LibSodium dependency review

This note records the dependency review for LibSodium.

Decision

LibSodium is accepted as the runtime cryptography dependency for password hashing, random token generation, content digests, Matrix event hashes, and Ed25519 signing support. It must remain behind project-owned crypto, media, event, and homeserver boundaries.

Why it is needed

Merovingian must not carry project-local cryptographic primitives. LibSodium provides reviewed primitives for hashing, password storage, random generation, and Ed25519 operations across Linux and BSD package managers.

Security boundary

• Password hashing and token generation flow through Merovingian auth helpers.
• Event hashing and signing use project event APIs rather than direct sodium calls from handlers.
• Media digests are calculated through the media repository boundary.
• Sodium initialization is checked before cryptographic operations proceed.
• Raw sodium key material must not be logged or stored outside explicit key storage records.

Maintenance and platform posture

LibSodium is resolved from the operating-system package and linked dynamically. The top-level Meson dependency sets allow_fallback: false, so clean builds must provide libsodium.pc through the host package manager even when the wrapper scripts use Meson's forcefallback mode for other dependencies. There is no subprojects/libsodium.wrap (ADR-0218).

Supported development paths install the OS development package explicitly: Debian-family hosts use libsodium-dev, Fedora-family hosts use libsodium-devel, FreeBSD uses libsodium, OpenBSD uses libsodium, and NetBSD/pkgsrc uses libsodium.

License

LibSodium is released under the ISC license (SPDX: ISC). It is compatible with Merovingian's GPL-3.0-or-later distribution and is resolved from the operating-system package.

Current limitations

• Runtime local signing-key materialization is deterministic scaffolding and must be replaced by a reviewed production key loader.
• Hardware-backed key storage remains future work.