Boost your Unique Humanity score with ZK Email Stamp through Amazon and Uber receipts
Oct 29, 2025
Human Passport’s new ZK Email Stamp to boost your Humanity Score, built in collaboration with ZK Email, lets you prove you’re human through everyday activity without revealing personal details. In just minutes, you can verify your Amazon shipping (purchase) history or Uber ride receipts for free, using trustless email verification powered by zero-knowledge proofs.
This lowers the barrier for newcomers, who can now build trusted onchain identities without additional wallet transactions or gas fees, and gives existing users a way to diversify their Passport credentials without exposing personal information. Because these proofs are based on ordinary digital life but expensive for Sybil farms to fake, they offer a unique and accessible path to Sybil resistance.
Most importantly, ZK Email shows that identity can be plural and shaped by experience, not dictated by one rigid credential. This approach sets a precedent not just for web3 but for the larger internet, showing how personhood credentials can be private, inclusive, and user‑controlled to make the internet a safer place.
No Silver Bullet for Sybil Resistance
Sybil resistance has been one of the internet’s most persistent challenges, with direct implications in web3 for governance, funding, incentive mechanisms, and community trust. CAPTCHAs, once the default solution, are now effectively obsolete, wasting an estimated 500 human years/day of effort each day while bots still thrive. Legacy identity systems that rely on collecting personal information create long-term risks, including data breaches leading to a surge in social engineering attacks, with real-world consequences for users.
The ZK Email Stamp takes a radical approach: it uses what people already do—buying things, taking rides—as proof of personhood, wrapped in zero-knowledge proofs that ensure no personal data ever leaves the user’s control. This makes it easy for newcomers, who can prove humanity without crypto expertise or invasive KYC, while also giving existing users new ways to diversify their identity credentials.
Cryptographically Verifiable Identity
Offchain credentials today, like ePassports, JWTs for web accounts, or web data backed by TLS and DKIM signatures, are cryptographically verifiable. But web data, in particular, has unique advantages: it is highly contextual and can signal strong human behavior patterns that are hard to fake yet easy to prove.
The advent of zero-knowledge proofs and improved client-side verification now allows users to prove facts about their web data, like confirmation emails or account ownership, without ever sending raw content to a server. ZK Email builds on this foundation, transforming existing web data into composable, privacy-preserving building blocks of identity that can be used onchain.
Human Passport is built on that philosophy where identity is not binary, but modular and plural by design, offering Stamps drawn from different parts of a person’s digital and social life. Stamps based on web data, like the ZK Email Stamp, further diversify this ecosystem, adding everyday behaviors as yet another independent proof of personhood.
What is the ZK Email Stamp?
The ZK Email Stamp verifies your inbox for Amazon shipping confirmations and Uber ride receipts—real-world signals of economic and mobility activity, without exposing personal content.
How it works:
Connect your Gmail (temporary, read-only access) via the Human Passport dashboard.
Pattern match + DKIM validation: ZK Email looks for specific receipt formats and uses DKIM signatures to confirm the emails are genuine. Forwarded, proxied, or forged emails are unable to defeat the system.
Generate a zero-knowledge proof: This proof is generated server-side to ensure fast processing times. Your matching emails are temporarily sent to ZK Email's servers to create the proof, then immediately deleted from their systems.
Receive credentials: Based on your history, you can earn up to six credentials:
Each of these credentials is converted into a Human Key by Human Network to further anonymize the data and help deduplicate the Stamp across accounts, so Sybils can’t use the same email across many wallets.
Constraints:
Only Gmail clients are currently supported, with a plan to expand the coverage soon.
Emails need to be in the inbox or in the archive. Sorry inbox zero users.
Each credential contributes points to your Unique Humanity Score, already used by apps for governance, rewards, Sybil resistance, and verified access.
The process takes less than 5 minutes, is free, and requires no additional wallet transactions beyond holding a Human Passport. It works for newcomers to build their trusted on-chain identity and for experienced users diversifying their identity credentials with real-world, privacy-preserving proofs.
Check the support knowledge base for more information on the ZK Email Stamp.
Looking ahead: We hope to evolve this Stamp to look at additional high-human signal email patterns, which might mean that we increase the Stamp weight, further improving the user experience for both crypto beginners and maxis.
Everyday Activity as a Human Signal
Why use shopping and ride history to prove identity? Because these are natural, everyday human behaviors that are difficult for bots to fake at scale.
In web3, Sybil attacks are often not just a few people with two or three wallets, but sophisticated farms or “Sybil-as-a-service” operations running thousands of wallets that look legitimate. Stamps based on everyday behavior, like Amazon purchases (shipping confirmations) or Uber rides, are extremely difficult to farm digitally and expensive to fake.
Here, identity is shaped by experience, and because it is one Stamp among many, it contributes to a broader picture of uniqueness without excluding people who choose other forms of verification.
Privacy by Design
Scanning your inbox may sound intrusive, but ZK Email is designed to protect privacy at every step. It requests temporary, read‑only access to your inbox and looks only for specific patterns, like Amazon shipping confirmations or Uber ride receipts. No message content or subject lines are stored or shared. Instead, ZK Email validates each matching email’s DKIM signature to ensure authenticity, then generates a zero‑knowledge proof locally on your device. Only the cryptographic proof, not your raw email data, is shared, and you can revoke permissions immediately after verification.
This reflects a broader shift toward programmable cryptography, where applications don’t just verify static credentials but can prove specific properties of user data without revealing everything. It moves identity away from fixed, one-time credentials and toward flexible, composable proofs that adapt to how people interact online, building trust while preserving privacy.
Phase 1 and What’s Next
We’re planning to establish a longer collaboration with the ZK Email team. The current release is Phase 1, focused on Amazon and Uber data because these are globally accessible, high‑signal behaviors. This phase lets us test user experience, monitor adoption, and measure how it deters Sybil attacks.
Phase 2 will explore a more advanced ZK Email scoring model. Instead of just threshold counts, it could combine multiple features from your inbox: travel confirmations, membership emails, and other signals, all converted into privacy‑preserving proofs. This model could use supervised machine learning, similar to how Passport’s onchain scoring works, making it harder for attackers to reverse‑engineer criteria while still protecting user data.
The end goal is a richer, modular identity ecosystem, where different users verify their humanity in ways that fit their life, and where verifiers can choose which combinations of signals to trust.
Ready to boost your Unique Humanity Score and earn HUMN Points?
Head over to HUMN Onchain SUMR Season 1 to learn how Human Passport users can earn HUMN Points by collecting credentials like ZK Email – each adding 100 to your points. This means that if you verify all six credentials within the ZK Email Stamp, you’ll earn 600 extra HUMN Points.
Want to integrate Passport’s proof of humanity tooling into your dApp? Reach out here.
About Human Passport (formerly Gitcoin Passport)
Human Passport is an identity verification application and Sybil resistance protocol with more than 2M users. It enables users to collect verifiable credentials, or Stamps, that prove their identity and trustworthiness without exposing personally identifying information. To date, Human Passport has protected over $380M in airdrop and grant funds.
About human.tech
human.tech is a suite of technologies designed to enhance personal freedom, privacy, and financial autonomy. human.tech provides innovative solutions for secure identity, data ownership, and private transactions, ensuring that technology remains a tool for human empowerment.
