Extensible Address Validation Tokens for QUIC

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Table of Contents

3. BDP Tokens

This document defines the BDP_TOKEN extension, designed to Congestion Control information for use in Careful Resume [I-D.ietf-tsvwg-careful-resume].¶

The format of a token extension containing BDP information is defined as follows:¶

BDP Token {
    Private Data Length (i),
    Private Data (..),
    Capacity (i),
    RTT (i),
    Requested Capacity (i),
}

The fields are as follows:¶

Private Data Length

A variable-length integer specifying the length of the Private Data field, in bytes. A value of 0 indicates that the server does not intend to store Congestion Control data on the client, and that the Capacity and RTT fields are merely informative.¶

Private Data

Opaque information specific to the server that it will use to prime its congestion controller state. This field SHOULD contain expiration/lifetime information, and any additional information that the server may need to validate that the same path is being used, such as an endpoint token as defined in Careful Resume [I-D.ietf-tsvwg-careful-resume]. The data MUST be signed, or otherwise protected against modification by the client. If the data contains information that could potentially be used to fingerprint the client, it MUST be encrypted, or otherwise protected against inspection by wire observers. An example method for protecting the Private Data field is provided in Appendix A.¶

Capacity

The estimated capacity of the path in bytes (congestion window), encoded as a variable-length integer.¶

RTT

The RTT of the path in microseconds, encoded as a variable-length integer.¶

Requested capacity

In a token sent by the server, this field is set to the same value as the Capacity field. If the client becomes aware of a change in the available bandwidth of the path, it can adjust this field to request a lower capacity be used by the server when priming its congestion controller state.¶

4. IANA Considerations

5. Security Considerations

The Congestion Control data MUST be protected against manipulation by malicious or mis-behaving clients. A client that can modify Congestion Control data could cause an overload of the network path.¶

Appendix A. Example method for protecting the BDP Token's Private Data Field

This section is non-normative.¶

Consider the following private data structure:¶

Private Data {
    IP Address (16 bytes),
    Expiry Timestamp (8 bytes)
}

This structure contains information that could be used to track a client (its previous IP address), and therefore MUST be protected from inspection by wire observers. Additionally the Capacity and RTT fields MUST be protected from modification by a client.¶

To this end this example uses the ChaCha20-Poly1305 [RFC8439] cipher with additional data. The ChaCha20-Poly1305 cipher encrypts data, and protects the encrypted data as well as additional unencrypted data against modification.¶

The additional data has the following structure:¶

Additional Data {
    Saved Capacity (8 bytes),
    Saved RTT (16 bytes)
}

After encryption the 12 byte nonce is appended to the Private Data structure to allow the encryption to be reversed when the token is later used.¶

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