toluTag

Touch-point On-chain Linked Universe. Bridging the physical world to decentralized, on-chain validation.

Open tooling for provisioning and using NXP SE05x secure elements as NFC-readable Ethereum signers.

toluTag is the root of trust that links a real-world object to on-chain validation. The tag is the primitive; what you build on top is up to you.

A toluTag is a passive NFC tag carrying an SE05x secure element. A secp256k1 key pair is generated on the chip and never leaves it; the private key is not extractable by design. The chip's public key yields an Ethereum address, and the chip can sign EIP-191 messages and EIP-712 typed data on demand, so a physical object can produce signatures that any Ethereum verifier (on-chain or off-chain) can check against a fixed address.

There is no server in the trust path: a verifier checks the signature directly against the chip's address, on-chain or locally. No central authority to spoof, go down, or disappear, and verification keeps working even if the original issuer no longer exists.

This repository holds two independent clients that speak the same SE05x APDU protocol:

Neither component has third-party dependencies. Keccak-256, secp256k1 public-key recovery, DER parsing, RLP-free EIP-191/712 encoding and the SE05x TLV/APDU layer are all implemented directly in this repo, in both languages.

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Free dev kit

Want to try a toluTag without building one first? Request a dev kit at tolu.network and experiment with a real tag.

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Shape the tag however you need

A toluTag is only two things that matter: the SE051C secure element and an NFC antenna tuned around it. Everything else is carrier. That leaves the outline free, so the tag can take the shape of the product it authenticates instead of forcing the product to make room for a tag. Change the board outline, keep the antenna geometry tuned, and the same key hierarchy, the same applet and the same apps work unchanged.

Two reference builds are in this repository.

1. PCB board. A rigid FR4 board, the card form factor in Hardware/PCB/card/. This is the one to start with: easiest to fabricate, easiest to hand-solder, and the most forgiving to probe while bringing a design up. Good for cards, tokens, coins, tags hung off a product, and anything with a flat place to sit.

2. Flex board. The same circuit on flexible polyimide, in Hardware/PCB/sticker/ and Hardware/PCB/textile/. Because it bends and is fractions of a millimetre thick, one design covers three very different products: a sticker applied to a finished item, a textile tag sewn or heat-pressed into clothing and bags, or a tag embedded into the object during manufacture, under resin or behind a laminate, where it is invisible and cannot be removed without destroying the item. That last case is the interesting one: the physical bond between object and key becomes as strong as the object itself.

In every case the flow is the same: scanning produces an ECDSA signature over a timestamped message, a smart contract checks that it comes from an authorized tag, and only then does the experience open. The gating lives in the contract, not in the app. Signatures are timestamped and accepted only within a tight window, so a captured signature can't be replayed later.

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Built on toluTag: 0xLimited

0xLimited is the first way to put toluTag to work on physical products. It pairs a physical item with an on-chain digital twin: attach a tag to a product, register its address in a product smart contract, and scanning the tag mints an NFT twin bound to that specific tag. From then on the physical item has a verifiable digital identity.

The 0xLimited repo ships an open smart-contract template plus a site that lets you create a product contract and link tags without writing code. It is a separate project that builds on the tag primitive in this repo.

Explore 0xLimited

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How it works

The applet

Both clients select the SE05x IoT applet (AID A0000003965453000000010300000000) over ISO 7816-4 and then speak the SE05x command set: WriteSecureObject, ReadSecureObject, CryptoObject / Signature, ManageSession, DeleteSecureObject. Everything is TLV-encoded under tags 0x41/0x42/0x43.

secp256k1 on an SE05x

The SE05x supports arbitrary Weierstrass curves but ships without secp256k1 provisioned. Both clients therefore:

1. Create the curve id for secp256k1 and push its parameters (p, a, b, G, n) one at a time, idempotently, so a tag that already carries the curve is left alone.
2. Generate an EC key pair at a caller-chosen 4-byte object id (e.g. 00002222), optionally under a policy.
3. Read back the uncompressed public point, keccak256(X‖Y)[12..] → the tag's Ethereum address.

