Example: Antiflood Token System

Purpose

The Antiflood Token System (AFT) is a decentralized system aimed to provide a simple, but general purpose solution to flooding, denial-of-service attacks, and spam.

AFT allows users to generate tokens through a "token generator", which is created by completing a "hard" task, such as making a donation to Freenet. Tokens are generated at a fixed rate and can be utilized to perform activities, such as sending messages.

The recipient can specify the required token "tier," with each tier being generated at different intervals (e.g. 1 minute, 1 hour). This way, if a recipient experiences a high volume of messages, they can increase the token tier to make it more challenging to generate, thus reducing the flood.

AFT Delegate

The AFT relies on a TokenDelegate that implements this DelegateInterface.

Token Generator

The TokenAllocContract keeps track of token assignments to ensure that tokens are not double spent. New tokens are generated at a fixed rate that depends on the tier required by the recipient.

Recepient Inbox

The recipient inbox contract keeps track of inbound messages sent to a recipient, verifying that each is accompanied by a valid token of the required tier.

Sequence Diagram

sequenceDiagram
  participant User
  participant Application
  participant Delegate
  participant TokenGeneratorContract
  participant RecipientInboxContract

  User->>Application: 1. RequestToken
  Application->>Delegate: 2. RequestToken
  Delegate->>User: 3. Allocate?
  User->>Delegate: 4. approved
  Delegate->>TokenGeneratorContract: 5. TokenAllocation
  Delegate->>RecipientInboxContract: 6. Message+TokenAllocation
  RecipientInboxContract->>TokenGeneratorContract: 7. verify
  TokenGeneratorContract->>RecipientInboxContract: 8. verified

  1. User requests a token from the application, perhaps by composing a message and clicking "send" in the UI

  2. The application requests a token from the delegate via its websocket connection to the Freenet node

  3. The delegate requests permission from the user to allocate a token, this occurs independently of the application, perhaps via an OS-specific notification mechanism

  4. The user approves the allocation

  5. The delegate allocates a token to the token generator contract

  6. The delegate sends the message and token allocation to the recipient inbox contract

  7. The recipient inbox contract verifies that the token allocation is valid before appending the inbound message to its state

  8. The token generator contract verifies that the token allocation is valid and adds it to its list of allocations