ibe

GitHub · Rust · Cryptographic Library

Collection of Identity-Based Encryption (IBE) schemes on the BLS12-381 pairing-friendly elliptic curve. This crate provides the cryptographic foundation that postguard (pg-core) uses for encryption.

Published on crates.io.

Supported Schemes

The crate contains both identity-based encryption schemes (IBEs, in src/pke) and identity-based key encapsulation mechanisms (IBKEMs, in src/kem):

• Waters (IND-ID-CPA IBE)
• Boyen-Waters (IND-sID-CPA IBE)
• Waters-Naccache (IND-ID-CPA IBE)
• Kiltz-Vahlis IBE1 (IND-CCA2 IBKEM)
• Chen-Gay-Wee (IND-ID-CPA IBE, IND-ID-CCA2 IBKEM)

References to the original papers appear in the respective source files.

Design Notes

• PostGuard's production build enables only the cgwkv and mkem features.
• An identity is SHA3-512 over the input (64 bytes), mapped to a scalar with Scalar::from_bytes_wide.
• A shared secret is SHAKE256 over the compressed Gt element, 32 bytes (kem::SS_BYTES).
• mkem encrypts one random session key per recipient with AES-128-GCM, keyed by HKDF-SHA256 over the encapsulated shared secret.
• BLS12-381 places the schemes at roughly 127 bits of security.

Technical Notes

• This implementation has not been audited. Use at your own risk.
• Uses Keccak for hashing to identities, hashing to secrets, and as symmetric primitives for the Fujisaki-Okamoto transform.
• Compiles on Rust stable.
• Does not use the Rust standard library (no_std compatible).
• All operations run in constant time.
• Byte serialization format is not guaranteed stable between releases.
• Performance depends primarily on the arithmetic in pg-curve. Optimizations to pg-curve directly improve this crate's performance.

Cargo Features

Feature	Description
boyen_waters	Boyen-Waters IBE scheme
cgw	Chen-Gay-Wee IBE scheme
cgwfo	Chen-Gay-Wee with Fujisaki-Okamoto transform
cgwkv	Chen-Gay-Wee KEM variant
kv1	Kiltz-Vahlis IBE1 scheme
waters	Waters IBE scheme
waters_naccache	Waters-Naccache IBE scheme
mkem	Multi-user key encapsulation
zeroize	Zeroize impls on the secret-bearing types. The types are Copy, so nothing is cleared on drop and callers must call .zeroize() themselves.

Development

Building

cargo build --release

Testing

cargo test --release --all-features

Releasing

Versions are published manually to crates.io. release-plz.toml sits in the repository root, but the release-plz.yml workflow it needs is not there yet, so the automation is not live.

CI/CD

Workflow	Trigger	What it does
ci.yml	Push/PR	Linting, tests on multiple OS, no_std checks (wasm32), all-features tests