Object policies

Keys are created with an explicit policy. By default the DELETE permission is omitted, meaning the object can never be wiped from the tag, the binding between chip and address is permanent. A deletable variant is available for development tags.

Keys may additionally be bound to a UserID authentication object holding a PIN. Using such a key requires opening an authenticated session (ManageSession → verify PIN) and wrapping every subsequent command in a ProcessSessionCmd. Both clients handle this transparently once a session is open.

Signing

The chip signs a 32-byte digest with ECDSA_SHA256 and returns a DER SEQUENCE { INTEGER r, INTEGER s }. The client then:

• parses r/s from DER,
• recovers the recovery id v by trying each candidate and comparing the recovered address to the chip's own address (rather than assuming a value),
• normalises s and emits Ethereum-ready r/s/v.

Two payload shapes are supported:

• EIP-191 (personal_sign), including the toluTag phrase template <address>_<uniqueId>_<value>, where address is the chip's own address or a caller-supplied msg.sender, and uniqueId is the SE05x factory-unique chip id.
• EIP-712: any standard eth_signTypedData_v4 document ({types, primaryType, domain, message}), the same shape MetaMask and ethers produce. The token {{signer}} anywhere in the JSON is substituted with the chip's address before encoding, so a signer field can reference the key that signs it.

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Repository layout

toluTag/
├── Software/
│   ├── IOS/toluTag/            # SwiftUI iOS app (Xcode project)
│   │   └── toluTag/
│   │       ├── Core/SE05x/     # applet constants, TLV, curve params, object ids, policies
│   │       ├── Core/NFC/       # CoreNFC session runner + Se05xTag read/write/sign
│   │       ├── Core/Crypto/    # Keccak256, secp256k1, BigUInt, EIP-191/712, address
│   │       ├── Features/       # Write / Read / Keys flows (View + @Observable ViewModel)
│   │       ├── Components/     # design-system views (buttons, hex fields, radar, …)
│   │       ├── Theme/          # ToluTheme, palette
│   │       ├── Services/       # KeyStore (Keychain + Face ID gate)
│   │       └── Navigation/     # AppRoute, Router
│   └── Java/                   # Java 21 / Maven CLI toolkit
│       └── src/main/java/org/example/tolutag/
│           ├── smartcard/      # PC/SC connection, channel, APDU errors
│           ├── se05x/          # applet services: keys, objects, sessions, curve, info
│           ├── eth/            # address, EIP-191, EIP-712 encoder + signers
│           ├── crypto/         # Keccak256, DER ECDSA, secp256k1 recovery
│           └── cli/            # interactive entry points (read/ and write/)
└── Hardware/
    ├── PCB/                    # card, sticker and textile form factors
    ├── STL/                    # printable models (tag carriers)
    └── BOM.md                  # bill of materials

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iOS app

Published on the App Store: toluTag. Install it to provision, inspect and sign with a tag from an iPhone, no build required. The source here is the same app.

Requirements

• Xcode 26+, iOS 26.0 target, Swift 5
• A physical iPhone with NFC (CoreNFC does not work in the Simulator)
• A paid Apple Developer account, the app needs the NFC Tag Reading capability and an entitlement whitelisting the SE05x AID

Entitlements

Info.plist declares the applet the app is allowed to select:

<key>com.apple.developer.nfc.readersession.iso7816.select-identifiers</key>
<array>
    <string>A0000003965453000000010300000000</string>
</array>

toluTag.entitlements must carry com.apple.developer.nfc.readersession.formats with TAG, and the provisioning profile must include the NFC capability.

Build

open Software/IOS/toluTag/toluTag.xcodeproj

Set your own team and bundle id (currently io.mwbp.toluTag), then run on a device.

