Content Access Ticket Protocol (CAT Protocol)

Overview

This repository provides a basic implementation of the Content Access Ticket (CAT) Protocol, focusing on demonstrating a content service and a ticket issuer. The CAT Protocol enables decentralized, signed, time-limited access to paywalled or premium content by issuing verifiable tickets.

For a detailed specification of the protocol, including sequence diagrams and technical details, please refer to CAT.md.

Implementation

This repository includes a demo implementation of a CAT content service using FastAPI and a ticket issuer using the cryptography library.

Content Service

The content_service.py file provides an example of how to verify CAT tickets and serve content. It uses a mock database for trusted issuers and content.

Usage

1. Install dependencies: pip install -r requirements.txt

2. Run the service: uvicorn content_service:app --reload

   This will start the FastAPI server, typically on http://localhost:8000.

3. Access content: GET http://localhost:8000/content?ticket=<base64_encoded_ticket>&lang=en

   • Replace <base64_encoded_ticket> with a valid ticket generated by the ticket issuer.
   • The lang parameter is optional and defaults to en (English). It specifies the language of the content to be returned.

Ticket Issuer

The ticket_issuer.py file provides an example of how to generate Ed25519 key pairs and create signed CAT tickets.

Usage

1. Run the script: python ticket_issuer.py

   This will generate a new Ed25519 key pair and a sample ticket. The output will include:

   • The public key (in hex format), which needs to be added to the TRUSTED_ISSUERS dictionary in content_service.py.
   • A base64 encoded ticket.

2. Update content_service.py: Copy the generated public key and add it to the TRUSTED_ISSUERS dictionary in content_service.py. For example:

   TRUSTED_ISSUERS = {
       "npub1test": "<your_generated_public_key_hex>",
       # ... other issuers
   }

3. Access content: Use the generated base64 encoded ticket to access content via the content service, as described above.

Example

Here's a complete example, assuming you've run both ticket_issuer.py and content_service.py:

1. Run ticket_issuer.py:

   python ticket_issuer.py

   This will output something like:

   Public Key (Hex): 710e354519c02461ceaf78e4febe6a0f01c422ca07d42a1be063ce13abdf9739
   Base64 Encoded Ticket: eyJyZXNvdXJjZSI6ICJodHRwczovL2V4YW1wbGUuY29tL2FydGljbGUvYWJjMTIzIiwgInRzIjogMTcwNzM3NzU0MCwgImV4cCI6IDE3MDczNzc4NDAsICJjaHVuayI6ICIxIiwgInB1YmtleSI6ICJucHViMXRlc3QiLCAic2lnIjogIm1vY2tz aWduYXR1cmUifQ==
   

2. Update content_service.py:

   TRUSTED_ISSUERS = {
       "npub1test": "710e354519c02461ceaf78e4febe6a0f01c422ca07d42a1be063ce13abdf9739",
       # ... other issuers
   }

3. Access Content:

   curl "http://localhost:8000/content?ticket=eyJyZXNvdXJjZSI6ICJodHRwczovL2V4YW1wbGUuY29tL2FydGljbGUvYWJjMTIzIiwgInRzIjogMTcwNzM3NzU0MCwgImV4cCI6IDE3MDczNzc4NDAsICJjaHVuayI6ICIxIiwgInB1YmtleSI6ICJucHViMXRlc3QiLCAic2lnIjogIm1vY2tz aWduYXR1cmUifQ==&lang=fr"

   This should return the French version of the content chunk "1" from the resource "https://example.com/article/abc123", which demos the granularity of the CAT protocol.

License

This project is licensed under the MIT License - see the LICENSE file for details.