Handshake Phase

The handshake phase extends the existing BitTorrent peer wire handshake (BEP 3) and extension protocol (BEP 10) to advertise SeedPay support and payment terms — without breaking compatibility with non-SeedPay clients.

Standard BitTorrent Handshake

When two peers connect over TCP, they first perform the normal BitTorrent handshake as defined in BEP 3:

• The protocol string "BitTorrent protocol"
• An 8-byte reserved field used for feature flags
• The torrent's info hash
• Each peer's 20-byte peer_id

SeedPay doesn't modify this message. Instead, it relies on the extension protocol flag in the reserved field. If both peers set the BEP 10 "extended messaging" bit, they proceed with the extended handshake.

Extended Handshake (BEP 10)

Immediately after the standard handshake, peers exchange an extended handshake (BitTorrent message ID 20, extended ID 0). The payload is a bencoded dictionary that advertises supported extensions via the m map.

SeedPay defines a new extension named "seedpay". A Seeder that supports paid seeding MUST include an entry in the m dictionary along with payment capabilities:

{
  "m": {
    "seedpay": 5,
    "ut_metadata": 2
  },
  "v": "SeedPayClient 0.3",
  "seedpay": {
    "wallet": "DYw8jCN...",
    "price_per_mb": 0.0001,
    "min_prepayment": 0.01,
    "chain": "solana"
  }
}

The seedpay dictionary contains:

The numeric value 5 is the local extension ID for SeedPay messages on this connection. It is implementation-defined and only needs to be consistent for this peer pair.

A Leecher that supports SeedPay also includes seedpay in its m map:

{
  "m": {
    "seedpay": 3
  },
  "v": "SeedPayClient 0.3"
}

Capability Detection

After both extended handshakes are exchanged, each peer:

1. Checks whether the remote m contains "seedpay"
2. Records the remote extension ID for "seedpay"
3. Parses the remote seedpay object (if present) to learn the counterparty's wallet and pricing

From the Leecher's perspective, this answers:

Based on this, the Leecher classifies the peer as:

• Free-only (no seedpay entry) — standard BitTorrent behavior
• Paid seeder (SeedPay with pricing) — can open a payment channel

Only after handshake completes does the protocol move to the Payment Channel Setup.