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<ol class="chapter"><li class="chapter-item expanded "><a href="about.html"><strong aria-hidden="true">1.</strong> About</a></li><li class="chapter-item expanded "><a href="concepts.html"><strong aria-hidden="true">2.</strong> Concepts</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="what_is_rln.html"><strong aria-hidden="true">2.1.</strong> What is RLN</a></li><li class="chapter-item expanded "><a href="uses.html"><strong aria-hidden="true">2.2.</strong> Uses</a></li><li class="chapter-item expanded "><a href="terminology.html"><strong aria-hidden="true">2.3.</strong> Terminology</a></li><li class="chapter-item expanded "><a href="under_the_hood.html"><strong aria-hidden="true">2.4.</strong> Under the hood</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="rln_circuit.html"><strong aria-hidden="true">2.4.1.</strong> Circom Circuit</a></li></ol></li><li class="chapter-item expanded "><a href="references.html"><strong aria-hidden="true">2.5.</strong> References</a></li></ol></li><li class="chapter-item expanded "><a href="code.html"><strong aria-hidden="true">3.</strong> Code</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="how_to_use.html"><strong aria-hidden="true">3.1.</strong> Usage</a></li></ol></li><li class="chapter-item expanded "><a href="theory.html"><strong aria-hidden="true">4.</strong> Theory</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="sss.html"><strong aria-hidden="true">4.1.</strong> Shamir's Secret Sharing</a></li></ol></li></ol>
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<h1 class="menu-title">Rate-Limiting Nullifier</h1>
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<h1 id="about"><a class="header" href="#about">About</a></h1>
<p>RLN (Rate-Limiting Nullifier) is part of Privacy &amp; Scaling Explorations (PSE), a multidisciplinary team supported by the Ethereum Foundation. PSE explores new use cases for zero knowledge proofs and other cryptographic primitives.</p>
<p><a href="https://appliedzkp.org">appliedzkp.org</a></p>
<div style="break-before: page; page-break-before: always;"></div><h1 id="concepts"><a class="header" href="#concepts">Concepts</a></h1>
<p>This section is a starting point for understanding the concepts of RLN.</p>
<div style="break-before: page; page-break-before: always;"></div><h1 id="what-is-rate-limiting-nullifier"><a class="header" href="#what-is-rate-limiting-nullifier">What is Rate-Limiting Nullifier?</a></h1>
<p><a href="https://ethresear.ch/t/semaphore-rln-rate-limiting-nullifier-for-spam-prevention-in-anonymous-p2p-setting/5009">Idea was proposed by Barry WhiteHat</a></p>
<p><a href="https://medium.com/privacy-scaling-explorations/rate-limiting-nullifier-a-spam-protection-mechanism-for-anonymous-environments-bbe4006a57d">RLN Overview</a></p>
<p><a href="https://hackmd.io/@aeAuSD7mSCKofwwx445eAQ/BJcfDByNF">RLN Spec</a></p>
<p><a href="https://rfc.vac.dev/spec/32/">VAC RLN Spec</a></p>
<div style="break-before: page; page-break-before: always;"></div><h1 id="uses"><a class="header" href="#uses">Uses</a></h1>
<div style="break-before: page; page-break-before: always;"></div><h1 id="terminology"><a class="header" href="#terminology">Terminology</a></h1>
<div class="table-wrapper"><table><thead><tr><th>Term</th><th>Description</th></tr></thead><tbody>
<tr><td>ZK-SNARK</td><td><a href="https://z.cash/technology/zksnarks/">z.cash/technology/zksnarks/</a></td></tr>
<tr><td>Stake</td><td>Financial or social stake required for registering in the RLN applications. Common stake examples are: locking cryptocurrency (financial), linking reputable social identity.</td></tr>
