wolfSSL adds HPKE encryption to wolfCOSE for IoT devices

wolfSSL has introduced experimental support for Hybrid Public Key Encryption (HPKE) in its wolfCOSE library, targeting constrained and Internet of Things (IoT) devices. The update enables these devices to encrypt Concise Binary Object Representation (CBOR) messages to one or multiple recipients without requiring custom key-wrapping implementations. HPKE, standardized under RFC 9180, combines a key encapsulation mechanism (KEM), a key derivation function (KDF), and an authenticated encryption with associated data (AEAD) scheme into a single, misuse-resistant public-key encryption framework.

Implementation details

The HPKE feature is disabled by default and must be explicitly enabled through the WOLFCOSE_EXPERIMENTAL flag alongside per-operation macros. This design ensures the core wolfCOSE library remains lightweight while allowing developers to opt into experimental functionality. The implementation supports both single-recipient (COSE_Encrypt0) and multi-recipient (COSE_Encrypt) encryption scenarios. All six HPKE enable selectors are available, each independently gated to provide granular control over feature activation.

wolfSSL has included paired command-line commands, self-tests, and a runnable HPKE example to facilitate adoption. The release also features negative acknowledgement tests to confirm the feature remains inactive unless explicitly enabled. Full command-line validation of 44 tests was conducted, with no failures reported. Despite its experimental status, the feature is positioned as foundational work, with a documented graduation path for future stabilization.

Practical implications

For developers working with IoT or embedded systems, the addition of HPKE to wolfCOSE reduces the complexity of implementing secure messaging. By eliminating the need for hand-rolled key wrapping, the feature lowers the barrier to entry for encryption in resource-constrained environments. However, its experimental status means adopters should expect potential changes as the implementation matures. The requirement to enable the feature through macros also ensures that production deployments remain unaffected unless explicitly configured.

The feature’s multi-recipient support could be particularly valuable for scenarios involving device fleets or distributed systems, where messages must be securely delivered to multiple endpoints. The inclusion of self-tests and validation tools further aids developers in verifying their implementations, reducing the likelihood of misconfigurations.

What to watch

As HPKE support in wolfCOSE is currently marked as experimental (P0), its evolution will depend on community feedback and adoption. The documented graduation path suggests wolfSSL intends to stabilize the feature in future releases, but no timeline has been provided. Developers integrating this functionality should monitor updates to the library and be prepared to adjust their implementations as the feature progresses toward general availability.