Mint Quote Lookup by Public Key spec fixes - #419
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The endpoint answers "which quotes does this key own", and a NUT-20 public key locks quotes of any payment method. Scoping the path by method makes a wallet issue one request per method just to enumerate what a single key holds, and leaves it no way to ask for everything. Nothing downstream uses the segment. The signature covers "Cashu_MintQuoteLookup_v1" || mint_pubkey || pubkey, with no method in it, so a method in the path is unauthenticated routing data bound to nothing the wallet proved. And every MintQuoteResponse already carries a `method` field, so a mixed-method response is unambiguous without the URL announcing one. Also state that the response spans every payment method, which the method-scoped path left implicit.
The endpoint is unauthenticated until the signatures verify, so the length of the request decides how much work an anonymous caller can ask the mint to perform: one Schnorr verification per public key, plus a query over the whole set. The mint cannot skip that work, because doing it is how it learns whether the caller is entitled to anything. Without a limit a small request buys arbitrary CPU. Every implementation therefore needs a cap, and with none in the spec each picks its own silently, leaving wallets to discover it by being rejected. NUT-29 already settled this shape for batch minting: an optional `max_batch_size` advertised in the mint's NUT-06 settings, and error 11017 when it is exceeded. Reuse both rather than invent a parallel mechanism. The advertised limit is optional, matching NUT-29, so a mint may keep its cap private as long as it still returns 11017.
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Can you do it as review comments |
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Two amendments to #341, one commit each — commit messages carry the full reasoning.
Drop
{method}from the path. The endpoint answers "what does this key own," and a NUT-20 key locks quotes of any payment method — so the segment forces one request per method and buys nothing. The signature doesn't cover it, and everyMintQuoteResponsealready carries a method field (NUT-04), so a mixed-method response is unambiguous without it.Bound the pubkey count. The mint must verify every signature before it can tell whether the caller is entitled to anything, so request length decides how much work an anonymous caller can demand. Adds a MUST to limit it, error
11017on overflow, and an optionalmax_pubkeysin the NUT-06 settings — the same shape NUT-29 already uses formax_batch_size.