A cryptographic coupon — one second of CPU time — replaces the per-transaction fee. The economics of micropayments become viable. Feeless is not free — feework is the shape of anti-spam when there is no fee market.
On a fee-based chain, the fee is the ledger's tax on motion. Every call, every stream frame, every sensor reading pays again. At machine frequency and micropayment size, the tax exceeds the payload and the model collapses.
Stealth takes the fee off the critical path entirely on stealthCORE. The sender does the work. The network charges nothing. Spam is still priced — just in seconds of compute, not dollars of block space.
A feework output is a digital coupon attached to a feeless transaction. Each coupon carries a 16-byte proof-of-work nonce, found by hashing the transaction data with Argon2d until the output falls below a fixed ceiling. The coupon is highly specific to both the transaction and the precise moment it was created. Verification is one hash. Production is many.
A feeless transaction that doesn't make it into a block within 24 blocks · 120 seconds is invalidated. The spammer's work expires — and must be redone from scratch.
Transaction expiration is a Stealth-pioneered innovation. Unconfirmed feeless transactions are valid only inside a rolling 24-block window — about two minutes — tied to the block height the feework committed to.
Expiration does two jobs at once. For users, a held-up transaction doesn't wait indefinitely — it invalidates cleanly, and the sender retries with higher feework difficulty rather than staring at a stuck pending state. For spammers, it neutralises mempool flooding at the root.
Without expiry, a spammer at just 100 extra TPS could fill a 1 GB mempool in roughly 11 hours. With 24-block expiry, sustaining that same flood indefinitely requires over 4,000,000 TPS of fresh feework — every two minutes, forever.
Every two minutes, stale feework vanishes from memory. The mempool has a drain. Spam that arrived at the top of the hour is gone by the five-past.
Picture the mempool — the waiting area where unconfirmed transactions sit before they're bundled into a block — as a small room, roughly three metres on a side. Now imagine two of those rooms, side by side. They're identical. Same volume. Same door. Same owner outside.
A vandal walks up and starts throwing books through the door of both rooms — one book per second, every second. Each book is a spam transaction; the rate is a cheap, sustained flood. The only thing that differs between the two rooms is a single rule written on the wall — do books expire, or do they stay forever? — and that rule is the entire difference between a chain that can be DoS'd to a halt and one that cannot.
The rule: once a book is in the room, it stays there until a block producer physically carries it out. Books never expire on their own.
After 2 minutes — 120 books. After 10 minutes — 600. After an hour — 3,600. The books never leave. Eventually the room is full and nothing new fits — legitimate users get turned away at the door.
This isn't hypothetical. In early 2021 Nano was hit with a months-long spam attack that peaked at nearly 5 million transactions per day. Because Nano transactions never expire, a determined attacker can also pre-prepare tens of millions of transactions over months and unleash them all at once.
Mempool · books over time
The rule: every book's feework is stamped with a block-height expiry. Exactly 2 minutes after it lands, the book vanishes on its own — no block producer required.
After 2 minutes — 120 books. But then something happens: feework expires after exactly 2 minutes. For every new book thrown in, the oldest one disappears. The count stays flat at 120, forever.
The room is self-cleaning. The vandal is running on a treadmill — going nowhere. To actually overwhelm the room, he'd need to throw books faster than 4,000,000 per second — and the work to produce each book is Argon2d, memory-hard, bounded by his RAM budget rather than his CPU.
Mempool · books over time
TL;DR. Stealth's 2-minute feework expiry is like a self-cleaning room. Nano's room has no drain.
Stealth completed the world's first feeless (spam-resistant) multi-signature round trip — both sending to and spending from a multisig account without a monetary fee. Nano, the only other cryptocurrency with true feeless transactions, has no multisig support and no plans to introduce it. Multisig lives on the BTC-style ledger; Stealth is the only BTC descendant where multisig is also feeless.
When a company holds a large balance in a single-signature account, one compromised key drains the treasury. Multisig forces a conspiracy across multiple individuals. Game theory makes such conspiracies unstable — any defector can turn the others in and have something to gain.
If a signatory's key is stolen, the thief can't send anything. They need to convince a valid subset of the other legitimate signatories to co-sign — which, in practice, is not going to happen. A stolen key in an n-of-m multisig is a key that does nothing.
If a signatory dies and their key is lost, the remaining signatories can still spend — as long as the account is structured n-of-m with n < m. This is the standard configuration. Single-signature wallets have no equivalent; key loss is terminal.
Most users can't be expected to secure private keys themselves — especially in times of urgency. They rely on exchanges and custodians, who in turn depend on multisig for their own security standards. Feeless multisig is therefore essential for mainstream adoption, not a niche feature.
The commands below are used by programs serving as interfaces to the underlying functionality — not by end users manually. Custodial parties build their own workflows from these primitives. Sending feelessly to a multisig address is the same sendtoaddress command; the multisig nature is carried by the P2SH address prefix.
Nano is widely considered the leader among feeless cryptocurrencies and is the most logical competitor to compare against. In early 2021, Nano suffered a months-long spam attack peaking at nearly 5M transactions per day. Their response was architectural: sort unconfirmed transactions into 129 buckets by account balance, prioritise less-recently-used accounts, and form a ~50,000-transaction Active Election Container.
