 blocks failed with -32012 requested range too large. At roughly two blocks per second, the author estimated that 9,999 blocks represented about 85 minutes.
This was an observation about that endpoint at that time—not a universal, permanent limit for Arc, Ethereum, or every RPC provider. Limits can depend on the provider and can change. The practical failure was that once the contract’s history exceeded the accepted range, a full-history refresh could fail instead of returning the logs needed to update an invoice.
How the scan was changed to avoid the range error
Cu describes a browser-side scanner that divides history into smaller sequential requests rather than asking for everything at once. The implementation details and test results below are reported by the author.
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Chunk the history and scan in order
The scanner caps each request at 9,000 blocks, below the reported 10,000-block rejection point. It tiles the requested range into sequential chunks, with pacing and retries. Cu reports tests intended to ensure chunks stay below 10,000 blocks, cover a range without gaps, and fetch 250,000 blocks without the range error.
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The app polls incrementally and saves completed chunks in localStorage, so a returning visitor need not repeat history it has already read. Invoice links can include a ?from= parameter giving the invoice’s creation block; this narrows the initial scan instead of starting at factory deployment.
For an old invoice URL without ?from=, Cu estimates about 38 log calls per day of chain at the reported RPC rate. The author says a first read of an old link can take minutes. The scanner keys logs by transaction hash and log index; reported tests checked that overlapping polls do not double-count the same log.
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Respect throughput as well as range limits
A request can fit under a provider’s block-span cap and still be slow or throttled. Cu reports sustaining approximately 0.5 eth_getLogs calls per second against an anonymous Arc RPC endpoint. That is an author-reported measurement, not a guaranteed service rate. Pacing and retries address this separate constraint, but they do not make an older first scan instantaneous.
What the reported figures do—and do not—establish
| Figure | What Cu reports | Qualification |
|---|---|---|
| 9,999 accepted; 10,000 rejected | Public Arc RPC log-query spans | Measured 2026-09-17; endpoint-specific observation |
| 9,000 blocks | Maximum chunk span in the described scanner | Implementation choice reported in the 2026 article |
| About 85 minutes | Approximate time represented by 9,999 blocks | Estimate using roughly two blocks per second |
| Approximately 0.5 calls per second | Rate sustained by the anonymous Arc RPC endpoint | Author-reported measurement, not a provider guarantee |
| About 38 calls per day of chain | Estimated calls for an old invoice URL without ?from= |
Author’s estimate at the reported RPC rate |
| 64,162 gas | Median balance-moving sweep | Reported across 25 benchmark rows |
| About $0.0013 | Estimated sweep cost | Author’s estimate using Arc’s stated 20 Gwei floor |
Cu also reports 12 Foundry tests, 25 Vitest tests including 20,000 fast-check property cases, and 34 read-only Playwright checks against mainnet. The author says an offline CREATE2 verification checked 50 random IDs against the on-chain predict() function. These counts describe project checks; they are not an independent audit or a guarantee that the system is free of defects.
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- Immutable destination: The factory’s treasury is immutable, with no beneficiary rotation. Cu says changing the beneficiary requires a new factory.
- RPC dependency: The page relies on anonymous RPC access for log history. Provider availability, request limits, throughput, and latency affect whether invoice status can be refreshed.
- Older links: A link without a
?from=hint may require a much longer initial history scan. PAID latency was not benchmarked in the article. - Verification limits: Cu says the explorer API was behind a challenge page and the factory source was not verified there. The author says the on-chain runtime matched
forge buildoutput by a truncated keccak hash; that claim is not an independent source verification.
The author identifies the factory as an Arc mainnet deployment on chain 5042 at 0x942b8c102e73aeea1a652ebC8F2d319fD08D9A40, and provides links to a payment transaction, sweep transaction, live page, repository, and short video in the original article. Those are author-supplied pointers, not independently checked here. The author describes the repository as MIT-licensed.
Questions to ask before using the pattern
- Does the target chain treat the asset as native balance in the way the sweep relies on, or is it an ERC-20 token?
- Are RPC log-range limits, throughput, and availability measured for the endpoint the app will actually use?
- Can the app scan in bounded chunks, checkpoint progress, retry failures, and deduplicate overlapping results?
- Is an immutable treasury acceptable, or does the recipient need a rotation mechanism?
- Would a maintained indexer or backend be more suitable than having each visitor scan history directly? Cu’s account does not test those alternatives.
Cu’s audit question captures the general engineering lesson: “what are the limits of the one external thing this depends on, measured, not assumed.”
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