<tr><td>Identity secret</td><td>An array of two unique random components (identity nullifier and identity trapdoor), which must be kept private by the user. Secret hash and identity commitment are derived from this array.</td></tr>
<tr><td>Identity nullifier</td><td>Random 32 byte value used as component for identity secret generation.</td></tr>
<tr><td>Identity trapdoor</td><td>Random 32 byte value used as component for identity secret generation.</td></tr>
<tr><td>Identity secret hash</td><td>The hash of the identity secret, obtained using the Poseidon hash function. It is used for deriving the identity commitment of the user, and as a private input for zk proof generation. The secret hash should be kept private by the user.</td></tr>
<tr><td>Identity commitment</td><td>Hash obtained from the Identity secret hash by using the poseidon hash function. It is used by the users for registering in the protocol.</td></tr>
<tr><td>Signal</td><td>The message generated by a user. It is an arbitrary bit string that may represent a chat message, a URL request, protobuf message, etc.</td></tr>
<tr><td>Signal hash</td><td>Keccak hash of the signal, used as an input in the RLN circuit.</td></tr>
<tr><td>RLN Identifier</td><td>Random finite field value unique per RLN app. It is used for additional cross-application security. The role of the RLN identifier is protection of the user secrets being compromised if signals are being generated with the same credentials at different apps.</td></tr>
<tr><td>RLN membership tree</td><td>Merkle tree data structure, filled with identity commitments of the users. Serves as a data structure that ensures user registrations.</td></tr>
<tr><td>Merkle proof</td><td>Proof that a user is member of the RLN membership tree.</td></tr>
</tbody></table>
</div><div style="break-before: page; page-break-before: always;"></div><h1 id="under-the-hood"><a class="header" href="#under-the-hood">Under the hood</a></h1>
<div style="break-before: page; page-break-before: always;"></div><h1 id="circom-circuit-for-rln"><a class="header" href="#circom-circuit-for-rln">Circom Circuit for RLN</a></h1>
<pre class="mermaid">flowchart TB
subgraph Generate Secret Key
random0(Random 32 bytes) --&gt; a_0(Secret key)
random1(Random 32 bytes) --&gt; a_0
end
subgraph RLN
subgraph Identity Commitment
a_0 --&gt; h0(Poseidon Hash)
h0 --&gt; q(Identity Commitment)
end
subgraph Calculate Internal Nullifier
a_0 --&gt; h1(Poseidon Hash)
epoch(Epoch) --&gt; h1
h1 --&gt; a_1
rln_identifier(RLN Identifier) --&gt; h2(Poseidon Hash)
a_1 --&gt; h2
h2 --&gt; nullifier(RLN Internal Nullifier)
end
subgraph Merkle Tree
q --&gt; merkle_tree_inclusion_proof(Merkle Tree Inclusion Proof)
merkle_tree_inclusion_proof --&gt; root(ZKP of Merkle Tree Root)
end
subgraph Shamirs Secret Scheme
a_0 --&gt; plus(+)
a_1 --&gt; multiply(*)
x(Hashed Messaage) --&gt; multiply
multiply --&gt; plus
plus --&gt; share_y
end
nullifier --&gt; proof(ZKP)
root --&gt; proof
share_y --&gt; proof
end
</pre>
<div style="break-before: page; page-break-before: always;"></div><h1 id="references"><a class="header" href="#references">References</a></h1>
<p><a href="https://ethresear.ch/t/semaphore-rln-rate-limiting-nullifier-for-spam-prevention-in-anonymous-p2p-setting/5009">Idea was proposed by Barry WhiteHat</a></p>
<p><a href="https://medium.com/privacy-scaling-explorations/rate-limiting-nullifier-a-spam-protection-mechanism-for-anonymous-environments-bbe4006a57d">RLN Overview</a></p>
<p><a href="https://hackmd.io/@aeAuSD7mSCKofwwx445eAQ/BJcfDByNF">RLN Spec</a></p>
<p><a href="https://rfc.vac.dev/spec/32/">VAC RLN Spec</a></p>
<div style="break-before: page; page-break-before: always;"></div><h1 id="code"><a class="header" href="#code">Code</a></h1>
<div style="break-before: page; page-break-before: always;"></div><h1 id="usage"><a class="header" href="#usage">Usage</a></h1>
