`zbase32 0.1.2` is LGPL-3.0+ — the only hard copyleft dependency in the whole
Rust graph and the last remaining blocker for the MIT release
(docs/LICENSE-COMPLIANCE-AUDIT.md §2). Statically linking LGPL code into a Rust
binary obliges us to ship relinkable objects, which is impractical for a node
image.
The audit offered two routes: the MIT `z32` crate, or an original
implementation. Took the latter — z-base-32 is an alphabet substitution over a
bit stream, so ~60 lines removes the blocker while adding *zero* new
dependencies rather than trading one supply-chain entry for another.
**Byte-compatibility was the requirement, not a nice-to-have.** A `did:dht`
identifier IS this encoding of an Ed25519 public key, so any drift would
silently rotate every node's DID and orphan its already-published DHT records.
So the semantics were not guessed: I read the vendored zbase32-0.1.2 source to
extract exactly what `encode_full_bytes` and `decode_full_bytes_str` do —
including that decode truncates to the next lower byte boundary, which is why a
52-character string round-trips to 32 bytes while discarding 4 padding bits.
A model implementation was then validated against three independent sources
before any Rust was written, all five vectors agreeing:
encode(b"testdata", 64) -> qt1zg7drcf4gn (crate doctest)
encode_full_bytes("Just an…") -> jj4zg7bycfzn… (crate doctest)
decode_full_bytes("qb1ze3m1") -> b"peter" (crate doctest)
encode([f0,bf,c7]) -> 6n9hq (Zimmermann spec)
encode([d4,7a,04]) -> 4t7ye (Zimmermann spec)
The module pins all of those plus four known 32-byte keys, a 0..40-byte
round-trip sweep, a 52-char/round-trip check over 64 keys, rejection of the
characters z-base-32 deliberately omits (`l`, `v`, `2`, `0`) and of non-ASCII,
and an alphabet/decode-table consistency check so the compile-time reverse table
can't drift from the alphabet.
`did_dht.rs` gains `did_for_a_known_key_is_stable`, which pins the full
identifier string for a known key — the regression that would actually hurt,
asserted at the call site that gives the string its meaning.
Dropped from Cargo.toml and Cargo.lock (7 lines); no other user in the tree.
Verified: 28/28 network tests pass, zero copyleft crates remain in the lockfile.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
