DIP Proposal: Dandelion++ Stem Submission for SPV/Light Clients

[JohnnyLawDGB]

Summary

This DIP proposes extending DigiByte's existing Dandelion++ implementation to allow SPV (lightweight/mobile) wallet clients to submit transactions into the stem phase. Currently, Dandelion++ only benefits full-node operators — SPV wallet users get zero transaction-origin privacy from the protocol.

The Problem

When an SPV wallet sends a transaction to a connected full node, that full node (and any network observer) can trivially determine which IP address originated the transaction. The Dandelion++ stempool routing only kicks in for transactions the full node considers "locally originated" from its own wallet. SPV-submitted transactions bypass the stempool entirely and enter normal diffusion relay.

With DigiByte's 15-second block time and growing mobile wallet usage, an increasing majority of users gain zero benefit from the Dandelion++ infrastructure that full nodes are already maintaining.

Proposed Solution

A lightweight protocol extension:

1. New handshake: SPV client sends dandelionsubmit message after verack. Full node responds with dandelionack if willing to accept stem submissions.
2. Stem submission: Once negotiated, SPV client submits transactions using the existing MSG_DANDELION_TX inventory type. The full node routes them into its stempool and through the existing Dandelion++ relay machinery.
3. Rate limiting: Per-peer rate cap (default 5 per epoch) prevents stempool abuse. Over-limit transactions gracefully fall back to standard relay — never rejected.

Key Properties

• Fully backward compatible — non-supporting nodes simply ignore the new handshake message
• No consensus changes — purely a relay-layer enhancement
• Reuses existing infrastructure — no new stempool logic, no new relay mechanisms
• Configurable — full nodes can disable via -acceptspvstem=0
• Composable with Tor — SPV clients using Tor + stem submission get layered privacy

Why This Matters

DigiByte is one of very few production chains shipping Dandelion++. Extending it to SPV clients would make DigiByte the first UTXO-chain cryptocurrency to offer stem-phase transaction privacy to lightweight wallet users. No Bitcoin, Litecoin, or Dogecoin wallet has this capability.

Draft DIP

Full specification: dip-johnnylaw-dandelion-spv.mediawiki

PR forthcoming. Looking for community feedback on the approach before formal submission.

cc @gto90

[lookintomyeyees]

I support this integration. Solid plan.