<div style="break-before: page; page-break-before: always;"></div><h1 id="theory"><a class="header" href="#theory">Theory</a></h1>
<div style="break-before: page; page-break-before: always;"></div><h1 id="shamirs-secret-sharing-scheme"><a class="header" href="#shamirs-secret-sharing-scheme">Shamirs Secret Sharing Scheme</a></h1>
<p><a href="https://en.wikipedia.org/wiki/Shamir%27s_Secret_Sharing">Sharmir's Secret Sharing wikipedia</a> is a good reference to understand the concept.</p>
<p>Reconstruction 1: https://github.com/akinovak/semaphore-lib/blob/5b9bb3210192c8e508eced7ef6579fd56e635ed0/src/rln.ts#L31</p>
<pre><code class="language-rs">retrievePrivateKey(x1: bigint, x2:bigint, y1:bigint, y2:bigint): Buffer | ArrayBuffer {
const slope = Fq.div(Fq.sub(y2, y1), Fq.sub(x2, x1))
const privateKey = Fq.sub(y1, Fq.mul(slope, x1));
return bigintConversion.bigintToBuf(Fq.normalize(privateKey));
}
</code></pre>
<p>Reconstruction 2: https://github.com/akinovak/semaphore-lib/blob/rln_signature_changes/test/index.ts#L250</p>
<pre><code class="language-rs">async function testRlnSlashingSimulation() {
RLN.setHasher('poseidon');
const identity = RLN.genIdentity();
const privateKey = identity.keypair.privKey;
const leafIndex = 3;
const idCommitments: Array&lt;any&gt; = [];
for (let i=0; i&lt;leafIndex;i++) {
const tmpIdentity = OrdinarySemaphore.genIdentity();
const tmpCommitment: any = RLN.genIdentityCommitment(identity.keypair.privKey);
idCommitments.push(tmpCommitment);
}
idCommitments.push(RLN.genIdentityCommitment(privateKey))
const signal = 'hey hey';
const x1: bigint = OrdinarySemaphore.genSignalHash(signal);
const epoch: string = OrdinarySemaphore.genExternalNullifier('test-epoch');
const vkeyPath: string = path.join('./rln-zkeyFiles', 'verification_key.json');
const vKey = JSON.parse(fs.readFileSync(vkeyPath, 'utf-8'));
const wasmFilePath: string = path.join('./rln-zkeyFiles', 'rln.wasm');
const finalZkeyPath: string = path.join('./rln-zkeyFiles', 'rln_final.zkey');
const witnessData: IWitnessData = await RLN.genProofFromIdentityCommitments(privateKey, epoch, signal, wasmFilePath, finalZkeyPath, idCommitments, 15, BigInt(0), 2);
const a1 = RLN.calculateA1(privateKey, epoch);
const y1 = RLN.calculateY(a1, privateKey, x1);
const nullifier = RLN.genNullifier(a1);
const pubSignals = [y1, witnessData.root, nullifier, x1, epoch];
let res = await RLN.verifyProof(vKey, { proof: witnessData.fullProof.proof, publicSignals: pubSignals })
if (res === true) {
console.log(&quot;Verification OK&quot;);
} else {
console.log(&quot;Invalid proof&quot;);
return;
}
const signalSpam = &quot;let's try spamming&quot;;
const x2: bigint = OrdinarySemaphore.genSignalHash(signalSpam);
const witnessDataSpam: IWitnessData = await RLN.genProofFromIdentityCommitments(privateKey, epoch, signalSpam, wasmFilePath, finalZkeyPath, idCommitments, 15, BigInt(0), 2);
const a1Spam = RLN.calculateA1(privateKey, epoch);
const y2 = RLN.calculateY(a1Spam, privateKey, x2);
const nullifierSpam = RLN.genNullifier(a1Spam);
const pubSignalsSpam = [y2, witnessDataSpam.root, nullifierSpam, x2, epoch];
res = await RLN.verifyProof(vKey, { proof: witnessDataSpam.fullProof.proof, publicSignals: pubSignalsSpam })
if (res === true) {
console.log(&quot;Spam proof Verification OK&quot;);
} else {
console.log(&quot;Invalid proof&quot;);
return;
}
const identitySecret = RLN.calculateIdentitySecret(privateKey);
const retreivedPkey = bigintConversion.bufToBigint(RLN.retrievePrivateKey(x1, x2, y1, y2));
if(Fq.eq(identitySecret, retreivedPkey)) {
console.log(&quot;PK successfully reconstructed&quot;);
} else {
console.log(&quot;Error while reconstructing private key&quot;)
}
// TODO: Add removal from tree example
}
</code></pre>
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