adapt-e2e-core

A standalone, pure-Rust, Signal-class end-to-end encryption engine — an X3DH-style handshake plus the Double Ratchet — exposed as a C-ABI library. It is a vendored, pinned fork of vodozemac (Matrix's Olm/Megolm implementation), focused on the Olm path, with a thin management layer and a stable extern "C" surface. Apache-2.0.

What makes it different

Two properties define the crate:

• Stateless. It holds no long-lived state. Every call takes an opaque, encrypted pickle blob in and returns the new pickle out — the caller owns and persists all state. The engine is a pure function f(state, seed, msg) -> (state', out).
• Deterministic via injected entropy. Randomness is never sourced internally — no getrandom, no OsRng, no thread-local RNG. Every key-generating call takes a caller-supplied 32-byte seed and expands it with a ChaCha20 CSPRNG, so identical (state, seed, message) inputs produce byte-identical output.

Together these make the engine reproducible (useful for consensus / replayable systems) and buildable with no operating system: it compiles to a no_std riscv32imac-unknown-none-elf bare-metal rlib that links no OS entropy source.

C-ABI surface

Ten extern "C" functions over opaque pickle blobs (const uint8_t* + length in; caller-allocated uint8_t* + size_t* out, using a two-call length convention). Every call returns an int32_t code (enum e2e_rc); no panic crosses the boundary. The generated header is include/adapt_e2e_core.h:

• e2e_account_create, e2e_account_gen_otks, e2e_account_gen_fallback, e2e_account_bundle — identity and prekey material
• e2e_session_outbound, e2e_session_inbound, e2e_matches_inbound — X3DH-style session establishment
• e2e_encrypt, e2e_decrypt, e2e_session_id — the Double-Ratchet channel

Building

cargo build --release                  # native staticlib + cdylib + rlib
cargo build --features generate-header # regenerate include/adapt_e2e_core.h
cargo test                             # full test suite

# no_std / bare-metal (riscv32, nightly + rust-src):
./scripts/rv32_baremetal_build.sh

The default std feature is native convenience only; --no-default-features builds the no_std + alloc library. See docs/PACKAGING.md for the full target matrix and docs/TESTING.md for the test and gate posture.

Caller obligations (important)

Because the crate is stateless, three load-bearing security invariants — seed uniqueness, one-time-key one-time-ness, and pickle persistence + integrity — cannot be enforced by the crate and are the caller's responsibility. Read docs/CALLER-CONTRACTS.md before integrating; violating any of them breaks a cryptographic guarantee.

Security status

The cryptographic core is inherited from vodozemac: the entropy-injection fork is purely additive, and the audited default code paths are unchanged (see PATCH.md, the vendored-fork ledger). The crate has been independently reviewed for hardening by an external security team, whose findings on test-completeness and caller-contract honesty are addressed in this tree. It has not yet undergone a formal third-party cryptographic audit — do not treat it as audited.

License

Apache-2.0. Vendored dependencies under vendor/ retain their own licenses; the vodozemac and base64 forks and their deltas are documented in PATCH.md.