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Layer 5 · §21 transport & push

Canonical reference: digstore-remote (axum server + reqwest DigClient) and its crypto/codec in digstore-core / digstore-crypto. This is the transport half of the scheme split: chia:// = content addressing; dig:// here = the §21 transport locator. Browser/agent reads use the POST JSON-RPC; CLI/peer sync + publishing use these authenticated REST routes.

These routes span both RPC tiers

Under the dual-transport tier model: the §21 GET content routes (content / proof / roots / descriptor) are on the PUBLIC READ tier — anonymous, CORS-enabled, browser-reachable, client-verified, decoy-on-miss. The §21 PUSH / WRITE routes (module/upload, module PUT, module/complete, tombstone) are on the PEER / CONTROL tier — mTLS-authenticated plus the per-request BLS signature below, and never reachable anonymously. See the tier map.

The dig:// transport locator​

dig:// is not spoken on the wire — it resolves client-side to https://<host>/stores/<id> (config.rs:89). The 32-byte store id is the wire address.

You write…Resolves to…
dig://<64hex>https://rpc.dig.net/stores/<64hex>
dig://<user>@<64hex>same (user stripped — informational only)
dig://<host>[:port]/<64hex>https://<host>[:port]/stores/<64hex>
dig://<host>/stores/<64hex>passthrough

The REST surface (under /stores/:id)​

descriptor, roots, module (GET/HEAD/PUT), module/upload + module/complete (the 2-leg push), content, proof, delta, tombstone (router server.rs:66-117). Middleware order: auth THEN rate-limit (an unauthenticated request is rejected before consuming a token). Status mapping (§21.8): UnknownStore/Root = 404, Unauthorized = 403, AuthFailed/MissingBearer = 401, NonFastForward = 409, TooLarge = 413, Validation = 422, RateLimited = 429. A content miss is never 404 — 200 + decoy.

Wire envelope: JSON outer / Chia-codec inner​

REST metadata (descriptor/roots/delta) is JSON for ergonomics; all content/proof/key-table blobs stay Chia-custom-streamable-codec encoded and base64-wrapped inside the JSON (lib.rs:3-7). The codec is big-endian fixed-width (codec/mod.rs:3-4), matching Chia framing: uintN BE; Option<T> = 1 tag byte + T; Vec<T> = u32 BE count + items; String = u32 BE byte-length + utf8; Bytes32/48/96 raw, no length prefix. The same codec frames the MerkleProof on the wire.

Authenticated head (PUSH_DST)​

push_signing_message(root, store_id) = SHA-256( PUSH_DST || root(32) || store_id(32) )   // bls.rs:194-200
PUSH_DST = b"dig-store:push:v1"

The signing message is domain-separated with PUSH_DST (bls.rs:194-200). The push signature authorizes the head and is persisted on accept, so a later clone/pull re-verifies the served head's authorization (StoreDescriptor.push_sig).

Push protocol v1 (2-leg)​

Two-leg because an HTTPS edge (Lambda) caps bodies below capsule size:

  1. push-init — POST /stores/:id/module/upload { parent_root, new_root, program_hash, size_bytes, store_pubkey } + header X-Dig-Signature (the authenticated head). The first push sends parent_root="" (empty), NOT the all-zero genesis root — the server matches empty parent iff served_root == Bytes32::default() (impl fast-forward rule). Up-front gates before any bytes: verify push sig (403) → fast-forward parent == served head (409). Reply { mode: "inline"|"presigned", upload_id, url? }. 2a. inline — PUT /stores/:id/module?root=<new_root>, streamed 256-KiB chunks. 2b. presigned (S3) — PUT the bytes as a single buffered body (fixed Content-Length; chunked TE breaks S3 SigV4), then POST /module/complete { upload_id, new_root }.

Client redirects are disabled (anti-SSRF of the signed push); an explicit User-Agent: digstore/<ver> is required or the WAF 403s.

Per-request auth (§21.9)​

Every guarded request is signed:

  • X-Dig-Identity — 48-byte BLS G1 identity pubkey hex
  • X-Dig-Timestamp — unix seconds
  • X-Dig-Nonce — 32 random bytes hex
  • X-Dig-Auth — 96-byte BLS sig over the request message:
SHA-256( REQ_DST || u32be(len(method)) || method || store_id(32) || u64be(ts) || nonce(32) )

Method tags: fetch/roots/module/push/push-init/push-complete/content/proof/delta/tombstone. Binding the method stops a read-auth sig replaying as a write. The freshness window is 300s: a request is accepted only while its timestamp is within 300s of now, which bounds the window in which a captured request could be re-presented.

Fetch / clone / pull, ETag & delta​

  • ETag = strong quoted hex of the generation root: "<64hex>"; HEAD returns ETag + Content-Length + application/wasm.
  • pull: if local == remote → UpToDate; else (prefer-delta) GET /delta?from=&to= with per-chunk SHA-256 integrity, else GET /module with If-None-Match → 304 or full module.
  • A server/MITM cannot substitute delta chunk bytes — each must hash to its advertised content id.

Tombstones (revocation)​

POST /stores/:id/tombstone { record = hex(canonical(Tombstone)), signature }; message = SHA-256(TOMB_DST || canonical(Tombstone)). Verified fail-closed against the store's published key; served in StoreDescriptor.tombstones; clients refuse to advance to a Root-revoked root (or refuse the whole store on a Store-scope tombstone).

Rate limiting & decoy indistinguishability​

Per-store token bucket (default 10,000 tokens, 60s refill, idle-eviction). serve_content never 404s on a miss — it returns a deterministic decoy keyed by retrieval_key (bucket = retrieval_key[0] % 8; len = 256 << bucket, 256 B..32 KiB, filled with SHA-256(retrieval_key || counter_be) blocks), byte-shaped identically to a hit.