In rough order of priority:
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OpenSSL API Compatibility Layer. Add an OpenSSL C API compatibility layer for adoption purposes.
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Support Encrypted Client Hello (Client Side). Encrypted Client Hello is an upcoming standard from the TLS WG providing better protection for some of the data sent by a client in the initial Client Hello message. rustls#1718
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Additional Performance Optimization. Additional performance optimization including CPU usage, latency, and memory usage. The goal is to outperform OpenSSL across the board if we are not already.
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Support RFC 8879 Certificate Compression. Support for a TLS extension that substantially shrinks certificates (one of the largest parts of the TLS handshake), improving handshake latency by decreasing bandwidth used. rustls#534
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Enforce Confidentiality / Integrity Limits. The QUIC use of TLS mandates limited usage of AEAD keys. While TLS 1.3 and 1.2 do not require this, the same kinds of issues can apply here, and we should consider implementing limits for TLS over TCP as well. rustls#755
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Support Post-Quantum Hybrid Key Exchange. Experimental, optional support for the
X25519Kyber768Draft00
key exchange. This should track the draft. rustls#1687
Delivered in 0.23:
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FIPS Certification for Default Cryptographic Library. Change the default cryptographic library to something with FIPS certification. rustls#1540
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Add No-Allocation / Write-Through API. Would make handshakes faster and give the caller more control over allocations. RFC: rustls#1420
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Support no_std. Enables use of rustls in more memory-constrained environments. RFC: rustls#1399
Delivered in rustls-platform-verifier 0.1.0:
- Improve OS Trust Verifier Support. While we currently have a way to trust certificates stored in the platform trust store, platform trust stores can have other ways of restricting how/when roots that they expose are trusted. In order to rely on these (on Windows, Android, and Apple platforms) we should rely on the platform verifier directly.
Delivered in 0.22:
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Enable Pluggable Cryptographic Back-ends. Allow plugging in different cryptographic back-ends. rustls#1184
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Comprehensive Performance Benchmarking. Performance should be a headline feature of Rustls. We need to develop a more comprehensive benchmarking system so that we can assess and improve performance from multiple angles, including CPU usage, latency, and memory usage.
Delivered in 0.21:
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Support IP Address Certificates. There are some popular use cases where applications want TLS certificates for services that don’t have their own host name, relying on the IP address directly instead. This is common in Kubernetes deployments and service meshes. rustls#184
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Implement RFC 8446 Appendix C.4 in session cache. TLS clients should use session tickets at most once for resumption. Without this, TLS clients may be tracked across connections through reuse of session tickets. Requires changes of the internal APIs to the session caching infrastructure. rustls#466
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Improve Client Certificate Authentication Support. Rustls and webpki currently do not provide access to client information supplied as part of the certificate, and there’s no infrastructure to deal with revocation checks. rustls/rustls-ffi#87
Delivered in 0.20:
- Add/extend support for TLS 1.3 Early Data. Early data allows clients to submit data before the TLS handshake is complete in some cases (idempotent requests, data where replay is not a risk), improving latency in the cases of, for example, HTTP requests by submitting the request in parallel with the TLS handshake.