Cybersecurity · Blockchain · Web3

Félix Loureiro Etcheverría — Trust at blockchain scale

I build on-chain products where documents, votes, memories and assets don't depend on anyone's word. And I defend them.

Chapter I · In progress

What I'm buildingright now.

These nine are the projects I'm immersed in today. Before them came many others that are now part of the chain's past. They all share one premise: the proof is written where no one can erase it.

Active · 2026

Earlier blocks: many other projects, now in the history · genesis 0xea0d76…8cad

Block #01 / 09ActiveCertification

Ciertis

Your document, sealed on the blockchain.

Register the SHA-256 fingerprint of any file on Polygon or Ethereum without the file ever leaving your device. You get a PDF certificate with a verifiable QR code: timestamped proof of existence and integrity.

  • SHA-256
  • Polygon
  • Ethereum
  • PDF + QR
prev
0xea0d76…8cad
hash
0x62802e…26e9
Block #02 / 09ActiveWeb3 development

BlockDevShop

Production-grade Web3, security first.

Blockchain development studio with 13 services: NFT contracts, custom tokens, DAOs and real-world asset tokenization. Live demo, multichain deployment and an audit before mainnet.

  • Smart contracts
  • RWA
  • DAOs
  • Audit
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0x62802e…26e9
hash
0xe08d3b…5fb0
Block #03 / 09ActiveGovernance

VotaciónLibre

One person, one vote. No tricks.

Secure, transparent online voting. Passwordless access with MetaMask or email, a single vote per poll and results that update instantly.

  • MetaMask
  • Single vote
  • Live results
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0xe08d3b…5fb0
hash
0x580648…ddea
Block #04 / 09ActiveTime capsules

Capschain

Messages that open in the future.

End-to-end encrypted messages or files for someone to open on a set date. Only the cryptographic fingerprint goes on Polygon: a tamper-proof timestamp and complete privacy.

  • E2E encryption
  • Polygon
  • Timestamp
prev
0x580648…ddea
hash
0x028620…b03a
Block #05 / 09ActiveSaaS · Sports clubs

Eternal Sports

Love for a club, forever.

White-label SaaS joining physical columbaria in the stadium with a digital legacy: memorials, matches attended, QR/NFC-authenticated memorabilia and private messages. All certified on-chain.

  • White label
  • QR / NFC
  • Digital legacy
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0x028620…b03a
hash
0x4de325…e438
Block #06 / 09ActiveMemorial · Camp Nou

Memorial FC Barcelona

What you live at the Camp Nou, recorded forever.

A place at the Spotify Camp Nou where members and fans record their stadium experiences on the blockchain: matches, visits and memories beside the pitch, timestamped and tamper-proof.

  • Physical experiences
  • On-chain record
  • Spotify Camp Nou
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0x4de325…e438
hash
0x4e4fd2…634c
Block #07 / 09ActiveDiamonds · STO

Dianelum

Sustainable diamonds, tokenized investment.

Spain's first tokenized debt issuance under the new Securities Market Law: a €5M security token backed by diamonds, supervised by the CNMV and traceable security by security on-chain.

  • Security Token
  • CNMV
  • €5M
  • Smart contract
prev
0x4e4fd2…634c
hash
0xffa3b0…dad5
Block #08 / 09ActiveBitcoin network · 3D

Sede Bitcoin

The Bitcoin network, alive before your eyes.

A 3D neural network of Bitcoin nodes where transactions leap from node to node like lightning. Rotate it, change its density and fire your own discharges with a click.

  • Bitcoin nodes
  • Interactive 3D
  • Three.js
prev
0xffa3b0…dad5
hash
0x9d42cc…2916
Block #09 / 09ActiveWallet · Email

MailCryptoWallet

Your crypto wallet, in your inbox.

A crypto wallet with nothing but your email address: no apps, no extensions and no seed phrases. Sign in with your email and start receiving, holding and sending crypto.

  • Email sign-in
  • No downloads
  • No seed phrase
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0x9d42cc…2916
hash
0xb877bd…206a

Chapter II · The shield

What I build,I also defend.

Half of my work is looking at the chain from the other side: following the money, finding the bug before the attacker does and designing systems that don't keep what they shouldn't.

  • 01 · OSINT

    On-chain investigation

    Tracing funds across wallets, exchanges and mixers. Address attribution and flow maps ready for a report.

  • 02 · FORENSICS

    Crypto forensics

    Reconstructing incidents, scams and thefts with verifiable on-chain evidence. Our own scam database.

  • 03 · AUDIT

    Smart contract audits

    Manual and automated review before mainnet: reentrancy, access control, oracles, economic logic.

  • 04 · ZERO-CUSTODY

    Privacy by design

    End-to-end encryption and architectures where sensitive data never touches a server. Only the fingerprint goes on-chain.

Console — felixle@sede

Illustrative simulation · fictitious data

Chapter III · Your block

Don't trust me.Seal something yourself.

Type some text or drop a file. Your browser computes its SHA-256 fingerprint and mines a real proof-of-work block. Nothing leaves your device.

sha256e3b0c442…b855

0/256 bits differ from the previous

Change a single letter and watch the fingerprint: the avalanche effect flips ~50% of the bits.

Height #10— pending
Previous block
b877bdccb4fde94cbd1c1357fae0ef1bedd859dbb3126b9a32c475650f6d206a
SHA-256 fingerprint
—
Difficulty
0000…
Nonce
—
Attempts
—
Timestamp
—
100% local · Web Crypto API

Chapter IV · The lab

The codeI study in depth.

Forks I study, audit and adapt: from Bitcoin's core to AI-driven pentesting. A selection here; the rest lives on GitHub.

Genesis of what's next

Shall we buildsomething immutable?

Web3 projects, audits or an on-chain investigation. I answer personally.

Don't expect a contact form like everyone else's. I'm different, and you're looking for the difference. I'm sure you'll find your way to me.

Direct messageTelegramCodeGitHub
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