java.lang.Object
net.i2p.data.ByteArray
org.klomp.snark.dht.Token
All Implemented Interfaces:
Serializable, Comparable<ByteArray>
class Tokenextends ByteArray
DHT token management for secure peer verification.

Tokens are used in the BitTorrent DHT protocol to prevent certain types of attacks. When a peer announces itself to a DHT node, it receives a token that must be included in subsequent get_peer requests. This verifies that the requesting peer has previously communicated with the DHT node from the same IP address.

This class handles both outgoing tokens (generated locally for sending to peers) and incoming tokens (received from remote DHT nodes). Tokens have limited lifetimes and are automatically expired to prevent replay attacks.

Security considerations:
- Outgoing tokens are 8 bytes of cryptographically secure random data
- Incoming tokens may be up to 64 bytes (to accommodate various implementations)
- Tokens are timestamped for automatic expiration
- Lookup-only tokens don't store timestamps to save memory

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    private final long
    lastSeen
    Timestamp when this token was created or last seen.
    private static final int
    MAX_TOK_LEN
    Maximum allowed token length for incoming tokens (64 bytes).
    private static final int
    MY_TOK_LEN
    Default token length for outgoing tokens (8 bytes).
    private static final long
    serialVersionUID
    Pinned for serialized-form compatibility.

  • Constructor Summary

    Constructors
    Constructor
    Description
    Token(byte[] data)
    Creates a lookup-only token without timestamp.
    Token(I2PAppContext ctx)
    Creates a new outgoing token for sending to remote peers.
    Token(I2PAppContext ctx, byte[] data)
    Creates an incoming token received from a remote DHT node.

  • Method Summary

    All Methods
    Modifier and Type
    Method
    Description
    long
    lastSeen()
    Returns the timestamp when this token was created or last seen.
    String
    toString()
    Returns a string representation of the token for debugging and logging.

    Methods inherited from class ByteArray

    compareTo, equals, getData, getOffset, getValid, hashCode, setData, setOffset, setValid, toBase64
    Modifier and Type
    Method
    Description
    final int
    compareTo(ByteArray ba)
    Compares this ByteArray with another ByteArray.
    final boolean
    equals(Object o)
    Compares this ByteArray with another object for equality.
    byte[]
    getData()
    Returns the underlying byte array.
    int
    getOffset()
    Returns the offset into the byte array.
    int
    getValid()
    Count how many of the bytes in the array are 'valid'.
    final int
    hashCode()
    Hash code based on the underlying byte array data.
    void
    setData(byte[] data)
    Sets the underlying byte array.
    void
    setOffset(int offset)
    Offset into the byte array.
    void
    setValid(int valid)
    Number of valid bytes.
    final String
    toBase64()
    Returns this ByteArray as a Base64 encoded string.

    Methods inherited from class Object

    clone, getClass, notify, notifyAll, wait, wait, wait

  • Field Details

    • serialVersionUID

      private static final long serialVersionUID
      Pinned for serialized-form compatibility.
      See Also:

    • MY_TOK_LEN

      private static final int MY_TOK_LEN
      Default token length for outgoing tokens (8 bytes).
      See Also:

    • MAX_TOK_LEN

      private static final int MAX_TOK_LEN
      Maximum allowed token length for incoming tokens (64 bytes).
      See Also:

    • lastSeen

      private final long lastSeen
      Timestamp when this token was created or last seen.

  • Constructor Details

    • Token

      public Token(I2PAppContext ctx)
      Creates a new outgoing token for sending to remote peers.

      Generates 8 bytes of cryptographically secure random data that will be used as a token. The token is timestamped for expiration tracking. This constructor is used when we are the DHT node responding to a get_peer request.

      Parameters:
      ctx - the I2P application context for random number generation and clock access

    • Token

      public Token(I2PAppContext ctx, byte[] data)
      Creates an incoming token received from a remote DHT node.

      Stores a token received from a remote DHT node for later use in announce_peer requests. The token is timestamped for expiration tracking. Tokens longer than 64 bytes are rejected to prevent memory exhaustion attacks.

      Parameters:
      ctx - the I2P application context for clock access
      data - the token data received from the remote DHT node
      Throws:
      IllegalArgumentException - if the token data exceeds 64 bytes

    • Token

      public Token(byte[] data)
      Creates a lookup-only token without timestamp.

      Creates a token instance for comparison purposes only, without storing a timestamp. This is useful when checking if a received token matches an expected value without needing to track its age for expiration.

      Parameters:
      data - the token data to use for lookup comparison

  • Method Details

    • lastSeen

      public long lastSeen()
      Returns the timestamp when this token was created or last seen.
      Returns:
      the timestamp in milliseconds since epoch, or 0 for lookup-only tokens

    • toString

      public String toString()
      Returns a string representation of the token for debugging and logging.

      Formats the token data as hexadecimal and includes the creation timestamp if available. The format is consistent with other DHT debugging output.

      Overrides:
      toString in class ByteArray
      Returns:
      a formatted string containing token length, hex data, and creation time