Features

Write

• Create key, provision the secp256k1 curve and generate a key pair at a chosen object id, optionally PIN-protected (creating or reusing a UserID object) and optionally deletable.
• Write text, store an arbitrary string in a binary file object on the tag.
• Delete, remove an object, pre-fillable from a saved record (carrying its PIN/UserID so the session can authorise the delete).

Read

• Scan tag, chip unique id, applet version, free memory, and per-object existence, type, size, origin (generated on-chip vs imported), policy, public point and derived Ethereum address. Every read is independent and best-effort: a rejected command is reported and the scan continues.
• Read text, read back a stored string.
• Sign message, EIP-191 signature over the toluTag phrase template or a custom message.
• Sign typed data, paste an eth_signTypedData_v4 document and sign it.
• Collect tags, a two-stage batch flow: configure an object id, phrase format and label, then tap tags one after another. Each tag's address and unique id are read, duplicates rejected, and the whole set saved as an exportable record.

Keys, records of created keys and stored strings, persisted in the Keychain and gated behind Face ID.

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Java CLI (Software/Java)

Requirements

• JDK 21+
• Maven 3.9+
• A PC/SC contactless reader (e.g. ACR122U, PN532-based readers) with the platform's PC/SC daemon running (pcscd on Linux; built in on macOS/Windows)

Build

cd Software/Java
mvn compile

Run

Each tool is an interactive entry point with its own main. Run them from the compiled classes:

java -cp target/classes org.example.tolutag.cli.<package>.<Tool>

Every tool that touches an object first asks whether it is PIN-protected; leave the prompt blank for unprotected objects.

Encoder self-test, verify the EIP-712 implementation without any hardware:

java -cp target/classes org.example.tolutag.cli.read.eip712Sign selftest

This prints the digest of the canonical EIP-712 "Mail" example for cross-checking against a reference implementation.

tags.json

collectTags (and the iOS Collect tags flow) emit the same structure:

{
  "objectId": "00002222",
  "format": "address_tagId_timestamp",
  "count": 3,
  "tags": [
    {
      "index": 0,
      "tagId": "0x00000400500138D472B915A6C7045A8482062090",
      "address": "0xee6ce30a5b4cd7eade1d6ec82f470c9a7040be27",
      "value": "1788259398",
      "phrase": "0xee6ce30a5b4cd7eade1d6ec82f470c9a7040be27_0x00000400500138D472B915A6C7045A8482062090_1788259398"
    }
  ]
}

format is one of address_tagId_timestamp, address_tagId_0 or address_tagId_count; phrase is exactly the string a tag is asked to sign, so the file doubles as the input list for a batch registration or allowlist.

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Hardware

The Hardware/ directory holds the KiCad projects, gerbers, STLs and BOM for building a toluTag yourself. Licensed under CERN-OHL-P-2.0.

Hardware/PCB/ carries the three board projects (card, sticker, textile) described under Shape the tag however you need, Hardware/STL/ holds printable carriers for them, and Hardware/BOM.md lists what goes into one tag.

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Notes

• Object ids are 4 bytes, entered as up to 8 hex characters and left-padded (2222 → 00002222). The two clients use the same convention, so a tag provisioned from the CLI reads correctly in the app and vice versa.
• Non-deletable by default. Keys created without the DELETE permission cannot be removed from the tag by any command. Use the deletable variant for development tags.
• PIN attempts on a UserID object are limited by the applet; exhausting them can lock the protected object permanently.
• tags.json in the repo is sample output, not configuration.

Status

Working tooling under active development. APDU-level behaviour has been checked against real SE05x hardware; the cryptographic layers are cross-checked between the Swift and Java implementations and, for EIP-712, against the reference "Mail" vector.

License

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_{toluTag hardware and the tooling in this repo are open, build and use freely. Some higher-level applications built on top of the tag are patented and available via the Portal platform.}

_{toluTag is part of the Portal platform, built by mwbp.io.}