Expand description
This section collects together goal-oriented documentation.
Customising private key usage
By default rustls supports PKCS#8-format1 RSA or ECDSA keys, plus PKCS#1-format RSA keys.
However, if your private key resides in a HSM, or in another process, or perhaps another machine, rustls has some extension points to support this:
The main trait you must implement is sign::SigningKey. The primary method here
is choose_scheme where you are given a set of SignatureSchemes the client says
it supports: you must choose one (or return None – this aborts the handshake). Having
done that, you return an implementation of the sign::Signer trait.
The sign() performs the signature and returns it.
(Unfortunately this is currently designed for keys with low latency access, like in a PKCS#11 provider, Microsoft CryptoAPI, etc. so is blocking rather than asynchronous. It’s a TODO to make these and other extension points async.)
Once you have these two pieces, configuring a server to use them involves, briefly:
- packaging your
sign::SigningKeywith the matching certificate chain into asign::CertifiedKey - making a
ResolvesServerCertUsingSniand feeding in yoursign::CertifiedKeyfor all SNI hostnames you want to use it for, - setting that as your
ServerConfig’scert_resolver
For PKCS#8 it does not support password encryption – there’s not a meaningful threat model addressed by this, and the encryption supported is typically extremely poor. ↩