cdk-ehash

A MintPayment processor for Hashpool mining-share rewards, built on the Cashu Development Kit (CDK).

Miners submit a valid proof-of-work share (identified by its header_hash). Once Hashpool validates the share it calls pay_ehash_quote() on the processor, which marks the corresponding quote as paid so the miner can mint ecash tokens.

Overview

The mint flow has four steps:

1. Quote — the miner's wallet calls POST /v1/mint/quote/ehash with {"amount": N, "unit": "ehash", "extra": {"header_hash": "<64-char hex>"}}. The mint returns a quote ID.

2. Validate — the miner submits the share to Hashpool. Hashpool verifies proof-of-work and calls EhashPaymentProcessor::pay_ehash_quote(header_hash, amount).

3. Poll — the wallet polls GET /v1/mint/quote/ehash/<id> until "state": "PAID".

4. Mint — the wallet calls POST /v1/mint/ehash with the quote ID and blinded messages to receive ecash tokens.

Wiring into Hashpool's mint binary

cdk-ehash plugs into CDK via MintBuilder::add_payment_processor. No cdk-mintd dependency is needed — Hashpool builds its own mint binary:

use std::sync::Arc;
use cdk::mint::{MintBuilder, MintMeltLimits};
use cdk::nuts::{CurrencyUnit, PaymentMethod};
use cdk_ehash::EhashPaymentProcessor;

let unit = CurrencyUnit::Custom("ehash".to_string());
let processor = Arc::new(EhashPaymentProcessor::new(unit.clone()));

let mut builder = MintBuilder::new(localstore.clone());
builder
    .add_payment_processor(
        unit,
        PaymentMethod::Custom("ehash".to_string()),
        MintMeltLimits::new(1, 1_000_000),
        processor.clone(),
    )
    .await?;

let mint = builder
    .with_name("Hashpool Mint".to_string())
    // ... other configuration ...
    .build_with_seed(localstore, &seed)
    .await?;

// Keep `processor` alive — call this when a share is validated:
// processor.pay_ehash_quote(&header_hash, amount).await?;

The cdk-axum router auto-generates all custom-method endpoints (/v1/mint/quote/ehash, /v1/mint/ehash, etc.) from the registered processor — no extra routing code required.

Dependency note

cdk-ehash targets CDK's upstream main branch. The hashed_derivation_index method for custom currency units landed in CDK 0.15.0 and is available in all current published releases. However, extra_json persistence for mint quotes (needed to survive mint restarts) was fixed in CDK PR #1742 and is targeted for the 0.16.0 release. Until that lands, patch the published crates with upstream:

[patch.crates-io]
cashu           = { git = "https://github.com/cashubtc/cdk" }
cdk             = { git = "https://github.com/cashubtc/cdk" }
cdk-common      = { git = "https://github.com/cashubtc/cdk" }
cdk-http-client = { git = "https://github.com/cashubtc/cdk" }
cdk-signatory   = { git = "https://github.com/cashubtc/cdk" }
cdk-sql-common  = { git = "https://github.com/cashubtc/cdk" }
cdk-sqlite      = { git = "https://github.com/cashubtc/cdk" }

Once CDK 0.16.0 is published this patch section (and the one in cdk-ehash's own Cargo.toml) can be dropped and the version deps bumped to "0.16.0".

License

MIT — same as upstream CDK.