Of Nano's 129 balance buckets, 87 serve accounts under 0.0001 XNO. Populating those buckets with 87,000 attacker-controlled accounts costs approximately $0.40. The bucket structure was meant to price legitimate users fairly; it also prices attackers at basement rates.
Nano has no analogue to Stealth's 24-block expiry. Spam accumulates in memory indefinitely. A patient attacker can pre-prepare tens of millions of transactions over months — then release them all at once as a single coordinated burst. There is no architectural counter.
There is also a utility cost: Nano accounts can only submit one unconfirmed transaction at a time. Each payee must be paid sequentially. Stealth's UTXO model — inherited from Bitcoin — supports full parallel spend across independent note outputs.
| Attack scenario | XST · Result | Nano · Result |
|---|---|---|
| Mempool flooding | Requires >4M TPS (24-block expiry) | Transactions never expire |
| Pre-prepared spam burst | Feework expires in 2 min | Accumulates indefinitely in memory |
| GPU DoS at 20% block fill | ~$14,000 of GPUs needed | Bucket structure exploitable for ~$0.40 |
| UX during attack | Pay tiny fee · unaffected | Sequential tx confirmation |
| Parallel processing | Full UTXO parallelism | Single unconfirmed tx per account |
"Stealth's feeless protocol was designed to thwart any conceivable exploit that may arise when offering feeless transactions."— Stealth R&D LLC
At maximum feework difficulty, the cost to keep Stealth's mempool saturated runs into millions of dollars per month. The numbers below are not aspirational — they fall directly out of the Argon2d work function, the 2-minute expiry window, and the block-binding requirement working together.
A typical node with 4 GB of RAM allocates roughly 1 GB to the mempool. Keeping it filled requires the attacker to generate nearly 2,880,000 transactions every two minutes — each requiring ~13 seconds of computation on a high-end Intel Xeon core.
At max difficulty, each core produces 9 transactions per 2-minute window. Filling the mempool requires 320,000 cores running non-stop. An 8-core machine runs ~$120/month; scaling to 320,000 cores runs approximately $4.8M/month, or $6,700/hour. Only nation-states could sustain this.
GPUs don't help. A Tesla V100 ($7,000) manages only ~88 feeless TPS under Argon2d. Filling blocks to just 20% capacity takes more than two such GPUs working continuously — and legitimate users can always outbid spammers by specifying higher hardness or paying a tiny fee. Memory-hard hashing flattens the attacker's structural advantage.
"A denial of service spam attack on Stealth's feeless transaction system is prohibitively difficult — and will always remain so by design."— Stealth R&D LLC · July 1, 2021
Junaeth targets a 5-second block interval (QP_TARGET_SPACING = 5 in QPConstants.hpp) — 12 blocks per minute, 720 per hour, 17,280 per day. Throughput scales along three orthogonal axes: block-size, core-count, and the micropayment multiplier that only a feeless chain can access.
1 MB block · single core · feework-verify
Baseline. Every node in the network meets this ceiling today with conservative parameters. Already 130× Bitcoin's observed throughput.
~10 MB block · single core · feework-verify
Larger blocks. Verifier advantage over an attacker holds at ~9,362× because Argon2d is asymmetric between mining and validation.
16-core parallel verify
Verifier-side parallelism. Signature checks, feework validation, and UTXO updates are embarrassingly parallel at the block level.
| Chain | Block time | Block size | Observed TPS | Feeless |
|---|---|---|---|---|
| Stealth XST | 5 s | 1 – 10 MB | 917 – 150,000 | Yes |
| Bitcoin | ~600 s | 1 – 4 MB | ~7 | No |
| Monero | ~120 s | Dynamic | ~30 – 50 | No |
| Litecoin | ~150 s | 1 MB | ~56 | No |
| Ethereum | ~12 s | ~1.8 MB (gas) | ~15 – 30 | No |
A fee chain's effective throughput for sub-dollar payments is zero. A feeless chain's effective throughput is its observed throughput.
= $10.00 of value moved
= $100.00 of fees paid (at $0.01/tx)
Economic collapse. Nobody sends $0.001 when the fee is 10×.
= $10.00 of value moved
= $0.00 of fees paid (Argon2d work only)
Micropayment market is reachable. So are IoT, machine-to-machine, and streaming.
Every 5 seconds, a deterministic quorum-elected validator publishes the next block. No mining race. No fork. No wait.
| Block time | 5 seconds | QP_TARGET_SPACING = 5 |
|---|---|---|
| Blocks per day | 17,280 | 12 / min · 720 / hr |
| Consensus | Junaeth (quorum PoS) | Mainnet · May 2021 |
| Feework algorithm | Argon2d | Memory-hard PoW coupon |
| Nonce size | 16 bytes | Per-transaction |
| Difficulty ceiling | 0x0006ffffffffffff | Max feework hardness |
| Tx expiry | 24 blocks (~2 min) | Unconfirmed feework drops |
| Validator advantage | ~9,362× | Verify / mine asymmetry |
| Base TPS | 917 | 1 MB · single core |
| Scaled TPS | 9,362+ | ~10 MB · single core |
| Parallel TPS | ~150,000 | 16-core verify |
| Transaction model | UTXO | BTC-descended |
| Multisig | Feeless · world's first | P2SH · any M-of-N |
| Fee for feeless tx | $0 | Argon2d work, not currency |