Document BBS keygen path for consumers (Generate(KeyType.Bls12381G2)); consider public raw keygen helper

[moisesja]

Context

net-did currently has a BBS test that mints keypairs by P/Invoking the internal ZkryptiumNative.bbs_keygen directly. After net-did deletes its in-repo BBS code, that FFI becomes internal to NetCrypto (InternalsVisibleTo = NetCrypto.Tests only), so no consumer has a raw BBS keygen path.

The public surface offers:

• DefaultKeyGenerator.Generate(KeyType.Bls12381G2) (and Bls12381G1) → returns a KeyPair
• DefaultBbsCryptoProvider.Sign / Verify / DeriveProof / VerifyProof

…but no public way to mint the raw 32-byte secret / 96-byte public key pair the net-did test uses.

Ask

1. Document that the supported BBS keygen path for consumers is DefaultKeyGenerator.Generate(KeyType.Bls12381G2) / Bls12381G1, and that raw sk/pk minting is intentionally internal.
2. (Optional, low priority) Expose a public BBS keygen helper if you want consumers to exercise raw-FFI keygen directly.

net-did will simply delete its FFI-based BBS test — BBS is now NetCrypto's responsibility and round-trip coverage already lives in NetCrypto.Tests. No upstream change is strictly required; this issue is primarily a documentation/clarification request.

Severity

Minor.

[moisesja]

Confirmed (documented in #9). The supported BBS keygen path for consumers is DefaultKeyGenerator.Generate(KeyType.Bls12381G2) (or Bls12381G1), which returns a KeyPair with the 32-byte BLS scalar + 96-byte G2 (or 48-byte G1) public key. Raw FFI keygen (bbs_keygen) is intentionally internal — no public raw-keygen helper, by design (frozen, backend-agnostic surface). This is now stated in the README and on DefaultBbsCryptoProvider's XML docs. net-did can safely delete its FFI-based BBS keygen test; round-trip coverage lives in NetCrypto.Tests.